any value you keep, and unreference (unref) any value you receive.
Collins had to pilot the shuttle through a 360 degree flip while flying beneath the International Space Station. It allowed colleagues on the orbiting lab to photograph the craft's underside and check if the heatshield had been breached.
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Additional reporting by Antoine Schirer, Rafid Hossain and Victoria Arakelyan.
I also expose the number of references the same way,