I/ FORWARO SEGMENT PROPELLANT

Atomized aluminum powder ( f u e l ) , 16 percent ,

Ammnium p e r c h l o r a t e FORWARD CENTER ( o x i d i z e r ) , 69.83 percent

¶SREI SEGMENT I yon o x i d e powder

(catalyst), 0 .¹¹ For the purpose of this report, a procedure is a formal set of instructions designed to guide and assist in the performance of a technical or management function. 7 percent ( v a r i e s ) polybutadiene a c r y l i c a c i d a c r y l o n i t r i le ( b i n d e r ) , 12 percent

AFT SEGMENT ' Empty: (193.000 p o u n d s ) P r o p e I l a n t : ( 1 ,¹¹ For the purpose of this report, a procedure is a formal set of instructions designed to guide and assist in the performance of a technical or management function. 0 7 , 0 0 0 pounds) WITH NOZZLE Gross: (1,300,000 pounds)

¶FIGUREV-2

¶Each motor case is made of 11 individual weld-free steel segments (Figure V-3). Averaging approximately 1.27 centimeters (0.5 inch) thick, the steel is a high-strength formulation. Each segment is heat-treated, hardened, and machined to the exact dimensions required. The 11 segments are held together by 177 high-strength steel pins at each case segment joint. The clevis-type joints are wrapped with reinforced fiberglass tape and sealed with a rubber seal band that is bonded to the case with adhesives.

¶AFT

¶V-3

¶In this report there are many references to the joint design, erosion and O-ring seals. There are several different joint designs used in the Solid Rocket Motor. The joint that failed on the last Challenger flight, the aft field joint, was not the one that had been giving NASA the most trouble. More O-ring erosion had been experienced on nozzle joints, the design of which is significantly different than the aft field joint. However, since NASA treated erosion as a problem that impacted both the nozzle and field joints, the data on erosion in this section includes that obtained from the nozzle joint.

¶Whenever a temperature is specified, it is essential that it be related to a specific medium such as air (or ambient temperature), rocket propellant, or casing joints, for example. The temperature of the joints, air and propellant can all be different at the same time, just as the ocean temperature at the beach on a 90-degree day could be 75 degrees.

¶Much of this discussion concerns heat, or the absence thereof. For example, if an O-ring had given up heat during the night, it would very likely be at a lower temperature than the temperature of the air in the morning after the sun had risen. This was the situation at the time Flight 51-L was launched. The heat gained by the joint in the time after sunrise was not sufficient to raise the temperature of the O-ring material to a level where Thiokol engineers believed the O-ring could respond and seal the joint under ignition pressures.

¶The following chart describes the principal steps in the evolution, flight, and reconditioning of the Solid Rocket Motors (Figure V-4).

SOLID ROCKET MOTOR PRINCIPAL STEPS I N THE EVOLUTION, FLIGHT AND RECONDITIONING OF SOLID ROCKET MOTORS

1 — 7

.. THAT OBJECTIVES ARE CONSISTENTLY MET. NASA

CONTRACTOR DESIGN DESIGN THE MOTOR TO MEET ALL PERFORMANC REQUIREMENTS DURING ALL ANTICIPATED

CONDITIONS OF FLIGHT. (_' ., TESTING AND ASSURE THAT DESIGN MEETS ALL REQUlREMEh NASA