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About me



  1. Hello friends, just wanted to share some music I made recently that's based off of KSP! Definitely one of my favorite songs so far this year Google drive link is below: https://drive.google.com/file/d/1LKBXoOcyCTbaRNoAuz3a3kDcUoZ_3G8t/view?usp=sharing Please let me know if the link doesn't work, sometimes my stuff gets messed up. Much love -Mieyo
  2. 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.
  3. This is just gonna document my missions in a new save I will call "Kerbol Space Program". No story, just me documenting missions. So far I havent started anything yet, so I'll begin that soon. Anyways, I hope this doesnt flunk. This is also modded, but really just to add some stuff like better graphics, some more parts, and better IVA.
  4. Naval Battle League Test your naval prowess in this extravaganza of Battleships, Bombs, and Booms. Rules Rules are mandatory in order to play and be counted on the league table 1- Battles are conducted by exchanging save or persistence files over sharing sites. 2- Each player takes it in turns to engage one target with one ship. Any number of ships may be moved in said turn. 3- Ships engage in order of tonnage, lightest to heaviest. Once all ships are used the cycle repeats. 4- The team with the last ship wins. Ties can be declared with both team's approval. 5- Screenshots or videos documenting all moves are needed to complete a turn. 6- Any mods which affect craft or persistence files are forbidden. 7- No quick-loading except in cases of game bugs. 8- All moves must be done manually, without the aid of autopilots. Previous Iterations Guidelines Guidelines are opt out additions to the rules to create as fair and free from exploits a stage as possible. 1- A ship is officially considered dead when the main body of the ship is incapable of fulfilling two of three goals unaided from other ships or on-board weapons... +Sustaining power +Moving +Firing weapons. 2- Weapons can only be fired from the original ship core and must be used within the the same turn that they are fired. 3- Players are not allowed to control enemy craft. 4- Players are not allowed to intentionally edit the orbit of enemy craft via weapons fire or any other method. 5- Any number of ships may be moved in a turn but only one may attack. 6- Ramming is disallowed. 7- Stealing is allowed under the pretense that the parent ship is dead and the items are disconnected from it. 8- Weapons must be fired between 5000 and 15 meters. 9- Surface to orbit weapons may be fired once per turn if applicable,and are exempt from Guideline 8. 10- A team may forfeit a turn at any point. Carriers Additional Guidelines to ensure carriers remain balanced in combat. 1- The total mass of carriers includes fighters and any other items being carried. 2- Carrier fighters have a mass limit of 15 tons, anything heavier will be included as a seperate ship. 3- Carriers will take their turn at the beginning of a cycle. 4- Fighters may be released from any distance but the fighters must still abide to Guideline 8. 5- Carriers may not use heavy armor on a majority of their area. 6- All fighters must return to the carrier by the end of the turn. 7- Carriers can not use their own offensive weapons. Settings -Body -Guideline exclusions -Maximum number of craft -Maximum total combined mass (These are recommended to be negotiated) Scoreboard MiffedStarfish: 3(5) Spartwo: 1(1) Alphasus: 0(3) Skriptkitt3h: 0(2) Quasarrgames: 0(2) DarkOwl57: -1(1) Sdj64: -1(1) Servo: -1(1) Shadowgoat: -1(2) Username: Score(number of battles) -1 from total for a loss +1 for a win 0 for a tie. Numbers increase according to the amount of players... -1/1 -1/0/1 -2/-1/1/2 -2/-1/0/1/2 ...and so on. Please @, quote, or PM me having completed a battle for updates to scoring Discord There was a demand. https://discord.gg/rqqe3u4T79
  5. ¡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
  6. first, here is how it works: take a famous quote that is space-related. then kerbalize it. just make sure it isn't offensive or against the guidelines. so, I'll start with two: John F. Kerman: "We choose to go to the mun, not because it is easy, not because it is hard but because we can use even moar boosters." Neil Kerman: "one small step for a kerbal, one giant leap for the tech tree" edit: once we reach a second page, I will nominate one comment as the winner and ask the mods to close the thread. Edit edit: aviation quotes are also allowed (but make sure they're kerbalized)
  7. We need more reasons to send rockets to space for progression in game. What if we add telescopes! If we add a science instrument to be able to detect other worlds and other solar systems and bodies. It would add to the game. Imagine, the only thing in the solar system is Kerbin, Mun, and the Sun. We want to explore! We send a telescope to low orbit and we discover a new moon, a new planet to explore and then we would have that accomplishment in finding new celestial bodies that we can visit!
