Good guess! Nuclear power plants are lightweight, compact, and last a long time. They have been used on many robot probes like Voyager and Cassini.

But some people worry about an accident spilling radiation into the earth's atmosphere, so it's not the safest choice. Try again!

Batteries (One kilogram of batteries produces X kilowatts)

Fuel cells (One kilogram of fuel cells produces Y kilowatts)

Solar energy (One kilogram of solar cells produces ZZ kilowatts)

© The Children's Museum of Indianapolis, 1999