Design a One Stage Launch Craft?

[Technical Ben]

Oh, I forgot the lunar lander left half it's cargo behind. Duh.

[Soralin]

Not to mention taking off and landing on the moon is significantly easier than taking off from Earth. From Atomic Rockets (definitely recommend looking through that, there's a topic list in the upper right) under the mission section, there's this:

From that, going from lunar orbit->lunar surface, or vice-versa is around 1.6km/s deltaV, each way. So land, and takeoff together would be about 3.2km/s deltaV. Going from Earth->low earth orbit is around triple that. So you could land, and take off again 3x on the moon, for the same deltaV it takes to go one way, from the surface of the Earth into orbit. (numbers may be slightly different in practice depending on how much acceleration your rocket can do, a rocket that can put out 1g of thrust is going to have a much easier time getting off the Moon then it is getting off of the Earth, there's formula there to calculate it more exactly if you like)

For mars there, you could land and take off for less than it takes to go one-way on Earth.

"Once you get to earth orbit, you're halfway to anywhere in the solar system."

[Technical Ben]

True. But on the earth we have an atmosphere to break with. I would guess, with space travel your looking at 2 or 3 types of landing craft at most. This is assuming, we only land regularly on the types of planet we can survive on.
We have a small atmosphere less planetoid like the Moon. Or a larger planet such as Mars with an atmosphere, but lacking free oxygen.
With atmospheres you can use that to slow down, or gain lift, and save fuel. With no atmosphere, you are probably on a smaller planet anyhow, so save on delta V.

Getting a craft that can cope with both would be a real trick though.

[bigglesworth]

For the aerobraking, how about having a regenerative heat-shield? It extrudes the heat shield from liquid reserves onboard.

[Soralin]

If you can make it work with less mass than a solid heat shield. I mean, you can make an ablative heat shield, which is basically the same thing, except it extrudes the heat shield from solid reserves on board (it heats up, wears away, and takes the heat with it, and then the whole thing gets replaced after you land for next time).

If you are doing it with liquid, you don't even need the liquid to actually be on the outer surface, you can just have it be coolant, just flow along the inside of the heat shield, and get boiled away and vented out (or just used to dissipate the heat elsewhere or such, and cooled back down to liquid again).

Whatever gets you the least mass, heat shields are used simply because they're much lighter than the fuel needed to come down on a powered descent would be for a chemical rocket.

[Technical Ben]

Inflatable heat shields. With a heat resistant skin using gas as an insulator/conductor is the way to go IMO. It also means you can have your heat shield protected in orbit. It's packed away. Then deploy it before/during re-entry. If you deploy it before, you know it's working without take the risk of it failing to deply. But if you're already trusting your life to a parachute, you can trust it to an inflatable heat shield.

[bigglesworth]

I was thinking of some kind of expanding foam, non-reusable so that you don't have to worry about damage to it.

[Kang]

How about rather having a classic heat shield covered with any protective material then? It doesn't need to be deployed in any way, thus cutting the number of operational parts and thereby the potential for failure, while it stays protected from whatever elements you might encounter until the protective coat burns off and the heat shield does its job.
Anything usable one time only means you reduce the number of journeys you can make unless you assume that besides fuel also spare heat shields are easily available everywhere (in fact something inflatable or foam-based would at least mean those parts would not need to be specific to a single type of craft, so maybe that is walkable after all).

[Roĝer]

An important point on reentry that you all seem to be missing: if you are coming from an orbit, the horizontal kinetic energy is larger (for LEO a lot larger) than the vertical potential energy. So if you want to deorbit and you have a lot of time, you can indeed lose most of the energy by skipping the upper atmosphere in an elliptic orbit. Mars landers can and do use this technique.
If however you are coming in directly from outside the object's sphere of influence, then this doesn't apply.

[Technical Ben]

Hmmm. If launching from a "mother ship" it's probably going to be in orbit. Would it be worth using up the larger ships fuel to slow down/speed up from orbit and just use a shuttle to land? Granted a larger ship has to use more fuel to accelerate or decelerate, but it's not restricted on payload size like the shuttle is. At least not in this instance, as the shuttle is the only thing I've considered to be limited in fuel, payload or resources. We could give the shuttle unlimited refuels/payloads/heatshields etc. It must be able to get back without a refuel though.

