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I'm trying do design a feasible passenger/cargo spacecraft stationed on a space station.

It's a far future setting, but I'd like to stay as close to real physics as possible, specifically, anti-gravity is not available. At the same time there are means to provide large amounts of energy. It doesn't matter how it's achieved. Some kind of a nuclear reactor or even something like a matter/antimatter reaction assembly would be ok.

The spacecraft should have following capabilities:

  • efficient and safe landing on a terrestrial planet or a moon without any pre-existing infrastructure;
  • atmospheric flight;
  • orbital launch without any pre-existing infrastructure;
  • able to carry at least 5 passengers and $\leq$ 50 metric tons / $\leq$ 200 $m^3$ of cargo to and from the surface;
  • landing and orbital launch with g-forces safe for regular untrained people;
  • reusable.

Other requirements:

  • single-staged system;
  • maximum dimensions: width: 90m, length: 90m, height: 50m.

Is that possible? Are there any problems with the concept I'm missing? What kind of propulsion system would be viable for this spacecraft?

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    $\begingroup$ You should play the game Kerbal Space Program, it will teach you a lot about space travell and it is a great game. KSP is ont 100% realistic, but it is a great source of learning if you just want to make spacetravel ralistic enough for a work of fiction. But be warned the tutorials are boring, but necessary, and the game is super addictive. $\endgroup$ – Marius Aug 5 '16 at 7:11
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    $\begingroup$ You allow antimatter drive. USE IT. $\endgroup$ – Joshua Aug 5 '16 at 15:39
  • $\begingroup$ Correct me if I am wrong, but isn't there a theoretical FTL drive that requires anti-gravity (or negative gravity) that is suggested by physics? $\endgroup$ – Jake Aug 5 '16 at 18:19
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    $\begingroup$ Atomic rocket's engine list: projectrho.com/public_html/rocket/enginelist.php. This shows almost everything you need to know about known and hypothetical rocket engines. $\endgroup$ – Thucydides Aug 5 '16 at 21:09
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Since you have rid yourself of The Tyranny of The Rocket Equation by solving the problem of fuel, you can make this in any way you want. Several emerging technologies, or technologies that have failed due to some limitations that we cannot get past yet, may serve you here. Things such as the aerospike engine (currently fails due to cooling / material requirements) might be useful for your design.

I would argue for a spaceplane that takes off conventionally to a high altitude, retracts its wings and goes hypersonic in excess of Mach 15, then "leaps" out of the atmosphere and gives itself a nice little orbital insertion boost.

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    $\begingroup$ But the ship would still need to expel some kind of working mass in order to accelerate, so I haven't rid myself of the Tyranny completely. There should be some kind of fuel, no matter how much energy the power source can provide. I assume that lots of available energy would lower the fuel requirements. Is that right or I'm missing something? $\endgroup$ – Elza Aug 5 '16 at 7:34
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    $\begingroup$ @Elza Use air! Heat it using whatever energy source you have available and expel it. For the orbital insertion you cannot do that, but it does not require much fuel. $\endgroup$ – MichaelK Aug 5 '16 at 7:56
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    $\begingroup$ You might even be able to use air for the orbital insertion. You could collect it during late takeoff, compress it into tanks, then heat and expel it for the orbital insertion. $\endgroup$ – Azuaron Aug 5 '16 at 12:29
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    $\begingroup$ @Azuaron Alternatively you could just have a propellant tank for orbital insertion. No need to tack on all the extra mass for intakes/compressors/pumps/ect. $\endgroup$ – UIDAlexD Aug 5 '16 at 13:08
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    $\begingroup$ @Elza you’re talking about reaction mass not fuel. You can trade mass usage — low thrust but more total ∆v vs higher instantanious thrust but needing more mass to be lost. Look up variable specific impulse rocket for a discussion. The situation was similar in the days of steam: a locomotive might have lots of coal left abord, but run out of water for steam. They would carry coal for the whole trip but take on water at every town. $\endgroup$ – JDługosz Aug 5 '16 at 15:51
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The spacecraft might be a wingless electromagnetic air vehicle (WEAV) which gets its lift by ionizing the surrounding air and gaining lift. Details here and it's not everyday the citation is to the Scientific American about a flying saucer.

The saucer will hover and propel itself using electrodes that cover its surface to ionize the surrounding air into plasma. Gases (such as air, which has an equal number of positive and negative charges) become plasma when energy (such as heat or electricity) causes some of the gas's atoms to lose their negatively charged electrons, creating atoms with a positive charge, or positive ions, surrounded by the newly detached electrons. Using an onboard source of energy (such as a battery, ultracapacitor, solar panel or any combination thereof), the electrodes will send an electrical current into the plasma, causing the plasma to push against the neutral (noncharged) air surrounding the craft, theoretically generating enough force for liftoff and movement in different directions (depending on where on the craft's surface you direct the electrical current).

