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I doubt a pysical nozzle would survive the reation. It sin't heat so much as ablation caused by the plasma. That is why I suggested using a magnetic nozzle, eliminating the need for the plasma to touch the nozzle's surface.
I could take up more space describing it but this site will give you the details. If I remember right a demonstator was actually built, although it no longer exists. 77 tonnes to LEO with virtually no new development costs.
Making virtually everything in the hab accessible is more then a long term solution, it is a required safety element. If the crew has to survive on a hostile world for 500+ days, they better be able to repair broken parts. It is a matter of survival. To assume that nothing will go wrong is to assume too much. Look at the early designs for interplanetary ships. They included a repair shop and machine tools, something you won't find in anyone's plans today. And they planned for flight times shorter then or equal to Mars-24's. While it unlikely you would need to do major repairs to the ship itself, carrying extra spares, or the tools to make them, or jury-rig them, on the ground should be considered. It may be more mass, but we are talking about people's lives here.
What about Jupiter's solid hydrogen core? Jupier has no moons of consequence to enact tidal forces, and is far less effected than Earth by the Sun's own forces. Yet it has a massive magnetic field. Just as the Earth's crust relies on plate techtonics, and Mars' doesn't, planet's geologic process are not always the same. Venus' core might not remain as liquid as Earth's beacuse the two act entirely different. Without analysis of the layout of Venus' interior, we can't tell.
If a push was made, NASA would have both, and the bulk of advanced propulsion research. Nothing would be worse then being passed enroute. Currently no one has a HLV, the Russians have the plans, but Energia only flew twice, with one failure. The US has the technology as well, we have flown a few big fireworks before.
I would like to see the ESA develope as an independant player in the manned arena. Europe has the resources to support a vast space program if they so wish. The more routs to space, the cheaper access will be.
Having all the major power really planning missions at once would get the world excited about space in a way never seen before. It would be just what we need to garner the support for a colony on Mars, one which could eventually include everyone.
This is exactly what the NASA needs, copetition! It got us into space, it got us to the moon, and it would sure get us to Mars.
The USA, Russia, or perhaps even the PRC, would not sit idle as the ESA takes the lead. Working together may reduce costs, but working abart may mean it actually happens.
I say make it a race, the ultimate World's Cup, and may everyone win in the end. Onward to Mars!
It all comes down to the need for a BDB. I think the designers of Sea Dragon may have had the right idea, reduce the cost of the booster by excepting sub-optimal proformance. By using cheaper materials, deadweight was increased, but the vehicle could always be scaled up to compinsate. Once it becomes cheap to place large payloads in orbit, expansion into space is inevitible.
Shuttle C was very similar to what you are describing, essentialy a partialy reusible cargo pod which would replace the shuttle for cargo capibility. The engines and boosters were reused, but the rest was expended.
There was a 200 kw ion engine from the 60's shown on the site, which is a lot closer to what you need. Ion engines, because of their carefully spaced grids, can be difficult to scale up. Hall thusters would be easier to scale, but are not quite as efficient. The others could take a decade or so of concerted development to make a large reliable engine suited for human spaceflight, their higher plasma temperatures complcate matters but provides high thrust, but since no one is even thinking about a mission until 2014-18, they could be used in time. In the final design, a small nuclear reactor could boost the ion engine from 100's of kws to 1000's, and with electric engines, more power is good.
There are several propellants which give off more energy the oxygen-hydrogen ones so common today. The problem with many of these is that the reaction product, or a signifigent portion, is not a gas, but a solid. Both NASA and the USAF experimented with adding hydrogen a working fluid in addition to the fuel and oxidizer in these higher energy fuels, such as Be-O2/H2 and Li-F2/H2. Ideal Isp for either fuel is around 700s. The tests were far from conclusive, as the Be-based fuel had low combustion efficiency and the Li-based fuel worked best for short missions, with F2/H2 being more efficient for longer ones. For boosters, tripropellent engines burn hydrocarbon fuel at low altitudes to minimize drag, and switch to hydrogen at higher altitudes to increase efficiency.
To get down to the size of a drop tank to power a booster or interplanetary craft, chemical propulsion just can't do it. Nuclear or plasma is the only way to do that in large craft, chemical combustion will never reach the effiency of either.
To answer the origonal question, yes I think you can create a continuous fission reaction. The fuel would have to be laced with fissionable components so if allowed to freely react, it would go critical. This is the idea behing the nuclear salt-water rocket designed by Robert Zubrin in the early 1990's. Such a concept needs far more then afew atoms to work, but would probly require an extensive magnetic nozzle to prevent the explosion from destroying the ship.
