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I still do not understand why everyone insists that a lifting body will be alot heavier or harder to fly; the Apollo CM capsule, which did not have enough power to make it to the Moon and would be a little too small for OSP duty weighed around 6,000kg, and I think a 15-20% mass penalty for larger batteries, room for four with Lunar suits, and other "not needed for ISS" stuff is reasonably putting it at ~7,000kg. The Apollo Service Module weighed in at around Twenty Five Thousand Kilograms without the CM at all!. And don't forget the extra mass of the escape tower you have to launch too...

A 75% scale version of HL-20, the ship I think that OSP should be, would weigh around 8,000kg using Shuttle-era technology. A few hundred more kilos for extra supplies seems reasonable and the pressurized interior would already be double that of Apollo CM from the get-go so Lunar suits would not be an issue, and with the OMS engines built in you have ALOT more maneuverability too, which should make up for any trajectory differences... also recall that in a vacuum, it doesn't matter what shape your vehicle is, only how heavy it is.

The supposed mass advantage of a capsule is a mere 1,000kg, and even if it were double that, I don't think it would be an advantage enough to abandon the clearly superior re-entry dynamics of a lifting body and/or building TWO seperate vehicles where one would suffice. Build a baby HL-20 with modern materials, add more batteries and air tanks, and skip the capsule entirely.

Why not land a lifting body on the Moon?

Futhermore...

Neither a capsule nor a baby HL-20 will be able to get to Lunar orbit, much less the surface, using the EELV launchers. It just isn't going to happen. If Nasa is going to be operating a serious Lunar base, they are also going to need a serious lander able to ferry substantial masses to the surface, none of this two-ton Progress style nonsense. Even if the crew vehicle is the heaviest payload it would have to handle, which I think a rediculus tradeoff of performance for mass, the cost of making a slightly larger decent/acent stage should be far lower then having Nasa spend the money to build TWO OSP's.

Further-futher, if Nasa builds an SDV or other more-than-medium launcher, putting a lifting body's extra ton or two up should simply not be a big deal compared to the cargo masses it would (or at least should) be launching.

Both vehicles will require some kind of a service module or generic transfer stage which will easily exceed the limits of either EELV combined with the mass of any version of OSP, so if EELVs are used for launching all crew transfer componets anyway, an extra ton or two should not be a serious problem.

"Smaller/lighter = cheaper" is just not always true... building one vehicle that does both Lunar and ISS duty instead of two with very similar capabilities simply makes terrible economic sense. I will not go deeply into the previous thread about how a capsule OSP will also not be nessesarrily any cheaper than a lifting body for ISS duty, but let me summerize that big issues are the ground support needed with a capsule's small cross-range with non-runway landing and the inherintly un-reuseable OMS service module. Also don't forget how a capsule will require subjecting returning crews to double or tripple the strain of a lifting body, no matter which way you lay it out.

Even if you could accuratly and reliably aim a meteor cannon at the Earth, you still-still have the problem of getting the stuff down to Earth's surface. And even if we did have a space elevator that could "capture" the Lunar ore payloads and send them down, a few tons at a time in two or three days, the economics just don't make sense. Except for He3 or rare minerals, there just isn't any profit in mining the Moon for minerals to be sold on Earth.

I'd also like to mention just how far we are away from being able to build spacecraft in orbit using base materials and only limited Earth-manufactured parts/materials. Its hard enough to build a space ship on Earth, I would hate to think of the mess of doing it anywhere but here for the forseeable future.

Ah yes and about OSP... since Congress/et al aren't going to want to spring for a new manned ship for a very long time, we will be stuck with OSP probobly until when we're ready for a Mars mission. I think it would be nice if the entire Mars crew could be ferried up in one shot, with simple economics of scale helping out. One OSP flight with six for ~$150M versus two with three + pilot for ~$300M.

