sevenperforce

It's not really accurate to compare the shift from 0 g to 1 g with the shift from 1 g to 2+ gees, because it's a completely different set of issues. In high gravity, your capillaries will expand and you'll have a heightened risk of embolisms. Your feet will swell and suffer permanent tissue damage. Your blood pressure will go up considerably, shortening lifespan, and you'll end up with a lot of scarring due to increased incidence of muscle microtearing. There is a limit to human adaptation.

Presumably "spaceplanes" may be divided into "suborbital spaceplanse" and "orbital spaceplanes", just as spaceflight itself is divided into "suborbital spaceflight" and "orbital spaceflight". Carl Sagan moment: how cool is it that we figured out how to stay in space above a friggin' massive ball of rock simply by going really, really fast?

One little difference: the Saturn rockets were ELVs. If your vehicle is designed to be expendable, then you'll make a lot of really specific choices. You're going to have a LOT of engines, each designed for a specific thrust profile and throttleability and burn time and fuel type, and you're going to throw them away at the drop of your hat to save every drop of fuel. With a reusable, on-orbit-refuellable vehicle, things will be very different. For example, the Apollo missions used two separate engines for the landing: one for descent and one for ascent, each with their own tanks, even though they used the exact same fuel mixture. That meant the 180-kg, 25.6 T/W ratio descent engine had to carry the dead weight of the 82-kg, 19.44 T/W ratio ascent engine down to the surface. But it turned out to be a better configuration than using a single engine. With reusability, on the other hand, you'd never dream of dumping your descent engine on the surface, so you'd bring a completely different design philosophy to the table. Maybe, maybe not. Using lunar landings as a test case but requiring full reusability and an artificial-gravity-equipped hab, and assuming Earth-orbit staging/refueling, you have a few different configurations. You need to get through the Van Allen belts quickly, keep your crew happy and gravitated during the trip, get them down to the lunar surface, keep them alive on the lunar surface, get them off of the lunar surface and up to LLO, then send them back to Earth alive and gravitated, then brake quickly since you have to pass through the Van Allen belts at high speed. How many engines do you use? How many fuel tanks? How many habs?

Fair enough.

Well, "wind" is a bit of an exaggeration.

Indeed. But it is a good enough insulator that we can construct internal trusses which will remain sturdy even while the surface is on fire. We will know the burn time of each rocket stage, after all. It's going to be a better choice than trying to forge metal with sufficiently heat-resistant properties, because metal is a much better heat conductor. Getting a liquid fuel at high grade might be a little easier than getting solid fuel at high grade. However, storing, pumping, pressurizing, and combusting in a bipropellant liquid-fueled rocket is going to require a set of tolerances far in excess of what we will be able to build without vast, vast industrial capabilities. And even if we could build such a rocket within the required tolerances, it would be so much heavier than modern designs that it would be pointless. Solid fuel rockets have excellent thrust to weight ratios, while liquid fuel rockets require extremely precise machining in order to get even decent thrust to weight ratios. I doubt a liquid rocket engine built any time before the 20th century would have sufficient thrust to get off the ground with any meaningful amount of fuel.

Alcohol and science have a long and sympathetic history. When the scientists at Los Alamos were working on The Bomb, they requisitioned 100% pure lab ethanol among their ordinary lab supplies in order to make spiked punch for their parties.

A sufficiently dense ring structure inside the Roche limit could sustain windborne microbial life. Average metallicity isn't really at issue; an M-class star can form in any protostellar nebula, so metallicity can be as high as you want it to be. In fact, IIRC, an M-class star in a nebula with available metal should have higher metallicity than a larger star, because larger stars more readily capture hydrogen and helium. The origin of life boils down to one thing: thermodynamics. Structures which can dissipate an energy flux last longer than structures which cannot. So what you need for life is an energy flux high enough to give life an edge, but not so high that every possible structure is continually being torched. Terran terrestrial life would probably not do well around an M-class star, with its high variability, but a world with subsurface oceans should be able to modulate the energy flux well enough to allow life to survive.

Autonomous self-replicating robots of any kind should be classified as artificial life. Not artificially intelligent life, of course, but certainly artificial life. I tend to assume that exotic-chemistry nonintelligent life is very common in the universe but intelligent life is fairly rare.

The whole jointed-leg thing seems unnecessarily complicated. Why not just use conventional skids, but mount them on telescoping struts instead of fixed ones?

Upgrading kiln tech to enable better ceramics will almost certainly be simpler than trying to upgrade metallurgy to a comparable level. Plus, you can mix and match properties; you can use a ceramic inner layer for thermal properties with a steel outer layer for mechanical properties. A kludge, perhaps, but a workable one. We certainly wouldn't be using cryogens, so the goal is to build the SRB body with enough axial compressive strength to support the rocket in flight and enough skin tensile strength to contain the solid fuel combustion gases. The latter isn't as challenging as it seems, because the solid fuel itself will act as a heat sink and load distributor for the majority of the burn period. In fact, stage separation could be accomplished by merely making the upper portion of the booster body too weak to contain the combustion gases at the end of the burn. I'm thinking an internal wooden frame (wood is a good enough insulator to remain strong during the relatively brief burn, and its tensile, compressive, and torsion strengths will be better than metal for weight cost at this era), wrapped in thin beaten metal, with a few thicker metal bands wrapped around the outside. Getting gyros to work is hard, I agree.

