So why couldnt one of the shuttles be rigged up to orbit the moon? it certainly had room in the cargo bay for a lander.
So why couldnt one of the shuttles be rigged up to orbit the moon? it certainly had room in the cargo bay for a lander.
The Shuttles didn't carry anywhere near sufficient orbital maneuvering propellant to reach the moon, particularly with a full cargo...made worse by the main engines, wings, landing gear, enclosed cargo bay, and a bunch of other structure that would be dead weight for such a journey. It would also be the last trip the Shuttle made, as its tiles and wings couldn't withstand a high-speed reentry from a lunar trajectory. After the Shuttle Orbiter reached low orbit, you'd need a bunch more launches to add propellant tanks and other equipment, and at that point there's little benefit to having the Orbiter involved...it's about 70 tonnes that you could fill with a much more useful vehicle.
So why couldnt one of the shuttles be rigged up to orbit the moon? it certainly had room in the cargo bay for a lander.
That makes sense , not enough fuel , wrong engines. but wouldnt they just establish earth orbit and then rentry? thanks
That makes sense , not enough fuel , wrong engines. but wouldnt they just establish earth orbit and then rentry? thanks
And then even supposing the shuttle did go to and from the Moon, it would then have the problem of encountering Earth's atmosphere at about 25,000 mph after the translunar coast rather than the 17,500 mph from Earth orbit. Not only is the shuttle's thermal protection system not rated for the level of heating this would cause, the shuttle's structural assembly is not built to withstand the aerodynamic forces involved at those re-entry speeds.
Well, of course it wouldn't necessarily have to re-enter at 25,000 mph. They could carry out an EOI burn to put them back into the usual 17,500 mph Orbiter orbit, but that would require shitloads of extra fuel for the EOI burn, and that extra fuel would require more extra fuel to be carried from the start to carry the extra weight.
Well, of course it wouldn't necessarily have to re-enter at 25,000 mph. They could carry out an EOI burn to put them back into the usual 17,500 mph Orbiter orbit, but that would require shitloads of extra fuel for the EOI burn, and that extra fuel would require more extra fuel to be carried from the start to carry the extra weight.
Um, see reply #8 by me just above... :)
In fact, that method could be used even with an Apollo-style (one-use) LM to reduce the total launch costs of a lunar mission; call it the "double LOR" method. The CSM would enter lunar orbit alone and rendezvous and dock with the waiting LM before landing, then rendezvous and dock again with the ascent stage after the surface crew returns.
Another issue is that the fuel itself makes up most of the launch mass of an Apollo-style mission. I'm not sure you'd get all that much savings with your profile, since all the fuel still needs to be lifted out of Earth's gravity well.
Missed that. I just wanted to kick off a reply before heading to work. My bad!
But just one other question since you seem to understand this stuff better than most:
To achieve TEI requires enough velocity to escape lunar orbit, right? Well surely, that isn't going to be 25,000 mph. Lunar escape velocity is 2.4 km/s which translates to about 5,400 mph. Is the other 20,000 mph picked up during the coast phase due to the gravitational pull of the earth,
Would it be possible, given the low gravity of the Moon to build a bigger, stronger Lunar Descent/Ascent Vehicle (LDAV) that carries down with it enough fuel (in the form of an exchangeable fuel module) to launch the entire LDAV back into orbit?You've hit on the crucial element in the design of a reusable LDAV, as you call it: the ability to make a round trip. However I was thinking of fueling it on the surface from locally produced propellants and carrying enough into orbit to do a subsequent powered descent.
The ERV and LDAV are reused - only the fuel modules and the earth launchers for them and the ERV are disposed of, and the launchers can be much smaller if they are only launching fuel tanks and the ERV.It's easy to forget since it wasn't visible, but 2/3 of the mass of a loaded LM was propellant. This is why I think lunar propellant propellant will be the only sustainable way; it'll just be too expensive importing it from earth.
Well, if we are going to speculate. I would consider a stepping stone approach. Say, establish a significant station at L1. If large enough, maybe this would allow for servicing of the posited lunar lander without requiring a return to Earth for same, and resupply without going all the way to the moon. Return trajectories to Earth from L1 would naturally be lower velocity with commensurate weight savings. Service trips for the reusable lunder (lunar lander) would be less fuel expensive as it only need reach L1. Missions of any type would become many smaller missions, not a single big one. Pure speculation, I have done no math on it, nor intend to. It's just an idea.Another issue is that the fuel itself makes up most of the launch mass of an Apollo-style mission. I'm not sure you'd get all that much savings with your profile, since all the fuel still needs to be lifted out of Earth's gravity well.
The propellant does, at least initially, but the rest of the vehicle can stay in lunar orbit. Consider sending a tanker and a multiuse lander, and conducting multiple expeditions to the surface during a single mission, refueling after each. Then park the lander into some stable orbit, and send another tanker when you do another mission. And when you make use of propellant from off-planet sources (LOX/CH4 from polar ices, for example), you drastically change the situation.