Fortunately the single-stage spacecraft is a far-future vehicle with possible matter-antimatter power system because that solves this problem with WEAV. Therefore, it is reasonable to assume that the practical problems of using antimatter as a power source have been solved. This vehicle is operating in the far-future after all.

The biggest hurdle to building a WEAV large enough to carry passengers would be making the craft light, yet powerful enough to lift its cargo and energy source.

A similar magnetohydrodynamic (MHD) vehicle was described in an article "How To Design A Flying Saucer" by Dr Richard J Rosa published in Analog and reprinted in The Analog Science Fact Reader (1974) edited by Ben Bova. That suggested that this type of craft could produce large volumes of low-speed ionized air for travelling slowly and hovering, but narrow its air intake to generate smaller volumes of high-speed ionized air to accelerate to high velocities. Rosa's proposed MHD vehicle could land and take-off VTOL style, so it wouldn't need extensive infrastructure.

A WEAV-type spacecraft could accelerate through the air and once it reached the upper atmosphere use its matter-antimatter power system to ionize reaction mass such as water stored in propellent tanks to attain orbital velocities to rendezvous with the space-station.

ADDED TO EDIT

A single-stage spacecraft with a matter-antimatter power source can effectively boost itself to whatever speed its operators desire. This will be more than sufficient to power itself during a WEAV flight mode. The WEAV flight modes will be for powered in the atmosphere during descent and ascent. Landings and take-offs will be VTOL.

With a matter-antimatter power source this will generate considerably more energy than needed to attain orbital velocity. Using direct mass annihilation of matter and antimatter for propulsion would produce large amounts of gamma radiation. This is not good. However, it could easily be used to drive a powerful rocket propulsion system.

There are two types of reaction mass the vehicle can use. One, as suggested above is water. Two, is liquid air. The liquid air could be produced while the spacecraft is landed. This assures the vehicle will be lighter during its planetary descent. Water might also be collected from the planet's surface. Otherwise it would have to be carried in the vehicle's fuel tanks.

Whichever type of fuel is for reaction mass, the procedure is the same. using the power output from its matter-antimatter system the reaction mass is totally ionized and accelerated via powerful magnetohydrodynamic accelerators. Instead of an exhaust velocity of 4 km/s from chemical rocket propulsion MHD accelerated ionized reaction mass could have an exhaust of 100 km/s. This means the vehicle will consume far less reaction mass than a chemical rocket system.

The vehicle will also be able to regulate its rate of acceleration, so even untrained personnel could fly this type of vehicle without too much discomfort or distress. This could be an acceleration that keeps itself to no more than two gravities during the rocket propulsion phase. However, with engines as powerful as these it would be easily possible to attain far greater rates of acceleration. But the for the sake of its personnel the acceleration can be kept within safe limits.

The MHD rocket mode would be used for approaches to take-offs and landings from and on to a planet. Either decelerating from or accelerating up to orbital velocity, for travel either from or to the space-station the vehicle could use a plasma propulsion system with an acceleration of about one centimetre per second squared.

This version of a single-stage spacecraft is designed to fully exploit the power capacity of matter-antimatter generator. It has three flight and propulsion modes: (1) WEAV plasma-lift technology for flight in atmospheres during ascent and descent. (2) A high-impulse fully ionized reaction mass rocket propulsion system enhanced by MHD accelerators with an exhaust velocity of around 100 km/s. (3) A plasma propulsion system for interplanetary travel at an acceleration of one centimetre per second squared. It also operates at levels of g-forces that are safe for regular untrained personnel.

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First off, I imagine medium future space launches to go one of two ways: Either a massive structure that ferries things to space like a space elevator or skyhook, or a ground based launch system that provides the energy needed for launch like a mass driver or beam launcher. These don't meet your specs, but the reason that I mention them is that if they become feasible, they will probably replace the development of any rocket-based systems because they are not subject to the tyranny of the rocket equation. So, if you want a universe where advanced rockets are the thing, it probably shouldn't have any of the aforementioned methods since they would out-compete said rockets.

Now on to rockets. The best idea I have seen thus far is SABRE which is really only a marginal improvement over a newer chemical rocket. Also important, is that SABRE may not work if your atmosphere isn't about the same pressure as earth's, and will not work if your atmosphere has too little oxygen. So you can't say its useful for all terrestrial plants/moons.