  8. KSP is a space exploration game that allows players to relive their childhood dreams of flying through the stars. It's a sandbox game in which players create and manage spacecrafts from scratch. You can also download add-on packs that let you explore other parts of the solar system and even nearby star systems. Realism mods allow you to experience spaceflight in a way that's much more true to reality than computer games have been in the past. Realism mods add attributes to KSP that make it more like real space missions. Some common mods include real fuel and crew limits, accurate values for spacecrafts' mass, weight, and thrust; realistic orbital periods; realistic rendezvous and landing procedures; realistic weather variations; realistic interstellar travel capabilities; and realistic galactic map rendering. Implementing these mods makes your space missions much more authentic and challenging. Space exploration is an ongoing process that pushes humans closer to reaching the limit of our knowledge. For example, getting a human on the moon was a huge accomplishment, but now we're trying to get humans off of Earth. To do this, we need to develop spacecrafts that can withstand extreme conditions in outer space - including zero gravity, high temperatures and low air pressure. These spacecrafts need to travel great distances and return with samples from other planets. The crews who do these great deeds are very dedicated and often willing to risk their lives to achieve their goals. To experience this type of intense gameplay, you'll need several realism mods installed. Some players use KSP as a tool for exploring other career paths in engineering. For example, one user developed a modded mission where players controlled a rover instead of a spacecraft. This let players experience land-based exploration without any risk of injury or death. Other popular mods let players control ocean vessels like ships or submarines. You can also control aircrafts through suborbital or orbital flights with modded tutorials. There are many ways to add variety to your space missions- just look around KSP for inspiration! Overall space exploration is one of mankind's biggest accomplishments thus far in our history. Games like KSP help us relive childhood dreams of flying through the stars or exploring other parts of our galaxy. Thanks to mods, now anyone can enjoy realistic experiences like these without sacrificing playtime or immersion! Can I please have links to realistic mods please. thank you. your work is deeply appreciated!!!
  9. 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.
  10. 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?
  11. 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
  12. Welcome to the Release thread for James Webb for Kerbal! James Webb For Kerbal 1.12.x "The Legend" Update This has been tested with Textures Unlimited, Tarsier Space Technology, Tweakscale and Cacteye2 for version 1.12.x. Recommended Mods: Reflections by Textures Unlimited by @Shadowmage Functional space telescope powered by Tarsier Space Technologies by @JPLRepo Functional space telescope powered by Cacteye2 by @linuxgurugamer DOWNLOAD 1.12.x: Download Old versions only: Download Installation: Extract the contents of the GameData folder to your GameData folder. Structure should then read GameData\JamesWebb Usage: I recommend taking a look at the component guides to get an idea of where the parts attach to the base structure. Please leave feedback, comments and suggestions and certainly some pictures! Select from multiple "Control From Here" points to orient vehicle control based on launch or telescope configuration. Changelog: Update 1.12.x "The Legend" Removed all dependency requirements Re-size the entire main structure Part is now considered a 3.75m part and not a 5m part (uses 2.5m decoupler) Re-size side solar panels to fit new structure size Re-create the entire sunshield and animation using bones to drop the Textures Unlimited (blend shapes animation loading) requirement Adjusted the timings of the entire deployment animation to be more equivalent to the real deployment Renamed the deployment animation action to "Open Aperture" to play nicely with Cacteye Model is loaded as a .mu and not an smf Re-texture entire main unit + solar panels Scale-down the RCS thrusters size Scale-down Main + Side antenna sizes Fix location of all attachment points due to structure's change in size Fix engine FX location Various Textures Unlimited (optional) changes: -Sunshield is now a flat texture -The body is all wrinkled and looks like actual foil -Secondary mirror is reflective -Camera/Sensor is reflective -Shiny flat sections on body ("flaps"/solar panel mounts) Added 5 new TSST telescope targets in infrared taken from Spitzer Added Cacteye