Premise: On February 1, 1990, during a spacewalk, Alexander Serebrov dons an experimental flying armchair that had been delivered to Mir with Kvant 2. Unlike U.S. astronauts, who flew untethered flights with a similar device, the Soviet cosmonaut remains attached to the station with a safety tether, since there is no space shuttle to pick him up in case of an emergency.
Hypothesis: U.S. astronauts remain attached to the space shuttle during spacewalks.