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.

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

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

No one can deny the excitement of visiting another world.

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