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Or capture the exhaust in a cave. Is there a cave somewhere large enough to capture the exhaust plume? Would cracks in the rock release radioactive exhaust into ground water? Nuclear activists would start by arguing that. One idea proposed in the 1960s for a permanent Moon base was to detonate a nuclear bomb underground. On the Moon. Then use the cave it makes as living space. This results in so much radioactivity that it would be un-livable. In fact nuclear bomb for peaceful use was tested once. A company drilling for oil found a large oil deposit, but beneath a very hard layer of rock. Too hard for them to drill through. So they used a small nuke to facture the rock. That did give them access to the oil, but the oil was so radioactive they couldn't use it. Underground tests produce a cave, but usually the cave collapses within seconds. If you detonate a nuke deep enough would a cave of sufficient volume remain intact? Could a cave made by a nuclear explosion contain radioactive exhaust, or would that fracture the rock sufficiently that radioactivity would still get into ground water? Could we start with a natural cave and spray a polymer sealant on the entire surface? The point of all this is an engineering test stand where we can develop an gas core nuclear rocket.
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I remember two Project Plowshare shots named gasbuggy1 and 2, if memory serves. I thought it was natural gas they were after. But you're right, it was too radioactive to use. Those underground shots all have the total mass of the bomb fragments (and the weapons guys SOOOOO love to go with plutonium), plus all the induced secondary radioactivity in all the debris and surrounding rocks. It stays lethal down there for many many, years.
There are a couple of caves that might contain the volume of a test or two, pressurized. But you can't leave it that way, you have to depressurize the cave or it'll leak. That still means cleaning the gas of radioactive debris. Might as well just build the rig to do it on-site as an artificial structure.
By the time you pay for building such a facility, you could have sent the whole kit and kaboodle to the moon. It's pretty expensive stuff. After about the first test or so, it'll begin to pay for itself in spite of the space travel costs, seeing as how with open-plume tests, you get to concentrate your funds on the testing, not the cleanup operation. On the moon, those plumes shoot straight out into space, never to return. The exhaust velocities are way far beyond lunar escape.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Ok, gas. Memory bad. We agree on the result.
Politicians will never approve a development program on the Moon. It doesn't matter if it costs more on Earth. As an example, as soon as George W. Bush was inaugurated in 2001, long before 9/11, he announce his missile defence system. It cost $80 billion for development and the first 10 missions deployed in Alaska. Mars Direct cost $20 billion for the first mission, plus $2 billion for each mission thereafter. That's according to NASA's budget guys; they costed-out Zubrin's Mars Direct. NASA's Design Reference Mission version 3 cost $55 billion. The missile defence system was tested, each missile only hit its target 1 time in 3, so those 10 missiles could only defend against 3 incoming warheads. Yet the whole thing cost more than an entire program of 7 missions to Mars. That money was spent, and an addition 10 missiles were deployed in Alaska as well as 20 in California. No cost was announced for the additional missiles. Notice the cost: massive spending for something (useless) on Earth, nothing for anything (useful) in space.
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RobertDyck:
Bad memory goes with the gray/white hair. Mine is getting pretty bad. I have to write everything down or it's lost.
I quite agree about absolutely idiotic, wasteful spending. Politicians ought to be the targets of the missiles that cannot hit the other missiles. Stationary targets, easier to hit. Their political window-dressing projects are just wasteful crap.
I cannot think of any politicians since JFK and LBJ that were actually really serious about any sort of space projects. JFK was just sort-of, he did the moon thing as a race with the Russians. It wasn't about the moon, it was about just beating the Russians at something big. Going to the moon was just a convenient "big" thing. But, I give him credit: once he decided, he stuck with it.
LBJ was actually a spaceflight hobbyist. By chance, we got him as VP, then Pres. He was in there just long enough to get done the follow-through necessary to actually carry out the plan, and thus actually go to moon. The next one, Nixon, killed it before we could make all the planned landings (all the way to Apollo-22 not just Apollo-17). Nixon thought spaceflight was useless.
All the ones since have been window-dressing projects, not properly formulated or funded. Botching the shuttle into a dangerous side-mounted cluster, just to hold down some yearly budgets, is really why two crews died. Nixon was part and parcel of that. His executive order didn't just kill Apollo, he killed all spaceflight outside LEO.
