America's Vanguard program had become a national embarrassment after a string of failed launches, including a Vanguard rocket exploding on the pad on live television in December 1957. On February 17, 1959, a Vanguard rocket put a 10.75-kilogram sphere into orbit. Photocells aboard Vanguard 2 were meant to map cloud cover over the sunlit side of the planet. A wobble in the satellite's spin made the data hard to read, but the mission proved the idea of watching the weather from space.
Vanguard 2 was a magnesium ball about 50 centimetres across, built by the Naval Research Laboratory. Two small telescopes with photocells looked down at the Earth as the satellite spun, measuring how much sunlight bounced back. Clouds reflect more than land or ocean, so scientists hoped to piece the readings together into a rough map of the world's cloud cover.
The physics worked against them. After separation, the rocket's final stage bumped the satellite and set it wobbling instead of spinning cleanly, so its instruments scanned the Earth in an unpredictable pattern. Its batteries ran out after 19 days, and the data turned out to be difficult to interpret.
Even so, Vanguard 2 marked the start of weather observation from orbit, and just over a year later TIROS-1 sent back the first television pictures of clouds from space. Vanguard 2 still circles the Earth: engineers expected its orbit to last for about 300 years, and it has been in orbit for more than six decades.