MatterBeam

I did some research! It is part of a write-up on interstellar propulsion designs here. The relevant section:

This is actually a good point. Anti-ballistic missile systems try to catch their targets during the slow ascent phase (like ABMs in South Korea) or during the terminal phase (over the US). Since project Star Wars (SDI) was never implemented, I don't think anyone has the capability of intercepting re-entry vehicles over the ocean. Of course, if you have stealth ships, regular space travel and settlements on other planets, then creating this capability might be an unintended consequence. I can give more details on how I arrived at certain numbers if you wish. The proposal should be applicable to the pre-orbital-insertion ("disguising a small spacecraft as an asteroid / comet") part of the scenario being described. The exact design on my blog was a strategic weapon, like a modern submarine. If you only plan to use it for a few days, a much smaller liquid hydrogen reserve, and a smaller overall size, could be used. Exactly! The steamer can stealthily deliver anything from secret agents to nuclear missiles. Sensor technology must still obey physical limits. We are reaching for those physical limits, so no matter how advanced the technology or how sensitive the sensors, we will not be detected. Absolute emissions stealth can be obtained by further cooling the hull to 2.71K. You will be indistinguishable from background radiations. It's just very hard to do and of little benefit compared to 4K or 22K temperatures, since they are so hard to detect already. What do you mean by assuming 100% efficiency? Which part of the design should be 'inefficient'? Sunlight hits a hull surface. A lossless process. Vantablack absorbs over 99.99% of the sunlight. 0.01% inefficiency? Vantablack conduct heat. A lossless process, only the rate matters. Liquid hydrogen channels at 20K are run through the hull panels. The pumps consume energy? The hydrogen warms to 22K and boils. A lossless process, only the rate matters. The boiling gasses are run through tubes to the exit point. That is the core process which allows for stealth, and it is only a ramped-up version of open-cycle cooling. Replace the sunlight by any hot component, and absorb the waste heat of secondary systems (coolant pumps ect.) by simply using more liquid hydrogen. I agree that there are limits to what can be achieved. The important fact is that these limits are high enough that useful levels of stealth (undetected at 100km for example) can be achieved. The example I gave in the previous post had two reactors: one small one to power the craft, another to propel the spaceship. The first reactor operates in a closed loop with something like sodium or heavy water moving heat from the nuclear reactor to a heat exchanger, then steam or CO2 to move heat from the heat exchanger through a turbine (to generate electricity). The final loop emits waste heat at 1300K. Normally, the heat goes through a second heat exchanger that shunts it into a radiator's coolant loop. Instead, we replace the radiator with liquid hydrogen and just throw the boiling gasses in the final expansion chamber. The second or propulsive reactor works with all the boiling hydrogen produced by cooling the spaceship's equipment and hull. This hydrogen is used like a propellant. From its current 1300K temperature, it is further heated by a nuclear core to 3000K. A de Laval nozzle takes this high temperature, high pressure, low velocity gas and expands it into a low temperature, low pressure high velocity gas. The conduction rate between gaseous hydrogen and the tube carrying it is very low, because the thermal conductivity of hydrogen gas is quite low. Nevertheless, I agree, insulation and a vacuum gas can prevent the hottest hydrogen being handled (1300K from the electric reactor's waste heat loop) from heating the interior. Then, whatever heat leaks back into the ship is dealt with by simply using more liquid hydrogen. Yes, more is always the answer. Thankfully, all cooling is done passively, because heat naturally moves out of the 300 to 1300K environments into the 20/22K heatsinks. No heat pumps are needed for this part. This is how cryostats work. The active cooling only comes into play of you want to cool the hull (nothing else) below liquid hydrogen's evaporation temperature. As for the 3000K you mention, it is inside the nuclear thermal rocket's core. Because you are matching your reactor output to what the hydrogen can absorb, no heat should leak out of the reactor. If the reactor walls still get hot... more LH2! 22K for a ship's hull is pretty darn cold. It would be radiating away less than 13.2 milliwatts per square meter and is undetectable by sensors not themselves cooled to below 22K. For comparison. back when the Spitzer infrared telescope was running at 5.6K cooling, it had a sensitivity of about 2e-18W/m^2. This means that the 22K hull cannot be detected unless the $720 million telescope was pointed right at it within 46000km for days on end.... which is unlikely to happen because any spaceship would cross that distance in a matter of minutes to hours. A 4K hull would allow for a 915-fold reduction in detection distances.

