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About me



  1. Ok so im planning on making a minmus base and i want to use a mass driver to transport recently fueled ships into Interplanetary space. I need the Strongest Liquid fuel engine for the driver. I need something with the most efficiency to launch a payload up to 200lbs. This mass driver will be used to establish other bases.
  2. Go At Startup a story of a space program destined to conquer the stars...
  3. Out-of universe notes will be in cursive As you know, in 1.12 fireworks were added to KSP. What you might not know is that you can overclock fireworks using a KAL controller. These overpowered fireworks can be used for propulsion, if you're careful enough. FROM THE DECLASSIFIED DOCUMENTS OF THE KERBAL AEROSPACE FORCE: THE ORION DRIVE Ever since kerbals created explosives, they've wondered: can I fly with it? The question had been answered a long time ago by solid-fuel motors, but some kept thinking if there was more to it. That day, they proved there was. The Orion test vehicle was sitting on the launchpad, waiting for further commands. Daredevil pilot Jebediah Kerman was sitting inside. Even Jeb, the famous Kerbal With No Fear, was pondering the absurdity of this idea. A couple tons of explosives were going to be shot out of a hole at supersonic speeds, an Jeb was going to ride the shockwave. Suddenly, he heard a command from Ground Control. CAPTAIN KERMAN, PREPARE FOR LIFTOFF IN 3, 2, 1... And like that, Project Orion was born. Not with a whimper, but with a bang. Jeb felt the vehicle accelerate rapidly. He struggled with his breath, and his ears were ringing. COMMANDER KERMAN, WE HAVE LIFTOFF, I REPEAT, WE HAVE... BANG! and another one and another one Getting used to this is gonna be hard, Jeb thought. 28 more explosions followed. WE HAVE REACHED 100 m/s, Mission Control stated. Beginning descent, Jeb replied. Commander Kerman parachuted to safety. While his vehicle was being recovered, his brother Gene, head of Kerbal Aerospace Forces, called him to his office. Great job, Jeb, he said. We've officially started the Orion Program, and the investors are impressed. We're going to need you again soon, Jeb. Do you want to continue? Oh boy, more explosions? Jeb replied with excitement. Count me in! I need a vacation, though, my back hurts from all the gees now. I knew you would be interested. We'll call you. Jeb, the Orion Rider. Has a nice ring to it, don't you think? Gene finished. Okay, I'm tired, I'll publish the next part later today or tomorrow, I hope. I have all the pictures ready. Did you like this? Any criticism, questions or recommendations? Please reply! Here are some bonus photos. They'll come with every episode. They are not canon, consider them bloopers. NEXT UP ON THUNDERSTRUCK: WHO PUT ORION ON A PLANE?
  4. The Hyperion Program: Kerbalkind's Return to Space Inspired by the Constellation Program Hello, and welcome to a new project that I am doing called the Hyperion Program, where after a long hiatus, kerbalkind returns to the Mun, and more. This is a stock part series, therefore it requires less time and effort than my more time-consuming series, 'Go For TLI', which was too much to keep up with schoolwork. Expect more frequent uploads than 'Go For TLI' for the time being, because of the reasons stated in the last sentence. The Hyperion Program will be more story-focused than my last series, although I'm not the best writer to grace this earth, so keep that in mind. Special Thanks: All of these ideas for my upcoming vehicles and plans didn't just come from me, they also came from things I have seen on this forum. @Kuiper_Belt's Shuttle Adventures, which is my original inspiration for this series. @Jay The Amazing Toaster‘s Kanawai: Ares to Mars thread. @AmateurAstronaut1969's ETS Space Station Freedom thread. @TheSaint's The Scrape of Things to Come. @track's One Giant Leap alternate history thread. @Angel-125's To the Mun!, Shuttle Launch System, and Commercial Space Ventures threads, for the cool mission ideas. And finally, me, for slapping myself enough times to stop being lazy in my free time to do this. I will update this original post to keep up with the current missions happening, so make sure to check the Mission and Vehicles List to get a more close-up view of the vessels of the program and a brief summary of the missions. Also, use the Chapters List if you want to quickly go to a chapter if you don't want to scroll through the pages. Chapter List: Mission and Vehicles List: Note: 1. If the text is slanted, it means that a kerbal is speaking from in-universe. 2. If the text is in (parentheses), it is a note from me, describing something from out-of-universe.
  5. Description The Blue Comet has its history debuting back in early 3480 A.E in the war against The Zxatan Imperium. One of the many heroes of the war, Zack Fireball Kerman and his trusty T-9 Specter. While this craft was feared for being a stealthy infiltration, he was known to show off with his flashy blue with reflective polished steel and signature Fireball. Flight Controls Action Groups Throttle - ascending kraken drive Full throttle - take-off (keep on to reach space) Half throttle - descending hover mode AG1 forward thrust kraken drive AG2 control from the command chair AG3 control from the probe unit AG4 open canopy Every time before the flight it will be controlled by default from the Probe unit tied to (action group 3) Press Radial Out and then throttle up to ascend with the vertical lifting Kraken drive. After you have achieved your desired altitude you can lower to half throttle to have a slow hover descend. When you are floating mid-air engage the forward thrust Kraken drive (action group 1) to achieve forward flight. Press (action group 2) to Control from your command chair and deselect Radial Out. Remain in half throttle and fly around in the atmosphere or fly off-planet. Adjust throttle for hovering on other planetary bodies. STOCK REQUIRES DLC DOWNLOADS Steam https://steamcommunity.com/sharedfiles/filedetails/?id=2734498805&searchtext= Kerbal X https://kerbalx.com/InterstellarKev/Blue-Comet Downloads for flags that are needed https://www.dropbox.com/s/23w6n1w8zvstdhl/bluecomet.zip?dl=0 https://drive.google.com/file/d/1BliF2g_CnBmm3v4vicypfMlvxJoM-kfi/view?usp=sharing
  6. Well, Well, Well. Another nation had the bold idea to start up a space program. Funds were allotted, engineers hired, and a suitable space center built. It was time for the great nation of United East Kerbonia to create the SENTINEL DESIGN BUREAU! (flag below): ____________________________________________________________________________________________________________ Chapters: Chapter 1 | Everyone has to Start Somewhere, Right? Chapter 2 | Higher and Higher! Chapter 3 | I'm BAAAAAACK ____________________________________________________________________________________________________________ This mission report is intended to be semi-serious, with a big dollop of realism and a big pinch of good o'l fashioned kerbal silliness. This is intended to last quite a bit longer than my last mission report, and my eventual goal is, as stated in the name, to go to the stars. You know, launch an interstellar ship the proper way, which I really haven't seen anyone really do yet. I'm also going to use a ton of mods, including Snacks-LS and 2.5X rescale. Anyways, lets go!
  7. Hello! I am happy to show you the Space industry job board I am working on. https://rocketcrew.space/ To populate the site with job offers, I created a web scraper for more than 25 Space companies. And I will include more in the future! Every apply link goes directly to the company career page. Let me know if you have any questions or feedback!
  8. Remember this rocket from Captain Earth when Globe launched it to prevent the alien menace? You know, the "Kill-T-Gang"? Now, this rocket has become a reality, in 5 different versions! Ladies and Gentlemen, I (and Mitsubishi themselves) present to you, the Pegasus rocket family! The rockets are as follows: Pegasus (the original) Pegasus-E (for Expendable) Pegasus-L (for Liquid, hinting at the liquid-fueled boosters) Pegasus-P (from "poudre", French for solid), and Pegasus-L Hydrolox , a more powerful (and environmentally friendly) version of the Pegasus, with 4 Hydrolox engines. Also included is the "X Base One Propulsion Section" for "X Base One" (in turn both based on NASA's Constellation program and the BBC's Doctor Who (Bowie Base One, The Waters of Mars), and the Pegasus 2, Pegasus-M for the MRC, Pegasus-H for my original "Hippogriff" spacecraft, Pegasus-O for the Orion spacecraft, Unicorn, EuroPegasus, DORUS, and a version for the launch of Mir's core module. See them on my hangar right here: https://kerbalx.com/hangars/145355
  9. Have you guys seen many rockets in anime? If so, just put the screenshots of the rocket's here.
  10. Since building common bases on celestial bodies are boring (no, they aren't) I decided to challenge myself to build the most unique and awkward base type in the game. The Hanging Base, on the Mün. This 5 part playlist will guide you through the process of how was it made, the failures and an expansion. Finally, I take a look at Tylo's Cave... Take a seat and enjoy!
