Fifty-five years ago today — March 17, 1958 — a Vanguard rocket carried the Vanguard 1 satellite to orbit out of Cape Canaveral.
(Vanguard 1. Note the very small solar panels on the side of the satellite. NASA image.)
Vanguard 1 was placed in an elliptical orbit with a perigee of 654 km (406 mi) and an apogee of 3969 km (2466 mi), inclined 34.25 degrees from the equator.
Original estimates had the orbit lasting for 2000 years, but it was discovered that solar radiation pressure and atmospheric drag during high levels of solar activity produced significant perturbations in the perigee height of the satellite, which caused a significant decrease in its expected lifetime to only about 240 years.
Vanguard 1’s batteries ran down in June 1958, stopping its battery-powered 10-mW transmitter, but its solar-powered 5-mW transmitter continued operating until May 1964. Vanguard 1 may still be optically tracked from Earth, and is the longest-orbiting man-made satellite.by