Vanguard SLV-3, also called Vanguard Satellite Launch Vehicle 3 hoped to be the second successful flight of the American Vanguard rocket following successful Vanguard 1 satellite on rocket Vanguard TV-4. Vanguard SLV-3 launched on September 26, 1958 at 15:38 GMT. It was launched from Launch Complex 18A at the Cape Canaveral Air Force Station. Low second stage performance resulted in insufficient velocity for the third stage and payload. They completed one orbit and reached a peak altitude of 265 miles before reentering over Central Africa. Investigation concluded that particles from a rubber helium fill hose had clogged a filter in the fuel feed system, resulting in the second stage engine being fuel-starved and operating at only 80% thrust. The fill hose was changed to metal on subsequent flights, the second stage propellant tanks heat treated to remove scale, and preflight procedures changed to reduce the need to open up the propulsion system and potentially introduce contaminants into it.
Vanguard SLV-3 hoped to put into orbit the Vanguard 2D satellite, a Lyman Alpha satellite, with a magnetosphere measurement device. The satellite payload was 10 kg (22 lb). Vanguard SLV-3 only reached an altitude of 426 km (265 mi), the goal was 3,840 km (2,390 mi) to orbit.
- Mallove, Eugene F. and Matloff, Gregory L. The Starflight Handbook: A Pioneer's Guide to Interstellar Travel, Wiley. ISBN 0-471-61912-4.