Spacecraft have gone bite-sized. On June 23, Breakthrough Starshot, an initiative to send spacecraft to another star system, launched half a dozen probes called Sprites to test how their electronics fare in outer space. Each Sprite, built on a single circuit board, is a prototype of the tiny spacecraft that Starshot scientists intend to send to Alpha Centauri, the trio of stars closest to the sun. Those far-flung probes would be the smallest working spacecraft yet.

“We’re talking about launching things that are a thousand times lighter than any previous spacecraft,” says Avi Loeb, an astrophysicist at Harvard University who is part of the committee advising the initiative. A Sprite is only 3.5 centimeters square and weighs four grams, but packs a solar panel, radio, thermometer, magnetometer for compass capabilities and gyroscope for sensing rotation.

These spacecraft are designed to fly solo, but for this test, they hitched a ride into low Earth orbit on satellites named Max Valier and Venta-1. Each satellite has one Sprite permanently riding sidecar, and the Max Valier craft has another four it could fling […]