The International Space Station actually spun one and a half times last week after the just-docked Russian Nauka module unexpectedly fired its thrusters.
NASA earlier said the sudden and inadvertent rocket burn nudged the ISS 45 degrees out of attitude. Zebulon Scoville, a flight director working at the US space agency’s mission control in Texas at the time of the accident, today said the effects of Nauka’s engines randomly firing were greater than previously reported.
The ISS in fact rotated a total of 540 degrees from the thruster fire, and had to flip another 180 degrees to get back into the correct position, he told the New York Times. The 45-degree angle disclosed by NASA soon after the blunder – which Russia blamed on a software failure in its Nauka module – was what the crew reported as their station was still moving, we’re told. The final number became apparent later.
Scoville – who wasn't even supposed to be working that day, and was overseeing operations for a colleague tied up in meetings – stressed that the space station was not spinning out of control, and that the seven people aboard the orbiting lab were not in danger. A "spacecraft emergency" was declared, however.
“Post-event analysis showed that we experienced an approximate total change of 540 degrees in attitude,” a NASA spokesperson told The Register.
“Both values are still correct – 45 degrees was the total change at that moment in time, 540 was the total determined after the event concluded – there’s just been some interpretation issues over what that 45 represented when it was reported.”
The thrust generated by Nauka’s engines overpowered the four large spinning gyroscopes that ordinarily keep the platform steady, resulting in an undesired change in attitude at a rate of less than a degree a second. Measuring 73 metres long and 109 metres wide, and with a mass of more than 400,000 kilograms, it was a hefty vehicle to shift.
The Nauka had rendezvoused with the ISS on July 29 at 1329 UTC, and about three hours later, at 1634 UTC, its thrusters began randomly firing in an attempt to separate from the station. The ISS then fired its own thrusters, including those on an attached cargo ship, to compensate for Nauka’s thrust and ultimately correct its position.
“Yeehaw! That. Was. A. Day,” Scoville tweeted after the debacle, which lasted about an hour. Nauka was sent commands by its controllers to not only shut off its engines but also to ensure they wouldn't unexpectedly fire again.
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“The maximum rate at which the attitude change occurred was approximately half a degree a second – well within the design limits of station systems and slow enough to go unnoticed by the crew members on board,” NASA's spokesperson added. “All preliminary analysis shows that the station remains in good shape.”
The accident delayed Boeing’s uncrewed test launch of its Starliner spacecraft, a vehicle the aerospace biz hopes will one day compete with SpaceX’s Crew Dragon capsule to take astronauts to the ISS and back. It was planned to fly on Friday, July 30, and then pushed back to today, August 3.
That test flight, dubbed the Orbital Flight Test-2 mission, has been stalled again. It was scrubbed “due to unexpected valve position indications in the Starliner propulsion system,” according to NASA. The space agency hopes to try again on August 4 at 1657 UTC. ®