  11. about the zephyr launch vehicle and Shetland launch site!!! i cant wait for zephyr to launch and also the Shetland launch site to be complete
  12. So I have a problem I have noticed others have had in the past with scatterer. I installed Graphics Enhancement Assembly, which comes with EVE and Scatterer along with some cloud and atmosphere textures for EVE to use. However I seem to be experiencing an issue. There is no skybox for space, instead of the many stars that should be there, there is only black. I am also missing an ocean surface, I can see the blue ocean bed, but no actual ocean surface. I saw another thread here and supposedly removing Transfer Window Planner did the job for them. That unfortunately didn't work for me. Screenshots: Missing Ocean Screenshot Black Skybox Screenshot Here are the mods I am using: B9 Aerospace BDArmoryContinued BDArmory Weapons Extension Cryogenic Engine Pack For Science! Kerbal Atomics Kerbal Engineer Redux Knes KSP Interstellar Extended KSP Recall MechJeb2 Mouse Aim Flight Near Future Electrical Near Future Launch Vehicles Near Future Propulsion Near Future Spacecraft Parts OPT Space Plane Parts 2.0 RCS Build Aid SpaceY Heavy Lifters Parts Pack Stockalike Station Parts Expansion Redux Time Control 2.0 Graphics Enhancement Assembly (includes EVE, BoulderCo, Distant Object, and Scatterer)
  13. From the original post: https://toughsf.blogspot.com/2020/07/tethers-all-way.html Space Tethers: Stringing up the Solar System All the methods we have used to reach space so far have been subject to the Tsiolkovsky rocket equation - propellant must be ejected and more and more of it is needed to go further. Art above is by Jullius Granada. What if we could break that equation with rotating orbital tethers? The tether I have worked with Kurzgesagt to write the following video on the topic of this post: https://www.youtube.com/watch?v=dqwpQarrDwk. It is highly recommended that you have watched it first before continuing, as it is an excellent introduction and explanation of momentum exchange tethers. The simple description is that a rotating tether, consisting of a strong cable with an attachment point at the tip and an anchoring counterweight at the center, will be able to catch and throw payloads without requiring a rocket engine. The process of hooking onto a payload to accelerate it into a new trajectory will transfer momentum from the counterweight to the payload, causing the tether to slow down. In reverse, a payload can be caught and slowed down, transferring momentum back into the counterweight and speeding it up. The ability to transfer momentum back and forth is why these structures are also called momentum exchange tethers. NASA has long studied this option. In this post, we will go into more detail on what is needed to create a functional rotating tether, how it can be used and what its potential effects are on space travel and industry could be. The mechanics Using a tether to move from one orbit to another, in this case LEO to GEO. The idea to use a long tether to climb into space without expelling propellant is an old idea. A huge tower extending up past the atmosphere was described by Tsiolkovsky. It is ironic that the person who first described how hard spaceflight by rocket is, due to the exponential nature of the deltaV equation, is also the person who described the best way to side-step that problem with non-rocket launch. The material requirements for a full space elevator are extreme. The only practical way to build it would be to use carbon nanomaterials, but extended to a scale of multiple kilometres instead of the micrometres we struggle to produce consistently in a laboratory today. It is why we must turn to something that provides some of the same benefits without the same stringent requirements. For this, there is the orbital tether concept. A large object in orbit, such as a satellite, space station, captured asteroid or similar, can serve as an anchor point to extend a strong cable down to a lower altitude. A payload can grab onto the lower end of the cable and climb up to the altitude of the anchor point. This climb does not require the use of propellant. The simplest design is a stationary orbiting elevator that provides a deltaV benefit based on the difference in orbital velocities at high and low altitudes. An LEO to GEO elevator. In the example above, an space station orbits at 2,000 km altitude, at an orbital velocity of 6.89 km/s. It performs one orbit in about 2 hours and 7 minutes. The lower tip extends down to an altitude of 200 km. It retains its orbital period but the distance it travels is much less, so velocity is reduced to 5.41 km/s. A circular orbit here is 7.78 km/s, so it provides a 2.37 km/s saving. The upper tip reaches up to 3,860 km altitude. It covers much more distance with the same orbital period, so velocity increases to 8.43 km/s, compared to the 6.24 km/s of everything else orbiting at that altitude. It is a 2.19 km/s boost. In total, we get a 4.56 km/s benefit. Huge altitude differences are needed to create the potential for significant deltaV savings. Because the lower tip of the tether is travelling at orbital velocity, it cannot extend too far down either; as it would encounter the atmosphere and burn up. A tether boost facility designed to be launched from a DeltaIV. A rotating tether does away with those limitations. The velocity of its tips and the speeds at which it can capture or release payloads can vary greatly from the orbital velocity of the anchor point. It can be much shorter too. At its lowest point, the tip of a rotating tether will be travelling at orbital velocity minus the rotation velocity. At its highest point, the two velocities will add up. The length of the tether itself will place the tips at very different altitudes at their highest and lowest points. Moving a payload between these altitudes is an additional benefit. Let’s imagine a modestly-sized tether orbiting at a high altitude above the Earth. It is 1,000 km long, orbiting at 1,100 km altitude and rotating once every 70 minutes. Its lowest point is 100 km above the surface of the Earth. Its highest point extends to an altitude of 2,100 km. Tip velocity is 1.5 km/s. It is tapered from base to tip to minimize its mass. Tapered tethers are the lightest design. Orbital velocity at 1,100 km is 7.3 km/s. At its lowest point, the tether tip will be travelling at 5.8 km/s relative to the ground. At its highest point, this value becomes 8.8 km/s. If a suborbital craft launched from the ground to try to catch up with the tip at its lowest and slowest, it would need to expend a deltaV of about 6.8 km/s. It can then quickly transfer a payload onto the tether. The payload then starts its 35 minute journey up around to the opposite end of the tether. It experiences an average acceleration of 0.23 g while doing so. At the top of the tether, it is released into a trajectory that forms an ellipse with its periapsis at 2,100 km altitude and its apoapsis at 13,500 km. It can then expend an additional 1.4 km/s of deltaV to reach the Moon, or about 1.6 km/s to escape the Earth entirely. If a typical 350s Isp kerosene-oxygen rocket is used, then it needs a total deltaV of about 8.2 km/s to ride the tether to the Moon. Meaning, it has an overall mass ratio of 10.9. However, if there is no tether available, then the deltaV requirement rises to 12.5 km/s and the mass ratio required balloons to 38! The tether is effectively saving 4.3 km/s of deltaV and leading to a much smaller rocket. The tether can also help with returning from the Moon. The spacecraft swoops down from lunar altitude (384,400 km) to a rendezvous with the tether at 2,100 km altitude. It would be travelling at 9.6 km/s, so it needs to spend an additional 0.8 km/s of deltaV to slow down enough to match the 8.8 km/s velocity of the tether's upper tip. In return, it avoids having to slam into the atmosphere and instead is swung down for much gentler aerobraking. The weight savings from having a thinner heatshield could more than make up for the propellant consumed, especially if this is a reusable vessel. Note that tethers do not have a single velocity for catching and releasing payloads. It is in fact a range of velocities, from zero up to the tip velocity. For capture at lower velocities, a payload can aim to intercept the tether at a point closer to the base of the tether. Halfway up the tether means a redezvous at half the tip velocity. The same goes for release; not releasing from the tether tip means a lower velocity. You can imagine a vehicle launching up from the ground to catch the tether tip at its lowest point, and instead of swinging around to the other side, just slowly climbing up the tether until it can hop off from the anchor station. This puts it in an orbit parallel to the anchor station, which is great if you are not trying to fly off to the Moon or beyond. However, making use of this flexibility means adding a way to prevent the unused length of the tether from striking the payloads coming in for a rendezvous, as well as providing structures that allow payloads to climb up and down the tether (although they can be as simple as a pulley and cables). The ISS regularly is regularly reboosted against the effects of drag. And of course, none of these deltaV savings are for ‘free’. Accelerating payloads means the tether will slow down. If it slows down too much, it will de-orbit itself. The momentum lost with each catch-and-release operation must be recovered either by absorbing momentum from payloads being slowed down, or by using its own propulsion system. A major advantage of an orbital tether is that you do not have to immediately recover that momentum - it gives time for slower but more efficient propulsion systems like a solar-electric thruster to gradually accelerate the tether. A chemical propulsion system limited to 450s of Isp is not needed as the acceleration can be done over time with something that has thousands of seconds of Isp. The propellant needed to run the tether’s engines is greatly reduced. Even more interesting is the possibility of propellantless propulsion, such as electrodynamic tethers that push off the magnetic fields around a planet. Electrodynamic tether reboost. Another advantage is that the tether can ‘store’ excess momentum. It can accelerate itself to a more energetic orbit with a higher velocity. For example, a tether in a 2,000x2,000 km circular orbit could accelerate by 1 km/s to reach a 2,000x9,565 km orbit. It can still capture payloads at the same 2,000 km altitude, but it will have an additional 1 km/s of velocity to use. The extra velocity can be used to accelerate the same payloads faster, more numerous payloads to the same speeds or larger payloads than possible before. Tether masses and velocities Tether structure and materials for the early TSS-1 experiment in orbit. The tether materials determine how fast the tips can rotate. Each material has a certain characteristic velocity, given by: Characteristic velocity = (2 * Tensile Strength / Density)^0.5 Characteristic velocity is in metres per second. Tensile Strength is in Pascals. Density is in kg/m^3. Steel is strong, with a maximal strength of 2,160 MPa for AerMet 340, but dense, at 7,860 kg/m^3. This gives it a characteristic velocity of 741 m/s. The aramid fiber Kevlar is stronger and lighter, managing 3,620 MPa with 1,440 kg/m^3. Its characteristic velocity is 2242 m/s. The strongest material we can mass-produce today is Toray’s polyacrylonitrile fiber T1100G. It can resist 7,000 MPa while having a density of 1,790 kg/m^3, so its characteristic velocity is 2,796 m/s. If we can describe the tip velocity as a multiple of the characteristic velocity, then we can use a much simpler equation to work out how much a tether will mass. We’ll call this the Velocity Ratio or VR. For example, 1.5 km/s is a VR of 2.02 for steel but only a VR of 0.54 for T1100G. The tether mass will be directly proportional to the payload mass. If it has to pull up a 1 ton payload, it will be ten times heavier than if it only needs to pull on 100 kg payloads. Using the VR, we can calculate the tether mass ratio using this equation: Tether Mass Ratio = 1.772 * VR * e^(VR^2) Tether Mass Ratio is a multiple of the payload mass, in kg. VR is the Velocity Ratio. Using the previous example, a 1.5 km/s steel tether will have to be 211.8 times heavier than its payload. A T1100G tether would only be 1.28 times heavier than its payload. This is a significant difference. The e^(VR^2) portion of the tether mass equation highlights just how important it is to use strong yet lightweight materials and to keep the tip velocity close to the characteristic velocity. Here is a graph showing how tether mass increases with the Velocity Ratio for different materials: It should be noted that all of these calculations are for a tether with no safety margins. Any sort of variation, such as vibrations from the counterweight or an imperfect capture of the payload, would snap it. A minimal safety margin might be 50%. Crewed spacecraft might demand a 200% margin or more. What this means in practice is that the maximum payload the tether could handle is reduced to create a safety margin. To overcome the limitations of the tether tip velocities, the tether can move into higher energy orbits. For example, a