compatibility (acts as the telescope part) Update 1.9.x (1.10LTE) Re-compile all parts on 1.10 part tools Tested with 1.9.x Textures Unlimited and TSST and also tested on KSP 1.10.1 Hotfix 1.4.2 Fixed transform issue where "Control from here" node for swapping back to vertical view not working Update 1.4 Rebuild and recompile for 1.4 Fixed base structure center point / origin Reassembled and exported model with very slightly altered scale Fixed center thrust point Re-aligned all attachment nodes Added 8x attachment points for the RCS thrusters RCS Thrusters now have an attachment node Fixed rear solar panel center point / origin Reduced SAS power Greatly increased SAS electricity cost to promote maneuver accuracy *** Be sure to upgrade to the latest versions of Textures Unlimited and Tarsier Space Technology Update 1.1 Increased zoom Built-in TSST hard drive Sunshield layers now "rise" into correct final locations Telescope orientation can now be switched between Engines / camera optics with multiple "control from here" options Tweakscale compatibility RCS thrusters 30% larger And please upgrade to the new textures unlimited to fix random exploding fairings. A VERY SPECIAL THANK YOU TO: @CobaltWolf , @Shadowmage, @Beale, @steedcrugeon, @dboi88, @Stone Blue, @Fengist, @JadeOfMaar, @Nertea, @JPLRepo, @Angel-125 and all of the other devs who have been incredibly helpful throughout this entire journey. It was 70 days in the making for James Webb for Kerbal 1.0. Brushes by 'tech brush by DayZee by dariaDZ' KottabosGames Review: James Webb For Kerbal is License CC-BY-4.0 https://creativecommons.org/licenses/by/4.0/
  13. Hi! I've got something new for y'all! Liquid Rhenium Solar Thermal Rocket The maximum temperature concentrated sunlight can heat a material to is 5800K. How do we approach this limit? We will describe existing and potential designs for solar thermal rockets. Solar thermal rockets The Solar Moth The principle of a solar thermal rocket is simple. You collect sunlight and focus it to heat a propellant headed for a nozzle. A rocket engine's performance is determined by its thrust, exhaust velocity and efficiency. A solar thermal rocket's thrust can be increased by sending more propellant through the nozzle. Its exhaust velocity can be increased by raising the propellant temperature. Doing either required more power, so more sunlight needs to be collected. Efficiency will depend on the design. The main advantages of a solar thermal rocket are its potential for high power density, high efficiency and high exhaust velocity. Collecting and heating with sunlight does not need massive equipment - unlike solar electric spacecraft that need solar panels, extremely lightweight reflective metal films can be used. A heat exchanger above a nozzle is compact and masses much less than the electrical equipment and electromagnetic or electrostatic accelerators a solar electric craft uses. Radiators are not needed either, as the propellant carries away the heat it absorbs with it. Put together, a solar thermal rocket can achieve power densities of 1MW/kg while solar electric craft struggle to rise above 1kW/kg. Sunlight would follow the same path as the laser beam here. As the sunlight is being absorbed by a propellant and expanded through a nozzle, there are only two energy conversion steps: sunlight to heat, then heat to kinetic energy. The first step can be assumed to be 99% efficient. The second step depends on nozzle design, but is generally better than 80%. Exhaust velocity will be determined by the root mean square velocity of the gas the propellant turns into. The equation is: Exhaust velocity: (3 * R * Temperature * 1000 / Molar mass ) ^ 0.5 Temperature is in Kelvins. Molar mass is the average g/mol value of the propellant at the temperature it is heated to. R is the molar gas constant, equal to 8.314 J/mol/K. For the very hot gasses we will be considering, we can assume complete dissociation of all molecules. H2 (2g/mol) will become atomic hydrogen (1g/mol), water (18g/mol) becomes a hydrogen-oxygen vapor (6g/mol) and so on. Low molar masses are preferred, with the best propellant being mono-atomic hydrogen unless other factors are considered. These advantages are all the critical elements that allow for travel throughout the inner solar system without requiring vast quantities of propellant. This means smaller spacecraft and lower travel times. Heat exchangers and exhaust velocity The limiting factor for solar thermal rockets is how hot they can heat the propellant. Directly heating the propellant is a difficult task. The lowest molar mass propellant, hydrogen, has terrible absorption. For all practical purposes, it is transparent to sunlight. Seeding the propellant with dust particles that absorb sunlight and heat the hydrogen