Most of the articles I have read by sonoluminescence researchers have been sceptical if the process can be scaled up to any sort of power producing levels.
Bush has proven himself static and resistant to change. He proposes spending hundreds of billions on threats his OWN intelligence agencies say are non-existant during a time of decreasing reciepts. He pushed massive tax cuts and other expenditures supposedly paid with by a surplus which never existed, when the governemt could no longer afford such cuts, Bush's origonal argument was conveniently forgoten. He argued for the unilateral aproach for Iraq before even trying to go to the UN, pissing everyone off in advance, and gureenteing no international support. He supported librarians spying on those who checked out books, and has frequnetly tried to trample on state's rights, something he ran on, when those states' decisions are not part of his doctrine. A wally gee-good job!
I think this falls into the "I'll believe it when I see it catigory". Outragous claims like this have been made before, with litrealy thousands of inertial propulsion machines patented. I have a feeling we will be left with chemical boosters for a very long time.
Who knows, without the moon we may not even have intelligent life on Earth. The moon allowed wide tides early in Earth's history, providing a requirement for life to start developing the ability to survive on dry land. The moon also stablizes the Earth's axil tilt, preventing the planet from wobbling as bad as Mars. And who knows what effect the event which created the moon had on Earth's development. The planet was not always a haven for life, life turned it into one.
If the hab did fall on its side and survived, and you had the rover already on the surface, you might be able to use it to slowly raise the hab up, using piled regolith to move it cm by cm. Or, you could undermine one side to right it, ending up with the hab in a hole. This is probably the best, if most tiresome meathod with the limited resources availible, as I don't think any earthmoving equipment besides shovels is coming along. The real problem would be injuries from such an offcenter landing.
It's not salt water, as in NaCL mixed in with water, it uses urainium tetrabromide in a 20% concentration, about the same as NsCl is in seawater. The fuel tank is designed to absorb neutrons, preventing a reaction. When it is pumped out the fuel will start reacting. The fuel, if ejected at the proper velocity can be made to react just behind the rocket, producing considerable thrust. Zubrin wrote about using it for a mission to Titan, but its high thrust and efficency would be perfect for a manned Mars mission as well. It also lacks the concentrated pile of a NTR, so may encounter less political resistance.
Try this link for a full explaination,
Soem people have considered using concentrators
Ion engines are very efficient, but their thrust is far too low for human spaceflight. A solar clipper would be good for cargo though, cheep and efficient.
Why not use a more powerful plasma engine then an ion thruster? You really want to limit flight times for humans. Other forms of plasma propulsion also ofer high Isp, many in the 3000-7000s range, with thrust ranging from 100N for MHDs, 2000N for VASIMR, or 4000000N for the more radical EPPP. Even if you do use an ion engine, powering it up from 400kw to Mw size would be advisible.
I agree, testing ISPP during the sample return is a good idea, and one of NASA's reasons for the sample return in the old DRM. In this case it would probably be best to just straight to earth.
In the actual human mission, however, it would be best to link up with a TEI hab already in orbit for the return mission, or even use the TMI hab/propulsion stage, depending on the propulsion system used. Limiting your return vehicle's fuel capacity, with low efficiency chemical fuel, to a landible size limits TEI velocities to 5-6km/s, if I remember Mars Direct's figures correctly. In reality 12-16km/s is perfectly doable with modern technology.
GCNR's have Isp's of about 3000s and can have farly high thrust, VSIMR combines both moderate thrust and high efficiency, an EPPR on the scale of NASA's plans would have an Isp of 4000s and produce 4.0x10^6N of thrust, and MPD, ion, Hall and other lower proformance plasma systems are excellent options for cheaping sending most of the mission hardware, and future cargo. All these sytems could be developed in time for a 2018 mission.
Nuclear power will likely be needed on the surface, so ignoring it for propulsive purposes is kind of like tying your hands.
ps- I forgot about Zubrin's NSWR (nuclear salt water rocket) which also offers high Isp and thrust.
Is it that bad of an idea to test the technology before we send in people? NASA orbited the moon many times before landing. Plus an orbital rendezous means you can mininize the astronauts exposure to radiation by allowing more rapid returns powed by nuclear or plasma engines. <60 day Earth-Mars tranists will improve eventual colinization anyways.