When Echo I soared into orbit last summer from Cape Canaveral, space scientists gave the giant balloon a modest life expectancy of two or three weeks. But this week, after 135 million miles. Echo I observed its first anniversary, still 1,000 miles aloft—and still going strong. Trackers now predict that the 100-ft. metalized balloon will probably stay up another two years, and possibly three.
The satelloon's unexpectedly sturdy lease on life is a gift from the sun, whose rays exert a faint pressure on it (one-fiftieth of an ounce). Most satellites are too heavy and dense to be affected. But on Echo's...