It has been explained many times, maybe we weren't clear. The heat that the Vantablack surface absorbs is absorbed by a liquid hydrogen heat sink. The liquid hydrogen boils. The boiling hydrogen is then expelled. The transition from liquid to gaseous state consumes energy. This energy is the heat we are handling. The scientific term is heat of vaporization. For liquid hydrogen, it is is 450kJ/kg. This means that each kilogram of liquid hydrogen onboard will absorb 450kJ of heat and boil away. The Vantablack, the gasses and the remaining liquid are all at 22K, which is about the boiling temperature of liquid hydrogen. There are several extra steps in the hydrogen steamer design made to maximize the amount of heat the hydrogen steals away before it is ejected. One of them is heating the gaseous hydrogen even further. By concentrating sunlight onto a heat exchanger, we can turn it into propellant for a rocket. Hydrogen gas heat capacity rises from 14kJ/kg/K to 22kJ/kg/K as it is heated from 22K to 3000K. This is a lot of extra heat we can absorb. The hotter the component we need to cool down, the more efficiently the hydrogen is used. A hull surface absorbing sunlight needs to stay cool at 22K, so we can only use the 450kJ/kg vaporization energy as the heat sink. A crew habitat at 300K allow for a additional heat capacity of (300-22)*14: 3892 kJ/kg for a total of 4342kJ/kg. A hot laser operating at 700K allows for a total waste heat absorbed of 10MJ/kg. Even nuclear reactors can be cooled: at 2000K, over 36MJ/kg can be absorbed. The best thing is that your 2000K superheated hydrogen gas can then be run through a rocket nozzle and expanded until it is a very cool but fast propellant stream, no warmer than your hull surfaces. Let me give you an example: A thin cylinder with a cold frontal area of 10m^2 absorbing sunlight at 1.37kW/m^2, a 5 crew habitat emitting 1kW of waste heat at 300K, a life support system emitting 10kW of waste heat at 500K and a 1MW reactor powering all the systems at 1300K. How much hydrogen do we consume? 1.37*10/450 + 1/[(300-22)*14+450] + 10/[(500-22)*14+450] + 1000/[(1300-22)*16+450] = 0.0304 + 0.00023 + 0.0478 = 78.5 grams per second. If we have 1000 tons of liquid hydrogen on-board, the ship can run undetected for five months. If we take that hydrogen at its different temperatures and quantities and run it through a 3000K nuclear rocket engine, we can absorb 3.8MW of propulsive power without needing any more hydrogen. I hope this answers some of your questions. Ballistic missile trackers and interceptors are designed to handle MIRVs turning at over 10G, in multiple directions, simultaneously. No human-occupied vehicle can outrun them.

I was explaining step 2 in the manufacturing process: -1) Obtain resources -2) Convert them into something useful. -3) Sell your product. -4) Profit! Each step implies a vast industry sitting behind the scenes to provide or demand your products (ores/uranium). I only explained the technically straightforward step.

