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.

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

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

In the past, on Earth, it has largely been to exploit foreign resources and to expand the domestic territory.

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

No one can deny the excitement of visiting another world.