Cymric wrote:
Then there is a different problem: how do you brake a probe equipped with only an ion engine? Right now they used the Moon's own gravitational field to capture the probe. Gravitational fields of sufficient strength are rare :-).
Simple, rotate craft by 180 degrees and the thrust will eventually slow the probe down. Okay it takes time to cancel out the velocities attained, but anyone who's ever played Frontier will understand the physics. The Ion drive will have a very low thrust to weight ratio, therefore will take longer to accelerate/decellerate.
It is a promising technology and deserves lots of further study, yes. But until an ion engine can deliver the same thrust that will propel us to the Moon in 4 days, and have the stamina to keep that same level of thrust up for years, then and only then will I begin to call it 'Star Trek' technology.
The attraction is that instead of building a 111 metre tall rocket at a cost of billions to propel a few meagre tons to the moon, a smaller rocket would only need to propel the cargo into a stable Earth orbit. A normal rocket not only has to propel the probe, but an extra stage containing sufficient propellant to enable the proble to attain escape velocity which means more mass for the initial stage to boost into the sky. Once in orbit the Ion drive would fire up and eventually propel the package to the moon. A conventional rocket cannot remain burning indefinitely, but an Ion drive can.
Every single interplanetary probe we've launched has had to rely upon the so called "slingshot" effect to accelerate / decelerate. We're a long way from having the ability to fly around the solar system at will a-la Frontier, but there is research into matter / anti-matter propulsion going on which may one day prove a viable proposition.