And NASA responded by killing the nuclear rocket program, which was just ready to fly. The official thinking was "why build the rocket if we aren't going to go?" How short-sighted and idiotically-foolish was that?
And, where is the medical centrifuge on the ISS that determines how much gee is enough to stave off microgravity illness? They had a module for that, but cancelled it! ISS as it is, will never give us that absolutely crucial answer for long space voyages. Very expensive window-dressing, as it is.
Reagan's X-30 scramjet in the 1980's had no hope of being feasible, even if scramjet had been ready for application (it still is not): airbreathers alone do not have the frontal thrust density to climb that steeply in air that impossibly-thin (at 100,000+ feet, the Mach-15+ compression of near vacuum is still near-vacuum). Several $B got spent to find out what we already knew. No craft ever flew, of course. Political window-dressing (it was never really intended to fly). Expensive. But just crap.
The smarts isn't in the government labs, and most certainly not the politicians themselves. The real smarts is out in the contractors, and the breakthroughs will not come from the long-time favorites that have been on the payroll so long. Example: The real breakthroughs in LEO access are coming from Spacex, not ULA.
Problem is, this is government-led stuff, because exploration and blue-sky R&D is generally not what business CEO's invest in. They do it only when paid to do it. If the government lab is too hide-bound to foster some new contractors for the breakthroughs, they won't happen. And the smarts that was in the unfunded contractors is lost: they die/retire/go elsewhere and do something completely different.
That third outcome is what happened to me personally. I was once one of about a dozen or so all-around experts in ramjet propulsion, in the whole US. Most of us are dead now. I haven't done ramjet since 1994. Now I teach math in a 2-year tech school.
Not very smart of the government. Penny-wise, pound-foolish, as the adage has it.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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A Lunar SSTO could potentially use pure oxygen as a propellant, derived from lunar ilmenite as modest energy cost using a carbon monoxide cycle.
The engine housing could be contructed from sintered fibreglass or glass-glass composite. The fuel itself would be in the form of uranium dioxide fibres. Nothing would oxidise as all components are oxides already.
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I would suggest resurrecting the LH2 NERVA of 1973 first, which should take a small, talented team, no more than about 5 years. This is Kelly Johnson-style Skunk Works stuff. As the design finally was, the plume was pretty clean. Didn't/doesn't need plume capture, just shoot it in the open. Get that thing operational, and use it ASAP for orbit-to-orbit transport purposes, not launch vehicle upper stage work. That takes care of the reactor-falling-from-orbit fear, pretty much.
Working in parallel, we need variants on the NERVA idea that upgrade its T/W and Isp, things like DUMBO and TIMBERWIND. These may need plume capture, at least at first. These would still be LH2 engines, and would be upgrades to the NERVA's being used, about 5-10 years down the line. Again, you have to have a small talented team doing this, not a government bureaucracy more interested in process than results. Skunk Works-type organization.
Once these things are operational, we need the water-propellant variant, which is a third item to be worked in parallel, starting right now. A water NTR could be refueled anywhere, because ice seems to be everywhere in the solar system. Plus, water is so easy to handle and store, even in space. THAT is where we need to go with solid-core NTR. It's a practicality and ISRU thing. Lowered Isp is quite acceptable if you can mine and melt ice and thus be free of refueling restrictions.
Within 5 years of cranking this solid-core NTR effort up, the gas core NTR needs the practical work it never got. I'd suggest doing that one on the moon, as we ought to be easily capable of planting a test base there with the rockets we have, especially if augmented by solid core NTR's. Open-cycle gas-core NTR always has a somewhat radioactive plume, and there's a risk of it even in the light-bulb concepts, should containment fail. But we need gas core engines. That's how you fly faster than the low-energy transfer orbits we use today. High Isp and high T/W at the same time is the payoff, something electric propulsion does not appear to be capable of offering.
And then there's the nuclear explosion drive. That works better in ships the size of naval battleships of WW2-vintage mass (20,000 tons and up). I'd reserve that for colony-planting missions down the road a bit. But we're going to need it. So we're going to need to test it out and get it working. No better, safer place to do that, than the moon.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I need some further understanding on the use of nuclear propulsion in space.