I wonder if pure oxygen could be used as a propellant without eating up the engine.
It's easy to forget since it wasn't visible, but 2/3 of the mass of a loaded LM was propellant. This is why I think lunar propellant propellant will be the only sustainable way; it'll just be too expensive importing it from earth.
So if you're going to have nuclear reactors for power, why not use them for propulsion too? The raw materials for chemical fuel are rare on the moon, but a nuclear thermal rocket doesn't need fuels and oxidizers; it only needs reaction mass. Hydrogen is ideal but I wouldn't want to squander the moon's limited polar reserves if there alternatives. I wonder if pure oxygen could be used as a propellant without eating up the engine.
And I favor LOX/CH4 ...
Are the materials and processes available to synthesize methane on the Moon? I've already heard about manufacturing methane on Mars, but my understanding in that the process uses carbon dioxide from the Martian atmosphere. If you know of a process that will work on the Moon, I'm interested in hearing more about it.
raven, aluminum/oxygen as a fuel has occurred to me too. After all, much of the exhaust of a solid rocket motor is aluminum oxide. I even thought of using finely ground raw lunar materials (which includes alumina) as the propellant in a nuclear thermal rocket, but the problems of high molecular weight and of erosion by solid refractory particles probably makes it a non-starter.
You could even use metallic aluminum or magnesium. That would avoid chemical attack on the rocket parts and both have atomic weights less than diatomic oxygen. Ideally you'd have to heat them to their gaseous phase. At STP aluminum boils at 2519 C (!) but magnesium at (only) 1091 C but they'd be significantly higher under pressure. Hmm. has anyone ever considered metallic propellants in any kind of rocket, thermal or electromagnetic?
You mention disassociation for hydrogen; how much would there be for methane or water at those temperatures?
Metallic propellants have been used in ion thrusters...mercury, cesium, bismuth, and lithium are ones I'm aware of.Xenon seems to have become the favorite propellant in ion thrusters. I wonder why; it's rare and expensive.
Xenon seems to have become the favorite propellant in ion thrusters. I wonder why; it's rare and expensive.
Metallic propellants can also be used in electromagnetic rail guns. Problem is you need either a very long barrel or extremely high power to get a reasonable exit velocity. Rail guns have frequently been proposed for launching stuff off the moon; it may turn out to be the most practical solution in the far future.
Plus, the thing looks like a sci-fi fan's dream...
The external shell (the aeroshell) is made from a fibre reinforced ceramic and carries only aerodynamic pressure loads which are transmitted to the fuselage structure through flexible suspension points. This shell is thin (0.5mm) and corrugated for stiffness. It is free to move under thermal expansion especially during the latter stages of the aerodynamic ascent and re-entry.(Red bolding mine.)
During re-entry, which occurs at an altitude between 90 to 60km the heat is radiated away from the hot aeroshell. Heat is prevented from entering the vehicle by layers of reflecting foil and the low conductivity shell support posts. Liquid hydrogen is evaporated in the main tanks, passed through thermal screens to intercept the small residual heat leak and then vented overboard.
Not being in the industry I don't know about the latest tech, but is there a "fibre reinforced ceramic" that in a 0.5 mm thickness can manage reentry temps and then be ready for another launch without extensive maintenance? I know there are some remarkable materials out there, but that claim seems a little... optimistic, to say the least.
How about Ozone for nuclear rocket reaction mass? Would that be better or worse than Oxygen?
Fuel Exhaust Products Mass Moles Mass/Mole
Hydrogen, H2 1 H2 2.02 1 2.02
Methane, CH4 1 C(s) + 2 H2 16.04 3 5.35
Propane, C3H8 3 C(s) + 4 H2 44.10 7 6.30
Pentaborane, B5H9 5 B(s) + 4½ H2 63.12 9.5 6.64
Ethanol, C2H6O 2 C(s) + 3 H2 + ½ O2 46.07 5.5 8.38
Ammonia, NH3 1½ H2 + ½ N2 17.03 2 8.52
MMH, CH6N2 1 C(s) + 3 H2 + 1 N2 46.07 5 9.21
UDMH, C2H8N2 2 C(s) + 4 H2 + 1 N2 66.10 7 9.44
Water, H2O 1 H2O 18.02 1 18.02
Fuel Exhaust Products Mass Moles Mass/Mole
Hydrogen, H2 2 H 2.02 2 1.01
Methane, CH4 1 C(g) + 4 H 16.04 5 3.21
Propane, C3H8 3 C(g) + 8 H 44.10 11 4.01
Pentaborane, B5H9 5 B(s) + 9 H 63.12 14 4.51
Ammonia, NH3 3 H + ½ N2 17.03 3.5 4.87
Ethanol, C2H6O 2 C(g) + 6 H + 1 O 46.07 9 5.12
MMH, CH6N2 1 C(g) + 6 H + 1 N2 46.07 8 5.76
Water, H2O 2 H + 1 O 18.02 3 6.01
UDMH, C2H8N2 2 C(g) + 8 H + 1 N2 66.10 11 6.01
Okay, then what about ammonia? Its molar mass is almost as low as methane but it liquifies at much higher temperatures and is about 3 times as dense. Nitrogen, assuming it doesn't dissociate, is pretty inert. And you won't get any soot fouling up your engine.
