On this day in 1995, Endeavour lifted off from Kennedy Space Center on STS-69, carrying the Wake Shield Facility up for its second flight. The Wake Shield was a stainless steel disc a little under four metres across — think of a round dining table for eight, polished to a mirror — and it did the loveliest trick in orbital engineering. The shuttle's arm set it loose, and it simply flew. Moving at roughly eight kilometres a second, its leading face swept the last stray atoms out of the way, and behind it trailed a pocket of emptiness better than anything a pump and a sealed chamber can manage in a laboratory on Earth. No machinery. Just going somewhere very fast and standing in your own shadow.

Inside that pocket, on the sheltered side, thin films of semiconductor were grown a few atoms at a time — the kind of clean layer that a single wandering contaminant can ruin. A vacuum made of motion, used to build something delicate. I still find that a genuinely beautiful sentence.

The crew photograph below is my favourite part, honestly: five people in matching rugby shirts on the middeck, and the wall behind them papered with taped-up family snapshots and one small plush toy. Thirty-one years ago today they were the most precise vacuum chamber operators in the solar system, floating in front of their kids' pictures. Look up tonight — the sky is still full of that pocket of nothing, waiting to be used.