Why did the Mir space station need someone to look after it at all times?

Question

"But Krikalev and the other cosmonaut on board quickly decided that, for them, the option was off the table. The two had been trained for years about the intricacies of the space station, and they knew that leaving it would mean that there would be no one to look after the Mir."

https://www.tiebreaker.com/soviet-astronaut-stuck-alone-space-300-days/4/

"In fact, he could have left. There was a Raduga re-entry capsule onboard the Mir, which was designed specifically for making the return to Earth. But taking it would have meant the end of Mir since there was no one else left to look after it."

https://www.rbth.com/history/330415-last-soviet-citizen-cosmonaut

Thats also kind of true for the ISS, they do more maintenance than science up there. — Polygnome, Apr 24 '21 at 08:12
Not really an answer, but the simplest explanation is: because it was designed that way. Slightly more expanded version: because it was not designed to be autonomous or robotic. — Jörg W Mittag, Apr 25 '21 at 13:52
@JörgWMittag I can confirm that it is not an answer. Do you know why it could not be left empty and returned to years later? — Matthew Christopher Bartsh, Apr 25 '21 at 13:58

score 7 · Answer 1 · edited Apr 25 '21 at 05:58

Late in its life, Mir suffered significant failures, a lot.

Designed for only a five-year life, the aging Mir suffered a series of equipment failures and accidents in 1996–97 but remained in service.

(Britannica)

Around the STS-86 time frame, Mir was prone to failures of its attitude control computer.

This made Mir start to rotate and the solar panels lose tracking. Then a massive powerdown was done to keep it from totally losing battery power until the panels could be manually pointed at the sun to charge the batteries. A slow manual recovery process ensued.

a sensor in the Spektr module failed, prompting the motion control computer to switch to a backup system. During the three-minute swap-over, all attitude control was lost. The crew placed the station in what called "free drift" and then used onboard thruster jets to stabilize its attitude. For most of that day, Mir remained in a "gravity gradient," which basically means that the most massive part of Mir naturally pointed toward Earth. Because this attitude did not keep tile solar arrays pointed at the Sun, the crew turned off the gyrodynes and Other equipment to conserve power. Late in the day, flight controllers uplinked a new attitude maneuver to the motion control system computer, and the crew restarted the gyrodvnes. The station's primary attitude sensor, called Omega, was still inoperable; so control was managed by a backup unit until the crew installed a spare Omega sensor and rerouted cables.

Official NASA Shuttle/Mir History

See also When Mir's attitude control computer failed, why did the station immediately start rotating?

This was happening so much that right before STS-86 launched they had special simulator sessions with the crew and flight control team to see how fast a loss-of-control Mir could be tumbling and still allow the shuttle to dock.

Since the Mir space station had been having trouble—losing attitude control and drifting into slow tumble—the STS-86 crew had trained until almost the last minute, practicing simulations of various docking situations. The crew was also bringing to Mir a new attitude control computer.

(official history)

Another time

On November 13, Mir suffered a temporary power loss during a test of the newly installed solar array on Kvant- I . This caused the shutdown of the motion control system computer and interrupted Wolf's scientific investigations. The crew transferred fully charged batteries from the Kristall module to the Base Block, and they restored power to five of the II gyrodynes that provided attitude control to Mir. However, the batteries alone could not support the many hours required to stabilize the station. So throughout the week- end, the three crewmates alternated shifts to monitor systems; and whenever Mir drifted into an attitude favorable for solar energy collection, they temporarily powered up the battery chargers.

(official history)

So while it's not necessarily true that leaving Mir uncrewed would have meant the end, it would have increased the chances of losing it a lot. (There were other problems too, not just the attitude control system. That's just one I'm most familiar with. The Burrough's book Dragonfly is a great history of this period.)

What do you mean by 'losing it' and how would the chances of that happening be increased by leaving Mir uncrewed? — Matthew Christopher Bartsh, Apr 25 '21 at 04:14

score 4 · Answer 2 · answered Apr 25 '21 at 08:33

Because previous Soviet experience (and Krikalev's personal experience) with uncrewed space stations did not go well.

Of the 9 Soviet space stations prior to Mir, only 5 were intentionally terminated: Salyut 1 (after the deaths of the 3 Soyuz 11 comsmonauts), Salyut 3, Salyut 4, Salyut 5, and Salyut 6. Two more stations (DOS-2 and Kosmos 557) failed to reach orbit.

After Salyut 2 reached orbit, its launch vehicle's spent third stage exploded. The cloud of debris eventually reached the station and damaged the hull and solar panels. The station lost attitude control and depressurized. Had the station been crewed, they may have been able to change the orbit so it would not be struck by the debris.

The final space station before Mir -- Salyut 7 -- had a dramatic history. In between crewed missions, the station lost electrical power, sending the station tumbling out of control. A two-person team of experienced cosmonauts (Soyuz T-13) were sent up to rescue the station. They found that the station was rotating erratically. Because the station was "dead", they could not use the normal docking radar, and instead relied on a handheld laser rangefinder to determine their distance to the station.

T-13 was eventually able to dock with the station, and they worked on getting the systems back on-line. The air was still breathable, although cold; frost covered the station's walls. The batteries were dead and were replaced. The electrical failure was traced to a faulty sensor which was supposed to keep the solar panels facing the sun. The station's water heater had burst due to the expansion of freezing water; this caused enormous amounts of condensation inside the station. After getting the attitude control system back on-line, they were able to send additional supplies in a Progress supply ship. It took almost 2 months to get the station back to working order.

It's worth mentioning that the cosmonaut cited in the question (Sergei Krikalev) was part of the support team in the rescue of Salyut 7:

When the Salyut 7 space station failed in 1985, he worked on the rescue mission team, developing procedures for docking with the uncontrolled station and repairing the station's on-board system.

So he knew first-hand the risks of leaving a space station uncrewed.

Why did the Mir space station need someone to look after it at all times?

2 Answers2