tether with a 1.5 km/s tip speed starts off in a circular 2000 km altitude orbit moves itself into a 2,000x1,000,000 km orbit. It can still capture payloads at the same altitude but it now does so at a velocity of 9,391 m/s instead of 6,897 m/s. This gives it 36% more momentum to give, and it can release payloads at a velocity of up to 10,891 m/s relative to the Earth. This is beyond the escape velocity at that altitude! If the tether had stuck to its initial 2000km circular orbit, its tip speed would have had to be 4 km/s instead, which would have meant an exponentially higher mass ratio. As the tether collects and releases payloads, it must adjust the distribution of its mass to maintain its center of rotation. Adjusting the tether with a moving counterweight on a 'crawler'. This can be done by shifting the counterweight, moving additional masses up and down the tether, changing the length of the tether using motors and/or having a dynamic suspension system that also helps dampen vibrations. In later sections, we will go through the various ways tethers can be used and combined to cover the entire Solar Systebm. Skyhook The skyhook process from Hoyt. The most immediately beneficial application of an orbital tether is the form of a Skyhook. This is a well-studied concept that dips the tether tip as low and slow as possible into the upper atmosphere, so that a suborbital craft can catch up to it, rendezvous, transfer a payload and then fly away. Getting off Earth and into orbit is a massive task. It requires that over 9 km/s of deltaV be delivered in one chunk, by a high thrust propulsion system. Chemical rockets can do this, but they end up as balloons of fuel with a small payload on the tip. A skyhook can help reduce deltaV requirements where they are hardest to deliver: at the end of a tiresome fight against Earth’s gravity. Because of the exponential nature of the Tsiolkovsky rocket equation, the last 1 km/s of deltaV costs much more than the first 1 km/s. The savings enabled by a Skyhook are therefore disproportionately high. Imagine a 200 km long tether anchored to a station orbiting at 400 km altitude. Its tip speed is 2.4 km/s. This means it travels over the ground at 5.3 km/s at its lowest point, and swings above at 10.1 km/s. A rocket trying to catch up with this tether at its lowest point must deliver 5.3 km/s of horizontal velocity, but also about 1.5 km/s to reach a 200 km altitude as well as make up for drag and gravity losses on the way up. Its deltaV requirement becomes 6.8 km/s. With kerosene and oxygen propellants delivering an average Isp of 330s, it would need a mass ratio of 8.17. This is well within the reach of a single-stage vehicle, even with margins to return and land vertically for reuse. For comparison, a kerosene/oxygen-fuelled vehicle that must make orbit would need 9.5 km/s and a mass ratio of 18.8. It would need multiple stages and it would be difficult to create deltaV margins for recovery. The tether-assisted rocket is 2.76 times smaller and lighter for the same payload! But that’s not all. The tether swings around and launches its payload into a 400 x 35,800 km orbit. This is also known as a geostationary transfer orbit (GTO) - an orbit where a rocket would only need an extra 1.5 km/s to turn into a 35,800 x 35,800 km geostationary orbit. The tether’s top-side boost is worth another 2.4 km/s. If it has to be delivered by the same vehicle that must reach orbit on its own, deltaV requirements would add up to 11.9 km/s. With 330s Isp propulsion, this means a staggering mass ratio of 39.5. Modern rockets get around this by fitting their upper stages with more efficient rocket engines, but they still take a huge hit to their payload capabilities when launching to GTO instead of LEO. ULA’s Delta IV Heavy could launch 28 tons into LEO but only 14 tons into GTO. We could do better. A faster tether that dips deeper into the atmosphere is possible, further reducing the deltaV requirements for meeting it and reducing the constraints on the vehicle we use. HASTOL. We don't really want the plane to exit the atmosphere. The lowest a tether tip could reasonably go is 50 km in altitude, making it 200 km long if it orbited at 250 km altitude. It could be pushed up to 6 km/s in tip speed, bringing its tip to a mere 1.7 km/s relative to the ground at its lowest point and to 13.7 km/s at its highest point. We can call this design a ‘Hypertether', inspired by works like HASTOL. 1.7 km/s corresponds to Mach 5 at this altitude. We have had aircraft reach these speeds and altitudes for decades, under rocket power. We have developed hypersonic scramjets that can sustain these speeds much more efficiently too. A large aircraft could meet a Hypertether using existing technologies reliably, without needing a lot of propellant or excessive thermal shielding. The exponential mass ratios that make rockets so expensive no longer come into play. Hypersonic rendezvous vehicles could climb to this altitude using engines with Isp exceeding 4000s (using hydrogen fuel), fly long enough to attempt multiple rendezvous with the tether (one attempt per tether rotation period) and land, ready to fly again within the hour. The downside to this approach is that the mass ratio of the tether itself becomes unwieldy. At 6 km/s, even T1100G tethers require a mass ratio of 379. The result is huge tethers in orbit needed to handle even the smallest of payloads. With a 200% safety margin, a 1 ton payload would need a 758 ton tether in these conditions. Launching such a mass into space and fitting it with an appropriately sized counterweight and anchor point would require hundreds of launches to break-even with the cost. A staged tether can get around some of these difficulties. Just like a rocket, a tether can be broken up into stages. Each stage uses the tip of the previous tether as its anchor point. If two 3 km/s tethers are staged, then they could achieve a combined 6 km/s tip velocity. However, each stage only needs a mass ratio of 6, with T1100G. A 1 ton payload would need 1x6: 6 ton first stage tether and a (1+6)x6 : 42 ton second stage tether. Add a 200% safety margin and it would still be an overall mass of 84 tons, which is much lower than the previous 758 tons for a single tether. Many difficulties must be overcome with this design. The first is the need to absorb any lateral movement which could cause tether sections to run into each other. The second is to create a stable joint that can operate under huge stresses. Using some of the mass savings from a staged tether design to alleviate these problems is recommended. Finally, each tether stage will be relatively short, leading to high centrifugal forces being imposed. If a 200 km long tether is divided into two 100 km sections, each rotating at 3 km/s, then payloads would be subjected to an acceleration varying between 9 and 18g. Much longer tethers would be needed for human travellers. Overcoming these difficulties would yield a flexible Hypertether with exceptional performance but low mass. A huge, slowly rotating skyhook would not look much different from a section of space elevator near the ground. The ideal skyhook, as originally conceived for science fiction, uses multiple stages so that its combined tether tip velocity matches its orbital velocity. It would become stationary relative to the ground with each rotation. This means a combined 7.7 km/s for a tether orbiting at 250 km altitude. No rendezvous vehicle is needed; payloads would simply sit on the ground and latch onto the descending hook from the sky. A huge number of additional challenges face this ‘perfect Skyhook’ design, ranging from the need to prevent unpredictable air turbulence from smashing tether stages into each other, to needing thermal protection for tethers that accelerate to multiple km/s while coming up through the thickest portions of the atmosphere. High performance skyhooks around Earth will mostly aim to lift payloads up from the ground and out into space. They are likely to run at a permanent momentum deficit; propulsion is essential. Obtaining propellant is an obstacle, as are the power requirements. The simplest solution is to sacrifice a portion of each payload using the tether to carry propellant. Low performance tethers that sit at high altitudes and with low tip velocities will make this a very expensive option. This is because they make rendezvous vehicles work hard to get to them. If a 1,000 ton tether station accelerated a 3 ton payload by 3 km/s from rendezvous to release, it would lose 9 m/s itself. Accelerating 1000 tons by 9 m/s using a 3,000s Isp engine requires about 305 kg of propellant. This means that, roughly, for every 9 payloads accelerated by the tether, a 10th launch is needed for refuelling. High performance tethers have it worse. They lose more momentum proportionally with each payload they accept, because of their higher tip speeds. Accelerating a 3 ton payload by 12 km/s slows down a 1,000 ton tether by 36 m/s, requiring 1,223 kg of propellant to recover! Thankfully, they make travel to space so much cheaper that sacrificing every third payload for propellant still makes for an overall saving over rockets. Extraterrestrial sources of propellant can be much more interesting. It normally takes less deltaV to move propellant from the Moon to LEO than it takes to move it up from the ground to LEO, at about 5.8 km/s vs 9.5 km/s. With aerobraking, the deltaV required to return from the Moon’s surface to Earth orbit is reduced to 2.8 km/s. Lunar sources of propellant remain interesting even when we adjust the deltaV requirements to account for the tether helping out. A tether with 3.1 km/s tip velocity would reduce the deltaV needed to lift off from Earth’s surface and enter into Low Earth Orbit to 6.4 km/s. It would also reduce the deltaV needed for a spaceship to launch off the Moon and enter Low Earth Orbit to 2.8 km/s. This keeps lunar sources of propellant the better option over terrestrial sources. Another advantage of extraterrestrial propellants for tethers is that capturing them ‘recharges’ the momentum of the tether. Catching 1 ton of propellant coming in at 3 km/s would accelerate a 1,000 ton tether by 3 m/s. Using that propellant for a 3,000s Isp thruster would further accelerate it by 29 m/s. That propellant is worth 10% more than expected! The absolute best propellant source of Skyhooks around Earth is the atmosphere itself. Atmospheric gas scooping is discussed in full detail here. A tether tip dipping into the atmosphere can ‘cheat’ the gas scooping retention equation by collecting gases at a lower velocity than the tether station’s orbital velocity. For example, a tether at 250 km altitude rotating at 3 km/s would collect gases at a velocity of 4.7 km/s. If a 3000s Isp engine running on nitrogen and oxygen is used, up to 84% of gases collected can be retained. The gases retained can then be fed to rockets using the tether, turning it into an orbital fuel depot. What’s more exciting is that it removes the restriction from the tether to have high Isp engines in the first place. They are bulky and power-hungry equipment. A tether that only aims to regain velocity would be satisfied with 0% gas retention. Lighter, simpler propulsion options like nuclear thermal rockets, with an Isp of just 480s, become acceptable. Alternatively, we could use hydrogen-oxygen chemical rocket where payloads coming up the tether provide 12% of the propellant and the remaining 88% is oxygen collected from the atmosphere. Better than any propellant source is not having to use any propellant. This is important for very high altitude tethers that do not meet the atmosphere. Electrodynamic propulsion pushes off the magnetic field around Earth. It only consumes electricity. Although the thrust per kW is very low, it is a reliable and already tested option. Powering all these propulsion options is another concern. Ideally, a tether station would want a compact and long-duration power source like a nuclear reactor. Solar panels are also available, but they require hefty energy storage solutions from the periods where the tether is in the Earth’s shadow, and the drag from the exposed panels adds to the momentum loss over time. Between these two options is the possibility for beamed power. Whether it is from the ground or a space station far above, energy can be transmitted over microwaves or a laser beam to the tether station, where it is converted back to electricity with high efficiency. Moonhook From Hop David's excellent blog. Getting off the lunar surface and into orbit involves much lower velocities than on Earth. There is no atmosphere imposing a minimum orbital altitude either. For these reasons, there are many proposals to install a rotating tether around the Moon first. Such a Moonhook would only need a tip velocity of about 1.5 km/s when orbiting at a 400 km altitude. Because of the lower velocities involved, it can be very lightweight, and easy to transport into a lunar orbit from Earth. There would be no erosion from passing through gases, and it would only have to avoid lunar mountains (up to 6km high) when coming down. This tether can help transfer payloads to the lunar surface, but also to other interesting locations, such as the L1 or L2 Lagrange points. It could be the centerpiece of a cislunar economy, and unlike the ‘lunar