Nitrogen's a bit harder to come by than carbon.Good point.
Perhaps you could scoop it from Earth's atmosphereHow practical is it to 'scoop' an atmospheric gas during an aerobraking pass? I'm also thinking of all that hydrogen at Jupiter. That would be a much faster pass than earth, though.
I think reactors are better put to stationary uses doing things like producing propellant.
Nitrogen's a bit harder to come by than carbon.
Sooting could be solved by the addition of oxygen. This could be a brief procedure done while shutting down to prevent accumulation or burn off any deposits that have formed, as well as something done when higher thrust is needed. Lift off on LOX-augmented CH4, burn to your desired orbit on plain CH4, and use a brief shot of LOX on shutdown to clean the engine out.
I favor just using LOX/CH4, though...I think reactors are better put to stationary uses doing things like producing propellant.
Okay, then what about ammonia?
Nitrogen, assuming it doesn't dissociate, is pretty inert.
How practical is it to 'scoop' an atmospheric gas during an aerobraking pass? I'm also thinking of all that hydrogen at Jupiter. That would be a much faster pass than earth, though.
What's wrong with nuclear thermal propulsion? You see how much bigger the Isp figures are. And they can be increased further if we can figure out how to run at higher temperatures. Chemical propellants, otoh, have characteristic Isps that are upper limits. You can't improve them without changing them or adding extra external energy.
Nuclear reactors on the lunar surface, though necessary, will need some pretty big heat sinks. There are no rivers or oceans for cooling on the moon, so large radiators will be required. How large depends on the required temperature at the radiator outlet as well as the rejected heat power.
Yeah, I would consider that under 'Only to be used in case of solar system emergency'. Seriously, it's like someone looked at Orion and thought "Hmm, how can we make this have more fallout?"
Actually, I bet the thought was 'How to make more efficient use of those massive energies,' but the results are definitely in the category of 'Don't point that at me!'
the neutron flux from standing next to an open and operating nuclear reactor would probably be more worrying.I think gamma would be the real problem since it takes a lot of mass to shield. It's important to conserve neutrons in a reactor like this so it would be surrounded by some high efficiency neutron reflectors.
There is no fallout, the exhaust consists of a sparse spray of moderately high energy particles that depart the solar system on essentially a straight line trajectory.Right, you beat me to this point. I don't know what effect the sun's magnetic field would have on them, but probably not much.
I think gamma would be the real problem since it takes a lot of mass to shield. It's important to conserve neutrons in a reactor like this so it would be surrounded by some high efficiency neutron reflectors.
Ok, maybe I am thinking of something different then.A nuclear salt-water rocket (http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket) maybe? I have occasional suspicious that it was created to make nuclear pulse propulsion look like a sane option.
If you're hanging around in the exhaust, there probably isn't any shielding at all between you and the reactor.I'm not talking about the gamma (or other radiation) from the decay of the fission products long after they're gone from the engine but the 3.5% of fission energy that comes out as prompt gamma before the fission products leave. Without sufficient shielding that would be a problem for a crew (or sensitive electronics) forward of the engine.
Even then, if you want to commit suicide, you're better off with a large chemical rocket. As for environmental concerns, you might avoid operating them in the area of magnetically-shielded habitats, but it's otherwise hard to see how they'd be a problem.My concern is trapping in the earth's magnetosphere. VAB protons can go upwards of hundreds of MeV, and about 169 MeV of the the total of 202 MeV from a U-235 fission appears as kinetic energy of the fission fragments so I wouldn't assume without some analysis that they'd just fly right out of the solar system.
A nuclear salt-water rocket (http://en.wikipedia.org/wiki/Nuclear_salt-water_rocket) maybe? I have occasional suspicious that it was created to make nuclear pulse propulsion look like a sane option.I think this could actually be cleaner, in terms of total radioactive waste released per unit impulse, than the fission product rocket. The extremely high Isp of the fission product rocket requires an extremely high ratio of reactor power to thrust, and the fission waste production rate scales directly with reactor power.
Here's a film of Orion subscale tests (https://www.youtube.com/watch?v=Pcidu6ppcFg) done in the late '50s. If you want to cut to the chase, go to the 9-minute mark.Amazing. I'd heard about Project Orion before but not see those videos. The shape of that test article makes me think of From the Earth to the Moon and the capsule being fired out of an enormous cannon. I remember the BIS and their Project Deadalus as a development of that (Project Orion) idea.
How close would antimatter catalysed nuclear pulse propulsion be?
How does antimatter catalyse the reaction?