There are millions of bits of space junk orbiting the Earth, many of them less than 10cm in size. But one object only slightly larger is Vanguard 1, launched on this day in 1958 from Cape Canaveral – the oldest artificial satellite in orbit.
Vanguard 1 is about 15cm in diameter and weighs about 1.5kg – small enough for the Russian president of the day Nikita Kruschev to call it the 'grapefruit satellite'. It featured a 10mW transmitter powered by a mercury battery and a 5mW transmitter powered by six solar cells. While the battery ran out after 20 days, the solar cells proved they could be used for power and kept the 5mW transmitter running for seven years.
While it has now been silent for 50 years, Vanguard 1 still performs a useful function – by tracking its orbit, scientists can determine the long term effect of the Sun and the Moon, as well as the Earth's atmosphere, on satellites.