New Mars Forums

Mmmm though it might eventually be practical for power on Earth, where reliability and availability are less of a concern (since we won't die in hours without power), it is for any space ship or base. Solar satelites are unproven technology, space reactors are. Solar satelites cannot provide power continuously, which nessesitates the need for batteries or fuel cells, so you might as well bring another reactor instead. Also, the collection station for the microwave beam will have to be rather large... on the order of hundreds of square meters or even square kilometers for a large one, clearly much more difficult to build and service than a reactor. Solar panels will also suffer micrometeor and solar flare damage over time but will more importantly would be far too hard to keep clean with the micro-fine dust environment on Mars, while a reactor will not. A large reactor, designed to be refueled, would obviously be the best choice for a Mars colony, and considering the energy density of Uranium, would also be competitive for a Moon base.

Even if the outlandish reliability requirements could be met on this "non user serviceable" nuclear rocket, there is no lake of ice to load it with. I think the any early base will be doing quite well to harvest two or three hundred tons of water a year. Clearly insufficent to power the water truck and give it enough fuel to lift to the transfer stage to compete with LH.

The rocket cannot be serviced because of its NTR engine, which produces substantial radiation even when shut down (after its initial startup), and would be deadly to aproach for weeks, if not months at least while the short-lived nuclides decayed. Shielding is too heavy, and a chemical engine need not carry a reactor or shielding.

The hydrogen condenser will not be a large device because it will not have to liquify much hydrogen, given a reasonably low boil off rate achieved through thermal isolation and solar shielding. It will not have lengthy plumbing, because it will be mounted near the reactor which powers it which is naturally near the fuel tanks in an NTR system, nor will it need the pipes to run far in/around the fuel tank. I propose that the compressor could be connected to the same turbine shaft that will provide electrical power to the engine, but electrical supply should not be an issue with a nuclear reactor if this is impractical.

A heat pipe system would require some plumbing to distribute the heat to the rather large water bag to prevent freezing if required which will be connected to a reactor coolant line, which reduces the modular construction of the reactor and simply makes me nervous. This plumbing must be able to survive Earth launch at 3-4G and the earthquake of launch vibration.

Although hydrogen tankage would be bigger than a water tank, it need not be that heavy. Keep in mind that the Shuttle main tank must be insulated against Floridian air, not the vacuum of space. The only heat sources in space I can think of are from the ship, which could be isolated with spacers at the attach points, and the sunlight which could be reflected with a mylar-style shiney skin. Also keep in mind that a space rated hydrogen tank does not have to hold a 100 ton airplane or resist the torque of several million pounds of rocket thrust... only enough to resist its loaded weight at launch and air resistance. It need not even be made of metal, it could be made of solid composit DC-X style.

Furthermore, I suspect running "simple" heating lines from the NTR or NEP reactor to keep water warm will be a bigger issue than it may first seem, with all the fragile plumbing - which must be launch hardend - and having to run coolant lines into your source of power and thrust. Having a centrally located hydrogen condenser would at least be easier to integrate.

About Mr. Anthony's water truck, I think it assumes an almost comedic amount of reliability... three flights a day... that would lead to its destruction rapidly. Also, I think that his estimate of reactor mass is somewhat, well, optimistic and that he has neglected to take into account that a reactor with that level of fuel burnup efficency is hard or impossible to create.

Lastly, on the Moon you could simply put the LH tanks in the shadows of craters and ridges and suspend them off the ground with pointed low-conductance "feet" to eliminate much of the headache of keeping the stuff cool, which ought not be a problem anyway with a hydrogen condenser powerd by a nuclear reactor and a plentiful supply of LOX for coolant. I wonder if a sealed glass blanket filled with oxygen would make good indigenous insulation.

I'm still convinced that chemical ISPP and the use of LOX/LH for Lunar travel and perhaps LOX/Methane or LH on Mars is preferred. Nasa's even got a itty bitty ISPP + model rocket motor to test on Mars I think... Such a device need not be very complex; only electric solenoid gas valves, rotary motion compressors, and mechanical switches asside from the reactor... the big issue I think would be how to keep the reactor cool; maybe suppliment rollable sheets of radiators with intentional boiloff of excess LOX?

