To put the decisions made during the flight of STS-107 into perspective, the Board asked NASA to determine if there were options for the safe return of the STS-107 crew. In this study, NASA was to assume that the extent of damage to the leading edge of the left wing was determined by national imaging assets or by a spacewalk. NASA was then asked to evaluate the possibility of:

1. Rescuing the STS-107 crew by launching Atlantis. Atlantis would be hurried to the pad, launched, rendez-vous with Columbia, and take on Columbia's crew for a return. It was assumed that NASA would be willing to expose Atlantis and its crew to the same possibil-ity of External Tank bipod foam loss that damaged Columbia.

2. Repairing damage to Columbia's wing on orbit. In the repair scenario, astronauts would use onboard materi-als to rig a temporary fix. Some of Columbia's cargo might be jettisoned and a different re-entry profile would be flown to lessen heating on the left wing lead-ing edge. The crew would be prepared to bail out if the wing structure was predicted to fail on landing.

In its study of these two options, NASA assumed the following timeline. Following the debris strike discovery on Flight Day Two, Mission Managers requested imagery by Flight Day Three. That imagery was inconclusive, leading to a decision on Flight Day Four to perform a spacewalk on Flight Day Five. That spacewalk revealed potentially catastrophic damage. The crew was directed to begin conserving con-sumables, such as oxygen and water, and Shuttle managers began around-the-clock processing of Atlantis to prepare it for launch. Shuttle managers pursued both the rescue and the repair options from Flight Day Six to Flight Day 26, and on that day (February 10) decided which one to abandon.

The NASA team deemed this timeline realistic for several reasons. First, the team determined that a spacewalk to inspect the left wing could be easily accomplished. The team then assessed how the crew could limit its use of con-sumables to determine how long Columbia could stay in orbit. The limiting consumable was the lithium hydroxide canisters, which scrub from the cabin atmosphere the carbon dioxide the crew exhales. After consulting with flight surgeons, the team concluded that by modifying crew activity and sleep time carbon dioxide could be kept to acceptable levels until Flight Day 30 (the morning of February 15). All other consumables would last longer. Oxygen, the next most critical, would require the crew to return on Flight Day 31.

Figure 6.4-1. The speculative repair option would have sent astro-nauts hanging over the payload bay door to reach the left wing RCC panels using a ladder scavenged from the crew module. Credit: CAIB

Repairing Damage On Orbit

The repair option (see Figure 6.4-1), while logistically vi-able using existing materials onboard Columbia, relied on so many uncertainties that NASA rated this option "high risk." To complete a repair, the crew would perform a spacewalk to fill an assumed 6-inch hole in an RCC panel with heavy met-al tools, small pieces of titanium, or other metal scavenged from the crew cabin. These heavy metals, which would help protect the wing structure, would be held in place during re-entry by a water-filled bag that had turned into ice in the cold of space. The ice and metal would help restore wing leading edge geometry, preventing a turbulent airflow over the wing and therefore keeping heating and burn-through levels low enough for the crew to survive re-entry and bail out before landing. Because the NASA team could not verify that the repairs would survive even a modified re-entry, the rescue option had a considerably higher chance of bringing Columbia's crew back alive.

Rescuing the STS-107 Crew with Atlantis

Accelerating the processing of Atlantis for early launch and rendezvous with Columbia was by far the most complex task in the rescue scenario. On Columbia's Flight Day Four, Atlantis was in the Orbiter Processing Facility at Kennedy Space Center with its main engines installed and only 41 days from its scheduled March 1 launch. The Solid Rocket Boosters were already mated with the External Tank in the Vehicle Assembly Building. By working three around-the-clock shifts seven days a week, Atlantis could be readied for launch, with no necessary testing skipped, by February 10. If launch processing and countdown proceeded smoothly, this would provide a five-day window, from February 10 to February 15, in which Atlantis could rendezvous with Columbia before Columbia's consumables ran out. Accord-ing to records, the weather on these days allowed a launch. Atlantis would be launched with a crew of four: a commander, pilot, and two astronauts trained for spacewalks. In January, seven commanders, seven pilots, and nine spacewalk-trained astronauts were available. During the rendezvous on Atlantis's first day in orbit, the two Orbiters would maneuver to face each other with their payload bay doors open (see Figure 6.4-2).

Figure 6.4-2. The rescue option had Atlantis (lower vehicle) rendezvousing with Columbia and the STS-107 crew transferring via ropes. Note that the payload bay of Atlantis is empty except for the external airlock/docking adapter. Credit: CAIB

Suited Columbia crew members would then be transferred to Atlantis via spacewalks. Atlantis would return with four crew members on the flight deck and seven in the mid-deck. Mission Control would then configure Co-lumbia for a de-orbit burn that would ditch the Orbiter in the Pacific Ocean, or would have the Columbia crew take it to a higher orbit for a possible subsequent repair mission if more thorough repairs could be developed.

This rescue was considered challenging but feasible. To succeed, it required problem-free processing of Atlantis and a flawless launch countdown. If Program managers had un-derstood the threat that the bipod foam strike posed and were able to unequivocally determine before Flight Day Seven that there was potentially catastrophic damage to the left wing, these repair and rescue plans would most likely have been developed, and a rescue would have been conceivable.