A decision to bring Wilmore and Williams home early aboard the Crew 9 ship ahead of Crew 10’s arrival would have left NASA astronaut Don Pettit, who flew to the ISS with a Russian crew last September, as the only American aboard the station, a rare staffing imbalance that NASA has said complicates maintenance of the station’s U.S. components.

The astronauts who crewed the Boeing Starliner will have to wait a few more days until making their homecoming after the SpaceX Crew-10 launch scrub.