The major showstopper achillies heel of using Lunar water as reaction mass in a NTR engine though is how to get enough water to use it straight as reaction mass for these massive "water bag" orbital transfer vehicles... it will be trouble enough to make fuel to operate an LBV and a manned Moon/LEO shuttle. I am also concerned about the water freezing; keeping it warm inside a big bag might be problematic, even if using a reactor waste heat. Hydrogen bubbles could at least be centrally collected and condenced. Also keep in mind that a nuclear engine doesn't have unlimited fuel, a very-long-burn NTR will nessesarrily have to operate at lower temperatures to preserve fuel payload of a reasonable mass that can be launched from Earth.

Another big issue is getting water off the moon "en masse," so to speak. The water-fueled NTR engine won't be enough to get off the ground with any substantial payload without operating at hydrogen-fuel temperature levels, which will cut the engine's life short. The source page at Neofuels suggests a operating temperature of only 1100C, a far cry from the 3000C needed to reach par with chemical fuel. Even if this temperature is reached, having to ground-launch lugging the weight of a nuclear reactor would take a bite out of payload mass I think: the production Nerva engine weighed around 11 tons for 75,000lbs which would be cutting it a little too close for comfort with sub-500sec Isp water fuel. The RS-24 SSME on Shuttle, the best and biggest reuseable chemical engine ever makes about half a million pounds, but weigh around 3.5 tons each. The RL-10 varient on the DC-X (which I think would make a dandy rocket to base LBV on) make 15,000lbs of thrust, yet only weigh 300lbs each... As with any rocket, you have to get out of the gravity well fast!

The LBV must be lightweight, yet even then, it will not haul anywhere near enough water to fill a "steam bag" rocket, and even with the high-nuclear-burnup ~400-500sec Isp possible, is not competitive with LOX/LH chemical engines due to their light weight and no need for radiation shielding. A chemical engine might actually last longer! Hydrogen tankage, the cheif cited advantage of water+NTR, also need not be all that sturdy since it won't be launched from Earth loaded. Shuttle's main hydrogen tank, which I think is a fuel-to-tank weight goal to aim for with (solid like DC-X, not honeycomb like X-33) composit instead of Al/Li alloy, lugs about eight pounds of hydrogen per pound of tank.

Oh, and let me reiterate my very-not-liking of a capsule, for the previously stated reasons which I won't repeat here... Although a capsule is the only PROVEN type of ship that can withstand direct return from the Moon, it is not inherintly the only way.

In any event, this method of returning to Earth would be too expendable... if it wern't for the need to beat the Communists to the Moon ASAP, I would have to label the Apollo architecture as a mistake, since the tiny scale and unreuseability of the system itself helped to hasten the end of manned exploration.

I think you guys may underestimate just how much power a large nuclear reactor can deliver... a few megawatts lets say of power put out by a few reactors is a quite a bit for a small settlement. Even a 100KW reactor is a fair amount of power.

Also don't forget about the huge amount of radiation they put out. If you put a reactor in the middle of a chimney greenhouse without massive shielding, I guarantee you that nothing will grow and nobody could get anywhere near the place. You'd be lucky if the radiation didn't depolymerize what you would use to make the chimney skirt with. In any event, do not underestimate the danger of doing anything near a running nuclear reactor; without signifigant distance and/or heavy shielding (park in a crater, ring with meters of regolith), anything living or chemicly delicate would be fried.

The big problem with using any moving Martian air to produce power is that its so thin: less pressure, less force on the turbine blades... using the waste heat from a reactor to power it helps, but not that much. It would be better to use the waste heat from the reactor in place of things you would use electricity to do. The heat could be piped to the ISPP system used to make fuel instead of just electric heating or at the very least use the heat from the reactor to keep the habitat and greenhouses warm.

Recycling is a good idea for many things, but it is NOT inherintly cheaper or easier than simply making more of it. For instance, the hardware required in trying to integrate a colony heat management system to a large low power Sterling engine would probobly outweigh simply bringing a slightly bigger reactor, or instead haul another roll of polymer solar pannels.

To summerize, recycling is good for things that are hard to get ahold of, like nitrogen and rocket fuel, or things that easy to recycle like plastic bags and chicken dinner leftovers, but the more you recycle the more the machinery you will have to lug from Earth, machinery you will have to power, operate, and maintain. There is a such thing as too much recycling!

