The Vanguard 1 satellite was launched

On March 17, 1958, the US Naval Research Laboratory placed Vanguard 1 into orbit from Cape Canaveral. It was a modest payload: an aluminum sphere just 16.5 cm across and weighing about 1.5 kg, which a deflated Soviet press dubbed “the grapefruit satellite.”

What the sphere lacked in bulk it made up for in influence. It carried six small solar cells powering a radio transmitter, an early demonstration that sunlight could keep a spacecraft alive long after onboard batteries died. Tracking its signal also let scientists measure Earth’s true shape, revealing a slight pear-like asymmetry.

Decades after its transmitters fell silent, Vanguard 1 is still up there.

It was only the fourth satellite ever launched, after two Sputniks and Explorer 1. Yet all the earlier craft have long since burned up in the atmosphere, leaving Vanguard 1 — together with its spent upper stage — as the oldest human-made object still in orbit.