[Soralin]

Hmmm. If launching from a "mother ship" it's probably going to be in orbit. Would it be worth using up the larger ships fuel to slow down/speed up from orbit and just use a shuttle to land? Granted a larger ship has to use more fuel to accelerate or decelerate, but it's not restricted on payload size like the shuttle is. At least not in this instance, as the shuttle is the only thing I've considered to be limited in fuel, payload or resources. We could give the shuttle unlimited refuels/payloads/heatshields etc. It must be able to get back without a refuel though.

I'm not sure exactly what you're referring to here, if you mean, using a surface-to-orbit shuttle to handle all of the planetary stuff, that's definitely a good idea, for multiple reasons. For one, a larger orbit-to-orbit ship would likely not be designed to be able to land on a planet. Also, it would likely use a high-efficiency method of moving around, if we're talking near future, then something like nuclear-electric drives like ion drives, vasimr, etc. which can have very high efficiencies, but not enough thrust to get you off of a planetary surface. Surface-to-orbit would have to use something like chemical drives, or nuclear-thermal stuff, something that can produce more than 1g of thrust, but which can end up being significantly less efficient. Or ground launchers, like a launch loop or space elevator or such, which can be quite efficient, but can't exactly apply much to an orbit-to-orbit ship.

If you mean something like a large ship decelerating, dropping a shuttle, and accelerating back into a proper orbit, that would not be a very good idea. The larger ship is obviously more massive, and you're going to use up much much more fuel, or reaction mass, trying something like that then you would otherwise. Fuel (and reaction mass), is everything, it is what will compose the vast majority of practically every ship, of every size. Even if you're using nuclear fuel sources, you still need reaction mass, and lots of it. Delta-V, (i.e. change in velocity), is what determines what you can do with a ship, where you can go, what you can do, how fast you can go, etc. and it all depends on how much fuel and reaction mass you have (and how efficiently you can use them, the higher speed that you can give to your reaction mass as you toss it out the back, the less of it you need, but the more energy that takes). Also, if the mothership here has a low-thrust engine, it likely wouldn't be able to do such a thing in the first place.

If you mean an orbit-to-orbit ship slowing down to achieve orbit, rather than just dropping off a shuttle as it passes by, that depends on what you want to do with it. Most of the time, you'd be stopping to achieve orbit, since you want your ship to still be there so you can get back on it again, and it makes getting back up and down easier again. Although there is a cycler ship design, where you can set up a ship with a power source, life support, radiation shielding, etc. on an orbit between say Earth and Mars, and then smaller ships could be launched, meet up with the cycler ship and attach to it, and then crew and such loaded into the large ship, and then use the same ship to drop off at the far end. Just looked at by itself, this doesn't save much in the way of fuel for a small ship, after all, the acceleration it needs to meet up with the big ship is the same as what it would need to go all the way to Mars on it's own, but, it means that the smaller shuttle doesn't need to have long-term life support, or radiation shielding, or provide power, etc., and so it doesn't have to carry the fuel to boost those things into orbit or bring them back down again. Although you probably weren't referring to that.

[Kang]

An important point on reentry that you all seem to be missing: if you are coming from an orbit, the horizontal kinetic energy is larger (for LEO a lot larger) than the vertical potential energy. So if you want to deorbit and you have a lot of time, you can indeed lose most of the energy by skipping the upper atmosphere in an elliptic orbit. Mars landers can and do use this technique.
If however you are coming in directly from outside the object's sphere of influence, then this doesn't apply.

Do you happen to know how that influences landing precision? I remember reading that the method was getting worse with the atmospheric density, since the denser the atmosphere in general, the more critical to deceleration is an exact altitude was. But that was a pretty old source and might not have taken into account modern computers.

