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.

Based on the paragraph above can we conclude that "U.S. astronauts remain attached to the space shuttle during spacewalks. "?