And the ISS... I simply think that we should not rely on Russia for manned trips to the ISS any more than is nessesarry. One ship to get crews to and from and one ship for a lifeboat saves having to spend $30M two or three times a year on Soyuz capsules, when we'll be flying OSP anyway. Adding room for two more seats and another 400-500Kg for passengers just doesn't sound all the difficult to me. If Russia is going to keep flying, then let them switch over to Progress vehicles to ferry up supplies, saving room on the AAS for science racks.

Lastly, I would like to say that small does not, DOES NOT, imply that it will be cheaper. The actual Shuttle Stack sans the cost of processing Shuttle and making the whole thing man-rated, is in fact not that much more expensive than a Delta-IV HLV, yet it can haul five times as much mass.

As far as short-distance flights, a GCNR would be mucho overkill unless you were trying to move a gigantic payload. What would nice for Earth/Moon-Moon/Earth flights is a solid core NTR which would be reuseable, relativly durable, but most importantly not require as large a fuel mass as a chemical engine.

If we are going back to the Moon to stay, then we ought to not bother with intermediate spacecraft with such poor capabilities that they will have to be disguarded if we want to do anything beyond a Lunar sardine can base and a telescope or two. So, we should develop only one the lifting body OSP with room for no less than six people to ferry crews to a waiting chemical-powerd transfer vehicle or then to a Lunar lander in Lunar orbit, or combine the transfer and lander vehicle into one ship. Another slightly more hairbrained idea is to use OSP as a "human cargo carrier" and simply dock it to a standardized chemicly powerd cargo transfer/lander in LEO.

Oh, and another-another thing about ISS still has that nasty orbit to deal with. The amount of energy needed to change the orbit of an object that size... as delicate as it is... would be a huge amount of trouble. Its high orbit might be good enough for a Lunar trip, but not without an extreme mass penalty. An SDV that could bring up 120 tons to equitorial LEO would only be able to haul like 80-90 tons to ISS.

Sorry if I seemed a little cranky and off-topic about my GCNR rant... i've been putting too much effort and emotional energy into the futility of trying to argue against anti-nuclear activists. Anyways, long story short that since a open cycle GCNR is not that much harder to build than a solid core NTR, we know that it will work unlike other methods, and has no "you want to put a nuclear howitzer in space!???!" (artillery cannon) of Orion, we ought to persue GCNR as soon as possible. If it will takes 20 or 25 years to make (perhaps a bit more) then thats just fine, since that is probobly how long it will take Nasa to assemble and test Mars hardware with their current funding level and safety phobias.

The science reason for getting man off this rock should be made secondary to other reasons, as it will result in a few small short duration missions like Mars Direct. ANYTHING would be better. Only a large ship that is reuseable with substantial payload mass... like the largest mass we can haul on a 5-segment SRB/Twin RS-68 SDV... and/or a fast ship with orbit-to-orbit trips of less than three or four months for a manned HAB would permit any practical perminant settlement of Mars for real.

I think I am beginning to agree that a trip to the Moon would have few advantages in the context of it being a proving ground for a Mars mission. The #1 big thing a Lunar trip would be good for is to build confidance of in-space transportation systems and life support. Since Nasa, which seems to have become soft and easily discouraged after Challenger and Columbia, frankly needs a confidance boost before really setting out for a Mars mission. It also wouldn't hurt Nasa's image to be doing somthing beyond going in circles in LEO, which might also be good for funding in Washington...

Now to be the devil's advocate...:

Enyo is correct that the testing of hardware on a Moon trip would be pretty useless; the lander would be different, the hab would be different, the fuel plant would be different, etc etc... If we are going to the Moon to test hardware for a Mars trip, then we're still going in very expensive circles.

This is doubly compounded if there is little or no water ice on the Moon, which would limit the size of any base or rocket-fuel self sufficency perminantly. And as far as other materials, well there aren't any of substantial usefulness considering the huge trouble of getting them off the surface and back to Earth.