Hello guys. Might I weigh in? In 50-70 years, unless an arms race comes along or a revolutionary technology like the Epstein Drive is developed, we will be unlikely to move far past the asteroid belt. The pessimist in me tell me we still won't have a permanent presence outside of low earth orbit, but that's another story. What this means is that there won't be constellations of thousands of satellites pointed outwards to spot anything in detail. There'll be sensors tracking spaceships going to and fro from known destinations, but most will be pointing inwards at Earth to detect cheap launch vehicles from being used in nefarious ways. Using methods detailed below, you can keep a spaceship undetectable until it gets close to Earth. Staying above the planetary plane and using eccentric polar orbits will avoid the bulk of the sensors. There's no simple way to get to the ground because re-entry is a very violent event that reveals a lot of information about what is coming in. The radio reflection on the re-entry vehicle can distinguish between a lumpy rock or a smooth metal container. The trajectory reveals whether it is a chaotic fragmentation with the g-force meter jumping up and down, or the human-survivable descent of a reentry vehicle. Either way, we've had the sensor technology and dozens of spy satellites watching the atmosphere from above watching for nuclear re-entry vehicles for decades. It'll be hard to escape their gaze. Your best option is to manoeuvre your stealthy spaceship near a automated cargo pod and either latch on to it or hide inside of it. These will exist because in 50 years, we will still be dependent on Earth-based manufacturing for high technology components, which needs rare metals obtained from asteroids to run. Once you are in the lower atmosphere, deploy wings and fly away from the landing point before the recovery team swoops in. Swoops, yes, because you don't want tons of platinum to be floating unattended in the Pacific ocean (a likely landing zone). I beg to differ! http://toughsf.blogspot.com/2016/03/stealth-in-space-is-possible.html http://toughsf.blogspot.com/2016/03/stealth-in-space-is-possible-ii.html http://toughsf.blogspot.com/2016/03/stealth-in-space-is-possible-iii.html http://toughsf.blogspot.com/2016/04/stealth-in-space-is-possible-iv.html The point of stealth is not to hide completely, but to reduce your detectability from sensors. Learning how sensors works allows you to defeat them. Infrared sensors measure photon 'hits' on a Charge-Coupled Device. Enough photons striking the same spot trigger a voltage-controlled switch, illuminating a pixel. Over time, enough pixels are collected to form an infrared image of the target. The objective here is to reduce the energy of these photons and their number down to levels where the sensor cannot distinguish incoming photon strikes from self-triggering 'noise'. The big sources of noise are quantum inefficiency in the CCD's pixels/cells, and the temperature of the device emitting photons onto itself. Future technology might increase quantum efficiency to extreme levels (99.99% of photon hits add to the trigger voltage instead of the current 85%). What technology cannot do is beat thermodynamics. A sensor cannot detect a target colder than the device itself, nor a target the same temperature as the universe's background radiation. In short, there is a temperature and a range at which it takes an inordinate number of hours of observation to collect enough photons to confirm a target's detection. This situation occurs for 22K (hydrogen-cooled) objects further than 10000km away, and for 4K objects a few hundred kilometers away. A 2.7K object sitting right in front of an infrared sensor is indistinguishable from background space. In practice, the sensors won't be perfect and won't be able to maintain 10^-19W/m^2 sensitivities in a real world situation. Anything colder than 22K will likely slip right through entire networks of sensors because even if they can detect it over time, their target is quickly moving across and out of their field of view. Asteroids at Earth orbit are actually sitting in very strong naked sunlight (1.3kW/m^2) and their exposed surfaces can reach toasty 200K+ temperatures. This is why the ices on their surface vaporize or sublimate. The problem is detecting the far away asteroids that sit at 150K, 70K or cooler. We have trouble detecting even these 'hot' objects in the asteroid belt. Quite right! The fresnel lens is not technically necessary - it is only an accessory meant to collect more sunlight to power the solar-impulse drive. Without it, it can only move by a few mm/s per day. If we want a powerful yet stealthy rocket, use a nuclear thermal drive. Run the exhaust through a massive exhaust nozzle. The nozzle starts off closed. Hot exhaust is injected into the nozzle... it is hidden while expanding and cooling by the shutter. Just as it reaches the nozzle's end, the shutter opens and allows it to leave the rocket. From the outside, the rocket is just emitting 20K puffs of gas. Or, find a way to curve the nozzle without shock-heating of the exhaust and you can run it at full output. We're talking gigawatts of undetectable drive power here. Quite a good plan. Make most of the trip on a registered civilian ship, then drop off a 'stealth pod' that finds its way to the ground without being detected. Any N-body physics simulator can handle the calculations needed, like Children of a Dead Earth. Or use an understanding of detection techniques and work against those! Vantablack's purpose is to not reflect any incoming radiations. 99.99% absorbance means 0.01% reflectivity, or better.... the heat you absorb, mostly from sunlight, is them passed by a heat exchanger into a liquid hydrogen heat sink. The heat sink boils, taking the heat you absorbed away with it. LH2 boils at 22K, so just like an ice cube stays at 0C until it has completely melted, LH2 will stay at 22K while it evaporates. If you want even lower temperatures, use liquid helium at 2-4K and use a heat pump to move the absorbed heat from the helium into liquid hydrogen. Supercooling the vantablack this way prevents it from emitting nearly anything. If it doesn't reflect or emit anything, how do you detect it? The perfect gas law gives a linear relationship between pressure, mass (moles), volume and temperature. If you expand a gas inside a de Laval nozzle, pressure drops and volume increases while mass stays constant. Consequently, temperature must drop. A real-world example of this effect is... real-world nozzles. The highest temperatures are near the throat, so that's where we see the active coolant loops concentrated. The lower half and the rim are much cooler. If we used a ludicrously big nozzle, the gasses will expand and expand to undetectable temperatures. Approaching from the sun against a well-designed sensor is a bad idea. It can adjust its sensitivity of multiple scales to make out your very cold outline against the very hot and bright background. The 4K temperature ship needs a heat pump to move heat up the 4K to 22K gradient. The pump itself must also be powered by a reactor, and that reactor must also be cooled. Altogether, the small drop in surface temperature will cost you up to 20 times more hydrogen expended per hour! We're working well within the confines of basic thermodynamics. An example would be the infrared telescopes being used to observe very cool stars. They have reserves of liquid helium on-board that they use to flush the CCD sensors and reduce the noise level until the stars are detectable. Once the helium is all used up, the CCD heats up and those stars become invisible, like what happened on the Spitzer Space Telescope: "Without liquid helium to cool the telescope to the very low temperatures needed to operate, most of the instruments are no longer usable. " We're only trying to do the same on a much larger scale - instead of just cooling a small CCD sensor, we're cooling the entire hull of a spaceship using hundreds of tons of liquid hydrogen. Your assumptions about thermodynamics are quite wrong. The only way that the spaceship's hull heats up is if the incoming radiations are not conducted to heat exchanger fast enough. That's a design problem, not a physics problem. Thankfully, Vantablack is just vertically-aligned carbon nanotube, which makes them thermal superconductors in the horizontal direction. Heat transfer rates will be incredible. Again, you need the maths to make those claims. A large cool hydrogen is exactly what the far away galaxies are. Why isn't the sky entirely lit up end-to-end in the infrared spectrum? Because those 'gas clouds' are simply too faint. And, even if stable H2 molecules manage to get ionized by sunlight (when actually 15.84eV is needed, 183815K temperature), they'd just point out that a hydrogen-propelled rocket was used within this hundred thousand kilometer volume within the past few minutes. A 9km/s hydrogen exhaust out of a 10m nozzle, released at 20K, would diffuse into a 42 billion m^3 volume within a single minute, more if it had any lateral diffusion. The specific hydrogen steamer design on my blog can stay undetected for decades at a time. The more you scale it up, the more endurance you get out of each kilogram of hydrogen on-board. Feel free to ask more questions!

That would be an excellent target in theory, yes, but in practice a regular asteroid covered in water ices would be more useful than a dry rock. Melt out the volatiles, centrifuge the slag and vaporize the densest layer to extract the full spectrum of elements.

Get the Better Time Warp and AtmosphereAutopilot mods. The better time warp allows you to physics warp far beyond an x4 multiplier. The autopilot mods smoothes out the SAS instructions so that your plane does not wobble or flip out at high warp. Together, you can fly planes over vast distances without it becoming a very boring task. It is exceptionally useful for exploring a planet by air, before you unlock hypersonic engines. The highest stable warp I manage to get is x6 at low altitudes and x12 at high altitudes... you can make proper use of your plane's range!

