Former Space Shuttle Program Manager Wayne Hale has posted a correction to NASA's history of STS-109, which he claims "is a lie" - although that may be a slight exaggeration.

STS-109, launched in 2002, was the last mission of Columbia before the STS-107 disaster. During the mission, the crew conducted a series of five spacewalks to service the Hubble Space Telescope.

It was a huge success. Hubble received new solar arrays and a replacement for the original power control unit, among other upgrades. However, it is the final paragraph of the history with which Hale took issue.

NASA's summary reads: "After a successful launch, flight controllers in Mission Control noticed a degraded flow rate in one of two Freon cooling loops that help to dissipate heat from the orbiter. After reviewing the loop's performance, mission managers gave the crew a 'go' to proceed with normal operations. The problem had no impact on any of the crew's activities. Both cooling loops performed normally on de-orbit and landing."

According to Hale, it wasn't quite as simple as that. The Space Shuttle had two Freon Coolant Loops (FCLs). These were critical pieces of equipment responsible for cooling the orbiter's electronics. Losing one would require landing the orbiter at the next available opportunity. Losing two would trigger a full emergency since temperatures would breach the specification operational limits of the Fuel Cells after 50 minutes, and keeping the fuel cells going after 75 minutes would be "questionable."

The Space Shuttle relies on electricity. No fuel cells, no electricity.

During the program, the Space Shuttle never lost both FCLs. Had it done so, the crew would have had to power down much of the electrical equipment on the orbiter before conducting an emergency landing. "The checklist was extremely complex, time consuming, and - worst of all - attempts to validate it were unsuccessful," Hale said.

As such, the probability of losing both vehicle and crew was high.

Before the orbiter was given a "go for orbit ops" (after the payload doors were opened and Freon loop cooling through the radiator was established, but before the crew could get out of their launch/entry pressure suits and switch on the toilet), the EECOM (Environmental Electrical, Consumables Manager) spoke up.

"The flowmeter in Freon Coolant Loop #1 was showing a flow of only 200 lbs/hour."

According to the Flight Rules, failure was anything less than 211 lbs/hour. Therefore, the loop should be considered failed, and the Space Shuttle should return to Earth.

As well as a First Day PLS (Planned Landing) at Edwards Air Force Base, which required everything to be in place for a retrofire in approximately 90 minutes, the rules meant the crew should also get cracking on the procedures for losing one FCL, and switch off much of the Space Shuttle's redundant electrical equipment. That, of course, would leave the vehicle open to other risks.

So what to do? Normally, the Mission Management Team (MMT) would be consulted as the MMT was the only element able to authorize a change to the Flight Rules. But the MMT was not there. With the launch complete, at least as far as Main Engine Cut Off (MECO), the MMT had departed for flights back to their various NASA centers and could not be easily contacted.

The team considered the problem. The crew was instructed to review the procedures but not do anything yet. The question was a simple one - had it failed or not? If the good FCL also failed, would the "failed" FCL provide enough cooling to avoid the dreaded two-FCL failure scenario?

In the end, the NASA team decided to continue with the mission. The MMT was advised and an awful lot of engineering analysis took place.

Hale observed: "FCL #1 never regained full flow during flight. So much for 'Both cooling loops performed normally on de-orbit and landing.'"

That said, the Flight Rules were revised after the mission. After the engineering analysis had been completed and reviewed, the new failure limit was reduced to 163 lbs/hour. Much later, the rules were changed to require the MMT to stay on station until after the "go for orbit ops" was given.

However, there is no getting around the fact that even though the decision turned out to be correct, a Flight Rule was broken by humans.

According to Hale, John Shannon was the Ascent Flight Director for the mission. Hale quoted a recent comment from Shannon: "This would be a good case for why you have a flight control team instead of just programming the flight rules into a computer.

"Human judgment and risk trades are critical to spaceflight operations." ®

https://www.theregister.com//2024/04/26/sts_109_shuttle_mission/