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New Ion Engine Enters Space Race
Bibek Paudel brings us a BBC report on the development and testing of an new ion engine by a security firm named Qinetiq. The engine will be used in an ESA spacecraft tasked with mapping the Earth's gravitational field from orbit. Only a handful of ion drives have been used for space missions before, some of which we have discussed. Quoting:
"Cryogenic pumps can be heard in the background, whistling away like tiny steam engines. Using helium gas as a coolant, they can bring down the temperature in the vacuum chamber to an incredibly chilly 20 Kelvin (-253C). The pressure, meanwhile, can drop to a millionth of an atmosphere. Ion engines ... make use of the fact that a current flowing across a magnetic field creates an electric field directed sideways to the current. This is used to accelerate a beam of ions (charged atoms) of xenon away from the spacecraft, thereby providing thrust."
Wouldn't a heavier material like lead be more efficient at mass transfere and therefor thrust?
"Persistance is Fertile" - Me. I can quote myself if I want to.
It depends on how long you mean. Its certainly still a long way from being able to run an interstellar mission, but for an interplanetary mission it provides a lot of benefits. Lower mass and faster travel times are the primary ones; even though its low thrust its constant thrust so it can build up, particularly on longer missions (think to Jupiter rather than the moon).
Also, the one problem I see with the idea of 'vacuuming' space, beyond the obvious engineering problems, is that in order to use them in a system you'd lose more momentum than you'd gain, at least using engine technology of this sort. Imagine it from the spacecrafts point of reference, all the very rarefied gas is coming towards it at the speed the spacecraft is traveling in the inertial frame. As it captures the gas, it has to slow it down to stationary, and then speed it up and send it back out; in doing so unless the exhaust velocity is faster than the spacecraft velocity, you're going to lose momentum rather than gain it.
Now if you could come up with a way to ionize the gas as it passes and use magnetic fields to accelerate it further (like a swimmer or an air-breathing engine) that would certainly be interesting.
of the NRX program. NRX (NERVA [NERVA - Nuclear Engine for Rocket Vehicle Application] Reactor-Experimental Research) was the engine that would power the spacecraft that was supposed to take us to Mars and beyond. Unfortunately it was cancelled because of 'environmental concerns' http://www.fas.org/nuke/space/kiwi.gif.
Sig this!
sort of what I was wondering. I suppose there's no escaping physics though, you have to use something for fuel. (ok "fuel" is a bad word for it, how about "mass"?) I was hoping ion drives could run without losing mass, but that's the only fundamental way to accelerate something in a vacuum isn't it? by throwing mass overboard, preferably at high speed? (the high speed part being what the ion drive specializes in)
I suppose the only way around this would be a solar sail, or perhaps such a thing powered by some sort of a beam (of mass, energy, or a combination of the two) from the origin.
I work for the Department of Redundancy Department.
The drag problem isn't that clear cut. The reference frame isn't "spacecraft velocity" in any sense you'd normally think of it -- it's the solar wind, at ~500,000 km/s. In interstellar space it slows enough that fusion engines could easily have a higher exhaust speed, up to several % c spacecraft velocity. The problem becomes one of collecting enough hydrogen, and getting it to fuse. In-system, though, you can use the solar wind drag to your advantage, at least if you want to head outbound. Wikipedia has a good discussion of the issues involved.
The only thing that matters is VELOCITY, not momentum. Mass flow RATE. At least if the test is "efficiency". That is what we (rocket scientists) call "Specific Impulse" (Isp). When you do the Delta-V equation, it's only
DeltaV = Isp*ln (m1 - m2) if memory serves. If not, someone will fix it for me. Nothing about momentum. The difference in mass is the only factor for a given propellant/engine combo
Whatever you can get out of the poopchute the fastest is the most efficient. Without speaking of the ionization process, hydrogen is prolly the best, being the lightest, BUT it's density is so low that the mass to contain it lowers the return. Recall that Clarke's Discovery had ammonia instead of hydrogen as Sakharov propellant, because it was denser (smaller, lighter tanks). And thus, it didn't leak out after 9 years (2010 - 2001)
Xenon is probably an optimum of mass and density. Plus whatever they said about ionization.
I've heard this before, this and there are many other reasons that don't make a pure Bussard ramjet possible. A few years ago I came across these guys. While I don't know how realistic their ship but one thing that did catch my eye was this.
I was especially fascinated by how they address the fuel problem. They created something called an acceleration track. The idea is that fuel is launched before the ship is in packages. The ship would over take each fuel and supply package as it left the system. I always thought that was a elegant solution to the fuel and supply problem.
Supporting World Peace Through Nuclear Pacification
Are these ion engines more efficient in turning the power stored in their fuel into kinetic energy of the vehicle than the efficiency of, say, liquid fuel rockets we use to launch satellites and the Space Shuttle?
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They may be harder to ionize than other substances, but it's not impossible to do so. Heck, if they could not be ionized, it would mean that they hang on to their electrons with infinite force
I'm not saying it would be better suited to the purpose. All I was refuting was the fact that Xenon is the heaviest noble gas. I don't think Radon would be the best thing to use, but that doesn't disprove that fact that there are heavier noble gases than Xenon.
Anthropic principle: We see the universe the way it is because if it were different we would not be here to see it.