Actually, I don't think the improvements will be that great. Even the toughest 'pebbles' in a pebble-bed reactor can only handle up to 4200K due to the melting point of Tantalum hafnium carbide. Previous nuclear thermal designs had the hot uranium oxide cores directly exposed to the propellant flow, limiting them to the melting point of the fissile fuel (3138K). This 33% increase in temperature, if we run it through this root mean square gas velocity calculator, would increase the maximum Isp on hydrogen propellant (1g/mol) from 8.8km/s to 10.2km/s, only 16% better. Only very large deltaVs would reveal savings in mass ratios. I think the true motivation for the development of pebble-bed technology is the safety factor. In case of a catastrophic failure that causes the rocket engine to explode, you'll only deal with rapidly cooling and inert golf-balls instead of a dust cloud of lethal radioactive particles. The formation of our solar system concentrated the small quantities of fissionable elements inside the cores of rocky planets and the largest moons. Very little managed to stay in the outer solar system. What we'll need to find is rocky asteroids that are billions of years old, composed of the same undifferentiated dust that planets are made up of. You'll find about 1 atom in 10,00,000 to be Thorium and 1 atom in 100,000,000 to be Uranium for every atom of iron or silicon there is. On Earth, geothermal and hydrological processes bring up heavy elements from the mantle and concentrate it in groundwater pockets. We mine 'veins' and 'deposits' of these ores. Despite being handily collected for us by natural processes, it is still a tiny fraction of the ores we mine, in this case pitchblende, so a lengthy process is needed to separate and extract uranium from it. It involves chemical baths and centrifuges. In space, the asteroids we will mine uranium from will not have any water features or tectonic activity. The uranium is as likely to be distributed at the center as it is to be concentrated on the surface. It is most likely that the uranium will be mixed into the rocky grain on which ices and frozen volatiles stuck to over time, forming the bulk of the asteroid. Mining it will involve digging out the ice crust, extracting the rocky core and running the ores in a high temperature plasma separator. The ores are first melted to remove the lower melting point minerals. The denser remains then have to be turned into plasma at a huge energy cost. Electrostatic or electromagnetic fields then sort the elements by charge to mass ratio. Uranium has one of the lowest charge to mass ratios possible, allowing it to be conveniently scooped out. Mining asteroids is not technically a decades-out project; we already have the plasma mass spectrometers which use the same principles. It's the massive energy requirements which will take a long time to be available.

I agree with your statement on fuel costs but the 300 mission figure I gave out was only to divide full cost of the vehicle over its service lifetime to provide a fairer price/kg comparison with expendable rockets. The only 'need' is for components to be used for more than one mission for them to massively win out against expendable rockets. Like the Falcon 9 booster: even if it only survives for 3 missions, it has already massively won out in prices against every single other rocket out there. I'm confused however by the 1km/s figure? I thought it was clear that the booster plane did not stage at Mach 3, but after switching to rocket mode and reach 3km/s and an altitude of over 100km. It is extremely hard to make ramjets in a vertical launch vehicle useful. The traditional gravity turn launch trajectory gives them a very very small window of usefulness before the atmosphere becomes too thin.

The point of re-usability and spaceplanes, which are 100% reusable, is that the cost of a mission gets reduced to the cost of fuel per mission plus the lifetime maintenance cost divided by the number of missions. If a 25t payload two-stage spaceplane costs $1 million in propellants and $100 million in lifetime costs, and it performs 300 missions, then the cost per kg into orbit is $53. If we add in the billion dollar or so price tag, it'll still amount to $186/kg over its lifetime. For comparable rockets, the lifetime is one single mission. Equipment is thrown away, which cannot be recovered, so you incur their full cost. Hence the current $20000/kg prices.

Well, the spaceships could be replicas of the fleet units they are representing. It would make it easy to track deltaV that way.

I have a suggestion! Use the KSP game as a map for a board game. The spaceships aren't ships, they're game pieces representing fleets. The engine burns and rotations aren't actual movements, they are depictions of player decisions and automated actions. When two spaceships pass within 1000km of each other in KSP at 1300m/s relative velocity, what is actually happening is two fleets passing within weapons range with a 75% chance to hit. Damage and weapons fire is handled by a hitpoint and damage model system. Each spaceship has a set of modules (engine, radar, propellant tanks, forward armor plating, side plating ect) with a number of hitpoints and incoming damage removes from this pool of hitpoints until they are destroyed. Depending on the flavour of the game, you can have the hitpoints be equal to a certain vaporization energy or equal to 1d6. Together, we can have an RPG-like game where the limitations of KSP are dealt with using behind-the-scenes mechanics. What do you think?

Good work. Just note, that for comparison, the Chinese Long March 5 also puts 25 tons into orbit but has a liftoff weight of 879 tons. The Ariane 5 ES puts 20 tons into orbit with a liftoff weight of 777 tons while the Delta IV Heavy puts 28.8 tons into orbit while lifting off at only 733 tons. The figures you propose are 1500 tons liftoff for 25 tons into orbit... not only would this be nearly twice less efficient than the Long March 5, which also uses a RP-1/hydrolox scheme, but it would have to take off from a runway. The heaviest plane to ever take off is the Antonov 225 with a maximum take-off weight of 640 tons. The Antonov struggles with 120 tons of turbofans just getting by with a TWR of 0.23... Due to the numbers you suggest, I strongly think that a purely rocket-powered spaceplane would not be economical for many flights compared to expendable rockets, and even less so compared to a re-usable rocket stack like the Falcon 9 Heavy plans to be. Try maybe taking off on jet power and climbing to an altitude where a vacuum optimised RP-1/LOX engine can produce thrust at an Isp of 353 seconds. Also, reduce the dry to wet mass ratio to closer to 5% than 10%, to take into account the fact that the booster plane will likely be built like a horizontal rocket than a plane. The Star-Raker program proposed pressurized tanks to supplement the structural strength of the wings on take-off.

