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The International Space Station, with a mass of over 900,000 pounds and spanning an area as large as a football field, is not designed to do back flips like an Olympic gymnast.
But when a newly attached Russian compartment suddenly tripped its thrusters on Thursday, NASA said on twitter that the station has tilted 45 degrees. In fact, it was way over 45 degrees.
“It was a little misreported,” said Zebulon Scoville, the flight director who was in charge of NASA’s mission control center in Houston during Thursday’s tumble incident.
In an interview, Scoville described how the International Space Station made a turn and a half – about 540 degrees – before stopping upside down. The space station then flipped forward 180 degrees to return to its original orientation.
The seven astronauts on board were never in danger, Mr Scoville said, and the situation did not escalate. Yet in seven years as a NASA flight director, this was the first time Mr. Scoville had declared a “spaceship emergency.”
Mr. Scoville was not even scheduled to work Thursday. Another flight director, Gregory Whitney, led operations on the NASA side while docking the 23-ton Russian module named Nauka – “science” in Russian.
But Mr. Scoville had already led the preparations for Nauka’s arrival, and he was curious. “So I decided to put on a tie and just go and watch it from the observation gallery behind the control room,” he said. “And I was there with Holly Ridings, who is the chief flight director, and Reid Wiseman, the chief of the astronaut office.”
After docking, Mr. Whitney was scheduled to attend a few meetings, so Ms. Ridings asked Mr. Scoville to take over the second half of Mr. Whitney’s shift. “And I’m like, ‘I’d be happy to do that. The mooring – the difficult part – is over. Let me go get a discount from it, ”Mr. Scoville said. “And so impromptu, I walked in and took it over from him. He unplugged, I plugged in and turned around, and the warning sign came on.
It was 11:34 a.m. Houston time.
“We got two messages – just two lines of code – saying something was wrong,” Mr. Scoville said.
The messages indicated that the space station had lost “attitude control”, meaning that it had started to tip over. Usually four large, heavy gyroscopes spinning at 6000 rpm keep the space station stable, but some force seemed to overpower them.
“And at first I was like, ‘Oh, is that a false indication?'” Mr Scoville said. “And then I looked at the video monitors and saw all the ice and rocket fire. This is not a joke. A real event. So let’s go. You get about a half-breath of “Oh, dammit, what now?” And then you push that down and you solve the problem. “
Nauka’s thrusters had started firing, trying to pull away from a space station he was securely docked to.
Worse, there was no way to turn them off.
His counterparts at mission control in Russia told him that Nauka was configured so that he could only receive commands directly from a ground station in Russia. The next pass over Russia was 70 minutes away.
The new Russian module is docked under the space station. When Nauka tried to move, he pulled the rear of the space station down and the front tilted up. “It’s just like doing a back flip,” said Scoville.
The spin rate peaked at 0.56 degrees per second, said Scoville. This rotation is not fast enough to generate significant artificial gravity – he said astronauts reported almost no noticeable change in conditions within the station.
However, a rotating space station places stress on the structure and the antennas no longer point where they are supposed to. Mission controllers quickly briefed the astronauts on what was going on and gave them instructions.
“We knew we had limited time,” said Scoville.
A spacecraft’s declaration of emergency activated additional antennas in the United States that could communicate with the space station. But again, the connection between ground and space was lost twice, once for four minutes, the other time for seven minutes.
The ground controls have stowed and locked the station’s solar panels. The astronauts were careful to lock the radiators, which emit heat from the station into space.
Although the Russian controllers had no way of regaining control of Nauka, they could activate thrusters on other parts of the space station.
Then the crew fired the thrusters at another Russian module, Zvezda, to counter those of Nauka. When it emerged that this might not be enough to stop the spinning, the thrusters of a docked Russian Progress cargo spacecraft also sank.
After about 15 minutes, Nauka’s thrusters extinguished. Mr Scoville said he did not know why, although reports indicated that the module had depleted its thruster. Mission controllers could then more easily shut down the station. “After doing that jump back one and a half times it stopped and then came back the other way,” said Scoville.
An hour had passed; everything was back to normal. Mission controllers told the astronauts to take the rest of the day and relax. Mr Scoville said the training exercises had prepared them well for what to do when the space station tipped over.
“The intensity is probably going up a bit,” he said, “but there’s a kind of calm all over the place in people who don’t panic and just look at the data, figure out what’s going on and do it. ‘try to solve the problem from there. “
A statement issued Friday by Roscosmos, the Russian space agency, said there was a software problem on Nauka, and that as a result, “a direct command has been given to fire the engines from the module.”
Preliminary analysis indicates that the space station remains in good condition.
Despite the incident and the friction between NASA and Russia over the future of the International Space Station, Scoville said he had no doubts about the station’s operations.
“I have complete confidence in the Russians,” he said. “They are a fantastic partnership with NASA and the entire International Space Station program.”
At the end of his unscheduled shift on Thursday, Mr Scoville let out an exclamation of relief on Twitter.
Oleg Matsnev contributed reporting.
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