I think many of you are missing the point of what a "Free Ranging" spacecraft is. Free ranging means that it can go to multiple
and be able to remain
at each of those destinations for a while to do science. The spacecraft we have now can't do that.
Right now, our spacecraft use 95%+ of all of their fuel on launch -- that is, the spend most of their lives coasting. There may be a little fuel
leftover for course corrections, but for the most part, the direction they originally go is the direction they will always be going (unless a planet's
gravity is used to alter its course). The spacecraft we have today can't go to a destination, stop to look around for a long period of time; then
move on to the next destination to stop and look around; then move on to another destination.
The spacecraft we have today can't move from place to place because they are so non
fuel efficient that they don't have enough fuel to
do that. For example, the voyager spacecraft could not stop to look at Jupiter, Saturn, an Uranus -- they could only do a one-shot fly-by encounter,
because they didn't have the fuel. The voyager spacecraft simply could not do anything other than zoom very quickly past those planets.
Now, consider a spacecraft with an engine that can be stopped and restarted over and over again, and is fuel efficient enough to do this for several
years. A free ranging spacecraft could -- for example -- go into robit around Europa, stay for a few months, than move on to Io (and stay a few
months), then move on to Ganymede, etc. The Galileo probe did look at these moons, but only when its orbit around Jupiter allowed the spacecraft to
fly-by those moons -- in a "fleeting glimpse". Free ranging craft would allow for stopping for a while at each target and do deatiled science.
is what's meant by free ranging spacecraft.
NASA is working on engines like this which have "Electric Propulsion", such as an Ion Thruster"
Ion Thruster Wikipedia
NASA's Deep Space 1 spacecraft was launched specifically to test new technologies, such as the ion engine:
Deep Space 1 Wikipedia
Deep Space 1
edit on 10/2/2010 by Soylent Green Is People because: (no reason given)