The Moon may be convienant and temporarily popular, but in the long run it will slow down a Mars mission most likly, especially when people get tired of seeing the familiar sight of astronauts bouncing around the Lunar surface.

If there does turn out to be enough ice on the Moon to make substantial amounts of rocket fuel, then a larger base becomes practical, but the question still begs: why? A mega space telescope doesn't need a large contingent of staff to operate, launching rocket fuel off the Lunar surface is only marginally easier than launching it from Earth's surface, and unless there is a huge market for He3 then there is nothing at all worthwhile there.

Now back to engines...

I'd like to reiterate that if we ARE going to use the Moon as a gas station on the way to Mars, then using a NTR/Oxygen Combustion hybrid engine to save on the amount of Lunar water needed still does NOT justify the reduced payload mass of a Mars ship. An extra 1/3rd payload mass is a HUGE difference, worth that of doubling or trippling of any Lunar mining operation. If there is concern about oxygen becoming a Lunar contaminant, which I feel is alarmist and silly, then you put the stuff as a liquid into tanks shaded by a crater rim/underground or bind it with metals in the Lunar soil.

It would also be really nice if we did have a Gas-Core nuclear engine, and it wouldn't take fifty years to build if we started on it January 1st, skipping solid-core engines alltogether clearly and deliberatly... of course, this would be neither quicker or cheaper than reviving an improved version of NERVA, though putting together a Mars mission will take a while anyway. And as far as radioactive material return to the Earth after a Mars mission, I think the government could get away with telling the anti-nukylur groups to take a long walk of a short pier.

In order to EASILY do serious water/H2/O2 mining in the Moon, there will have to be signifigant quantities of ice. No meter-thick polar glaciers is no huge deal, but to have only barest traces would pretty well doom any kind of large lunar base or future colonization... I hope that the ice question is solved BEFORE Bush/Et al. decide to "do a Kennedy" for the Moon. Without ice at least for Lunar fuel, then anything more than a lunar cottage for a half dozen people becomes an extremely difficult proposition. If the idea is to build infrastructure without the nasty 1G earth gravity, then any plan to return to a waterless Lunar surface should be abandoned.

Oh yes...:

"There's not much point breaking down water, throwing away 88% of it, and using 11% for fuel; it's more efficient using the oxygen as well."

This would be true maybe if your rocket were carrying the water being broken down maybe, but its not if it is mined from Lunar ice. If you can make that 11% work with ~1000ISP in a NTR, then that other 89% is more mass you have to lug with you. Since you want to make your rocket as light as possible, oxygen is heavy, if there is any way you can avoid carrying it the better. The biggest reason why hydrogen is the perfect fuel is that its light, so you have to expend a minimum of thrust to push the reaction mass. Not to mention, the best LOX/LH engines only get around ~440ISP.

Hmmmm but it still isn't a large amount of radioactive material in the first place, so we find a cave with an underground river far away from people then. Plus I think that above-ground testing would be tollerable with safety precautions, like firing the engine down a long tube lined with water sprayers to condense and trap the worst of the fuel vapors perhaps. *shrug*

If we are going to take a "side trip" to the Moon, then its quite possible that a Mars trip would have to wait a while anyway. The deciding factor in how long GCNR takes is when we start really, if Nasa sent a few million its way tomorrow and resolved to use it, I think it would be done when we are ready to move beyond the Moon.

Lunar testing would be a problem because down-mass to the surface will have to be kept pretty low for the forseeable future until a Moon Megalander is built and signifigant fuel supplies are exploited from Lunar ice. The GCNR engine chaimber and fuel pump/capsule will be pretty heavy. And the engine would probobly have to be brought back to Earth for study, which would be alot of trouble.