elevator’ concept, it does have to extend across hundreds of thousands of km to be useful. Phobos elevator suggested here. Reasons for a moonhook also apply to other moons. Phobos is a popular destination for small moonhooks, enabling access to the martian surface for 2.14 km/s. It could relay work with a tether around Deimos to enable a zero-propellant transfer into and out of the martian system. Interplanetary trajectories As mentioned in the previous section, tethers can easily fling payloads far beyond Earth. Here is a table of tether tip velocities needed to place payloads on Hohmann transfer trajectories to different planets: Injection DeltaV is the velocity increase in meters per second that the payload must receive to enter a trajectory that takes it near the destination. Another propulsion system is needed to actually slow down once it arrives. The mass ratio calculations are done for T1100G cables. You will notice that some destinations, like Mars or Venus, are well within the capabilities of reasonably sized tethers. Mercury or Ceres can be reached with very heavy tethers. Going beyond Jupiter strictly necessitates the use of staged tethers, with Neptune probably off-limits for an Earth-based tether. The DeltaV values listed above are for Hohmann trajectories. For the Outer Planets, minor increases in deltaV (8400 m/s instead of 8200 m/s for Uranus, for example) were selected to enable missions that took less than 10 years to perform. Tethers can speed up travel between planets, by entering payloads into higher energy trajectories. Here is another table showing how much travel times (in days) can be reduced by tethers with 4, 6 and 8 km/s tip velocities. Venus and Mars are the greatest beneficiaries of an extra boost from a faster tether. Mars sees up to 5 times shorter trips when using an 8 km/s tip velocity tether. When the injection deltaV becomes more demanding, the benefit is reduced. A good idea is to have spacecraft using tethers employ their own propulsion system. They can act as an additional ‘stage’ with their own mass ratio between propellant and payload. As we calculated before, staging massively reduces the difficulty of reaching a certain velocity. Here is an example: A spaceship using 450s Isp chemical rockets loads up 2 kg of fuel for each 1 kg of dry mass. This gives it a mass ratio of 3 and a total deltaV of 4850 m/s. It performs a rendezvous with a 6 km/s two-stage tether made out of T1100G cables. The first tether stage has a mass ratio of 12, to get a tip velocity of 3000 m/s and a 100% safety margin on top. The second tether stage also has a mass ratio of 12. Mass ratio of this system is 3 x 12 x 12: 432. The final velocity of 10,850 m/s enables trips to Jupiter in as little as 325 days, or to Uranus in 1551 days. A two-stage tether that tries to achieve this velocity would have had a mass ratio of over 22,000, while a single stage tether would have needed a ridiculous 23.8 megatons of cables for each ton of spaceship. Working through calculations like these really helps highlight just how similar a tether stage and its characteristic velocity is to a rocket stage and its exhaust velocity. Tether trains and interplanetary networks A tether can hand over a payload to another tether. These tethers can be in different orbits, and have different tip velocities, so long as the relative velocity falls to zero during a rendezvous. Three interesting scenarios for tether handovers can be considered: -Exchange between circular orbits A tether in a low orbit can fling a payload up to an altitude that intersects with a tether in a higher orbit. It is caught and further boosted from this higher orbit. Or, payloads can be sent down from the higher tether. Here is an illustrated example: It can work best when the higher tether is a geostationary space station, or these tethers are transporting payloads between different moons around a gas giant like Jupiter. The most interesting aspect is that the tethers can keep each other from losing momentum, so long as the masses they exchange are balanced. The lower tether is naturally larger, as it has to send payloads up with a greater velocity. It could set up a ‘train’ of many momentum-neutral exchanges with several tethers. -Exchange with eccentric orbits In this exchange, one of the tethers is in a low circular orbit and the second tether is in an eccentric orbit with the lowest point (the periapsis) intersecting the first tether’s orbit. Here is an illustrated example: The main advantage is that the tether’s own velocity is added to the boost it can provide a payload. Multiple tethers can be used in sequence, bridging the velocity gap between a tether in a low circular orbit and a very eccentric, near-escape orbit. Low Jupiter Orbit at 42 km/s and Jupiter Escape Velocity at 60 km/s are separated by an 18 km/s gap. Three tethers with tip velocities of 4.5 km/s can relay a payload between them. It does not have to be done all within the narrow window where tethers are all lined up at the lowest point of their respective trajectories. The transfer between orbits can be done one by one. The tether in the lowest orbit accelerates a payload at 4.5 km/s. It is received by a second tether with a tip velocity of 4.5 km/s. The combined boost is 9 km/s. This is done again, to reach a third tether station that is on a near-escape trajectory, with a periapsis velocity of just under 60 km/s. Any extra boost from this third tether would allow a payload to escape into interplanetary space. A full 4.5 km/s boost can put it on a trajectory that sends it all the way back to Earth. Using tethers like this will put the deep gravity well of Jupiter on the same level of accessibility as Mars or Venus. The energy-intensive transfer of crew or cargo up and out of Jupiter can be compensated for by slowing down equal masses of ‘junk’ such as iceball comets or discarded asteroids. We can also expand the use of ‘tether trains’ to interplanetary space. Stations orbiting the Sun on circular or eccentric orbits could pass payloads between them for ‘free’, so long as momentum exchanges are balanced. A tether attached to a small body, as envisioned here. These tethers can be anchored to asteroids, moons or mobile bases, much like the slow Aldrin Cycler concepts. Payloads can hop between tethers at these points gaining or losing velocity. A cycler station makes a trip between Earth and Mars on a regular orbit. Cyclers are most interesting as they perform orbits that take many years, but with tethers, they can send payloads between them much faster. Moving between cyclers in this manner can take on aspects of a train stopping between towns, especially if the cyclers gain large enough populations to become noteworthy destinations on their own. This can lead to a ‘Wild West’ aesthetic, or fulfil the need to visit new locations without having to cross interplanetary distances. A Solar System tethered together A switch in transport of payloads from expensive, slow, propellant-consuming rockets to rapid, low to zero-propellant tethers would have an outsized effect on human expansion into the Solar System. Human passengers will see great reductions in travel times. The combination of an initial boost from a tether, with deltaV provided by a spaceship’s propulsion system, will connect the Inner planets within a matter of weeks. Tethers provide the option to collect propellant more easily, which means those spaceships can afford to spend a lot more propellant than they otherwise could, in turn making travel even faster. Even the Outer planets could be reachable within a few months of travel time. That’s a great step up from multiple years. Enough perhaps to prevent distant colonies from becoming the destination for a ‘once-in-a-generation migration’. Cheaper, quicker travel for humans means that automation is not needed as much. Machinery doesn’t have to work for years on end without maintenance, as a repair crew could arrive regularly. A more mobile population means that space becomes open to less skilled, less experienced workers to fill in job positions wherever they appear, instead of every station or outpost having to rely on multi-skilled workers that can handle prolonged isolation. More people moving around means better chances that ‘extras’ like luxuries and personal services can be accommodated, improving living conditions and so on, in a positive feedback loop. Inert cargo will also benefit from tether transportation. High value goods can be exchanged quickly. A latest generation computer processor wouldn’t have to spend years being exposed to cosmic rays before it reaches a colony around Jupiter as an out-of-date and damaged product. Profits can be made on platinum ground metals a few weeks after they are mined; this means adventurous asteroid mining companies don’t have to hold onto cash reserves so that they can operate for months in between deliveries. They can be smaller, leaner and take more risks. On the other hand, larger payloads can be moved at the same speed with tethers for much less cost. An exchange between two tethers, one on Mars and one on Earth, can take the regular minimal-energy Hohmann trajectory. However, far less propellant would be needed (if any at all, with momentum-neutral exchanges). The payloads would not need any engines, heatshields or large cryogenic propellant tanks. With the use of tugs to maneuver the payloads into a rendezvous at either end, they won’t even need expensive guidance systems. Such cheap travel opens up many new possibilities. Asteroid mining usually considers elements like iron and aluminium to be ‘wastes’ as their value is too low to be worth moving around. Their only use would be at the site they are extracted from. This no longer has to be the case; a much larger fraction of an asteroid becomes exploitable. A beneficial side-effect is that accessing these low-value resources to build up a colony in a remote corner of the Solar System becomes even more affordable. Complete this scene with a spinning tether in the background. Large, slow payloads that can easily be outrun by tether-boosted spacecraft opens the door to piracy. A better transportation system helps with the methods discussed in these previous posts. A ‘pirate tether’ can fling spacecraft into intercepts with payloads in transit. Criminal ports would have higher performance tethers to catch diverted goods from odd angles and high velocities. This is especially useful for stealth craft that can use a tether to boost into a trajectory without announcing themselves, and don’t want to reveal the location of their safe haven by slowing down using rockets. Anything criminals can do, the military can do better. Tether boosts means warships are closer to targets than before. Reduced reliance on onboard propulsion for deltaV means that more mass can be dedicated to armor and weapons instead of propellant tanks. Also, as mentioned before, a secret network of tethers can be employed to move stealth craft around the Solar System. Munitions launched like this can be smaller and easier to hide too. Further developments Everything mentioned so far is only the start of what is possible with tethers. The use of tethers as aerodynamic devices is under-explored. Their use and performance can be expanded over time, as new ideas appear or better technologies are matured. We could consider a hybrid of a stationary and rotating tether. A rotating hub could be installed at the lower end of a very long stationary tether. It would collect a payload and transfer it to another rotating tether at the upper end by climbing up a stationary segment. The main advantage of this hybrid tether is that it can greatly extend the use of small, low velocity rotating tethers, while also not having to fully cover the distance to the destination like a simple stationary tether would have to. Supermaterials can also be considered. Tethers don’t need carbon nanotubes to function, but they can make great use of them. The characteristic velocity of graphene (130 GPa strength, 2267 kg/m^3) is 10,709 m/s. A tether to payload mass ratio of 10 enables a tip velocity of 12.3 km/s. A staged tether can get this up to 24.3 km/s with a total mass ratio of 100. That’s enough to fling a payload out of Low Jupiter Orbit with one single tether, or enable trajectories from Earth to Mars in 34 days, or to Saturn in 360 days. Between two tethers, we could see velocity gains of over 50 km/s… the main limitation would become human endurance. Even with a 6g tolerance limit, a tether tip velocity of 24.3 km/s means a minimum tether length of 10,000 km to reduce centrifugal forces! Going further, tether transport networks can be tied into the Inter-Orbital Kinetic Energy Exchange networks for transporting and generating energy, described here. Tethers can set up the exchange of masses, or even convert them into electricity themselves by using an electrodynamic tether in reverse: instead of consuming electricity to push against a magnetic field, using the field to generate a current while braking against it. Finally note that we haven’t considered the Oberth effect and that tethers can exploit it. Sending a payload down into a gravity well before rapidly accelerating it gives it an extra boost that does not match the momentum lost by the tether. The faster the tether tip, the greater the effect.
