9. Improve technology

There are very few critics for the idea that space exploration induces technology and health spin-offs that benefit economies and society. Yet many scientists question whether the current space program, which consists of endless trips around Earth, is worth the investment.

Hartmann says "crewed missions" to the Moon and Mars would be far more beneficial than "our present crude missions" to Earth orbit.

Bigger goals are needed, scientists reason, to spur the sort of advancements in technology worthy of a multi-billion dollar annual budget.

Of course no one knows what might be invented in an effort to set up lunar colonies, reach Mars or mine for metals on an asteroid. But a lot of scientists think it's worth finding out.

Next page: Stepping stone to Mars