How the International Space Station lost control

The International Space Station overturned on the back on July 29.

It was a significant, but thankfully not catastrophic, episode lasting nearly an hour for humanity’s largest and oldest space outpost. The station slowly turned one and a half times. (Or as NASA describes it, the space station experienced a “total attitude change” of about 540 degrees, “attitude” being the lingo for the orientation of a spacecraft.) The new Russian module “Nauka “docked at the important 356-foot-long station, but Nauka’s thrusters fired when they shouldn’t have, causing the space station to start spinning unexpectedly.

“It was quite an event,” said Keith Crisman, assistant professor of space studies at the University of North Dakota, who studies security systems for human spaceflight. “It was a potentially serious problem,” Crisman added, noting that an uncontrollable spacecraft is one of the riskiest events in space.

Later on July 29, after flight engineers straightened the space station, NASA held a press conference to address the unusual event. The agency’s summary: All is well, the space station was back to normal, and no one on board was in danger. In fact, a NASA public affairs official said in an email that the station’s rotation was “slow enough to go unnoticed by crew members on board” (until they received messages warning), and everything else was working normally.

While it is fortunate that the astronauts and cosmonauts on board are doing well, the event still raises questions about what happened, as well as future concerns about the safety of the space station.

“When a spaceship misfires, it’s a serious thing.”

“When a spacecraft misfires, it’s a serious thing,” said Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who tracks rocket and spacecraft launches. “I can’t imagine that there aren’t some very serious conversations at NASA.”

What went wrong

As noted above, the thrusters on Nauka began firing after the module docked with the space station, forcing the station to spin (slowly) to a maximum of half a degree per second. He ended up backwards, before the correction. On spacecraft, these types of misfires sometimes happen, and more easily than engineers would like, explained Kurt Anderson, professor of aerospace mechanical engineering at Rensselaer Polytechnic Institute.

In 2016, for example, a thruster from the 46-foot Japanese astronomy satellite Hitomi failed. Hitomi spun uncontrollably and parted. And perhaps most famous, the tiny Gemini VIII spacecraft (piloted by legendary astronaut Neil Armstrong in 1966) got violently out of control after a thruster issue, but Armstrong impressively halted the savage fall and narrowly avoided. national tragedy.

(The space station, thankfully, is a large object weighing over 925,000 pounds with a lot of gear to spin, so Nauka’s thrusters haven’t had a chance to spin the station treacherously.)

Life on the space station in 2020.
Credit: NASA

But what triggered Nauka’s accident? A software problem probably played a role. Nauka encountered some minor software glitches before arriving at the space station, Crisman noted. The day after the unexpected turnaround, Russian space agency Roscosmos officially blamed the event on a software glitch, causing the thrusters to fire and attempting to remove Nauka, which had just docked several hours earlier. That’s all we currently know, which comes from a four paragraph press release from Roscosmos.

After the thrusters began to misfire, the space station quickly entered an official “loss of attitude check”, the NASA representative told Mashable. The blast thrusters were countered by other space station thrusters firing in the opposite direction to regain the station’s normal orientation, NASA said. The station had to turn completely – 180 degrees – to straighten out.

Real worries

With the excitement of the space station comes notable concerns, according to experts outside of NASA.

1. The space station is old and not intended for acrobatics. People first inhabited the station over two decades ago. “The ISS is older equipment. We call it legacy equipment,” Crisman said.

It is not a brisk vehicle meant to overturn, although the overturn in this case was not nearly violent. However, the station has seen thrusters fighting against each other for control of the craft, McDowell noted, which is undoubtedly somewhat of a pain for a spacecraft with attached instruments, such as huge panels. solar leaves from the station. “You have torque on relatively old pieces,” Crisman explained.

2. Valuable wasted fuel: Stopping the station rollover required firing thruster from thrusters, which is problematic as the thruster in space is limited and sometimes necessary to maneuver the space station. There is no other way to deliberately move.

“The propellant is blood.”

“The propellant is blood,” Anderson said. Unlike most spacecraft, however, NASA can launch more thruster at the space station, but at a cost.

3. Failed thrusters could not be immediately disabled. To prevent the station from spinning, ground control operators in Russia had to tell the automated Nauka to stop firing. But it didn’t work, requiring counter-thrust. “The fact that they couldn’t shut down the thrusters immediately bothers me,” said aerospace engineer Anderson.

4. Things could have been worsewell, much worse.

Any incident on the space station has the advantage of happening under the watchful eye of the NASA Space Station team in Houston. “They have a really great flight control team,” said McDowell of the Center for Astrophysics.

NASA flight controllers, like flight director Zebulon Scoville, immediately noticed the station’s unexpected behavior and quickly declared a “space emergency.”

Still, there should never have been an emergency, Crisman stressed. Yes, errors are inevitable, but the system should not allow such a problem to turn into a potentially serious active problem. “We should have systems in place to mitigate these errors,” he said.

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Basically, these systems should follow the “Swiss cheese model,” Crisman explained. Different layers of naturally imperfect departments (or layers of Swiss cheese) like mission control, computer programmers, engineers building spaceships, etc. should make it extremely difficult for a mistake to find its way through the small holes in the swiss slice of each department. In the case of the space station flip, a mistake crept into many, many layers of international Swiss cheese.

“Humans are perfectly fallible and machines are perfectly fallible.”

Typically, the space station is a quiet place, in a quiet orbit some 250 miles above Earth. It’s an afterthought for many of us. But things can go wrong. It is extremely lucky, for example, that Nauka did not start to misfire while docking, which could result in an impact with the space station.

This recent turnaround was not terrible, but it is a poignant warning of our vulnerabilities in the harsh realm of space, even on the reliable space station.

“Space is dangerous,” Crisman said. “Humans are perfectly fallible and machines are perfectly fallible.”



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