Not Your Grandpa's Rocket Engine

Oh, there have been myriad technical and chemical advances that have improved both hardware and propellant, but consider that the last major engine development program undertaken by NASA was the design and construction of the Space Shuttle Main Engines. Marvelous pieces of equipment, especially from the standpoint of their useful life, but still and all just cryogenic hydrogen-oxygen motors. The third stage of the Saturn V had one of those.

In the 1960's we were developing nuclear thermal rockets and talking about propelling an interplanetary cruiser using nuclear bombs. Nuclear-electric ion-driven spaceships shaped like umbrellas and arrows were on the drawing boards for use on a manned expedition to Mars. And no less a personage than Wernher von Braun himself was willing to speculate on the future utility of an interstellar photon rocket, albeit with the caveat that such an invention was far, far off in the future.

Nowadays, all things nuclear are anathema to space applications, and ion propulsion has only gone as far as satellite attitude control and small unmanned probes like Deep Space 1.

Now, it is true that there are still futurists willing to talk about magsails and fusion engines, and advances in materials and superconductors and so forth are all bringing daunting technical challenges within reach. Privately funded enthusiasts are still in the game, as well, pushing such things as solar sails that would be microscopically thin and miles across and harness the force of sunlight itself. But the advanced propulsion community proper remains in dire straits.

Consider the bizarre story of the most promising near-term propulsion breakthrough that, presently, hangs just out of reach--that of the VASIMR, the Variable Specific Impulse Magnetoplasma Rocket. Being developed under the leadership of Dr. Franklin Chang-Diaz, a veteran astronaut, this system is basically a poor man's fusion engine. Instead of creating and sustaining a high-energy plasma in a reactor until self-sustaining ignition is achieved (the enthralling task that confronts researchers interested in developing a fusion power plant), they took their cue from the difficulty said researchers were having containing their plasma. (As the temperature in the reactor reaches obscenely high levels, the electromagnetic fields needed to create and sustain the plasma begin to destabilize.) Since the high-energy stuff wanted to leak out of the reactor, they wondered why not let it?

Consequently, they now create the plasma in something along the lines of a large microwave oven (it's easier than initiating a fusion reaction) and expel it electromagnetically in order to provide thrust.

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