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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Space Shuttle thermal protection system | 4/5 | https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system | reference | science, encyclopedia | 2026-05-05T13:22:37.256899+00:00 | kb-cron |
Tiles often fell off and caused much of the delay in the launch of STS-1, the first shuttle mission, which was originally scheduled for 1979 but did not occur until April 1981. NASA was unused to lengthy delays in its programs, and was under great pressure from the government and military to launch soon. In March 1979 it moved the incomplete Columbia, with 7,800 of the 31,000 tiles missing, from the Rockwell International plant in Palmdale, California to Kennedy Space Center in Florida. Beyond creating the appearance of progress in the program, NASA hoped that the tiling could be finished while the rest of the orbiter was prepared. This was a mistake; some of the Rockwell tilers disliked Florida and soon returned to California, and the Orbiter Processing Facility was not designed for manufacturing and was too small for its 400 workers. Each tile used cement that required 16 hours to cure. After the tile was affixed to the cement, a jack held it in place for another 16 hours. In March 1979 it took each worker 40 hours to install one tile; by using young, efficient college students during the summer the pace sped up to 1.8 tiles per worker per week. Thousands of tiles failed stress tests and had to be replaced. By fall NASA realized that the speed of tiling would determine the launch date. The tiles were so problematic that officials would have switched to any other thermal protection method, but none other existed. Because it had to be ferried without all tiles the gaps were filled with material to maintain the Shuttle's aerodynamics while in transit.
=== Concern over "zipper effect" === The tile TPS was an area of concern during shuttle development, mainly concerning adhesion reliability. Some engineers thought a failure mode could exist whereby one tile could detach, and resulting aerodynamic pressure would create a "zipper effect" stripping off other tiles. Whether during ascent or reentry, the result would be disastrous.
=== Concern over debris strikes === Another problem was ice or other debris impacting the tiles during ascent. This had never been fully and thoroughly solved, as the debris had never been eliminated, and the tiles remained susceptible to damage from it. NASA's final strategy for mitigating this problem was to aggressively inspect for, assess, and address any damage that may occur, while on orbit and before reentry, in addition to on the ground between flights.
=== Early tile repair plans === These concerns were sufficiently great that NASA did significant work developing an emergency-use tile repair kit which the STS-1 crew could use before deorbiting. By December 1979, prototypes and early procedures were completed, most of which involved equipping the astronauts with a special in-space repair kit and a jet pack called the Manned Maneuvering Unit, or MMU, developed by Martin Marietta. Another element was a maneuverable work platform which would secure an MMU-propelled spacewalking astronaut to the fragile tiles beneath the orbiter. The concept used electrically controlled adhesive cups which would lock the work platform into position on the featureless tile surface. About one year before the 1981 STS-1 launch, NASA decided the repair capability was not worth the additional risk and training, so discontinued development. There were unresolved problems with the repair tools and techniques; also further tests indicated the tiles were unlikely to come off. The first shuttle mission did suffer several tile losses, but they were in non-critical areas, and no "zipper effect" occurred.
== Columbia accident and aftermath ==
On February 1, 2003, the Space Shuttle Columbia was destroyed on reentry due to a failure of the TPS. The investigation team found and reported that the probable cause of the accident was that during launch, a piece of foam debris punctured an RCC panel on the left wing's leading edge and allowed hot gases from the reentry to enter the wing and disintegrate the wing from within, leading to eventual loss of control and breakup of the shuttle. The Space Shuttle's thermal protection system received a number of controls and modifications after the disaster. They were applied to the three remaining shuttles, Discovery, Atlantis and Endeavour in preparation for subsequent mission launches into space. On 2005's STS-114 mission, in which Discovery made the first flight to follow the Columbia accident, NASA took a number of steps to verify that the TPS was undamaged. The 50-foot-long (15 m) Orbiter Boom Sensor System, a new extension to the Remote Manipulator System, was used to perform laser imaging of the TPS to inspect for damage. Prior to docking with the International Space Station, Discovery performed a Rendezvous Pitch Maneuver, simply a 360° backflip rotation, allowing all areas of the vehicle to be photographed from ISS. Two gap fillers were protruding from the orbiter's underside more than the nominally allowed distance, and the agency cautiously decided it would be best to attempt to remove the fillers or cut them flush rather than risk the increased heating they would cause. Even though each one protruded less than 3 cm (1.2 in), it was believed that leaving them could cause heating increases of 25% upon reentry. Because the orbiter did not have any handholds on its underside (as they would cause much more trouble with reentry heating than the protruding gap fillers of concern), astronaut Stephen K. Robinson worked from the ISS's robotic arm, Canadarm2. Because the TPS tiles were quite fragile, there had been concern that anyone working under the vehicle could cause more damage to the vehicle than was already there, but NASA officials felt that leaving the gap fillers alone was a greater risk. In the event, Robinson was able to pull the gap fillers free by hand, and caused no damage to the TPS on Discovery.