[HopDavid]

Hmmm. If launching from a "mother ship" it's probably going to be in orbit. Would it be worth using up the larger ships fuel to slow down/speed up from orbit and just use a shuttle to land? Granted a larger ship has to use more fuel to accelerate or decelerate, but it's not restricted on payload size like the shuttle is. At least not in this instance, as the shuttle is the only thing I've considered to be limited in fuel, payload or resources. We could give the shuttle unlimited refuels/payloads/heatshields etc. It must be able to get back without a refuel though.

I'm not sure exactly what you're referring to here, if you mean, using a surface-to-orbit shuttle to handle all of the planetary stuff, that's definitely a good idea, for multiple reasons. For one, a larger orbit-to-orbit ship would likely not be designed to be able to land on a planet. Also, it would likely use a high-efficiency method of moving around, if we're talking near future, then something like nuclear-electric drives like ion drives, vasimr, etc. which can have very high efficiencies, but not enough thrust to get you off of a planetary surface. Surface-to-orbit would have to use something like chemical drives, or nuclear-thermal stuff, something that can produce more than 1g of thrust, but which can end up being significantly less efficient. Or ground launchers, like a launch loop or space elevator or such, which can be quite efficient, but can't exactly apply much to an orbit-to-orbit ship.

If you mean something like a large ship decelerating, dropping a shuttle, and accelerating back into a proper orbit, that would not be a very good idea. The larger ship is obviously more massive, and you're going to use up much much more fuel, or reaction mass, trying something like that then you would otherwise. Fuel (and reaction mass), is everything, it is what will compose the vast majority of practically every ship, of every size. Even if you're using nuclear fuel sources, you still need reaction mass, and lots of it. Delta-V, (i.e. change in velocity), is what determines what you can do with a ship, where you can go, what you can do, how fast you can go, etc. and it all depends on how much fuel and reaction mass you have (and how efficiently you can use them, the higher speed that you can give to your reaction mass as you toss it out the back, the less of it you need, but the more energy that takes). Also, if the mothership here has a low-thrust engine, it likely wouldn't be able to do such a thing in the first place.

If you mean an orbit-to-orbit ship slowing down to achieve orbit, rather than just dropping off a shuttle as it passes by, that depends on what you want to do with it. Most of the time, you'd be stopping to achieve orbit, since you want your ship to still be there so you can get back on it again, and it makes getting back up and down easier again. Although there is a cycler ship design, where you can set up a ship with a power source, life support, radiation shielding, etc. on an orbit between say Earth and Mars, and then smaller ships could be launched, meet up with the cycler ship and attach to it, and then crew and such loaded into the large ship, and then use the same ship to drop off at the far end. Just looked at by itself, this doesn't save much in the way of fuel for a small ship, after all, the acceleration it needs to meet up with the big ship is the same as what it would need to go all the way to Mars on it's own, but, it means that the smaller shuttle doesn't need to have long-term life support, or radiation shielding, or provide power, etc., and so it doesn't have to carry the fuel to boost those things into orbit or bring them back down again. Although you probably weren't referring to that.

Here's a rough delta V map of the earth and Mars systems. It assumes circular, coplanar orbits and so it's not perfect:



The most massive vehicle would be the one ferrying humans between Mars and Earth neighborhoods. It'd need life support of 7 to 8 month trips as well as lots of radiation shielding. This vehicle, in my opinion, should move between EML1 and Phobos. If there were fuel at these locations, it's delta V budget would be around 4 km/sec between opportunities to "gas up"

The vehicle for moving between Phobos and Mars need only support life for a few hours and could thus be much less massive. Having a separate martian lander/ascent vehicle would also reduce the mass of the interplanetary vehicle. The interplanetary vehicle would need no ablation shield, thermal protection, etc.



Of the vehicles above, I believe the green and red ones could be singlestage reusable. The yellow may also be multi-state expendable.

[Roĝer]

Would it not be better to have a ship with life support systems cycling between Earth and Mars in elliptical orbit, using shuttles to access it from EML1 and Mars orbit when it passes by? That way you only need to accelerate the crew and supplies (and the small shuttle), not the whole craft with life support and radiation shielding.

