Reflective spheres observed floating near spacecraft during cryogenic venting

During flight over multiple days·In orbit during GT-5 mission·NASA·identified

The astronauts observed floating spheres of vented cryogenic material (liquid oxygen and hydrogen) that would drift past the spacecraft under certain lighting conditions, visible as silver balls when vented at low sun angles during sunrise or sunset.

“We could see liquid oxygen when we vented it, if we vented it under the right light conditions. We could see when we vented hydrogen under the right lighting conditions. It would all float by the space craft and at low sun angles, either at sunup or sundown any one of these quantities, ECS o2, CRYO o2, or RSF hydrogen, you could see it come whistling by the space craft. We were continually floating around in these old silver balls of either hydrogen or oxygen.”
Verbatim from NASA-UAP-D020.pdf · View original on war.gov

Case details

Date: During flight over multiple days
Date exactness: Not exact
Location: In orbit during GT-5 mission
Branch: NASA
Unit: Spacecraft Operations Branch, Flight Crew Support Division
Sensors: eyewitness
Shape: Spheres or balls

Resolution

Identified as cryogenic propellant (liquid oxygen or hydrogen) vented from Environmental Control System (ECS) or cryogenic tanks, visible under low-angle lighting conditions