Science: Pioneer Post-Mortem

The moon-probe Pioneer, which burned out over the South Pacific after staying in space for 43 hours, rose 79,000 miles—or only one-third of the distance to the moon. But it made a much nearer miss than the figures seem to show. The earth's gravitational field drops off with the square of the distance. With only 2% more thrust or only about 580 more m.p.h. peak velocity. Pioneer could have passed the moon* and escaped from the earth forever.

The reason that Pioneer lacked those few more miles of speed is still being debated by...

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