FIGURE 6–2 Critical penetration risk vs. shuttle orientation (BUMPER prediction for 10-day mission, 400 km altitude, 51.6 degree inclination, 1996 environment). Source: NASA.

(Heflin, 1997). NASA considered developing a portable shield to protect astronauts during ISS assembly operations, but that option was determined to be impractical (Simonds and Julian, 1997).

NASA has developed damage control procedures for the shuttle crew in the event that a pressurized compartment is penetrated. Access to the pressure hull in the orbiter cabin, the Spacelab, and the Spacehab in most cases requires removing racks and storage lockers, which will take significant time and effort. NASA estimates that about 60 percent of the interior of the pressure vessel would be accessible in 30 minutes to two hours, the next 20 percent in two to three hours, and the last 20 percent in more than three hours (Combs, 1997). Given these constraints, NASA has focused on expediting reentry in the event that a pressurized compartment is penetrated.

If the crew detects a penetration of the crew cabin that they believe does not require immediate reentry, they will first attempt to locate the hole. If the hole is accessible, they will attempt to repair it with an epoxy material or sealing tape, which are carried on all flights (Reeves, 1997). The limiting consumable in the event of a leak is the on-board nitrogen gas (N₂) supply. The N₂ supply was