indirectly through conduction has a major catch: the dust particles get dragged along by the hydrogen propellant flow and increase the average molar mass. A single millimeter-sized carbon dust particle in a cubic meter of hydrogen increases the molar mass from 1g/mol to Indirect heating involved using a heat exchanger as an intermediary between the sunlight collected and the propellant being heated. So far, designs have required the use of a solid mass of metal that is heated up by concentrated sunlight. The propellant is run over the metal, or through channels in the metal, to absorb the heat. Tungsten is often selected for this task, as it has a high resistance to heat, is strong even near its melting point and has a good thermal conductivity. Testing a Hafnium/Silicon Carbide coating. More modern designs make the most of the latest advances in materials technology to allow for higher operating temperatures. Carbon, notably, stays solid at temperatures as high as 4000K. Tantalum hafnium carbide and a new Hafnium-Nitrogen-Carbon compound melt at temperatures of 4200 and 4400K respectively. However, looking at our exhaust velocity equation, the limits of modern materials technology will only provide a 21% increase over common tungsten. This is the reason why so many propulsion technologies that rely on exchanging heat between a heat source, such as a nuclear fuel or a laser beam, and a propellant using a solid interface are said to be 'materials limited' to an exhaust velocity of 9.6km/s with tungsten, or 10km/s with carbon. THC or HNC would allow for an exhaust velocity of 10.5km/s. This is the deltaV equation, also known as the Tsiolkovsky rocket equation: DeltaV = ln (Wet mass / Dry mass) * Exhaust Velocity Wet mass is how much spaceship masses with a full load of propellant. Dry mass is the mass without any propellant. The wet to dry mass is also referred to as the 'mass ratio' of a rocket. We can rewrite the rocket equation to work out the required mass ratio to achieve a certain deltaV using a rocket engine's exhaust velocity: Mass ratio = e ^ (DeltaV required/Exhaust Velocity) 'e' is the exponent 2.7182... in simpler terms, the mass ratio increases exponentially as the deltaV required increases. Or, put another way, the mass ratio required decreases exponentially as the exhaust velocity rises. It is critical to have a higher exhaust velocity for rapid space travel without requiring massive rockets and towers of propellant. You might also have noticed that 'solid' is a keyword up to this point. Why must the heat exchanger remain solid? Liquid Rhenium There is a method to achieve the true maximal performance of a solar thermal rocket, which is heating up the propellant as far as it can go. This is incidentally the temperature of the surface of the sun (5800K). At this temperature, hydrogen propellant reaches an exhaust velocity of 12km/s. A rare, silver-black metal. Rhenium is a rare metal with a surprising number of qualities, one of which is a very high boiling point. Rhenium melts at 3459K but remains liquid up to 5903K. The trick to achieving higher exhaust velocities is to use a molten heat exchanger, specifically liquid rhenium at a temperature of 5800K. Rhenium is also very stable and does not react with hydrogen even at high temperatures, which is something carbon-based materials struggle to survive. It has already been considered as a heat exchanger, in solid form, by NASA. Here is a design that can use liquid rhenium as a heat exchanger: The diagram is for illustrative purposes only - a functional schematic would be more detailed. Here is an explanation for each component: Solar collector: A very large, very lightweight reflective film based on solar sails that can collect sunlight and focus it through a series of lens onto the heat exchanger fluid's inner surface. Rotating drum: The drum's inner surface contains a liquid heat exchanger. The outer surface is actively cooled. The drum is dotted with tiny channels that allow the propellant to enter the liquid from the bottom and bubble through to the top. It is made of Tantalum-Hafnium Carbide. Fluid surface: The fluid here is liquid rhenium. Its surface is heated to 5800K by concentrated sunlight. The lower layers nearer the drum holding the fluid is cooler. The centripetal forces hold the fluid in place Pressure chamber: The rotating gas mix gets separated here. Dense rhenium vapours fall back down, hot hydrogen escapes. Bubble-through heating: The rotation induces artificial gravity, allowing the hydrogen to heat up and rise through the denser rhenium. As it rises, it reaches hotter layers of the fluid heat exchanger. At the surface, it has reached 5800K. Small bubbles in direct contact with the rhenium allows for optimal thermal conductivity. More detail