  14. I am building a really random space station and need help to think of ideas for it. I got the idea off "Matt Lowne "Collaboration station"" (pronounced mat lan) Don't feel bad if your idea is too ridiculous or has already been logged as an idea. instead be proud of it. just think: you've managed to make something too ridiculous even for me. or you had a good enough idea for it to already be logged. BTW, we've got stuff like cat repair droids and lawn mowers, you should find your idea accepted (unless it's not ridiculous enough. then I will make it a bit more interesting.) R.I.P fingers died from typing
  15. Since the first planes evolved, kerbals always wanted to ride them without flying them. Then, they were able too with the airliner. But ever since the founding of the Kerbal Space Center, kerbals have wanted to go to space without all the training. Well, let’s see if they can! CHALLENGE- Build 1 (or many) passenger SSTO’s that fit with the rules, categories, and qualifications. RULES- The craft must be an SSTO that takes off from the runway and lands on a runway (doesn’t need to be KSC, modded runways allowed). The craft must have pilot(s) and flight attendants unless stated. The craft must be able to land on and return from the destination. No mods or DLC’s involved in the craft. MechJeb autopilot not allowed, though orbital information and planners are allowed. Visual and informational mods allowed. No cheating with hyperedit, debug menu, etc. Craft must be of your own design. Please post the craft launch cost (cost displayed in SPH minus amount gained in recovery). When posting, please put your: company name, type of category, launch cost, passenger/crew/pilot count, and Delta V amount. Also include at least 3 pictures proving the functionality of the craft. CATEGORIES- Private SpaceLiner: 2-6 passenger capacity, 1 crew, 1-2 pilots. Destinations- Mun, Minmus, Gilly, Ike. Small SpaceLiner- 12-36 passenger capacity, 2 crew, 2-3 pilots. Destinations- Mun, Minmus, Gilly, Ike, Duna, Dres. Medium SpaceLiner- 37-55 passenger capacity, 3-4 crew, 2-3 pilots. Destinations- Mun, Minmus, Gilly, Ike, Duna, Dres, Eeloo. Large SpaceLiner- 56-125 passenger capacity, 5-7 crew, 3-4 pilots. Destinations- Mun, Minmus, Gilly, Ike, Duna, Dres, Eeloo, Pol, Bop, Val. Huge SpaceLiner- 125-250 passengers, 6-10 crew, 4 pilots. Destinations- Mun, Minmus, Gilly, Ike, Duna, Dres, Eeloo, Pol, Bop, Val, Laythe, Tylo, Moho. Super SpaceLiner- 250+ passenger capacity, 12-30 crew, 4-7 pilots. Destinations- Mun, Minmus, Gilly, Ike, Duna, Dres, Eeloo, Pol, Bop, Val, Laythe, Tylo, Moho, and Eve (if you dare). ADDED NOTES: The stated destinations does not mean you can only visit those places. As an example, you can take a private SpaceLiner to Ike, refuel, go to Duna, back to Ike, refuel, and go home as if they are connection flights. When I see a craft that catches my eye, I will ask for further details and/or craft file. If it is up the the highest standards, then it will go onto the Best SpaceLiners Leaderboard. Have fun designing and flying! Best SpaceLiners Leaderboard
  16. I am trying to design the a rocket that has the exact right amount of Delta-V required to get to the Mun and back. The first stage should be capable of getting the rocket clear of the atmosphere. I have looked everywhere for how much Delta-V the first stage needs and have found nothing. How much Delta-V should I be aiming for for my first stage to be able to get above 70 km?
  17. based on freedom space stationand the lunar getaway stationi will use a space craft called orionis
  18. This is fan made in photoshop, please consider the inaccuracy of my hand and sometimes this software. Kerbin scan: This is one of the hardest to scan, due to it's cloud layers. Using science, magic and photorock scientist made it clear to view it in an infrared light. The problem with infrared light that you cannot capture it with your eye. So scientists and wizards summoned the snack monster, and for a snack they made this picture in infrared light, sadly, the sun and other stars decided to interfere into the picture without an invite: (Taken using VASA's space-probe Interscarf. Camera Infradead. Editing software: Akode Photorock.) Using the same probe, we tried to capture it ultraviolet light. Sadly radiation interfered again, and we got this interesting picture to analyze.Maybe it's because of the transmission of the previous image. We wanted to take the image using Cameron, but it had an RTG: (Taken using VASA's space probe Interscarf. Camera Ultraviolin. Editing software: Akode photorock.) A gravity scan showed this image, the image was a hard capture due to the fluctuation of the radiation due to an RTG. This is the most accurate image that we got(not faked trust us: (Taken using VASA's space probe Cameron. Camera Cryptogravity. Editing software: Nopetad.) More celestial bodies photos soon. Copyright of VASA's space program under the license kreative kommons section 4.000001
  19. Europa Explorer is a project I have been working on to create a game inspired by real world science. You drive a robotic probe exploring the ocean on the moon Europa. You can download the alpha build from www.EuropaExplorerGame.com or Itch. This is a solo dev project by myself, so it is self promotion, but not for profit, so hopefully this post is within the forum rules. I have been doing bi-weekly video updates on my progress. If you want more info. Alpha 1 Update - Tools Alpha 2 Update - Systems Alpha 3 Update - World
  20. This is from Nuclear Reactor Lasers: from Fission to Photon: http://toughsf.blogspot.com/2019/04/nuclear-reactor-lasers-from-fission-to.html Nuclear Reactor Lasers: from Fission to Photon Nuclear reactor lasers are devices that can generate lasers from nuclear energy with little to no intermediate conversion steps. We work out just how effective they can be, and how they stack up against conventional electrically-powered lasers. You might want to re-think your space warfare and power beaming after this. Nuclear energy and space have been intertwined since the dawn of the space age. Fission power is reliable, enduring, compact and powerful. These attributes make it ideal for spacecraft that must make every kilogram of mass as useful and as functional as possible, as any excess mass would cost several times its weight in extra propellant. They aim for equipment for the highest specific power (or power density PD), meaning that it produces the most watts per kilogram. Lasers use a lasing medium that is rapidly energized or ‘pumped’ by a power source. Modern lasers use electric discharges from capacitors to pump gases, or a current running through diodes. The electrical power source means that they need a generator and low temperature radiators in addition to a nuclear reactor… these are significant mass penalties to a spaceship. Fission reactions produce X-rays, neutrons and high energy ions. The idea to use them to pump a lasing medium has existed ever since the first coherent wavelengths were released from a ruby crystal in 1960. Much research has been done in the 80s and 90s into nuclear-pumped lasers, especially as part of the Strategic Defense Initiative. If laser power can be generated directly from a reactor, there could be significant gains in power density. The research findings on nuclear reactor lasers were promising in many cases but did not succeed in convincing the US and Russian governments to continue their development. Why were they unsuccessful and what alternative designs could realize their promise of high power density lasers? Distinction between NBPLs and NRLs Most mentions of nuclear pumped lasers relate to nuclear bombpumped lasers. They are exemplified by project Excalibur: the idea was to use the output of a nuclear device to blast metal tubes with X-rays and have them produce coherent beams of their own. We will not be focusing on it. The concept has many problems that prevent it from being a useful replacement for conventional lasers. You first need to expend a nuclear warhead, which is a terribly wasteful use of fissile material. Only a tiny fraction of the warhead’s X-rays, which are emitted in all directions, are intercepted by the metal tube. From those, a tiny fraction of its energy is converted into coherent X-rays. If you multiply both fractions, you find an exceedingly low conversion ratio. Further research has revealed this to be on the order of <0.00001%. It also works for just a microsecond, each shot destroys its surroundings and its effective range is limited by relatively poor divergence of the beam. These downsides are acceptable for a system meant to take down a sudden and massive wave of ICBMs at ranges of 100 to 1000 kilometers, but not much else. Instead, we will be looking at nuclear reactor pumped lasers. These are lasers that draw power from the continuous output of a controlled fission reaction. Performance We talk about efficiency and power density to compare the lasers mentioned in this post. How are we working them out? For efficiency, we multiply the reactor’s output by the individual efficiencies of the laser conversion steps, and assume all inefficiencies become waste heat. The waste heat is handled by flat double-sided radiator panels operating at the lowest temperature of all the components, which is usually the laser itself. This will give a slightly poorer performance than what could be obtained from a real world engineered concept. The choice of radiator is influenced by the need for easy comparison instead of maximizing performance in individual designs. We will note the individual efficiencies as Er for the reactor, El for the laser and Ex for other components. The overall efficiency will be OE. OE = Er * Ex * El * Eh In most cases, Er and Eh can be approximated as equal to 1. As we are considering lasers for use in space with output on the order of several megawatts and beyond, it is more accurate to use the slope efficiency of a design rather than the reported efficiency. Laboratory tests on the milliwatt scale are dominated by the threshold pumping power, which cuts into output and reduces the efficiency. As the power is scaled up, the threshold power becomes a smaller and smaller fraction of the total power. Calculating power density (PD) in Watts per kg for several components working with each other’s outputs is a bit more complicated. As above, we’ll note them PDr, PDl, PDh, PDx and so on. The equation is: PD = (PDr * OE) / (1 + PDr (Ex/PDx + Ex*El/PDl + (1 - Ex*El)/PDh)) Generally, the reactor is a negligible contributor to the total mass of equipment, as it is in the several hundred kW/kg, so we can simplify the equation to: PD = OE / (Ex/PDx + Ex*El/PDl + (1 - Ex*El)/PDh) Inputting PDx, PDl and PDh values in kW/kg creates a PD value also in kW/kg. Direct Pumping The most straightforward way of creating a nuclear reactor laser is to have fission products interact directly with a lasing medium. Only gaseous lasing mediums, such as xenon or neon, could survive the conditions inside a nuclear reactor indefinitely, but this has not stopped attempts at pumping a solid lasing medium. Three methods of energizing or pumping a laser medium have been successful. Wall pumping Wall pumping uses a channel through which a gaseous lasing medium flows while surrounded by nuclear fuel. The fuel is bombarded by neutrons from a nearby reactor. The walls then release fission fragments that collide with atoms in the lasing medium and transfer their energy to be released as photons. The fragments are large and slow so they don’t travel far into a gas and tend to concentrate their energy near the walls. If the channels are too wide, the center of the channel is untouched and the lasing medium is unevenly pumped. This can create a laser of very poor quality. To counter this, the channels are made as narrow as possible, giving the fragments less distance to travel. However, this multiplies the numbers of channels needed to produce a certain amount of power, and with it the mass penalty from having many walls filled with dense fissile fuel. The walls absorb half of the fission fragments they create immediately. They release the surviving fragments from both faces of fissile fuel