Nuclear rockets do not have what it takes. NERVA was the closest to operational that such a rocket has ever been. It had a thrust to weight ratio of 1:5.2, so it couldn't make it to space. Nuclear reactors are heavy and I'm confident no fission system could ever have a thrust to weight above 1. For fusion rockets, the mechanics are anyone's guess at this point so too I can't say if you could use them to get to space. The various electromagnetic propulsion methods produce great specific impulse, but at the cost of low thrust and thrust:weight of less than one.

So in conclusion, I'm just not aware of a proposed technology that gets you into space out of a earth-like gravity well much more efficiently than a chemical rocket. I feel that for realistic sci-fi, humanity will be divided between those who live in gravity wells, and those who don't, and there won't be too much intercourse between them.

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  • $\begingroup$ Couple points. First, SABRE isn't actually an improvement over conventional rocket engines - pound for pound it's inferior in almost every regard. What it is, however, is an improvement in Fuel storage - Notably the precooler allowing you to used the oxidizer "Stored" in the atmosphere. That' mostly semantics. Second, while it's true that the (Very few) NTRs built and tested in the real world had very poor TWR, from what I've read that's more because they were designed for orbital operations and not because of a limitation with the concept of an NTR. $\endgroup$ – UIDAlexD Aug 5 '16 at 13:06
  • $\begingroup$ I can tell you with certainly, that a fission NTR will not work. Fission reactions produce serious neutron flux, and to stop the neutrons from activating your entire payload, you need lots of water and lead, neither of which is light. Also, you can't say that SABRE isn't an improvement then admit that it is an improvement in fuel storage. It's either better or its not. The answer is, that its better because you can drop part of your fuel load. Thrust to mass ratio of the engine is a useless number; Thrust to (mass_engine + mass_fuel) is not useless. $\endgroup$ – kingledion Aug 5 '16 at 13:26
  • $\begingroup$ It's better in one extremely specific area - getting to near-orbital speed in earths atmosphere. The question specifies that the craft should be able to land on a moon, and in that regime the big fancy preecooler is dead-weight, as is the oversized LH2 and almost non-existent LOX tank. For that matter, Skylon actually carries a smaller OMS engine in the tail. I get your point about NTRs, though. $\endgroup$ – UIDAlexD Aug 5 '16 at 13:42
  • $\begingroup$ I specifically asked about a planet without infrastructure, because the space station and its spacecraft are the only samples of advanced technology in the planetary system. $\endgroup$ – Elza Aug 5 '16 at 15:50
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Propulsion Tech

Nuclear-Thermal rockets have already been mentioned, but let's tailor that more towards your question. You said there's no tech limit? Then let's go with a Fusion-Thermal rocket! Working principles are the same - instead of burning two reactants for thrust you pass liquefied-gas over something hot to make it turn into a gassy-gas. The difference is our heat source (and level of heat.)

Using your star-core hot fusion reactor as a heat source makes things a lot more efficient - the higher temperature exhaust plasma means it's moving at a higher speed, and thus our Specific Impulse (Gas mileage for rockets) is far, far superior. It also opens up an interesting tradeoff. Since our reactor outputs a fixed amount of heat energy per second, if I run my engines in low thrust mode I can get absurdly high ISP. This is because I'm putting a huge amount of heat energy into a tiny amount of fuel. Great for orbital ops, but not so much for launch/landing. For that I'd dump more fuel into the rocket for worse efficiency but vastly increased thrust.

As for fuel, you can just use air. If you're in a planetary atmosphere, just scoop up whatever's there and pass it over your engine - it'll work just as good in inert atmospheres as oxygenated ones. When you're in space, rely on an internal supply of liquid hydrogen. It's not a huge issue because you're probably going to need low-thrust high-efficiency maneuvers for orbital ops anyway.

SCRAMJets are another option, but one that comes with some issues. They only work at already-high speeds in earths atmosphere, and they're very fault-intolerant. This has mostly to do with shaping the shockwaves to stay inside the engine - there's some speculative designs for variable-geometry SCRAMJets that remain viable over a wider range of airspeeds.

Problem is, engines are heavy, and tend to work best only in specific areas. I could keep tacking on different types of engines, but that will add a huge mass-penalty. SCRAMJets have a slight advantage here because they require no moving parts, but they still have to be very robustly built to handle the forces and heat loads they're put under.

The craft itself

The fact that we're dealing with hyper-sonic flight and re-entry limits our options for shape a lot. Something like an X-33 Venture Star like lifting body would work well in those regimes (And you want to optimize it for those regimes, because if you don't it'll shred your SSTO and crew. The space-planes from Avatar are - regrettably - another good example, but not quite as good as the first, because those thin wings aren't too good for hyper-sonic flight.