I think that any sort of rotating tether system is still a distant technology if it is possible at all. The USAF can't even make an autopilot that can do mid-air refueling with planes going similar speed to hook up a hose, the ability to connect structurally to a teather accuratly as it wizzes by is impractical, if you could do the timing reliably at all. Picking up paylaods from the ground sounds like a nightmare to do accuratly, and won't the tether end be traveling at extremely high speeds? What if you miss and hit your pick-up pad? BOOM, ready made space inertia powerd kenetic missile. No mechanical or especially no manned system could survive the acceleration of a ground pickup either.

Making a tether strong enough in the first place is questionable even with the coming of continuous carbon nanotube polymer composits. Then there is the question if the tether could withstand micrometeoroid impacts at all... If there is any incarnation of a tether, it will be in the form of a space elevator that stays put. Also, a Lunar space elevator is impractical given the Moon's rotation and orbit. But in any event, I say with certainty that an Earth space elevator that can do more than haul small satelites is some distance away.

I reiterate that mining asteroids for minerals is a terrible idea economicly, since flooding the market with cheap precious minerals would destroy said market. Base minerals are much easier to mine here and will be for the foreseeable future, even with low ore quality, compared with how hard it would be to push an asteroid or its ores back to Earth.

Now, if you found a dead comet with alot of water ice, then it might be useful to mine it for rocket fuel, but any sort of operation will have to be highly automated, since Astronauts can't spend more than about 6mo up before getting dangerously deconditioned. Such a zero-G mining aparatus would be pretty heavy and extremely expensive too I imagine.

I would be interested to see a cost comparison between water mining and simply launching 120 tons of LH/LOX from Earth with SDV to a LEO "gas station" equipped with boiloff liquifiers. If Nasa does SDV right, and scuttles as much of the Shuttle = Manned overhead, each SDV could perhaps cost only a quarter billion apiece or less.

In the long run, when ice cracking and zero-G mining becomes much more refined, then the ease of mining asteroids for water might make sense. However, even this is questionable if a Scramjet SSTO really could make simply hauling up Earth fuel competitive as Nasa seems to think.

ISS is useless for travel beyond LEO. The amount of propulsion required to push the ISS out of the "Russian Partnership" orbit and down to equitorial is substantial, and I don't think ISS will be in service long enough to make such a large project worthwhile. Nor is ISS very useful in the first place for basing such missions... what do you really need? A truss for some fuel tanks, some solar pannels, and boiloff liquifiers. It doesn't even need to be manned with the aid of a orbital tug and docking beacons. Everything but the tanks could be lofted with a single SDV launch.

If your ship requires some assembly, then it should be done like the first componets of ISS; two modules, one with propulsion for docking mates with the other at least structurally. An OSP crew goes up and attaches any hoses and wires then does startup and testing. Or if it is more than two modules, or perhaps you are building a space station, a refuelable orbital tug would be ideal. Perhaps it could be powerd by nuclear electric, with its excelent fuel efficency?

I have little faith in taxpayer attention span... as much as I hate the analogy, manned spaceflight must take a more "highway building" stance: start a perminant manned base on the Moon (provided fuel is easily available) with no "end of life" as with ISS, and make the investment so irrevocable that the future government just can't pull the plug.

I would love to set out on a trip to Mars, but that is still a far bigger undertaking than a trip to the Moon if for no other reason the sheer distances involved. Zubrin's MD concept is also shakey due to many shortcomings and frankly is simply not very robust. A really robust mission that would actually permit real work to be done is a major national decision that would take a great deal of investment... which is just not going to happen any time soon.

I agree that using the Moon as a testing ground for Mars hardware is not a good idea. Hence, the Moon itself should be the destination. At the very least, it would be good experience in having humans live further from Earth with a minimum of imported reasources. Any activity that advances that capability is a worthwhile investment.

Although the idea of using metalic aluminum and LOX for fuel is a interesting idea, I doubt that it would be practical. You can't really "feed" solid aluminum powder at the nessesarry pressures into the reaction chaimber: the fuel must be pushed into it (hence the extremely powerful turbopumps) to achieve decent thrust per amount of engine weight. A solid-core hybrid engine somehow based on aluminum without the polybutadiene binders would also be difficult to operate and probobly be of low performance. You must also consider the huge energy investment in seperating and cracking the aluminum oxide, which I am certain is at least as bad or worse than cracking water.

If there is insufficent water ice in the Lunar soil to make signifigant amounts of rocket fuel, then we should forget the Moon and focus on Mars hardware even if budgets will be slashed and public interest dissapates, since we really have no place else to go.