wall. So, a large fraction of the fission fragment power is wasted. They are also limited by the melting temperatures of the fuel. If too many fission fragments are absorbed, the heat would the walls to fail, so active cooling is needed for high power output. The FALCON experiments achieved an efficiency of 2.5% when using xenon to produce a 1733 nm wavelength beam. Gas laser experiments at relatively low temperatures reported single-wavelength efficiencies as high as 3.6%. The best reported performance was 5.6% efficiency from an Argon-Xenon mix producing 1733 nm laser light, from Sandia National Laboratory. Producing shorter wavelengths using other lasing mediums, such as metal vapours, resulted in much worse performance (<0.01% efficiency). Higher efficiencies could be gained from a carbon monoxide or carbon dioxide lasing medium, with up to 70% possible, but their wavelengths are 5 and 10 micrometers respectively (which makes for a very short ranged laser) and a real efficiency of only 0.5% has been demonstrated. One estimate presented in this paper is a wall-pumped mix of Helium and Xenon that converts 400 MW of nuclear power into 1 MW of laser power with a 1733 nm wavelength. It is expected to mass 100 tons. That is an efficiency of 0.25% and a power density of just 10 W/kg. It illustrates the fact that designs meant to sit on the ground are not useful references. A chart from this NASA report reads as a direct pumped nuclear reactor laser with 10% overall efficiency having a power density of about 500 W/kg, brought down to 200 W/kg when including radiators, shielding and other components. Volumetric pumping Volumetric pumping has Helium-3 mixed in with a gaseous lasing medium to absorb neutrons from a reactor. Neutrons are quite penetrating and can traverse large volumes of gas, while Helium 3 is very good at absorbing neutrons. When Helium-3 absorbs neutrons, it creates charged particles that in turn energize lasing atoms when they enter into contact with each other. Therefore, neutrons can fully energize the entire volume of gas. The main advantages of this type of laser pumping is the much reduced temperature restrictions and the lighter structures needed to handle the gas when compared to multiple narrow channels filled with dense fuel. However, Helium-3 converts neutrons into charged particles with very low efficiency, with volumetric pumping experiments reporting 0.1 to 1% efficiency overall. This is because the charged particles being created contain only a small portion of the energy the Helium-3 initially receives. Semiconductor pumping The final successful pumping method is direct pumping of a semiconductor laser with fission fragments. The efficiency is respectable at 20%, and the compact laser allows for significant mass savings, but the lasing medium is quickly destroyed by the intense radiation. It consists of a thin layer of highly enriched uranium sitting on a silicon or gallium semiconductor, with diamond serving as both moderator and heatsink. There are very few details available on this type of pumping. A space-optimized semiconductor design from this paper that suggests that an overall power density of 5 kW/kg is possible. It notes later on that even 18 kW/kg is achievable. It is unknown how the radiation degradation issue could be solved and whether this includes waste heat management equipment. Without an operating temperature and a detailed breakdown of the component masses assumed, we cannot work it out on our own. Other direct pumped designs Wall or volumetric pumping designs were conceived when nuclear technology was still new and fission fuel had to stay in dense and solid masses to achieve criticality. More modern advances allow for more effective forms for the fuel to take. The lasing medium could be made to interact directly with a self-sustaining reactor core. This involves mixing the lasing medium with uranium fluoride gas, uranium aerosols, uranium vapour at very high temperatures or uranium micro-particles at low temperatures. The trouble with uranium fluoride gas and aerosols or micro-particles is the tendency for them to re-absorb the energy (quenching) of excited lasing atoms. This has prevented any lasing action from being realized in all experiments so far. As this diagram shows, uranium fluoride gas absorbs most wavelengths very well, further reducing laser output. If there is a lasing medium that is not quenched by uranium fluoride, then there is potential for extraordinary performance. An early NASA report on an uranium fluoride reactor lasers for space gives a best figure of 73.3 W/kg from what is understood to be a 100 MW reactor converting 5% of its output into 340 nanometer wavelength laser light. With the radiators in the report, this falls to 56.8 W/kg. It we bump up the operating temperature to 1000K, reduce the moderator to the 20cm minimum, replace the pressure vessel with ceramics and use more modern carbon fiber radiators, we can expect the power density of that design to increase to 136 W/kg. Uranium vapours are another option. They require temperatures of 4000K and upwards but if the problem of handling those temperatures is solved (perhaps by using actively cooled graphite containers), then 80% of the nuclear output can be used to excite the lasing medium, for an overall efficiency that is increased four-fold over wall pumping designs. More speculative is encasing uranium inside a C60 Buckminsterfullerene sphere. Fission fragments could exit the sphere while also preventing the quenching of the lasing material. This would allow for excellent transmission of nuclear power into the lasing medium, without extreme temperature requirements. Nuclear-electric comparison With these numbers in mind, it does not look like direct pumping is the revolutionary upgrade over electric lasers that was predicted in the 60s. Turbines, generators, radiators and laser diodes have improved by a lot, and they deliver a large fraction of a reactor’s output in laser light. We expect a space-optimized nuclear-electric powerplant with a diode laser to have rather good performance when using cutting edge technology available today. With a 100 kW/kg reactor core, a 50% efficient turbine at 10 kW/kg, an 80% efficient electrical generator at 5 kW/kg, powering 60% efficient diodes at 7 kW/kg and using 1.34 kW/kg radiators to get rid of waste heat (323K temperature), we get an overall efficiency of 24% and a power density of 323 W/kg. A more advanced system using a very powerful 1 MW/kg reactor core, a 60% efficient MHD generator at 100 kW/kg with 1000K 56.7 kW/kg radiators, powering a 50% efficient fiber laser cooled by 450K 2.3 kW/kg radiators, would get an overall efficiency of 30% and a power density of 2.5 kW/kg. Can we beat these figures with reactor lasers? Indirect pumping The direct pumping method uses the small fraction of a reactor’s output that is released in the form of neutrons, or problematic fission fragments. Would it not be better to use the entire output of the nuclear reaction? Indirect pumping allows us to use 100% of the output in the form of heat. This heat can then be converted into laser light in various ways. Research and data for some of the following types of lasers comes from solar-heated designsthat attempt to use concentrated sunlight to heat up an intermediate blackbody that in turn radiates onto a lasing medium. For our purposes, we are replacing the heat of the Sun with a reactor power source. It is sometimes called a ‘blackbody laser’ in that case. Blackbody radiation pump At high temperatures, a blackbody emitter radiates strongly in certain wavelengths that lasing materials can be pumped with. A reactor can easily heat up a black carbon surface to temperatures of 2000 to 3000K – this is what nuclear rockets are expected to operate at anyhow. Some of the spectrum of a blackbody at those temperatures lies within the wavelengths that are absorbed well by certain crystal and gaseous lasing mediums. Neodymium-doped Ytrrium-Aluminium-Garnet (Nd:YAG) specifically is a crystal lasing medium that has been thoroughly investigated as a candidate for a blackbody-pumped laser. It produces 1060 nm beams. Efficiency figures vary. A simple single-pass configuration results in very poor efficiency (0.1 to 2%). This is because the lasing medium only absorbs a small portion of the entire blackbody spectrum. In simpler terms, if we shine everything from 100 nm to 10,000 nm onto a lasing medium, it will convert 0.1 to 2% of that light into a laser beam and turn the rest into waste heat. With this performance, blackbody pumped lasers are no better than direct pumped reactor laser designs from the previous section. Instead, researchers have come up with a way to recover the 99 to 99.9% of the blackbody spectrum that the lasing medium does not use. This is the recycled-heat blackbody pumped laser. An Nd:YAG crystal sits inside a ‘hot tube’. Blackbody radiation coming from the tube walls passes through the crystal. The crystal is thin and nearly transparent to all wavelengths. The illustration above uses Ti:Sapphire but the concept is the same for any laser crystal. Only about 2% of blackbody spectrum is absorbed with every pass through the crystal. The remaining 97 to 98% pass through to return to the hot tube’s walls. They are absorbed by a black carbon surface and recycled into heat. Over many radiation, absorption and recycling cycles, the fraction of total energy that becomes laser light increases for an excellent overall efficiency. 35% efficiency with a Nd:YAG laser was achieved. The only downside is that the Nd:YAG crystal needs intense radiation within it to start producing a beam. The previous document suggests that 150 MW/m^3 is needed. Another source indicates 800 MW/m^3. We also know that efficiency increases with intensity. If we aim for 1 GW/m^3, which corresponds to 268 Watts shining on each square centimetre of a 1 cm diameter lasing rod, we would need a 1:1 ratio of emitting to receiving area if the emitter has a temperature of at least 2622K. From a power conversion perspective, a 98% transparent crystal that converts 35% of spectrum it absorbs means it is only converting 0.7% of every Watt of blackbody radiation that shines through it. So, a crystal rod that receives 268 Watts on each square centimetre will release 1.87 W of laser light. We can use the 1:1 ratio of emitter and receiver area to reduce weight and increase power density. Ideally, we can stack emitter and receiver as flat surfaces separated by just enough space to prevent heat transfer through conduction. Reactor coolant channels, carbon emitting surface (1cm), filler gas, Nd:YAG crystal (1cm) and helium channels can be placed back to back. The volume could end up looking like a rectangular cuboid, interspaced by mirror cavities. 