Ion-Engine Spacecraft On Moon Mission

anactofgod writes "The Times On-line and space.com reports that the European Space Agencies Smart-1 probe has cleared the Lagrangian point between the Earth and its moon and is due to enter lunar orbit on Nov 15th. Smart-1's mission is to make observations related to the moon's formation and composition. What's cool about this mission, other than this is the first European mission to Earth's moon, is that the probe is using solar powered ion engine thrusters. Ion engines are an order of magnitude more efficient than chemical engines. NASA flew the first ion-powered spacecraft, Deep Space 1, in 1998. Smart-1 is the second spacecraft to use the technology, and was designed as a testbed for future ESA missions. The ESA is scheduled to fly the ion-powered BepiColombo on a mission to Mercury in 2009."

Comments

Nuclear Thermal vs. Ion Thruster designs

[justanyone]

I heard recently about a new Nuclear Thermal design (in http://www.wired.com/). I'm wondering if this is better (higher ISP per unit cost) than an Ion thruster.

Obviously, if you're headed inbound into the solar system, you're destined for more light therefore more available energy. And, going outbound (Pluto-wise), sunlight gets scarce. So, where is the breakeven? Solar panels cost weight, and Ion engines mass a lot for the miniscule thrust they generate. Nuclear thermal (or Nuclear/Ion) combinations also mass a lot but have the added advantage of much higher available thrusts for short bursts if needed.

What about pairing Nuclear thermal with Ion thrusting? Generate a plasma by heating it with a slow fission or plutonium decay reaction, and also generate electricity from the waste heat. Use the electric power to do microwave heating. Or, directly accelerate the plasma ions using a magneto-hydrodynamic MHD setup?

Is anyone actually actively developing anything like this? It seems to me that the fundamental limitations of our current space delivery systems are NOT who can build a better mousetrap, but that all the mousetraps are using cheese (LH2+LOX) instead of peanut butter (NTR, MHD, Ion engines, etc.).

Also, are there any somewhat-better-than-rumors of USAF designs using these that are flying but that people can't talk about?

Re:Nuclear Thermal vs. Ion Thruster designs

[Christopher Thomas]

Nuclear thermal is limited by the need to keep the exhaust temperature to something the core materials can withstand. Ion drives have no such limitation, and can in principle achieve exhaust velocities close to C (though in practice you'd never want to build a drive that did this). This gives ion drives far higher Isp.

You can in principle build a magnetically confined nuclear thermal drive that holds a uranium plasma in a magnetic field and reaches very high temperatures, but this turns out to have many practical problems (not the least of which is a fairly large minimum size), so don't expect it to be done soon.

Nuclear-electric drives are the way of the future for craft outside the inner solar system. They use a small fission plant to generate electricity, which then drives an ion drive or hall effect thruster or plasma drive or what-have-you.

Re:Nuclear Thermal vs. Ion Thruster designs

[cjameshuff]

Look into gas core rockets a bit more. The confinement is inertial, not magnetic...though magnetic fields might be used for controlling the vortex. In the "nuclear lightbulb" form, the gas core surrounds a cylinderical quartz window cooled by liquid hydrogen. The working mass is forced through the center, and is heated by radiant UV. However, you are basically correct...none have been built, they would need to be big, and the biggest problem is finding materials and cooling systems that can handle the extreme temperatures. (Up to 55000 K)

Nuclear electric is fine for probes...higher efficiency, and very long operation times. However, for many things they are simply too low-thrust. Nuclear thermals spit out greater amounts of reaction mass at a lower velocity than ion thrusters, and can't produce as much delta-v from a given amount of propellent, but they are far better than chemical rockets and produce much greater thrust than ion thrusters. I think they are most promising for any manned craft and unmanned craft that need to make high-acceleration maneuvers.