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There are four sets of brakes, one for each main gear tire. Each
brake uses four rotors and three stators. The stators are attached to a torque tube. Carbon pads are attached to provide the friction surface. The Orbiter brakes were designed to provide 36.5 million footpounds of energy for normal reuse limit stops and 55.5 million footpounds of energy for an abort maximum use stop. The brakes were tested and qualified using standard dynanometer tests.

Actual flight experience has shown brake damage on nearly all flights. The damage is classified by cause into dynamic or thermal. Both types of damage are common in the industry, especially with the beryllium design. The dynamic damage is usually characterized by damage to rotors, carbon lining chipping plus beryllium and pad retainer cracks. On the other hand, the stator damage has been due to thermal heating of the stator caused by energy absorption during braking. The beryllium becomes ductile and has a much reduced yield strength at temperatures possible during braking.

These brake damage situations have resulted in special crew procedures to assure successful braking. To minimize dynamic damage and to keep the loose parts together so that the brakes behave as brakes, the crews are told to hold the brakes on constantly from the time of first application until about 40 knots. For a normal end-of-mission landing, braking is initiated at midfield at about 130 knots. For abort landings, braking is initiated at about 165 knots. These braking windows attempt to control the maximum use temperature of the stator and take advantage of aerodynamic braking. The earlier the brakes are applied, the higher will be the heat rate. The longer the brakes are held on, the higher the temperature will be no matter what the heat rate. The trick is to get the brake energy out of the brakes before the beryllium yields resulting in a low speed wheel lockup, probably after the antiskid system is automatically disengaged.

STS 5, STS 51-D, and STS 61-C had forms of thermal stator damage. The STS 61-C case did not progress to a lockup but was very close. The
STS 51-D case resulted in a wheel lockup and a subsequent blown tire at KSC. It appears that the amount of brake energy that can be obtained using current braking procedures is about 40 million foot-pounds of energy before the first stator fails. The STS 61-C damage occurred at 34 million footpounds but had not progressed to the lockup condition. Inspection of failed stators clearly shows the plastic failure response of the beryllium and, hence, it is believed that this failure mechanism cannot contribute to a high-speed lockup and subsequent tire failure. It should be noted that the brake specification called for a maximum energy of 55 million footpounds. 

Qualification testing showed that 55 million footpounds was the point of first stator failure and was obtainable if maximum braking procedures were used. This has been confirmed in recent tests.
During qualification tests, the brakes continued to operate as brakes until all stators failed yielding about another 5 million footpounds of energy. Based upon the thermal response of beryllium under load,
it appears that the early heavy braking required for TAL aborts may be able to get more than the 40 MFP seen in normal braking problems, but

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