The Laythian culture would first and foremost be RICH. It would be the central hub for all Jool-based industries, as both an industrial and administrative hub, because it would be so much cheaper to expand infrastructure and keep people alive on that moon than anywhere else in the Solar System. Combined with the fact that it is very easy to reach and depart the planet, and the money will just roll in! Ammonia and water have different vapor pressure and evaporation points, so it is likely that a hot day will result in basic rains while a cool day will have a concentrated ammonia mist. Pure oxygen and nitrogen bubble out of the ammonia/water sea over time. I think habitats would need to have air filters for the ammonia and acid sprinklers to neutralize the basic solutions that ammonia creates. Another option is to create ammonia-free zones by boiling a lake and building in the middle of it. Hotter areas will cause denser water vapour to rise and displace the lighter ammonia gasses, but the difference is so small (17g/mol vs 18g/mol) that it might not be a realistic option. On a larger scale, increasing the water temperature of the moon even by a few degrees will lead to a massive release of ammonia, where it will be broken down into nitrogen and water compounds in the air. For construction materials, I think simple concrete will be best. You have the rocks, air and water for decent cement. Water makes for an excellent glue, so you could potentially build dried mud walls with plastic or fibre sheets on the inner and outer surfaces to make them last much longer. It would be a fictional setting, so the 'politics' rule wouldn't apply. The problem with space war and alternative launches is that KSP doesn't handle them well. You can't model damage or non-physical weaponry, and even if you ignored that, how would you handle the constant updates and reactions to the movements two fleets of spaceships would have, alone?

The ramjet flameout and switch to rocket engines happens within the atmosphere. The booster plane expends its propellants and reaches 100km+ altitudes travelling at about 3 to 3.5km/s. It is in this airless above-the-atmosphere environment that separation will happen. Both stages will be on a ballistic trajectory with mostly negligible aerodynamic effects. Blended wings where fuel is stored within the wings with very little 'empty space' means that the booster plane should not mass much more than a vertical, cylindrical rocket stack with the same engines. Are you advocating for or against rail-launch in the last sentence? The cold reservoir would have been the 270 to 700K air. The hot source is the 70K liquid oxygen. The point of a heat pump is to move heat against the temperature gradient, requiring energy input to do so. The point is moot now: an error in my calculations gave an unreasonably good estimate of the equipment masses involved. Collecting LOX with a mechanical heat pump requires massive increases in pump kW/kg ratings to become competitive with liquid-hydrogen heat exchangers. The empty booster plane would re-enter the atmosphere at about 3km/s and it will have an excellent lift-to-drag ratio. Together, these factors greatly reduce the heat load compared to a full 7.5km/s re-entry and would not require ablative thermal protection.

Damn! You're quite right. Even if we start collecting LOX at subsonic speeds at low altitude, where air temperature is closer to 270K and heat pump efficiency is 17.5% instead of 5.6%, and continue the collection for 30 minutes instead of 10 minutes, we'd still need 51MW of pump power or 102MW of shaft horsepower, with equipment massing tens of tons. The only way that would be worthwhile is if the entire craft was converted into LOX/RP-1 and launched with empty LOX tanks and an excess of RP-1. The excess RP-1 is burned in the turbo-ramjets and the moment the LOX tanks are filled, we switch the rocket mode. Problem is, you'd then need to collect and process 603 tons of air and the equipment mass would explode to hundreds of tons. I think this concludes it. Mechanical heat-pumps are not worthwhile until they become massively more powerful per kg, in the range of 50-100kW/kg. I think that the separation event being described here is very close to a vertical stack separation, much like what rockets perform regularly. The difference is that the bodies are not cylinders but blended wings... but in the near-vacuum it should not make a big difference. The ramjets are actually turbo-ramjets. They lift off horizontally on turbojet mode, probably with a TWR of 0.4 or so. As the velocity increases, the turbo-ramjets only need to maintain a TWR high enough to overcome drag forces. At Mach 3, they are operating in pure ramjet mode, at which point the craft pitches up and ignites its TWR >1 rocket boosters. No vertical ramjet flight is involved.

I must pre-face that I started this thread to propose a modification to a concept I found. I didn't intend to discuss the plausibility of the design itself or the viability of space-planes in general. Trying to ridicule the entire thing by picking on flaws in the original proposal is just pathetic. It doesn't advance the discussion and just marks you as a dishonest participant. Probably not. I was basing myself on the work done on the LACE and Skylon engines and assumed that developing these engines to function in much less extreme environments would be simpler. The data that supports a TSTO that collects up to 72% of its reaction mass while in flight is the simple rocket equation. For a hrydrolox rocket, this fraction can be as high as 89%, hence the incredible advantage that comes from in-flight oxygen collection. I thought that a small collection plant that only fills up the second stage's oxygen tanks would fit into the proposal's general theme of using less advanced, lower development costs systems. The heat pump efficiency equation for moving heat from a cold source to a hotter environment is T(cold)/[(Thot)-T(cold)]. Any inefficiency on top of that is due to the pump's design... a pump which is based on a Stirling engine working in reverse can approach 50% efficiency, hence the numbers I posted above. The wing shape and the overall shape of the concept is based off Concorde and it's vortex lift wing-tips. Why would you assume and ask me to stop drinking schnapps? ? I agree with this - Skylon's design managed to reduce landing gear mass to 1.5% of take-off mass, so there is no need for the awkward launch cradles and un-safe landing skids. As I understand it, the separation between the stages occurs after the booster plane reaches Mach 3 or so on turbo-ramjets then switches to rocket mode and lifts itself well out of the atmosphere. It is in this vacuum environment, going at about 2.5-3km/s that staging occurs. During this rocket boost phase, the center of mass necessarily moves forwards as the front-mounted second stage remains fully fuelled while the rear booster stage empties its tanks. The only issue I have is that after separation, the booster plane's COM might be too far aft due to the mass of its engines and the empty fuel tanks for stable flight back to the ground. DeltaV breakdown was not specified in the proposal I linked to, I had to work it out from a single table of data. Mach 3 is achieved on ramjet power, then the rockets ignite and start climbing for a final velocity around 3km/s and an apoapsis above the atmosphere. The second stage does the bulk of the work by delivering about >5km/s. I've determined that the best velocity/altitude for collecting LOX is during the climb from subsonic to Mach 3, where the ramjets cut off. At high intake temperatures, the heat pump efficiency drops, going from a COP of 0.3 to about 0.1... the heat sink is the heat exchanger block cooled to about 70K by compression/expansion cycles of the heat pump's nitrogen working fluid. The heat of the air is moved into the oxygen-devoid exhaust at the cost of a lot of energy. The SABRE's heat exchanger is a much more complex version of my proposal despite the seemingly simpler mechanism: super-cool the exchanger by circulating LH2 over and and just scoop up the liquid oxygen that condenses out of the air. The problem is that Skylon is trying to do that at hypersonic speeds, so cooling must take place in milliseconds, and then recover the boiling H2 for use as propellant in a scramjet that shares a reaction chamber with a closed rocket engine... The wings allow a take-off TWR of less than 0.5. Rockets are cheap but a recoverable craft only has to count the propellant and refurbishment costs as the mission price. Unless refurbishment costs more than throwing a rocket engine stack away (Shuttle?), it will be massively cheaper. The problem with rail launch is that you lose the airliner-like flexibility of flying the craft between the construction point and the payload delivery, mating and launch airport. You'd need to build a special space-port that services that exact craft in that specific configuration, making it a very inflexible investment. This sort of reasoning is why SpaceX is not building its own launch site and instead using existing infrastructure. As I understand from missile propulsion, you can only really push a ramjet to Mach 4+ if you intend to use it once. Mach 3 and below allows for more reusable ramjet designs, hence the need to switch to rocket mode after Mach 3.

