Space Shuttle thermal protection system

[1] The TPS covered essentially the entire orbiter surface, and consisted of seven different materials in varying locations based on amount of required heat protection: Each type of TPS had specific heat protection, impact resistance, and weight characteristics, which determined the locations where it was used and the amount used.

The orbiter reentered the atmosphere as a blunt body by having a very high (40°) angle of attack, with its broad lower surface facing the direction of flight.

Over 80% of the heating the orbiter experiences during reentry is caused by compression of the air ahead of the hypersonic vehicle, in accordance with the basic thermodynamic relation between pressure and temperature.

Similarly, ablative TPS would be heavy, possibly disturb vehicle aerodynamics as it burned off during reentry, and require significant maintenance to reapply after each mission.

Ninety percent of the volume of the tile was empty space, giving it a very low density (9 lb/cu ft or 140 kg/m3) making it light enough for spaceflight.

An uncoated HRSI tile held in the hand feels like a very light foam, less dense than styrofoam, and the delicate, friable material must be handled with extreme care to prevent damage.

The coating feels like a thin, hard shell and encapsulates the white insulating ceramic to resolve its friability, except on the uncoated side.

While more impact resistant than other tiles, white versions conducted more heat which limited their use to the orbiter's upper body flap and main engine area.

[11] This white low-density fibrous silica batting material had a quilt-like appearance, and replaced the vast majority of the LRSI tiles.

The light gray material which withstood reentry temperatures up to 1,510 °C (2,750 °F) protected the wing leading edges and nose cap.

It was stronger than the tiles and was also used around the socket of the forward attach point of the orbiter to the External Tank to accommodate the shock loads of the explosive bolt detonation.

RCC was the only TPS material that also served as structural support for part of the orbiter's aerodynamic shape: the wing leading edges and the nose cap.

All other TPS components (tiles and blankets) were mounted onto structural materials that supported them, mainly the aluminium frame and skin of the orbiter.

It was possible that the gap filler could cause turbulent airflow further down the fuselage, which would result in much higher heating, potentially damaging the orbiter.

While reinforced carbon–carbon had the best heat protection characteristics, it was also much heavier than the silica tiles and FIBs, so it was limited to relatively small areas.

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.

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.

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.

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.

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.

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.

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.

As of 2010[update], with the impending Space Shuttle retirement, NASA was donating TPS tiles to schools, universities, and museums for the cost of shipping—US$23.40 each.

The Kuiper Airborne Observatory took an infrared image of the underside of Columbia during the reentry of STS-3 to study temperatures. The orbiter was 56 kilometers (184,000 ft) high and travelling at Mach 15.6.
Space Shuttle Discovery as it approaches the International Space Station during the STS-114 on 28 July 2005.
Thermal protection system for orbiter 103 and subsequent orbiters
Endeavour in the California Science Center museum, showing tiles near door
Discovery' s under wing surfaces are protected by thousands of High-Temperature Reusable Insulation tiles.
A closer view of the tiles under the forward fuselage and the front end of the left wing. The corner of the nose-gear door can be seen at the lower left. The dark solid black tiles are new ones which have yet to go through a reentry. (At top, the white object is the open left cargo bay door.)
Silica tile from Atlantis
An HRSI tile. Note the yellow markings, which denote its exact location on the orbiter.
Diagram of a HRSI tile.
Diagram of a HRSI tile.
Columbia in the Orbiter Processing Facility after its arrival at Kennedy Space Center on 25 March 1979, showing many missing tiles. 7,800 of 31,000 tiles were still to be attached. [ 12 ]