If the design can allow it, having tilting engines in the craft would work pretty well for your VTOL requirement. The mechanisms to do this add a lot of weight, complexity, fragility, and space requirements to the vehicle, though. What I'd do is mount my fusion reactor(s) so that they're in-line with the center of mass. This way I can vent the hydrogen plasma straight down for VTOL thrust, and then backwards for forward thrust.

If you want the multi-engine option and you can come up with a way to make low-mass SCRAMJets, you can tuck a few of them into the craft. This also depends on how powerful your fusion drives are - too good and the energy release of burning hydrogen in your SCRAMJet is going to make them pathetic and worthless.

This is all very speculative, but you did say no tech-limit. PS. Stay away from Antimatter. It sounds cool but the problems are almost too numerous to count.

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To land on planets without infrastructure, the ship would have to take off and land like a helicopter since a runway would not be available. To fly at speed through the atmosphere, an aerodynamic 'plane' design would be needed. I imagine your ship would look something like a reaver from planetside2: Reaver

The wings on this craft rotate, so that the jets can point either downwards to hover, or backwards for flight. The advantage of wings is the craft can glide on re-entering the atmosphere, removing the need for extra fuel until it comes to land.

As michael Karnerfors said, a spaceplane is your best bet. The problem here is fuel:

Space shuttle

Using a realistic fuel, this craft would need a new set of rockets every time you wanted to go back into space. According to wikipedia:

No completely reusable orbital launch system is currently in use. The closest example was the partially reusable Space Shuttle. The orbiter, which included the Space Shuttle main engines, and the two solid rocket boosters, were reused after several months of refitting work for each launch. The external tank and launch vehicle load frame were discarded after each flight. However, several at least partially reusable systems are currently under development, such as the Falcon 9 full thrust (first stage).

The falcon 9 is the only other existing reusable system, however it cannot fly in the atmosphere (apart from going straight up and straight down).

Your best bet is something like the reaver, but with a futuristic fuel which is both light and powerful, and can be obtained on most planets to refuel after landing. (maybe something radioactive, however this may damage the atmosphere significantly with radiation.)

EDIT:

Assuming, as the question states, a new fututistic fuel is readily available, the reaver design would work well. A futuristic fuel might produce enough energy to repeatedly enter and leave orbit without needing a refuel or using dispensible rockets.

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  • $\begingroup$ You seem to imply that a completely reusable rocket is not feasible, simply because nobody has done it so far. I'm not sure that is true, especially given that the question is about far future tech? $\endgroup$ – user16107 Aug 5 '16 at 11:27
  • $\begingroup$ misread the question slightly. $\endgroup$ – Aric Aug 5 '16 at 11:58
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The best general answer is that you will need to use some sort of external power source to provide the energy needed for flight operations. Laser thermal or microwave beaming of energy to heat and expel reaction mass such as water or liquid hydrogen is a near term possibility, but even with an ISP of 8-1200, you will still probably be strictly limited to how much cargo or passengers you can carry. You also have the issue of restocking your ship with reaction mass for every flight, and the laser infrastructure to provide the energy (not just the laser, but the tracking infrastructure, heat rejection devices and other ancillary equipment).

a4android's answer provides an alternative, and Leik Myrabo worked on variations of this idea through the 1980's and 90's. Direct thrust by heating the air to a plasma or indirect thrust using MHD accelerators on the outer surface of the craft were all explored in various levels of detail, and a laser driven rocket was launched at a test range (the limit was preventing the laser from "blinding" satellites passing overhead). This video gives you an idea of what was being done.

So the short answer is that there are technologies which can bring you close to the goal you are seeking, but generally require external energy infrastructure for propulsion. Flight within an atmosphere is no problem, but flight in free space or to an airless moon/asteroid will still require the heating and expulsion of reaction mass, limiting you to vehicles with ISP's of between 8-1200. (For comparison, the best chemical reaction of H2 and O2 gives you an ISP of 425-450. The Space Shuttle carried about 2000 tons of propellant in the External Tank, and still needed two solid fuel boosters to assist it in lifting off).

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  • $\begingroup$ Why would I need an external power source if I have enough power on board? It seems that you have misread the question somehow. $\endgroup$ – Elza Aug 5 '16 at 17:24
  • $\begingroup$ No. The "Tyranny of the Rocket equation" practically demands that you offload as much as posit le from the rocket. It takes something like 35 GW of energy to launch a space shuttle or Saturn V, so it makes a lot more sense to have the 35 GW energy source sitting on the ground or in orbit, rather than carrying the mass of chemical or nuclear energy generating equipment along (yes, a rocket motor is used to convert chemical energy into thrust). $\endgroup$ – Thucydides Aug 5 '16 at 21:06

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