An uncrewed Russian Soyuz spacecraft was forced to abort an attempted docking at the International Space Station early Saturday (Aug. 24) due to rendezvous system malfunction.

The Roscosmos Soyuz MS-14 spacecraft, which is carrying supplies and a humanoid robot called Skybot F-850, was on its final approach to the space station when its automated docking system failed to lock on to its intended docking port: a space-facing module called Poisk. Cosmonaut Alexey Ovchinin, the station's commander, triggered an abort command for the Soyuz at 1:36 a.m. EDT (0536 GMT) after multiple attempts to make the rendezvous with primary and backup systems failed.

"At no point was the crew in any danger," NASA spokesperson Rob Navias said of the station's six-person Expedition 60 crew during live commentary.

The Soyuz is now trailing the space station at a safe distance away in a so-called "race track orbit" that can allow additional docking attempts every 24 hours, Navias said. The next attempt will occur no earlier than overnight Sunday or early Monday (Aug. 25-26).

Infographic: How Russia's Soyuz Space Capsules Work

Image 1 of 7 The Russian Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 is seen during final approach to the International Space Station on Aug. 24, 2019. The Soyuz's docking was aborted due to a problem with its Kurs rendezvous system. (Image credit: NASA TV) Image 2 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV) Image 3 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV) Image 4 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV) Image 5 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV) Image 6 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV) Image 7 of 7 An uncrewed Soyuz MS-14 spacecraft carrying the humanoid robot Skybot F-850 and supplies approaches the International Space Station during an aborted docking attempt on Aug. 24, 2019. (Image credit: NASA TV)

Docking abort

Roscosmos flight controllers suspect that a bad signal amplifier on the station's Kurs rendezvous system may have led to the docking abort. They've asked Ovchinin and his fellow cosmonaut Alexander Skvortsov to replace the amplifier in the hopes that solves the problem.

While the Soyuz abort posed no danger to the station's crew, NASA flight controllers did make sure that the outpost's U.S. crewmembers were alert and monitoring the situation.

"We just wanted to let you know that the Kurs is having difficulty locking onto the target and we wanted to make sure that you were awake," Mission Control radioed the astronauts from NASA's Johnson Space Center in Houston.

Soyuz MS-14 is carrying about 1,450 lbs. (660 kilograms) of supplies for the station's crew and a robotic crewmember: Skybot F-850. The humanoid FEDOR-type robot will be used for experiments on the station and returned to Earth once the Soyuz MS-14 mission is complete.

Video: Watch the Soyuz Docking Abort as It Happened

A Soyuz test flight

The dramatic docking abort came after a flawless two-day flight of the Soyuz following a smooth launch from Baikonur Cosmodrome in Kazakhstan earlier this week. This is a rare uncrewed test flight of the Soyuz MS-14, which launched on a Soyuz 2.1a rocket typically used to carry robotic Progress cargo ships to the space station.

The test flight is aimed at verifying that Soyuz capsules can fly safely on the Soyuz 2.1a vehicle ahead of the first crewed flight on the booster in March 2020. Russian engineers equipped the Skybot F-850 robot with sensors to record conditions on the Soyuz during liftoff see what future human crews will experience.

Russia's Soyuz and Progress vehicles are designed to dock themselves at the International Space Station using an automated rendezvous system called Kurs. If that system fails on an uncrewed Progress spacecraft, cosmonauts on the station can take remote control of the freighter using a system called TORU to pilot the ship in manually.

Since Soyuz spacecraft are designed to carry human crewmembers, they do not carry a TORU system. If a Kurs system fails on a Soyuz, the capsule's cosmonaut commander can take control of the spacecraft and perform a docking manually.

But because Soyuz MS-14 launched on an uncrewed test flight, it does not have a TORU system aboard for cosmonauts to use. That was by design, since the station cosmonauts could always command it to abort if something went awry, just as they did during Saturday's docking attempt.

Still, it did sound as if some on the station lamented not being able to take remote control of Soyuz MS-14 during the abort.

"It's such a shame that we were not able to use TORU," one of the cosmonauts radioed Mission Control in Russian at one point. "We could have grabbed it to bring it in."

Email Tariq Malik at tmalik@space.com or follow him @tariqjmalik. Follow us @Spacedotcom and Facebook.