[Soralin]

Would it not be better to have a ship with life support systems cycling between Earth and Mars in elliptical orbit, using shuttles to access it from EML1 and Mars orbit when it passes by? That way you only need to accelerate the crew and supplies (and the small shuttle), not the whole craft with life support and radiation shielding.

It really depends on what you need and what technology you have available. Radiation shielding is nice to be able to leave behind, because you probably don't need it down on the surface much. Life support would be useful to have on a cycler ship, but only if it's long-term stuff, recycling air and water, even breaking down CO₂, or growing plants or such. If it's just using up consumable supplies, then you have to bring more of those next time anyway and it doesn't save you anything. Power is nice too, especially since for fission, the reactor is going to likely be quite a bit heavier than just the fuel it needs.

But, on the other hand, the cycler ship is only really useful for human cargo, or anything else that needs radiation shielding and life support. If you're sending a hab module, or a new reactor, or a crate of CPUs or something, then there's not really anything to gain from a cycler, you can just send it straight there. Also, in order for a cycler to be useful, you have to catch up to it, getting into the same orbit as it anyway, which used the same amount of energy as if you were going to mars without it being there at all(minus the mass you don't have to bring). But more than that, you have to catch up to it relatively quickly, which depending on the technology available, might be using high-thrust, low-efficiency engines. I mean, it doesn't help you out much if you spend 2 months accelerating up to the cycler, and then just get off again shortly after and spend another 2 months decelerating again. And, if you do have really good engines, given that the cycler is only really useful for living cargo, it might be more beneficial to use a craft with a high efficiency engine, that can slowly accelerate and decelerate, to make the trip to mars in one month rather than 5. Especially if you can say, use a ground launcher to launch more fuel or reaction mass up from the surface.

[HopDavid]

Would it not be better to have a ship with life support systems cycling between Earth and Mars in elliptical orbit, using shuttles to access it from EML1 and Mars orbit when it passes by? That way you only need to accelerate the crew and supplies (and the small shuttle), not the whole craft with life support and radiation shielding.

What you propose is the cycler concept advocated by Buzz Aldrin and some others.

The large interplanetary craft he calls "Castles". The shuttle betweens the castle and planet he calls "Taxis"

Aldrin's proposed shuttle would fly by earth as well as Mars each earth-Mars synodic period (about 2.14 years).

Some problems with Aldrin's cycler: It would need it's line of apsides rotated about 57 degrees each trip. Planetary gravity assist could accomplish some of this, but it would stll take substantial propellant to maintain the orbit.

The aphelion of the Aldrin's cycler goes clear out to Main Belt. It's orbit crosses Mars at a substantial angle. So the taxis between Mars and the castle would have a big delta V budget, around 10 km/sec.

There are also Niehoff cyclers. These cycler orbits are much more Hohmann like than Aldrin's and thus take less delta V. Although they fly by earth and Mars on a regular basis, their visits aren't as frequent as Aldrin's cyclers.

All the cycler schemes rely on the fact that 7 earth-mars synodic periods is fairly close to 15 years. But the synodic period is different enough from 2 1/7 years that Mars can drift substantially from being at the right place at the right time for rendezvous.

Mars orbit is noticeably eccentric, which is also a headache for cyclers.

Venus, on the other hand, is much more amenable to cyclers.

[Technical Ben]

Ok, this looks just as cool as a one stage for a sci-fi setting.
http://youtu.be/sSF81yjVbJE

Space X idea for a fully reusable 3 stage.

[Soralin]

Yeah, SpaceX has been doing some awesome stuff. And not just planning, but actually successfully making everything, and carrying through with what they plan.

[idobox]

Making it fully reusable is a tough challenge, and some experts doubt they will manage.
But they look like serious people, and if they claim they can do it, then it's probably feasible.

[BlackHatSupport]

Thinking this over, I've kinda tenatively designed a spaceplane (delta wings, flattened hull, the lot)....but with the approximate dimensions of a 747 and 9/10th fuel storage, and then there's the problem of "flying brick" during approach and landing.


I might make a mock-up. And y'all are free to refine this idea, as it's rather sketchy.