There are alot of caves in places where people don't live. If the engine were tested in a cave in the middle of nowhere, the ground itself would act as a sufficent "filter" to protect groundwater, since nobody lives nearby. Seepage takes a while, long enough for the worst of the daughter chemicals to decay probobly. Even if this scheme were abandoned and the engine tested above-ground, the fallout would be pretty mild and localized in the long run. And frankly, a pro-nuclear US administration could tell the eco-nuts to go to he||, the only BIG political hurdle is the rediculus court order system.

Sorry if I was not being clear, I was referring to the operating temperature of the engine. In rocket engines, nuclear engines imparticularly, the operating temperature large determines the propellant velocity, which determines the Isp. The operating temperature for a GCNR engine (open cycle) i've read of starts at around 25,000 Kelvin, and could go as high as 50,000K with similar Isp to what you have. Lots higher than the 3,000K limit of a solid-core NTR engine or typical SSME (lower Isp from higher gas mass), the big trouble is how to make the LH2 opaque to enough of the energy to prevent it from "shining" through the fuel and melting the engine and/or how to keep it cool while operating.

If such an engine with a little lower thrust (say 35,000 or 40,000lbs) could be kept to around 80-90 tons, that would make it practical to integrate into a single package that can ride on an SDV to orbit to stay within the "two SDV's per Mars ship" ease of construction envelope. This stage would also carry a Prometheous power reactor to operate the LH2 condenser. It could be fueled by EELV HLVs or if it were cheaper a 3rd SDV loaded with LH2.

Uranium Hexaflouride is nasty, but not unreasonably so. The radioactive effects are almost negligible. We have alot of experience with handling it in our fledgling nuclear power industry, and I think it would be easy to build a UF6 vapor "dispenser" like Zubrin's "Salt Water Rocket" graphite-straws fuel tanks but tiny instead.

As far as testing the thing, the solution is pretty simple... test it in the desert. It doesn't put off that much radioactive material compared to bomb testing. But, if that were totally unacceptable, then the easy thing to do is test it in a cave. Concrete over the cave face, bolt the engine with the nozzle inside, and fire her up...

So, one GCNR powerd stage on SDV #1, the manned Hab module (maybe) with the Mars lander on SDV#2, and 5-9 EELV HLV launches for fuel tanks, a pair of OSPs for crew, and perhaps one for the Mars lander. With the power of the GCNR, the trip could be made in only a few months perhaps and have enough fuel to return to Earth without having to gas up at Mars.

Replacing the materials, the engines, the control systems, etc on the old Saturn-V would seem to me to be too much trouble, and sub-optimal since the S5 was built with the old technology in mind, even if it wern't reverse engineered persay. Frankensteining old and new is usually not the best way to go, provided it works at all.

Now about using the same basic strategy... really big LOX/RP1 first stage (possibly reuseable) and multiple staging for various purposes does make sense when the time comes to replace a SDV type launcher with a minimum of trouble does make sense, but with the power offerd by SDV and the pre-exsisting infrastructure, that will be quite some time probobly.

Although the technology does exsist to get us to Mars, the kind of hardware needed to do more than science expeditions does not. In this reguard, a return to the Moon for good would permit these kinds of technologies to develop while being close enough to Earth to be supported by "traditional" methods in the mean time.

At least initially, a crewed Moon base would be very dependant on Earth for supplies and such, besides crew exchange, so it would force Nasa/et al. to get in the habit of REGULAR rocket launches, which would in tern demand better reliability which would get us to Mars more reliably. The Mars crew lander might be based on a flown-a-hundred-times DC-X like Moon lander... it has to work right the first time.

As far as stuff on the Moon reasource wise, that isn't going to happen... be practical people, how in the world are you going to get signifigant mineral mass back to Earth? Even getting it back from a NEA borderlines on nonsense economicly. The only thing on the Moon worth mining is water and Helium-3. What Lunar reasources are good for is making fuel to get us places... don't bring the wealth of the Solar System to the people of Earth, its too heavy, instead bring the people of Earth to the Solar System.