Years of science fiction have produced a mindset that it is human destiny to expand from Earth, to the Moon, to Mars, to the stars.

The factor most ignored in discussing interstellar flight is the kinetic energy that must be invested in the ship to make its tons of matter move at a substantial fraction of the speed of light.

It would be a pity if, frustrated by the price of travel, we elected to become a society that never made contact, that never gave SETI a fair chance.

No one can deny the excitement of visiting another world.

Above all, I would not expect a wise race, at great expense, to set loose an army of self-replicating robots.

The sun and its retinue of planets drift as a group through the vast gulfs of space that separate the stars.

Present annual world energy consumption is about equal to the annihilation energy of 4 tons of matter.