below. Active cooling loop: liquid hydrogen from the propellant tanks makes a first pass through the drum walls, lowering the temperature below the melting point of THC. It emerges as hot, high pressure gaseous hydrogen. High pressure loop: The heated hydrogen is forced through the channels in the drum. It emerges into the fluid heat exchanger as a series of tiny bubbles. Here is a close up of the drum wall, which contains both active cooling and high pressure channels: The configuration displayed above allows the hydrogen to enter the basin bottom at 4000K, then be heated further to 5800K before being ejected into the pressure chamber. If higher quantities of liquid hydrogen for active cooling are used, the drum and high pressure channel temperatures can be lowered to 3800, 3500, 3000K or lower. This pebble-bed nuclear thermal reactor has most of the components of our solar thermal rocket, except that instead using pebbles of nuclear, fuel, we use a liquid rhenium bed heated by sunlight. If the liquid hydrogen active cooling cannot handle the full heat load, radiators will be needed to cool down the drum below its melting point of 4215K. Thankfully, these radiators will receive coolant at 4000K. Their operating temperature will be incredibly high, allowing for tiny surface areas to reject tens of megawatts of waste heat. Electricity can also be generated by exploiting the temperature difference across the radiators' entrance and exit flows, and at very high efficiency. Operation The design is a Rotating Drum Fluid Heat Exchanger Solar Thermal Rocket (RD-FHE STR). It allows for hydrogen propellant to reach 5800K and achieve the maximum performance of a Solar Thermal Rocket. Liquid rhenium does not boil at 5800K, so it remain liquid and can be held inside the basin by simple centripetal forces. Vapor pressure of rhenium at 5800K (0.was determined to be low enough for our purposes. A surface of rhenium exposed to vacuum at that temperature would lose 0.076g/cm^2/s, or 762g/m^2/s. It is unknown how much centripetal force affects the loss rate of rhenium. The pressure chamber would operate at several dozens of atmospheres of pressure, which is known to increase the boiling point and reduce the evaporation rate of fluids. The same techniques used in Open-Cycle Gas Core nuclear reactors to prevent the loss of uranium gas can be applied to reducing the loss of rhenium vapours. At worst, the rhenium heat exchanger loses 0.76 kg of rhenium for square meter per second of operation. Looking at the designs below, the mass flow rate is measured in tons of hydrogen per second. This is a ratio of 1000:1, to be improved by various rhenium-retaining techniques. It should also be noted that rhenium is a very expensive material. A tungsten-rhenium mixhas very similar thermal properties and is much cheaper. Sunlight at 1AU provides 1367W/m^2. A broad-spectrum reflecting surface such as polished aluminium would capture and concentrate over 95% of this energy, so more than 1298W would be available per square meter. Solar sails materials such as 5um Mylar sheets are preferred, massing only 7g/m^2. More advanced materials technology, such as aluminium film resting on graphene foam, might mass as little as 0.1g/m^2. The 'Solar Moth' used inflatable support structure for its mirrors. Based on data for the Solar Moth concept, we have estimated that a solar thermal propulsion system can attain power densities of 1MW/kg. So, each square meter of collector area will require another 1.29 grams of equipment to convert sunlight into propulsive power. Performance Robot Asteroid Prospector We will calculate the performance of two versions of the RD-FHE STR. The first version uses modern materials and technologies, such as a 7g/m^2 Mylar sheet to collect sunlight and a 167kW/kg engine power density. The second version is more advanced, using 0.1g/m^2 sunlight collectors and a 1MW/kg power density. Modern RD-FHE 5 ton collection area => 714285m^2 927MW of sunlight focused onto the drum. 5.56 ton propulsion system Exhaust velocity: 12km/s Thrust: 123.4kN (80% efficiency) Thrust-to-weight ratio: 1.19 Overall power density: 87kW/kg Advanced RD-FHE 5 ton collection area =>50000000m^2 64.9GW of sunlight received 64.9 ton propulsion system Exhaust velocity: 12km/s Thrust: 10.8MN Thrust-to-weight ratio: 15.75 Overall power density: 928kW/kg The principal argument against solar thermal rockets, that their TWR is too low and their acceleration would take too long to justify the increase in Isp, can be beaten by using very high temperatures and very low mass sunlight collectors. For example, a 50 ton propulsion system based on the modern RD-FHE STR design, would be able to push 100 ton payloads to Mars (6km/s mission deltaV) using only 97 tons of propellant. It would