20 kg/m^2 carbon layers and 45.5 kg/m^2 crystal layers that release 1.87 W per square centimetre, with a 15% weight surplus for other structures and coolant pipes, puts this component’s power density at about 250 W/kg. The laser crystal is cooled from 417K according to the set-up in this paper. Getting rid of megawatts at such a low temperature is troublesome. Huge radiator surface areas will be required. As we are using flat panel radiators throughout this post, we have only two variables: material density, material thickness and operating temperature. The latter is set by the referenced document. We will choose a 1mm thick radiator made of low density polyethylene. We obtain 0.46 kg/m^2 are plausible. When radiating at 417K, they could achieve 3.73 kW/kg. It is likely that they will operate at a slightly lower temperature to allow for a thermal gradient that transfers heat out of the lasing medium and into the panels, and the mass of piping and pumps is not to be ignored, but it is all very hard to estimate and is more easily included in a 15% overall power density penalty for unaccounted-for components. A 100 kW/kg reactor, 250 W/kg emitter-laser stack and 3.73 kW/kg radiators would mean an overall power density of 188 W/kg, after applying the penalty. Gaseous lasing mediums could hold many advantages over a crystal lasing medium. They require much less radiation intensity (W/m^3) to start producing a laser beam. This researchstates that an iodine laser requires 450 times less intensity than an equivalent solid-state laser. It is also easier to cool a gas laser, as we can simply get the gas to flow through a radiator. On the other hand, turbulent flow and thermal lensing effects can deteriorate the quality of a beam into uselessness. No attempts have been reported on applying the heat recycling method from the Nd:YAG laser to greatly boost efficiency in a gas laser. Much research has been performed instead on direct solar-pumped lasers where the sunlight passes through a gaseous medium just once. The Sun can be considered to be a blackbody emitter at a temperature of 5850K. Scientists have found the lasing mediums best suited to being pumped by concentrated sunlight – they absorb the largest fraction of the sunlight’s energy. That fraction is low in absolute terms, meaning poor overall performance. An iodine-based lasing medium reported 0.2% efficiency. Even worse efficiency of 0.01% was achieved when using an optically-pumped bromine laser. Similarly, C3F7I, an iodine molecule which produces 1315 nm laser light, was considered the best at 1% efficiency. Solid blackbody emitters are limited to temperatures just above 3000K. There would be a great mismatch between the spectrum this sort of blackbody releases and the wavelengths the gaseous lasing mediums cited above require. In short, the efficiency would fall below 0.1% in all cases. One final option is Gallium-Arsenic-Phosphorus Vertical External Cavity Surface Emitting Laser (VECSEL) designed for use in solar-powered designs. It can absorb wavelengths between 300 and 900nm, which represents 65% of the solar wavelengths but only 20% of the radiation from a 3000K blackbody. This works out to an emitter with a power density of 45.9 kW/kg. The average efficiency is 50% when producing a 1100nm beam. Since it is extracting 20% of the wavelengths from the emitter, this amounts to 10% overall efficiency. Using the numbers in this paper, we can surmise that the VECSEL can handle just under 20 MW/kg. The mass of the laser is therefore negligible. With a 100 kW/kg reactor, we work out a power density of 3.1 kW/kg. VECSELs can operate at high temperatures, but they suffer from a significant efficiency loss. We will keep them at 300K at most. It is very troublesome as 20 MW of light is needed to be concentrated on the VECSEL to start producing a laser beam. 90% of that light is being turned into waste heat within a surface a few micrometers thick. Diamond heatsink helps in the short term but not in continuous operation. Radiator power density will suffer. Even lightweight plastic panels at 300K struggle to reach 1 kW/kg. When paired with the previous equipment and under a 15% penalty for unaccounted for components, it means an overall power density of 91 W/kg. This illustrates why an opaque pumping medium is unsuitable for direct pumping as it does not allow for recycling of the waste heat. Filtered blackbody pumping A high temperature emitter radiates all of its wavelengths into the blackbody-pumped lasing medium. We described a method above for preventing the lasing medium from absorbing 98 to 99.9% of the incoming energy and turning it immediately into waste heat. The requirement was that the lasing medium be very transparent to simply let through the unwanted wavelengths. However, this imposes several design restrictions on the lasing medium. It has to be thin, it has to be cooled by transparent fluids, and it might have to sit right next to a source of high temperature heat while staying at a low temperature itself. We can instead filter out solely the laser pumping wavelengths from the blackbody spectrum and send those to the lasing medium while recycling the rest. The tool to do this is a diffraction grating. There are many other ways of extracting specific wavelengths from a blackbody radiation spectrum, such as luminescent dyes or simple filters, but this method is the most efficient. Like a prism, a diffraction grating can separate out wavelengths from white light and send them off in different directions. For most of those paths, we can put a mirror in the way that send the unwanted wavelengths back into the blackbody emitter. For a small number of them, we have a different mirror that reflects a specific wavelength into the lasing medium. A lasing medium that receives just a small selection of optimal wavelengths is called optically pumped. It is a common feature of a large number of lasers, most notably LED-pumped designs. We can use them as a reference for the potential performance of this method. We must note that while we can get high efficiencies, power is still limited, as in the previous section. Extracting a portion of the broadband spectrum that the lasing medium accepts also means that power output is reduced to that portion. Another limitation is the temperature of the material serving as a blackbody emitter. The nuclear reactor that supplies the heat to the emitter is limited to 3000K in most cases, so the emitter must be at that temperature or lower (even if a carbon emitter can handle 3915K at low pressures and up to 4800K at high pressures, while sublimating rapidly). Thankfully, the emission spectrum of a 3000K blackbody overlaps well with the range of wavelengths an infrared fiber laser can be pumped with. A good example is an erbium-doped lithium-lanthanide-fluoride lasing medium in fiber lasers. We could use it to produce green light as pictured above, but invisible infrared is more effective. As we can see from here, erbium absorbs wavelengths between 960 and 1000 nm rather well. It re-emits them at 1530 nm wavelength laser light with an efficiency reported to be 42% in the ‘high Al content’ configuration, which is close the 50% slope efficiency. In fact, the 960-1000 nm band represents 2.7% of the total energy emitted. It is absorbing 125 kW from each square meter of emitter. If the emitter is 1 cm thick plate of carbon and the diffraction grating, with other internal optics needed to guide light into the narrow fiber laser, are 90% efficient, then we can expect an emitter power density of about 5.6 kW/kg. Another example absorbs 1460 to 1530 nm light to produce a 1650 nm beam. This is 3.7% of the 3000K emitter’s spectrum, meaning an emitter power density of 7.7 kW/kg. The best numbers come from ytterbium fiber lasers. They have a wider band of wavelengths that can be pumped with, 850 to 1000 nm (which is 10.1% of the emitter’s output), and they convert it into 1060 nm laser light with a very high efficiency (90%). It would give the emitter an effective power density of 23.4 kW/kg. More importantly, we have examplesoperating at 773K. The respected Thorlabs manufacturer gives information about the fiber lasers themselves. They can handle 2.5 GW/m^2 continuously, up to 10GW/m^2 before destruction. Their largest LMA-20 core seems to be able to handle 38 kW/kg of pumping power. It is far from the limit. Based on numbers provided by this experiment, we estimate the fiber laser alone to be on the order of 95kW/kg. Another source works out a thermal-load-limited fiber laser with 84% efficiency to have a power density of 695 kW/kg before the polymer cladding melts at 473K. We can try to estimate the overall power density of a fiber laser. A 100 kW/kg reactor is used to heat a 23.4 kW/kg emitter, where a diffraction grating filters out 90% of the output to be fed into a fiber laser with 90% efficiency and negligible mass. The waste heat is handled by 1mm thick carbon fiber panels operating at 773K for a power density of 20.2 kW/kg. Altogether, this gives us 11 kW/kg after we include the same penalty as before. If it is too difficult to direct light from a blackbody emitter into the narrow cores of fiber lasers, then a simple lasing crystal could be used. This is unlikely, as it has already been done, even in high radiation environments. Nd:YAG, liberated from the constraint of having to be nearly entirely transparent, can achieve good performance. It can sustain a temperature of 789K. We know that Nd:YAG can achieve excellent efficiency when being pumped by very intense 808nm light to produce a 1064nm beam, of 62%. It is hoped that this efficiency is maintained across the lasing crystal’s 730 to 830nm absorption band. A 3000K blackbody emitter releases 6% of its energy in that band. At 20 kg/m^2, this gives a power density of 13.8 kW/kg. We will cut off 10% due to losses involved in the filtering and internal optics. As before, the laser crystal itself handles enough pumping power on its own to have a negligible mass. The radiators operating at 789K will require carbon fiber panels. They’ll manage a power density of 22 kW/kg. Optimistically, we can expect a power density of 3.7 kW/kg (reduced by 15%) when we include all the components necessary. Ultra-high-temperature blackbody pumped laser We must increase the temperature of the blackbody emitter. It can radiate more energy across the entire spectrum, and concentrates it in a narrower selection of shorter wavelengths. Solid blackbody surfaces are insufficient. To go beyond temperatures of 4000K, we must consider liquid, gaseous and even plasma blackbody emitters. This requires us to abandon conventional solid-fuel reactors and look at more extreme designs. There is a synergy to be gained though. The nuclear fuel can also act as blackbody emitter if light is allowed to escape the reactor. Let us consider two very high to ultra-high temperature reactor designs that can do that: a 4200K liquid uranium core with a gas-layer-protected transparent quartz window and a 19,000K gaseous uranium-fluoride ‘lightbulb’ reactor. For each design, we will try to find an appropriate laser that makes the best use of the blackbody spectrum that is available. 4200K: Uranium melts at 1450K and boils at 4500K. It can therefore be held as a dense liquid at 4200K. We base ourselves on this liquid-core nuclear thermal rocket, where a layer of fissile fuel is held against the walls of a drum by centrifugal effects. The walls are 10% reflective and 90% transparent. The reflective sections hold neutron moderators to maintain criticality. This will be beryllium protected by a protected silver mirror. It absorbs wavelengths shorter than 250 nm and reflects longer wavelengths with 98% reflectivity. We expect the neutron moderator in the reflective sections, combined with a very highly enriched uranium fuel, to still manage criticality. The spinning liquid should spread the heat evenly and create a somewhat uniform 4200K surface acting as a blackbody emitter. The transparent sections are multi-layered fused quartz. It is very transparent to the wavelengths a 4200K blackbody emitter radiates – this means it does not heat up much by absorbing the light passing through. We cannot have the molten uranium touch the drum walls. We need a low thermal conductivity gas layer to separate the fuel from the walls and act like a cushion of air for the spinning fuel to sit on. Neon is perfect for this. It is mentioned as ideal for being placed between quartz walls and fission fuel in nuclear lightbulb reactor designs. The density difference between hot neon gas and uranium fuel is great enough to prevent mixing, and the low thermal conductivity (coupled with high gas velocity) reduces heat transfer through conduction. We might aim to have neon enter the core at 1000K and exit at 2000K. There is still some transfer of energy between the fuel and the walls because the mirrors are not perfect; about 1.8% of the reactor’s emitted light is absorbed as heat in the walls. Another 0.7% in the form of neutrons and gamma rays enters the moderator. We therefore require an active cooling solution to channel coolant through the beryllium and between the quartz layers. Helium can be used. It has the one of the highest heat capacities of all simple gases, is inert and is even more transparent than quartz. Beryllium and silver can survive 1000K temperatures, so that will set our helium gas temperature limit. A heat exchanger can transfer the heat the neon picks up to the cooler helium loop. The helium is first expanded through a turbine. It radiates its accumulated heat at 1000K. It is then