Vanguard 1 is an American satellite that was the fourth artificial Earth-orbiting satellite to be successfully launched, following Sputnik 1, Sputnik 2, and Explorer 1. Vanguard 1 was the first satellite to have solar electric power. Although communications with the satellite were lost in 1964, it remains the oldest human-made object still in orbit, together with the upper stage of its launch vehicle.

Vanguard 1 was designed to test the launch capabilities of a three-stage launch vehicle as a part of Project Vanguard, and the effects of the space environment on a satellite and its systems in Earth orbit. It also was used to obtain geodetic measurements through orbit analysis. Vanguard 1, being small and light enough to carry with one hand, was described by the Soviet Premier, Nikita Khrushchev, as "the grapefruit satellite".

On 17 March 1958, the three-stage launch vehicle placed Vanguard into a 654 km × 3,969 km (406 mi × 2,466 mi), 134.27-minute elliptical orbit inclined at 34.25°. Original estimates had the orbit lasting for 2,000 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 about 240 years. Vanguard 1 transmitted its signals for over six years as it orbited the Earth.

After its scientific mission ended in 1964, Vanguard 1 became a derelict object – as did the upper stage of the launch rocket, after it finished the delta-v maneuver to place Vanguard 1 in orbit in 1958. Both objects remain in orbit.

The Vanguard 1 satellite and upper launch stage hold the record for being in space longer than any other human-made object, and as such have traveled farther over the Earth's surface than any other human-made object.

According to Wikipedia