leave Earth orbit at a decent 0.24g of acceleration, averaging 0.32g. The departure burn would take only 20 minutes. Using the advanced version of the RD-FHE solar thermal rocket would allow for a positively impressive acceleration of 3.1g. With 12km/s exhaust velocity, multiple missions that chemical rockets struggled to do with low-energy Hohmann transfers can be avoided. A chemical rocket such as SpaceX's BFR might achieve an Isp of 375s, which corresponds to an exhaust velocity of 3.67km/s. It would need a mass ratio of 5.13 to barely produce enough deltaV for a Mars mission. Earth to Destination. If our solar thermal rocket is granted the same mass ratio, it would have a deltaV of 19.6km/s. This allows for a Mars mission to be completed in under two months (10km/s departure, 9km/s insertion). It is also enough deltaV to reach Jupiter with a single stage. Other benefits include a vast reduction in the propellant-producing infrastructure needed to supply orbital refuelling depots and the ability to land on Mercury. Alternative versions: Blown hydrogen: Instead of bubbling hydrogen from the bottom of the liquid rhenium basin, hydrogen is blown into the pressure chamber from the top. It is heated by simply passing over the fluid heat exchanger. The advantage is that the rotating drum does not have to be riddled by microchannels, allowing it to be stronger and rotate faster, which would reduce rhenium losses, and also accept a higher rate of active cooling by leaving more room for liquid hydrogen channels. Another advantage is that there is less chance of hydrogen bubbles merging and exploding in showers at the surface, dragging along rhenium as they escape. The disadvantages is vastly reduced heat conduction rate between the rhenium and the hydrogen. This would require a long and thin pressure chamber to increase the time the hydrogen stays in contact with the rhenium, potentially making the propulsion system heavier than it needs to be and forcing sunlight to enter the chamber at very acute angles. ISRU propellants: Instead of hydrogen, other gaseous propellants might be used. Nitrogen is a good choice, as it is inert and only reduces the exhaust velocity by a factor 3.7 compared to hydrogen. Powering a hydrogen extraction process on Mars requires huge areas of solar panels. Nitrogen is easily sourced from Earth's atmosphere by gas scoops. Other options, such as water or carbon dioxide, are also viable and available on other planets. The advantage is that non-hydrogen propellants are easy to contain and are much denser than hydrogen, so their propellant tanks can be lightweight and small. They are easily sourced and only need to be scooped up and filtered, unlike hydrogen that has to undergo electrolysis. The disadvantage is that there propellants cannot serve as expandable coolant for the rotating drum. A radiator using a closed gas loop is necessary - helium is a likely candidate. This adds mass. A lower exhaust velocity also removes the principal advantage the RD-FHE STR has over other propulsion systems.
  14. 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!
  15. 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!
  16. 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
  17. Have you guys seen many rockets in anime? If so, just put the screenshots of the rocket's here.
  18. 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!
  19. I'm closing down the project. If you are looking for the observation save, click underneath here: Hello all. This was a continuation of @DMSP's thread as the leader of the project since he has resigned due to personal issues. If you want to look back, here is the original forum thread: http://forum.kerbalspaceprogram.com/index.php?/topic/146267-stock-community-space-program-looking-for-people-to-take-the-torch/&page=1 Everything in this thread will be preserved that is no longer in use under this spoiler here. Latest pictures of the stations: Art for the project: We have made a wiki as part of the program containing details are missions that took place in the past. Over time, this will be updated with more recent information: http://kspstock-community-space-program.wikia.com/wiki/Stock_Community_Space_Program_Wiki Scientia1423.
  20. 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
  21. 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)
  22. So I opened up a new space program yesterday. I came up with a good plan for advancements, and I have worked on upgrading the space program until it is fully functional and is publicly open for use. Place your newest addition to the space program please. (the next person down the line may continue) Added a basic VAB.
  23. 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.
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