R oughly 300 miles above our heads, three washing machine-sized capsules are orbiting the Earth. Inside one of them, tiny crystals of a potential cancer drug are being grown in the weightlessness of space. The others are testing heat protection materials and navigation systems for when the capsules plunge back through Earth’s atmosphere at hypersonic speeds. Together, they represent a small but significant step towards what some hope will become a lucrative new industry: manufacturing drugs and other materials in space.

The spacecraft belong to California-based Varda Space Industries. On 1 October, it launched two onboard the same rocket, followed by the third on 20 October.…