Shuttle Columbia was plagued by more than a few gremlins as workers prepared her for launch of a Spacelab on the STS-83 mission.
The April 3, 1997 launch was delayed a day because additional thermal insulation was needed on a payload bay coolant line. Then, on April 4, the liftoff was delayed for about 20 minutes more when the Orbiter’s crew access hatch wouldn’t seal properly, prompting a replacement seal.
Columbia finally lifted off to begin a planned 15-day mission with the Microgravity Science Laboratory 1.
But NASA hadn’t flushed out the most troublesome and very dangerous demon within Columbia.
Space Shuttle electrical power was supplied by fuel cells. A technology first used on later Gemini missions and all Apollo flights, the fuel cell takes in hydrogen and oxygen, combining it to form electricity with water as a by-product: reverse hydrolysis.
Compared to their Apollo versions, the three fuel cells on Orbiters were comparably slim. These powerhouses also didn’t suffer from the limitations of their lunar-bound kin, with many safeguards and maintenance modes to keep the devices hale and hardy.
The most common task maintaining for the health of the fuel cell was purging. Completed twice daily, usually automatically by computer control, a purge pushes the hydrogen and oxygen reactants at slightly higher pressures through the cell’s three substacks, where energy is generated, to push out contaminants or other gases in order to keep the overall efficiency of the cell’s electricity generation at its peak.
But for STS-83, one of the three substacks in fuel cell #2 began to make too much voltage, suggesting a serious imbalance. That same cell was also plagued by a potential gremlin during the pre-launch checkout, but was eventually cleared to fly.
Despite repeated purge attempts, the fuel cell would not behave as it should.
Fuel cells are the closest our modern spacecraft have to the “matter/antimatter” power concepts in the Star Trek universe. To stretch the analogy further, fuel cells must stay within a certain balance of pH as well as reactants and temperature. If the balance is thrown off too wildly, with reactants mixing poorly and for too long, a fuel cell could explode, seriously damaging or even crippling an Orbiter.
This wasn’t new territory. STS-2, the second Shuttle flight, had a fuel cell that also had a substack that was breaking down much more dangerously than on STS-83, mixing hydrogen and oxygen. Quick moves by the flight controllers and flight directors shut down that cell as well, and STS-2 was the first of three Shuttle flights to end early.
STS-83 would become another mission with a early conclusion.
The mission management team eventually commanded that the misbehaving fuel cell be shut down as a precaution. This also caused a mission-end known as a “minimal duration flight”: Flight rules require all three fuel cells be operational on any Shuttle mission or it’s time to come home. One fuel cell alone can easily power an Orbiter. However, if a second one failed, all hopes would hang on a single working fuel cell during re-entry and landing, a scenario NASA refused to allow.
So with only two days in space, a dejected STS-83 crew returned home.
But STS-83 would not stay home.
Taking advantage of Columbia’s relative freshness from a shortened mission, NASA was able to repair and refurbish her in far less time than a typical mission.
Three months later, the crew changed the mission number and few colors on their old mission patch, and STS-83 returned to Columbia to fly as STS-94, again with the MSL-1 Spacelab.