This is planetary radio. Last week it was Galileo the man. This week it's Galileo the man. This week it's Galileo, the incredibly successful spacecraft, and the woman who serves as its last

boss.

Hi everyone, I'm Matt Kaplan.

Planetary scientist Claudia Alexander joins us for a visit to Jupiter.

Later Bruce Betts will have a space trivia contest that will make a deep impact on you

and something else. Here's a brief visit with Emily to get us started, or maybe I should say a fast visit.

Hi, I'm Emily Lochuwala with questions and answers.

A listener asked, if we were to design a robotic

interstellar mission to travel to the nearest star system,

what's the shortest time in which such a mission could be accomplished using current propulsion technology?

The nearest star system is Alpha Centauri about 4.5 light years or 4 trillion kilometers away.

Engineers have estimated that currently available electrical thrusters powered by large nuclear electric power plants

might be able to get robotic spacecraft up to a speed of 150 kilometers per second or only 1 2,000th of the speed of light.

At that speed, it would take almost 9,000 years to reach the nearest star system.

The fastest speed that any spacecraft has actually achieved is much slower.

The Voyager 1 spacecraft, the fastest man-made object ever, travels at only 30 kilometers per second.

At that rate, a spacecraft would take over 40,000 years to get to Alpha Centauri.

So we can't currently launch a mission to another star that would arrive in a reasonable amount of time.

Is there any hope for interstellar missions?

Stay tuned to planetary radio to find out. It's a good thing we call them planetary scientists. They all seem to have interests and expertise as wide

as a planet. Dr. Claudia Alexander is a good example. Her doctorate from the University of Michigan is in space plasma physics, but she seems quite comfortable

with many other disciplines.

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