compressed by a shaft driven by the turbine. If we assume that the reactor has power density levels similar to this liquid core rocket (1 MW/kg) and that 2.5% of its output becomes waste heat, then it can act as a blackbody emitter with a power density of 980 kW/kg. Getting rid of the waste heat requires 1 mm thick carbon fiber radiators operating at 1400K. Adding in the weight of those radiators and we get 676 kW/kg. A good fit might be a titanium-sapphire laser. It would absorb the large range of wavelengths between 400 and 650 nm. That’s 18.5% of a 4200K emitter’s spectrum. If we use a diffraction grating to filter out just those wavelengths, and include some losses due to internal optics, we get 125 kW of useful wavelengths per kg of reactor-emitter. The crystal can operate at up to 450K temperature, with 40% efficiency. Other experimentsinto the temperature sensitivity of the Ti:Al2O3 crystal reveals lasing action even at 500K, with mention of a 10% reduction to efficiency. We will use the 36% figure for the laser to be on the safe side. Based on data from this flashpumping experiment and this crystal database, we know that it can easily handle 1.88 MW/kg. The mass contribution of the laser itself is negligible. Any wavelengths that get absorbed but are not turned into laser light become waste heat. At 450K temperature, we can still use the lower density by HDPE plastic panels to get a waste heat management solution with 4.6 kW/kg. Putting all the components together and applying a 15% penalty just to be conservative, we obtain an overall power density of 2.2 kW/kg. 19,000: If we want to go hotter, we have to go for fissioning gases. Gas-core ‘lightbulb’ nuclear reactors will be our model. The closed-cycle ‘lightbulb’ design has uranium heat up to the point where it is a very high temperature gas. That gas radiated most of its energy in the form of ultraviolet light. A rocket engine, as described in the ‘NASA reference’ designs, would have the ultraviolet be absorbed by small tungsten particles seeded within a hydrogen propellant flow. 4600 MW of power was released from an 8333K gas held by quartz tubes, with a total engine mass of 32 tons. We want to use the uranium gas as a light source. More specifically, we want to maximize the amount of energy released in wavelengths between 120 and 190 nm. 19,000K is required. It is within reach, as is shown here. Unlike a rocket engine, we cannot have a hydrogen propellant absorb waste heat and release it through a nozzle. The NASA reference was designed around reducing waste heat to remove the need for radiators, but we will need them. Compared to the reference design, we would have 27 times the output due to the higher temperatures, but then we have to add the mass of the extra radiators. About 15% of the reactor’s output is lost as waste heat in the original design. It was expected that all the remaining output is absorbed by the propellant. We will be having a lasing gas instead of propellant in between the quartz tube and the reactor walls. The gas is too thin to absorb all the radiation, so to prevent it all from being absorbed by the gas walls, we will use mirrors. Polished, UV-grade aluminium can handle the UV radiation. It reflects it back through the laser medium and into the quartz tubes to be recycled into heat. Just like the blackbody-pumped Nd:YAG laser, we can create a situation where the pumping light makes multiple passes through the lasing medium until the maximum fraction is absorbed. Based on this calculator and this UV enhanced coating, we can say that >95% of the wavelengths emitted by a 19,000K blackbody surface are reflected. In total, 20% of the reactor’s output becomes waste heat. Since aluminium melts at 933K, we will keep a safe temperature margin and operate at 800K. This should have only a marginal effect on the mirror’s reflective properties. Waste heat must be removed at this temperature. As in the liquid fuel reactor, the coolant fluid passes through a turbine, into a radiator and is compressed on its way back into the reactor. Neon is used for the quartz tube, helium for the reactor walls and the gaseous lasing medium is its own coolant. Based on the reference design, the reactor would have 4.56 MW/kg in output, or 3.65 MW/kg after inefficiencies. If the radiators operate at 750K and use carbon fiber fins, we can expect a power density for the reactor-emitter of 70.57 kW/kg. 28.9% of the radiation emitted by a 19,000K blackbody surface, specifically wavelengths between 120 and 190nm, is absorbed by a Xenon-Fluoride gas laser. They are converted into a 350nm beam with 10% efficiency in a single-pass experiment. In our case, the lasing medium is optically thin. Much of the radiated energy passes through un-absorbed. The mirrors on the walls recycles those wavelengths for multiple passes, similar to the Nd:YAG design mentioned previously. Efficiency could rise as high as the maximal 43%. This paper suggests the maximal efficiency for converting between absorbed and emitted light is 39%. We’ll use an in-between figure of 30%. This means that the effective power density of the reactor-emitter-laser system is 6.12 kW/kg. The XeF lasing medium is mostly unaffected by temperatures of 800K, so long as the proper density is maintained. We can therefore cool down the lasing medium with same radiators as for the reactor-emitter (17.94 kW/kg). When we include the waste heat of the laser, we get an overall power density of 2.9 kW/kg, after applying a 15% penalty. A better power density can be obtained by having a separate radiator for each component that absorbs waste heat (quartz tubes, lasing medium, reactor walls) so that they operate at higher temperatures, but that would be much more complex. Aerosol fluorescer reactor The design can be found with all its details in this paper. Tiny micrometer-sized particles of fissile fuel are surrounded in moderator and held at high temperatures. Their nuclear output, in the form of fission fragments, escapes the micro-particles and strikes Xenon-Fluoride or Iodine gas mixtures to create XeF* or I2* excimers. These return to their stable state by releasing photons of a specific wavelength through fluorescence. Their efficiency according to the following table is 19-50%. Simply, it is an excimer laser that is pumped by fission fragments instead of electron beams. I2* is preferred for its greater efficiency and ability to produce 342 nm beams. Technically, this is an indirect pumping method, but it shares most of its attributes with direct pumping reactor lasers. The overall design is conservatively estimated at 15 tons overall mass, but with improvements to the micro-particle composition (such as using plutonium or a reflective coating), it could be reduced even further. It is able to produce 1 MJ pulses of 1 millisecond duration. With one pulse a second, this a power density of 66 W/kg. One hundred pulses mean 6.6 kW/kg. One thousand pulses, or quasi-continuous operation, would yield 66 kW per kg. The only limit to the reactor-laser’s power density is heat build-up. At 5% efficiency, there is nineteen times more waste heat than laser power leaving the reactor. We expect that using the UV mirrors from the previous design could drastically improve this figure by recycling light that was not absorbed by the lasing medium in the first pass through. Thankfully, the 1000K temperature allows for some pretty effective management of waste heat. Carbon fiber panels of 1mm thickness, operating at 1000K would handle 56.7 kW/kg. It would give the reactor a maximum power density of 2.4 kW/kg, including a 15% penalty for other equipment. If the reactor can operate closer to the melting point of its beryllium moderator, perhaps 1400K, then it can increase its power density to 8.3 kW/kg. Conclusion Reactor lasers, when designed appropriately, allow for high powered lasers from lightweight devices. We have multiple examples of designs, either from references or calculated, that output several kW of laser power per kg. The primary limitations of many of the designs can be adjusted in ways that drastically improve performance. The assumptions made (for instance, 1 cm thick carbon emitter or flat panel radiators) are solely for the sake of easy comparison. It is entirely acceptable to use 1mm thick emitting surfaces or one of the alternate heat radiator designs mentioned in this previous blog post. Even better, many of the lower temperature lasers can have their waste heat raised to a higher temperature using a heat pump. Smaller and lighter radiators can then be used for a small penalty in overall efficiency to power the heat pumps. Most of the lasers discussed have rather long wavelengths. This is not great for use in space, as the distances they beam has to traverse are huge and it multiplies the size of the focusing optics required. For this reason, a method of shortening the wavelengths, perhaps using frequency doubling, is recommended. Halving the wavelength doubles the effective range. However, there is a 20-30% efficiency penalty for using frequency doubling. Conversely, lasers which produce short wavelength beams have a great advantage. The list of laser options for each type of pumping is also by no means exhaustive. There might be options not considered here that would allow for much greater performance… but research on such options is very limited. For example, blackbody and LED pumping seems to be a ‘dead’ field of research, now that diodes can produce a single wavelength of the desired power. Up-to-date performance of those options is therefore non-existent and so we cannot fairly compare their performance to lasers which have been developed in their stead. It should be pointed out that a direct comparison between reactor and electric lasers is not the whole story. Reactor lasers can easily be converted into dual-mode use, where 100% of their heat is used for propulsion purposes. A spaceship with an electric laser can only a fraction of their output in an electric rocket. For example, the 4200K laser can have a performance close to the liquid-core rocket design it was derived from. Other, like the aerosol fluorescer laser, can both create a beam and heat propellant at the same time. A nuclear-electric system must choose where to send its electrical output and must accept the 60% reduction in overall power due to the conversion steps between heat and electricity at all times. Finally, certain reactor lasers have hidden strength when facing hostile forces. Mirrors work both ways. The same optics and mirrors that transport your laser beam from the lasing medium out into space and to an enemy target can be exploited by an enemy to get their beam to travel down the optics and mirrors and reach your lasing medium. The lasing medium, assumed to be diodes or other semiconductor lasers, has to operate at relatively low temperatures and so it will melt and be destroyed under the focused glare of the enemy beam. Tactics around using lasers and counter-lasers, something called ‘eyeball-frying contests’ can sometimes lead to a large and powerful warship being brought to a stalemate by a small counter-laser. A nuclear reactor laser’s lasing medium can be hot gas or fissioning fuel. They are pretty much immune to the extra heat from an enemy beam. It would render them much more resistant to ‘eye-frying’ tactics. This, and many other strengths and consequences, become available to you if you include nuclear reactor lasers in your science fiction. PS: I must apologize for using many sources that can only be fully accessed through a paywall. It was a necessity when researching this topic, on which little detail is available to the public. For this same reason, illustrations had to be derived from documents I cannot directly link to, but they are all referenced in links in this post.
  21. I wonder how long would take ISS to do decay it's orbit and burns up if no one would boost it to its proper orbit?
  22. Anyone know what the heck is VVV-WIT-07?
  23. ¡Buenos días! ¿Como están?, Vengo a darles una invitación para entrar a un grupo de Whatsapp en español de ksp. Si están interesados mandarme un mensaje al privado Saludos
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