Russian spacecraft docks at ISS

The Soyuz TMA-12M spacecraft finally docked with the ISS on Thursday, two days after a maneuvering thruster had failed to kick into gear as planned, forcing the capsule to orbit the Earth until the next docking opportunity.

The arrival of Russian cosmonauts Alexander Skvortsov and Oleg Artemyev and NASA astronaut Steven Swanson (pictured above) brings the ISS to its full capacity of six people. They replaced three crewmen who returned to Earth this month.

The three-man crew relief had blasted off from the Baikonur Cosmodrome in Kazakhstan on Tuesday, and they were supposed to reach the ISS six hours later. But two hours after launch, the Soyuz capsule failed to fire one of its thrusters.

The spacecraft had to orbit the Earth 34 times until it could finally dock with the ISS. According to NASA, the Soyuz capsule was “unable to complete its third thruster burn to fine tune its approach” to the space station.

Mathematical problem?

It's unclear what caused the thruster to fail. But the head of the Russian state rocket firm Energia, which supplies the Soyuz's thrusters, said that a mathematical miscalculation was probably responsible for the mishap.

"It could be mathematics, it could be a transmitter problem or that the engine choked," said Vitaly Lopota on Wednesday, according to the Interfax news agency. "But most likely it was a mathematical problem."

NASA mission commentator Rob Navias said that the cause of the thruster failure was still under investigation. But preliminary analysis indicated that the spacecraft was one degree out of alignment with its planned course, he said. That could have caused the Soyuz's computers to automatically abort the thruster burn.

slk/av (AFP, Reuters)