You are correct about the state of high-speed cry-collection technology, but it is only one technology that must be developed instead of multiples, such as on the Skylon. Also, the range of operating parameters is not as extreme as what is being attempted by the LACE, so I'm guessing it would rather easier to collect oxygen at Mach 0.9-3 than Mach 5-8. The efficiency of the oxygen extraction method? Well how would you measure a loss of efficiency in this process? Condensed liquid oxygen being blown away or gasses escaping somehow? We can reduce it all to how much more kW is needed from the heat pump. I already gave that component a 50% cut to efficiency when it could approach instead be approaching ideal efficiency, to demonstrate that the scale of the task is manageable even with pessimistic predictions. My understanding of the concept proposed on the website I linked to is that every technology in use has been matured over decades. 'Edge of technology' would be stretching what we can do, such as taking a laboratory experiment (beaming laser power, cryo-cooling at hypersonic speeds) into a real world situation (HX laser thruster, Skylon Reaction Engines). Trying to perfect the in-line separation of two components on a ballistic trajectory in near-vacuum is very much easier than attempts at edge-of-technology R&D. The small payload low-cost launcher business is promising enough for companies such as Rocket Labs, Virgin Orbit and more to vie for the market. A fully reusable HTOL craft would beat expendable small rockets in the race to the lowest $/kg. The cryo-collection machinery and power generation equipment would mass much less than the savings of not having to lift off with a full load of oxidizer, for significant net savings. Please do not be disingenuous. The concept of in-flight cryo-collection of liquid oxygen has been seriously studied and experimental results are already available. Attempting to accomplish this in a supersonic regime is easier than in a hypersonic regime. Liquid oxygen is not liquid hydrogen. Storing it is much, much easier... so easy and safe that large tanks of liquid oxygen are proudly displayed behind hospital buildings. During the fill-up process, losses are compensated for by collecting more LOX than is needed. It is then held for a few minutes. I think you are vastly overestimating the losses involved in holding LOX for a couple of minutes - they should be on the order of 0.1% or less. Here is a commercial solution that holds LOX with a loss rate of 0.2 to 1.2% per day. ULA managed to bring LH2 losses to less than 0.1% per day, so LOX losses must be 0.05% per day or lower.

'Free' meaning that you do not have to 'pay' in propellants, engine thrust, landing gear and wing area to get them up to the altitude and speed where they start being used. Due to the rocket equation, 17 tons less mass at liftoff is actually a much greater saving once the booster plane is at Mach 3 and switching to rocket mode. Yes, I found the correct temperatures and pressures at the altitudes I noted and calculated the air density using online calculators. Scramjets is not a currently available technology and will not be mature enough for routine spaceflight for a very long time. It is better to focus on existing tech, like ramjets and cryo-collection of air at moderate velocities, for cost and development time reasons. Which efficiency are you referring to? This design is far from the 'edges of engineering'. I don't understand what you mean by 'looks conventional'. If you mean the overall shape of the plane, it is based on a Concorde. The fuel consumption increase from using a multi-megawatt generator is truly insignificant. As noted above, 4000 horsepower would have to drawn from a turbo-jet's shaft. According to this source, the old J-58s produced up to 160000 shaft horsepower each. The advantages are more Isp, lighter gear, smaller wings, less drag, less thrust, less fuel consumption in flight and use of existing LOX/RP-1 engines instead of developing a modern HTP/RP-1 engine. The boiloff as noted before would be low and easily compensated for by just scooping up more oxygen. You only have to hold the oxygen liquid for the few minutes between stage separation and circularization, which should not last more than a handful of minutes.