Perhaps more critically, SEL2 is not actually stable. You either have to sit still with constant station-keeping, or you have to stay in a kidney-bean-shaped orbit that takes you above and below the ecliptic, exposing you to sunlight for most of the time.

Ceramic nozzle; banded metal for the body. Guidance is tricky, sure, but we could come up with something. Fuel chemistry is the main challenge.

Absolutely. Not to derail on the first reply, but if Saturn or Jupiter was teeming with microbial life right now, would we know? Jupiter's atmosphere is thousands of times the volume of our entire lithosphere; the odds seem fairly good that life could have arisen. But would we be able to see anything anomalous from here?

I can solve the rocket equation myself, but it's typically easier to just plug the values into something like this calculator (thus avoiding the potential for math errors). I'm not quite sure why you'd want to use escape velocity; the goal is merely to get to orbit. We can say 10.5 km/s to give ourselves a margin. Unfortunately, using the above calculator shows that with an ISP of 80, you would need over 655 tonnes of fuel for every kilogram of dry mass to get that kind of delta v. That's a mass ratio of 655000:1.

If ISP is too low, not even staging can save you. See what-if #24.

Because I was greedy and wanted a thread specific to my design. =P I'm not sure yours will be cheaper. Your mothership still needs a superstructure in order to support centrifugal gravity, and it needs some sort of basic shielding to protect the fuel tanks and the hab from micrometeoroid strikes. It won't cost significantly more to design your ship with the capacity to aerobrake. The aeroshell only limits geometry if you're intending to enter an atmosphere during a given mission. If your specific mission is limited to vacuum operations, then you can add whatever geometry you want -- auxiliary tankage, solar sails, massive amounts of cargo -- to increase delta V or to tow a new space station into orbit or whatever else you want to do. And once you reach your destination, you retain the flexibility to leave the vacuum-limited components in a high parking orbit and aerobrake your main ship. For each mission, the optimal landing configuration will be a function of the destination's surface gravity, escape velocity, atmospheric properties, and surface resources, plus the intended duration of your surface mission. There will be missions where it's cheaper overall to land the whole ship, there will be missions where it's cheaper to bring along a separate but reusable descent/ascent vehicle, and there will be missions where it's cheaper to bring along an expendable descent vehicle and a reusable ascent vehicle. And while the extra fuel to land on certain bodies might mass more than individual landers, fuel is cheap and simple and may be accessible on-orbit, while landers may not be any of those things.

That works to decrease overall launch costs, but it means you have to plan missions much further in advance and greatly limits flexibility. Having a landing-capable mothership in no way prevents you from bringing along one or more smaller landers. Nor does it prevent you from carrying additional fuel. The flying-saucer design in the other thread would probably be provided with a standardized on-orbit docking spire mating through the open center to which added cargo, added fuel reserves, and additional vehicles could be docked. I'm simply arguing that if you are using centrifugal gravity for your hab, then it makes more sense to rotate your entire mothership than to try and have a separately-rotating hab. And if you're rotating your entire mothership, then it makes sense to enclose your essential components -- the hab, the primary engines, and the primary fuel supply -- inside a single robust structure. And if you already have all those essential components inside a single robust structure, then it makes sense to make that structure an integrated aeroshell so that your mothership can aerobrake for 0 dV orbital insertion (for example, at Mars or Venus or Earth).

Hmm, good question. I don't know whether the Lissajous orbit around L2 would keep a spacecraft in Earth's shadow or not.

The mothership can certainly tow along any number of other vehicles. Of course, those vehicles will need to be launched separately from Earth, which is a substantial cost. Logistics starts to play a part, however, when you look at the necessary requirements for your mothership. It already needs to have enough structural integrity to provide artificial gravity by rotation. Thus, slapping a lightweight aeroshell around it so that it can aerobrake for orbital insertion from a transfer won't really incur much additional weight cost. While towing along a separate descent/ascent vehicle is fairly reasonable, it doesn't really make sense with landings on airless worlds. It is cheaper to simply carry extra fuel to deorbit/reorbit the entire ship them it would be to carry a separate landing vehicle and ascent vehicle. So it only makes sense to equip the mothership with powerful enough engines to support descent and ascent on airless worlds all by itself. And once you have both aerobraking capability and lunar SST-LEO capability, you might as well give it Martian landing/ascent capability.

A fascinating possibility. What kind of ISP could that develop, and how would you stage/contain it?

Well, as I explained in the other thread, once you are talking about multiple interplanetary missions you really want more flexibility. Unless you have dedicated orbital space ports at every possible destination, then the spaceship has to bring along a lander of some kind. You can only aerobrake on Earth, Mars, and Titan. Thus, for any realistic mission flexibility, it will usually make more sense to equip the mothership for powered landing and ascent instead of dragging a bunch of other spacecraft along, which would themselves need to be launched from Earth to resupply for every individual mission.

I can't see how they could get away without a reentry burn. Otherwise that booster will smack into the atmosphere like an egg hitting concrete.

And the ballistic performance of a cylindrical rocket is anything but simple.

So what's the most likely failure mode? Breakup during re-entry, or a missed/hard landing?