Columbia returned to the Kennedy Space Center piggyback on NASA's 747 after its "60 Million mile checkup" in March 2001 and STS-107 was supposed to be its next mission. However NASA managers decided to give the STS-109 Hubble servicing mission priority over STS-107 and pushed it ahead.
STS-109 launched on March 1, 2002. The crew made five spacewalks to add a new advanced camera and make improvements to the Hubble Space Telescope.The shuttle has two independent Freon loops that are used for cooling, similar to the Freon loops in an air conditioner. Every piece of electrical equipment on the shuttle, many chemical reactions, and even the crew generates heat. The Freon loops are used to maintain proper temperatures for the equipment and a comfortable crew cabin temperature for the astronauts. If one loop doesn't work the shuttle can still safely return to Earth. The flow in the primary loop dropped from 305 pounds per hour to 225 pounds per hour after Columbia arrived on orbit. Fortunately the leak didn't get worse and the rest of the mission was accomplished as planned.
The STS-109 mission ended with a landing March 12. Nobody knew that that would be Columbia's final successful mission.
After the STS-109 mission the cooling lines were X-rayed to determine the clog's location. The clog was caused by material which had somehow been left behind when the lines were upgraded in the early 1980s. The piece of brazing material had flown on over a dozen missions until it was dislodged during STS-109’s launch where it fluttered in front of the orifice causing the reduced Freon flow. The Freon was removed from the lines and recycled, the piece of metal which caused the clog was removed and the system was repressurized.
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Columbia was ready to leave its hangar on June 24th but put on hold when tiny cracks were discovered on the 'flowliners' of Atlantis and Discovery. The flowliners act like baffles to keep the propellants flowing smoothly through the shuttle's plumbing on its way to the main engines. Because of the flowliner cracks NASA decided to delay STS-107 until after STS-112 and STS-113.
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Columbia's rollover from the OPF to VAB |
Columbia enters the VAB |
Columbia's rollout as seen from inside the Launch Control Center |
Columbia arrives at launch pad 39A |
Columbia on its launch platform |
One other issue was a potential delay to Columbia's launch. Each of the propulsion lines has several "Ball Strut Tie-rod Assemblies" (BSTRAs). The BSTRAs are ball-and-socket joints which give the propulsion lines some flexibility as they vibrate back and forth during launch. Cracks were discovered on Discovery's BSTRAs and NASA went through several weeks of analysis before concluding that it was okay to fly as is, without inspecting Columbia's BSTRAs.
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