I will try to answer everyone. I believe the payload is so small because the author used real world data on wing area to estimate if the craft could fly with its wing loading. To fit within this data set, the wings cannot be gigantic, so the final craft must be small. Once a demonstrator for the technology is made to work, I am certain larger payloads can be scaled up. The carrier planes after separation only needs to remain stable as it decelerates down from high speed flight. Its natural half-saucer teardrop flying wing/blended body shape does contribute towards stability at high speed, even if its engines will not be able to overcome the drag. On the subject of heat pumps: LOX is created from air cooled down to 90K. The working fluid is likely to be liquid nitrogen, so the cold end of the heat pump is at about 70K. The hot end is the incoming air. At Mach 3, this is about 700K. A perfectly efficient heat pump would need 9 watts of power to move 1 watt of heat across this temperature range. A more realistic heat pump would maybe need about 18 watts. In the rocketplane, the only data provided is a propellant mass figure of about 52000 pounds. Assuming a 2.5:1 oxidizer to RP-1 ratio, we'll need about 17 tons of liquid oxygen. This means we'd have to process about 81 tons of air. Air has a heat capacity of roughly 1kJ/kg/K, so to cool down 81 tons of air from 700 to 70K, the heat pump must remove 51MJ of heat. At the efficiency quoted above, it will consume up to 923MJ. RP-1 delivers 43.5MJ/kg upon combustion so this shouldn't be a problem. How long do we take to collect the liquid oxygen? Minimizing flight time reduces fuel consumption but increases the power rating of the heat pumps necessary. A 10 minute flight time translates into 1.6MW heat pumps. They could mass about 4.6 tons, but it is extremely likely that the data from here is not optimized for power density at all. The aerospace grade heat pumps could mass under a ton. A dynamo would need to convert 3MW of shaft power into electricity. This would mass between 300 and 600kg. Add insulation and tanks of another 400kg and we'll round up the assembly to 2 tons. In return, we can save 17 tons of liftoff mass and gain 10% Isp on the second stage. Good point. If we collect the liquid oxygen at subsonic or low supersonic speeds, the air temperature would be about 300K instead of 700K, bringing the heat pump efficiency up to 6 W per watt moved. This makes them three times smaller. Since we do not need to hold the liquid oxygen for long and losses can be compensated for by just collecting more air, simple insulated tanks with boil-off valves can replace a 'massive onboard cryogenic plant'. 3MW is 4000 shaft horsepower. The main reason for the whole LOX collection concept is that you can lift off with the LOX tanks empty and fill them while flying for 'free'. Filling them up on the ground would negate this advantage. If the two-stage spaceplane concept is proven, then you'll only be paying fuel costs. ISRO throws away its engines, tanks and stages for a strictly higher cost per launch. This is why it is not so bad if the spaceplane has a bad payload fraction. As for actually collecting 81 tons of air for processing, you'd need maybe 50 to 100kg/s flow rate. At Mach 3.2 (1088m/s) and an altitude of 25.9km and external air temp of -50 degrees C (0.039kg/m^3), intakes will take in 42kg/m^2/s. Two inlets of 1.12m diameter will do the job. At Mach 1 (330m/s), an altitude of 4.5km and an external air temp of -20 degrees C (0.791kg/m^3), an intake will take in 261kg/m^2/s. Considering all the above factors, it might just be worthwhile to collect LOX at near-supersonic speeds at relatively low altitude and just use more thrust to boost up to Mach 3. LH2 is extremely problematic for flying vehicles. It requires massive fuselages that must also be insulated against high temperatures, large engines to overcome the drag and heavy structure to keep them rigid enough in flight. Also, the scramjet requirement for Mach 3 to 8 flight is just something we do not have, so that's gambling on technologies currently unavailable. Despite recent advances in lightweight structural materials, I do not think we will have the technology to make an LH2 spaceplane work. The advantages are not currently great enough to compete with a less efficient by simply cheaper 'brute force' solution of using a heavier spaceplane with RP-1 fuels. Thank you for the references though. I personally am very interested in spaceplane concepts since the 70's, with the Star Raker being the pinnacle of re-usable design. This would very likely work, but the initial set-up cost of deploying hundreds of megawatt lasers is just impossible to cover unless the US/EU/China decide it is a matter of national interest or if laser power per $ cost drops rapidly. I do play RSS exclusively and I do have a good feel for the deltaVs and mass ratios required. The booster plane here is supposed to reach Mach 3 on turbo-ramjet power while collecting LOX for the second-stage rocketplane. The booster plane then switches to rocket mode and adds another 2.5km/s to its velocity, adding up to around 3.5km/s. Orbital velocity is 3km/s. Upon separation, the second stage needs to deliver another 4.8 to 5km/s to circularize. With a 320s Isp engine, this requires a mass ratio of 4.9, with an RP-1/LOX alternative, the mass ratio required drops to 4.2. Center of mass/center of lift is not a big problem. Flight controls can correct imbalances in the lower atmosphere while it is quite neutral. As Mach 1 is passed, the center of lift is dragged backwards due to mach tuck while the center of mass moves forwards as the second stage rocketplane's LOX tanks are filled. The whole plane presented above is modelled quite around the wing shape of a Concorde for extra lift at the rear. The point of a spaceplane is that you recover 100% of the equipment that leaves the runway. Your marginal cost is just the propellants, which as you mentioned, is very cheap. The two stages can have an integrated fuel line running back to front through the entire craft. Nothing would be exposed to the exterior environment.

