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SpaceX's New Combustion Technologies
An anonymous reader shares this story that takes a look at some of the advances SpaceX is working on. "Getting a small group of human beings to Mars and back is no easy task, we learned at the recent GPU Technology Conference in San Jose hosted graphics chip and accelerator maker Nvidia. One of the problems with such a mission is that you need a very large and efficient rocket engine to get the amount of material into orbit for the mission, explained Adam Lichtl, who is director of research at SpaceX and who with a team of a few dozen programmers is try to crack the particularly difficult task of better simulating the combustion inside of a rocket engine. You need a large engine to shorten the trip to Mars, too....Not only do you need a lot of stuff to get to Mars and sustain a colony there, but you also need a way to generate fuel on Mars to come back to Earth. All of these factors affect the design of the rocket engine....As if these were not problems enough, there is another really big issue. The computational fluid dynamics, or CFD, software that is used to simulate the movement of fluids and gases and their ignition inside of all kinds of engines is particularly bad at assisting in rocket engine design. 'Methane is a fairly simple hydrocarbon that is perfectly good as a fuel,' Lichtl said. 'The challenge here is to design an engine that works efficiently with such a compound. But rocket engine CFD is hard. Really hard.'"
As it happens, back in the '80s I worked at a company (Commonwealth Scientific) that built ion-beam guns based on the Kaufman duoplasmatron, which was the basis of the mercury-vapor thrusters that NASA had developed in the 1960s. The company was trying to make the aperture of the guns as wide as possible, and the difficulties included neutralizing the ion beam on the way out, keeping the plasma inside the gun stable, and keeping the beam density even. Basically, the bigger the gun, the harder it was to make it run steadily. When I was there, they had 8" apertures and were working on scaling them up to 12" apertures.
-jcr
The only title of honor that a tyrant can grant is "Enemy of the State."
The gravitational constant is G, and is the same everywhere...it's a physical constant. The surface gravitational acceleration of Mars is different because of its lesser mass. And apart from the problem of the atmosphere, having surface gravity of about 1/3 of Earth's is nowhere near enough to make ion propulsion useful for launch, an ion propulsion system with a nuclear reactor and propellant would easily weigh around ten thousand times what it could actually lift on Mars. The only bodies where launch could be usefully performed or assisted by ion thrust are asteroids and comets.
Ion engines use very high amounts of power and very low flow rates of propellant. They provide a benefit when you need low amounts of thrust for a long period, and have either plentiful solar power or a nuclear power source. They could be used for shipping bulk supplies ahead of a manned expedition, but a manned expedition itself or any other mission with tighter than usual time constraints will use chemical propulsion, or at most nuclear thermal propulsion. These relatively low-Isp systems require more propellant for a given delta-v, but can achieve accelerations millions of times higher than ion engines, and do so without heavy power systems and gigantic radiators.