WASHINGTON — Russia plans to fly two missions of its Soyuz-U rocket, which failed Aug. 24 while attempting to deliver supplies to the international space station, prior to launching a new crew to the orbital outpost atop a similar launch vehicle, a senior NASA official said.

At minimum, the failure will force NASA and Russia’s Roscosmos space agency to operate the space station with a three-person crew, or half its normal complement, between mid-September and mid-November, the U.S. space agency said. But if Roscosmos fails to clear the Soyuz rocket for crew launches prior to mid-November, the orbital outpost will have to be abandoned altogether, if only temporarily, Michael Suffredini, NASA’s space station program manager, said.

Three of the station’s current six crew members are now scheduled to return to Earth Sept. 15, one week later than previously planned, aboard a Soyuz-TMA capsule that has been docked at the outpost for roughly six months, NASA said in a Sept. 1 press release. The extra time was allotted “to extend the presence of six people onboard for as long as possible to try to minimize impacts on scientific research,” NASA spokesman Rob Navias said.

NASA would have preferred to keep a six-person crew aboard the station even longer, Navias said Sept. 2. However, after Sept. 19, it would not be possible to land in the Kazakhstan Steppes during daylight hours. A nighttime landing greatly increases the difficulty of recovering the returning crew members, he said.

The three remaining station crew members will “stay there until their normal landing time on Nov. 16,” Suffredini said during an Aug. 29 briefing from NASA’s Johnson Space Center in Houston. “Our next focus is try and keep the [station] manned until return to flight,” he said.

Russian authorities have traced the Aug. 24 Soyuz-U failure, which was carrying a Progress capsule filled with space station cargo, to a malfunction of the vehicle’s third stage. Experts say the rocket, in particular its third stage, is similar to the Soyuz-FG variant used to launch crew-carrying Soyuz-TMA capsules to the space station.

Immediately following the failure, Roscosmos postponed the launch of a three-person crew aboard the Soyuz-FG/Soyuz-TMA system that had been scheduled for September. With NASA’s space shuttle fleet now retired, that system is the only means of crew access to the space station.

According to reports in the Russian media, Roscosmos has traced the failure to a malfunction of the gas generator in the rocket’s third stage. However, Russia has yet to formally convey findings of its failure investigation to NASA, according to Navias.

“In reality, what the Russians actually said, skewed by foreign reports, is that they believe the most probable failure component is a gas generator component in the third stage,” Navias said. “But they have not yet officially concluded that, nor have they concluded a cause for any such failure. We have not been officially informed of that.”

Russian rockets typically are not grounded for long following failures. For example, Roscosmos on Aug. 30 cleared the Russian Proton rocket for flight less than two weeks after an Aug. 18 failure in which the vehicle’s upper stage malfunctioned, leaving a telecommunications satellite in a useless orbit.

Suffredini said the next scheduled Soyuz-U flight will be a commercial mission. He did not identify the payload but currently there are two commercial Soyuz missions planned for October, one to launch six Globalstar communications satellites from Baikonur Cosmodrome in Kazakhstan and one to launch a pair of European Galileo navigation satellites in the first Soyuz mission from Europe’s Guiana Space Center in Kourou, French Guiana. The launch from Baikonur is of a Soyuz variant that has the same third stage as the vehicle that failed Aug. 24.

The Progress mission, previously scheduled for late October, could now be moved up to mid-October, according to Suffredini.

“That will give you two flights of the third stage that had the problem and, hopefully, convince you that you’ve resolved the anomaly and you’re ready to put humans on a Soyuz,” Suffredini said.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.