Typically I have read that Hydrogen is the prefered propellant, because of it's expansion properties.
I have also seen reference to water as the propellant mass, because it is availble many places in space.
I am wondering about a hybrid.
What might be possible where you would have a pressurized tank, and pumped water into it and also Hydrogen in a compressed gas form. An agitator would be needed to mix it into a slurry of water and compressed Hydrogen bubbles.
Having that could you heat it in a nuclear propulsion system, and get the advantage of Hydrogens expansion properties, and also the mass of the water?
(I am guessing that cavitation might be a problem with the metal parts).
I am thinking of a bullet. The rifle recoils when the burning explosion pushes the bullet out of the gun barrel. So the water is the bullet, but it also vaporizes and expands in the rocket nozzle, and the Hydrogen is an even more expanding gas.
I understand that water could be corrosive, but could the Hydrogen counteract that as well?
Alternately you could push heated steam out of the nozzle, and inject liquid Hydrogen?
Last edited by Void (2013-02-15 17:56:01)
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Hi Void:
In a thermal rocket engine, you run the propellant fluid (whatever it is) through some sort of passages through the hot reactor core. That turns it into very hot gas under high pressure inside the strong shell containing that core. I'm not sure, but I think hot steam will absorb more heat from the reactor core at something near a 3000 F (would have to look up the old records on reactor operating temperatures to be accurate), allowing a higher operating power, but steam is corrosive to the materials they used in NERVA. Higher power might lead to higher effective outlet gas temperatures, but I'm not sure of that.
From the outlets of the passages through the core, the gas is gathered in a space and then sent through the throat into the expansion bell, trading temperature for kinetic energy, at the cost of a pressure drop (to nearly nothing). The variables there that control Isp are chamber temperature and molecular weight. I think that Isp is proportional to the square root of the ratio of absolute temperature over molecular weight. That's why they liked hydrogen: it drives up Isp, being only MW=2, versus water's 18.
But, like I said, the availability of ice nearly everywhere in the solar system as a simple, easy-to-clean ISRU "fuel" might well offset the decrement in NTR Isp. The main thing is getting high thrust for impulsive delt-vee out of a device with 500+ sec Isp to beat any possible chemical propulsion. I've been told a water NERVA might be around 500-600 sec, but I don't know for sure. With gas core, that might well be over 2000 sec Isp.
Hope that helps.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Thanks for the reply on the Nuclear part.
However, given an energy source nuclear or non nuclear, does it make sense that a "Mix" could be useful as a propellant?
One part which expands more with the application of heat, and one part which has greater mass per volume.
The example of water with Hydrogen bubbles in it, becomming water steam at a high temperature, and also Hydrogen which expands more, pushing the water steam to expand more. I have woried about the Hydrogen becomming disolved into the steam but I believe that at least for liquid water, you can saturate it and then add more.
Obviously if you have water, you can have Hydrogen. What you do with the excess Oxygen beyond breathing it of couse is another issue. I have tried to consider if it can provide propulsion by being expelled with a linear accelerator (Magnetic), or if you could inject it into the steam stream as well. Perhaps not only normal nuclear heating could be applied, but could you also boost the thrust by applying some microwave energy to expand the down stream flow just a bit more at the outlet?
Of course handling plasma might be something you would not want to go to. Just superheated gasses?
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However, given an energy source nuclear or non nuclear, does it make sense that a "Mix" could be useful as a propellant?
Something like this?
LOX-augmented Nuclear Thermal Rocket. This concept involves the use of a "conventional" hydrogen (H2) NTR with oxygen (O2) injected into the nozzle. The injected O2 acts like an "afterburner" and operates in a "reverse scramjet" mode. This makes it possible to augment (and vary) the thrust (from what would otherwise be a relatively small NTR engine) at the expense of reduced Isp
Last edited by Rusakov (2013-02-20 11:14:39)
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Thank You,
Rusakof
It is nice to get an answer.
Of course I have made a complex and perhaps unressonalble request, but you gave me part of what I wanted. As did GW.
Really thanks.
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