The main oxygen generator aboard the international space station (ISS) quit operating Sept. 6 and had not been restarted after several days of trouble shooting.

NASA said the two-person crew is in no immediate danger because there are several backup oxygen sources on board, including more than a month’s supply stored inside the Progress resupply ship docked to the station.

The Russian-made Elektron oxygen generator has shut down before, usually due to air bubbles. Engineers in Moscow initially suspected a clogged line was to blame in the latest shutdown, but a potential software glitch became the prime suspect Sept. 10 after ISS Crew Commander Genady Padalka spent the better part of the day rebuilding Elektron and clearing its lines.

NASA spokesman Rob Navias said Padalka was able to restart the oxygen generator after rebuilding the device, only to see it shut down again after about an hour. Navias said the shutdown was prompted by a command from software that controls the device’s gas analyzer.

Russian specialists advised Padalka to leave the device off through the weekend while they analyze the problem, Navias said. “Its possible that a software solution that commands the gas analyzer could solve the problem early next week,” he said.