With the cost of building X-38 starting to mount up to over half a billion dollars, and HL-20 only projected to cost two billion, and all of these estimates probobly low by around 100% knowing contractors, building X-38 and OSP would be more expensive than building just OSP and leaving a copy of it docked at ISS perminantly.

Now, how many times must I say it, a tiny lift body is not like shuttle! Even if it did use tiles, there would only be a few strong ones, not the thousands on Shuttle! Dealing with a small spacecraft is infinatly easier than having to prepare the US's "Battlestar Gallactica" for launch. HL-20 is just so much smaller that it isn't that hard to service. No massive ultra-high-pressure LH2/LOX engines, no hydraulics, no truckloads of equipment to remove, and all the systems are accessable through convienant hatches:
http://oea.larc.nasa.gov/PAIS/HL-20-fig6.gif
It could even have a METAL heat sheild.

There is no good reason that a lift-body ship could not also travel to the Lunar surface or to GEO or to Lagrange, none at all. Let me reffer you to a concept cooked up by the Pentagon in ages past...: http://www.astronautix.com/articles/lunpter1.htm Yes, that caption with the lifting body and super-trans-stage does indeed read "LUNAR LANDER." Capsules hold NO SPECIAL MONOPOLY over space travel outside of LEO. A capsule can do it, well guess what, a lift body can too.

Instead of building capsules AT ALL, we build only one ship, a HL-20 style craft. This craft could handle all the crew launch/return needs from LEO, and could be mated to a tranfer/lander stage for travel outside LEO. No version of the EELV boosters could carry a capsule or lift body AND the fueled trans-stage/lander to a Lunar transfer orbit, they are all just too small, thus the extra weight of HL-20 would not be a signifigant launch issue. There would be no need for this heat-shield-less flying capsule cockpit thingie for another space craft, HL-20 OSP IS the spacecraft. Flying one ship and one ship only means you have to develop one manned ship, which would probobly more than make up for the small extra launch mass requirements. "More bang for your buck!"

Furthermore, as i've mentioned on more than one occasion in these various threads, the only way man will REALLY leave the Earth for keeps is when we move away from this "save ever gram" style of thinking. An extra metric ton or two that a mini-HL-20 might weigh is simply worth the extra launch mass. Its worth it, its as simple as that.

There needs to be a little clarification about the return mission... it cannot be planned on any convientant schedule. If there is a disaster on ISS, the capability should exsist to come back down immediatly. Without a large number of landing sites, this is hard to do without ladening your capsule with large fuel tanks like on Soyuz. With HL-20 it would be easier, since it can simply use its orbital momentum, with the aid of lift and control surfaces, to fly hundreds of miles to safety. Plus, if a capsule goes off course during re-entry, then you are out of luck and have to come down near your re-entry vector, with HL-20 you just turn and glide. The number of field hospitals that would have to be air-portable through the world to meet Nasa's 24-hour mark would be rediculus.

I would also like to note more about where HL-20's G-loading advantage comes from... from the more mild re-entry dynamics, which translates into lower heating, which translates into a lighter heat shield than is possible with the firey death plunge capsules.Wings are an ADVANTAGE when done properly, not a liability.

OSP is required to operate as a crew launch and return vehicle, which most certainly does not spend its entire mission in space. Wings are the superior choice for returning to Earth and could be built inherintly more reuseable.

A winged/lift body craft would have such similar capabilities to a capsule in space, that it makes good fiscal sense to only build one, not both. The lift body might be a little heavier with its wheels and stubby fins, but not by alot, probobly to such a small degree that Delta IV modifications would be simple.

Why will a lift body not be able to go beyond LEO and a capsule can? The shape does not matter when there is no air as you have pointed out clark, only structural stresses and mass. A lift body is roomier per-mass too, given the low weight of its heat shield per area. A capsule OSP would be too heavy for a direct flight to the Moon or Lagrange anyway, so any incarnation would have to dock with an orbiting transfer/lander section, and if Nasa builds a dedicated manned Lunar transfer/lander, then a lift body would be even nicer.

Simply "have the army/navy pick them up" is a far stickier proposition than you may think... Unlike Apollo that was equitorial nearly, OSP will be returning from an ISS orbit which covers nearly the entire globe. That increases the number of recovery sites/teams dramaticly. Plus, in order to return to proper medical care in only 24 hours from undock, a capsule would have to carry considerably more fuel for cross-range maneuvering. This is to say nothing of "what if" you have to come down in the water or far from civilization, that it may simply be hard to guarantee 24-hour-to-hospital even with extra fuel. You have to FIND the thing, and fast.