Hi! I came across a very well thought-out design for re-usable launch vehicles, describes in this article: VISION. The concept involves solving the problems SSTO spaceplanes have by separating the vehicle into two sections: a hypersonic carrier plane and a nose-mounted rocket-plane. The innovative part is to mount them end-to-end. The booster plane carries the rocketplane to a high altitude and gives it about 3km/s initial velocity. The rocketplane stages and completes the climb into orbit, unburdened with air-breathing jet engines. The propellants selected were RP-1 and H2O2 for their density and non-cryogenic storage, important factors for an airplane that needs to fit its propellant tanks into wings. For overall simplicity and technology readiness, no scramjets are used. Instead, simple turboramjets bring the booster plane up to supersonic speeds. Rocket engines take over at high altitude and add about 2km/s until the booster stage runs out of propellants. The second stage is a pure rocketplane that can deliver 6km/s of deltaV. Payload is about 450kg. Re-entry is made easier with the massive airbrakes the rocketplanes has on the back. https://exospace.files.wordpress.com/2017/03/a14.jpg My suggestion is that we slightly modify the propellant choices and the ascent profile for a massive boost in performance. Due to the propellant choices, air cannot be cooled and liquefied like in a SABRE engine. There needs to be a reserve of liquid hydrogen to provide the heatsink for this to happen. However, there is a way to liquefy air without using liquid hydrogen. Heat pumps can be used to cool a metal heat sink down to cryogenic temperatures, using evaporation and compression cycles. When air is run through the heat sink, which acts as a heat exchanger, oxygen condenses on it and can be collected. This costs power to run... power which can be derived from the turbo-ramjet's turbines. Of course, equipping heat pumps large enough to fill the entire booster and rocketplane with liquid oxygen as it flies up through the atmosphere instead of simply using liquid hydrogen as a heat sink is a massive mass and power penalty. This penalty can become minor if we only equip pumps capable enough to fill up only the rocketplane with liquid oxygen. About 5 times less liquid oxygen would be needed. By collected liquid oxygen this way, you can launch the upper stage with RP-1 tanks full and liquid oxygen tanks empty. The liquid oxygen tanks would be larger than peroxide tanks by about 22% in volume and be slightly heavier due to insulation. The benefit is a 30 to 50 second jump in Isp and about a 50% drop in rocketplane mass on liftoff. This means smaller booster plane engines and wings, larger payload and so on.

Not having to use pressure domes for every living space is a massive cost saver. You can use simple positive pressure environments to keep out the external gasses instead of hermetically sealing everything too. And the coloniusts won't have to be scared! The psychological factor is often overlooked - not everyone is a steely-eyed former test pilot on a glorious mission to beat the Russians. The average colonist would be a white-collar guy with two degrees and debt to pay. I think habitats would be quite in-land. Even if you keep every piece of equipment out of the water, there's still sea spray and mist to consider. These would be worse than the most damaging acid rains. Its the equivalent of a drain cleaner. To remove it... heat the water up? Ammonia in the water decomposes over time and leaves the water as ammonia gas. Heating the water accelerates this process. I'd be sure to boil the water if I plan to drink it though. The problem with the other sources of energy I mentioned is that they consume a lot of energy to be developed. Geothermal energy requires deep holes into the ground, fission energy requires deep mines and centrifuges, fusion reactors likely need large, high-quality magnets made out of rare earth metals... If you arrive at Laythe with only the solar panels and RTG that powered your spaceship, you're going to have a hard time. It's good stuff.

THANK YOU!

Lovely pictures. The effort you put into these posts shows! A few notes about colonizing Laythe: -A small moon with a thick atmosphere for aerobraking and oxygen to burn going back up means it is extremely cheap to reach Laythe and bring back its resources compared to other planets. -Having habitable conditions makes exploiting Laythe much more attractive and much cheaper than say, Duna or Eve, despite the 'distance'. -Water and ammonia... makes for a basic solution. You wouldn't want to swim in that! -High CO2 in the atmosphere can VERY quickly be adjusted by seeding the oceans with cyanobacteria. Breathing it should be as easy as attaching CO2 scrubbers to gas masks. -The main obstacle to colonizing Laythe will be obtaining cheap energy. Electro-dynamic tethers, geothermal resources, fission fuels and fusion reactors are difficult, expensive or complicated to use. If you have access to giant orbital mirrors, a instead of trying to scavenge the dim sunlight, better use for them would be to capture and focus lasers from beaming stations around Jool. An energy idea I thought up for Jupiter could be used here: In low Jool/Jupiter orbit, a lightweight mag-sail is released. This sail latches onto the flow of charged particles around the gas giant. The strong magnetic fields follow the rotation of the planet, so they can reach very high velocities. The lightweight mag-sail accelerates quickly in this particle wind, to far above escape velocity. At a higher altitude, slightly to the right, a power station awaits. It is mostly a big magnetic ring. Inside this ring, a bag of gas sits tethered by plastic strings, like a bag caught in a spider web. The bag is transparent to UV wavelengths. The power station sits in the path of the mag-sail. Just before the sail impacts the bag, a very short pulse of UV laser ionizes the gas inside. On impact, the ionized gas is heated as it absorbs the mag-sail's kinetic energy, causing it to fly apart. A charged particle moving inside a magnetic field causes an electric current to run through the ring's wires. This is how Magneto-hydrodynamic generators work: they slow down the charged particles moving through a magnetic field to create energy at high efficiency. Around Jupiter, these particles reach 74km/s (https://en.wikipedia.org/wiki/Io_(moon)#Interaction_with_Jupiter.27s_magnetosphere). A 100 gram mag-sail would deliver 273MJ per impact, and the mag-sail release station could be stocked up with thousands of them.

Hello! I remember back in 1.0, you could press the middle mouse button on a part in the VAB and a simple box would appear with information such as an engine's thrust, cost, Isp and so on. Is there a mod out there which re-enables this option?