It gets better... a capsule, in any form, by nature of its ballistic trajectory will expose the crew to 3-5G loads. No matter the shape. Thats the way it is. This is not a good thing when flying back deconditioned or injured crewmen; Nasa even considerd changing the seat arrangement on Shuttle to make the return flight easier on them. A injured crewman could quite possibly die... did I mention that HL-20 would have a maximum load of around 1.5G? And no bone-jarring hard landing or finicky landing rockets that can blow up, just wheels which have worked for decades.

Since a lift body also has a much more benign re-entry profile, it can get away with improved Shuttle TPS systems, which should be more than sufficenct with hardening, or could possibly use a METAL shield. Metal heat shield materials have already been tested through re-entry on Shuttle in low heating areas. Check the thing between flights, shine it up, and its ready to go... a far cry from having to half-dismantle a capsule to replace its ablative shield every mission.

A lift body could, in theory, be able to integrate the OMS engines into the craft proper, which would simply negate the need an expendable "service module." That would add up to signifigant savings on every flight, for a modest design/building investment... I think the Air Force is getting ready to test a Peroxide/Kerosene OMS engine for their unmanned space bomber which would be ideal.

Its also easier to handle a ship with built in wheels that integrates horizontally... did I mention that Delta is assembled horizontally? You can tow the thing around with an airport tractor... Lockheed destroyed a communication satelite just trying to turn it over for shipment at their factory.

The Nasa specs are that it should (though this is possibly optional) four people to the ISS orbit for as low a cost as possible, be safer than either Soyuz or Shuttle and with the ability to re-enter with no active control at all, plus be able to reach a hospital within 24 hours from undocking. Oh yeah, and it has to be able to work completly automaticly, including docking.

The absolute upper limit of its mass is around 20,000kg and preferably less, which is about the maximum payload for the heavy version of the Atlas/Delta rockets. It would be highly desireable for OSP to ride on the single-liquid-engine version of either rocket and with a minimum of solid rocket boosters.

What I think it ought to be able to do...

-Carry a crew of six minimum, preferably seven, so that it could completly replace Soyuz for ISS duty if need be, or for taking down a Shuttle crew if they are stranded in orbit, and to make ferrying larger Mars teams and/or Lunar base crews. Also, place a larger docking hatch to the rear to permit the transfer of ISS science racks in a automated cargo hauler mode for speciality cargo return.

-Be easily modified for medium duration manned flights (two weeks) needed to reach the Moon or a LaGrange point, so OSP could be "just another cargo" out that just happens to carry people. It should likewise be able to depressurize to let the suited crew egress without an airlock. It should also be easily refueled remotely, which would preferably be storables like peroxide and kerosene, for missions based from the Moon or for orbital maneuvering without a stop at Earth.

-Be a lift body style vehicle, capable of cross-ranges similar to that of Shuttle to lower the number of emergency landing sites and be able to land a runway with wheels, to permit soft recovery and ease of handling. This design would be easiest on a injured or deconditioned crew and would minimize the amount of logistics needed for recovery. Just pack the thing in a transport plane and fly it back to the Cape.

SRM = Sample Return Mission, a robotic mission to Mars to physicly bring samples back to Earth for study.

We DO need a signifigant long-range goal, I think on the order of 20-25 years would be appropriate, since that would be at least until the end of ISS.

Frankly, flying Soyuz as the "offical" CTV ship to ISS is a bad idea, first because you would need double the launch rate to support a six-man crew with a three-man capsule, second because capsules put a terrible physical strain on the crew, which will hopefully be of persons who are a little less fit than your average military pilot, and simply put America will not send that much money overseas for other people to build space ships, especially when Shuttle is retired. Not to mention how much nicer and less expensive it is to handle a small airplane than it is a space capsule.

X-38 was axed so Nasa could divert its funds to building ISS if memory serves, and since Bill & Al could make more work for Russian missile builders. The X-33 with the bad new composit fuel tank could have worked, but once it became clear that X-33's fuel tank would cost alot of money to redesign, and nobody launches lots of satelites anymore, Lockheed bailed.

Space ships with wings haven't been finished since they are more expensive to build and because there was no need for them. Now there is.