Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SHUTTLE/TPTA.TXT

Text File | 1993-02-05 | 6KB | 101 lines

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                   TRANSIENT PRESSURE TEST ARTICLE (TPTA) PROGRAM

         TPTA Purpose

              As part of the overall redesign program for the Space
         Shuttle solid rocket motor (SRM), a series of tests of the
         effects of pressure transients and loads encountered by the
         redesigned solid rocket motor during ignition is required.  The
         Transient Pressure Test Article (TPTA) tests to be conducted in
         the East Test Area of NASA's Marshall Space Flight Center in
         Huntsvile, Ala., will provide data to verify the sealing
         capability of the redesigned SRM field and case-to-nozzle
         joints.
              The test program will consist of 10 separate tests.  A
         minimum of four tests are planned prior to resumption of Space
         Shuttle flights.  Additional tests may be conducted prior to the
         STS-26 mission to further assess the redesigned joints under
         external loads.

         Test Article Configuration Description
              The TPTA is a short-stack solid rocket motor test article.
         It is  more than 52 feet (633 inches) in length and 12 feet in
         diameter.  The motor weighs 548,144 pounds, including 400 pounds
         of propellant to simulate the pressure rise for ignition.
              The TPTA consists in part of two case segments loaded with
         inert propellant connected by two redesigned field joints. The
         field joints are of the redesigned capture feature tang and
         clevis design with Viton (TM) O-rings.  The mating insulation
         surfaces at each field joint are bonded with an adhesive, and
         include a non-flight type J-shaped seal utilizing motor internal
         pressure to increase the sealing action of the bonded surfaces.
              The TPTA includes a redesigned factory joint which connects
         a stiffener segment loaded with inert propellant to a external
         tank attach (ETA) segment.
              Flight configuration joint heaters are mounted around the
         motor case at the top and bottom dome joint locations.  Each
         heater contains two independent electrical power circuits
         thermostatically controlled to maintain joint temperatures at a
         minimum of 75 degrees F.
              The motor case-to-nozzle joint will be of the redesigned
         configuration with 100 radial bolts added.  The 7/8-inch diameter
         radial bolts with Viton Stat-O-Seals (TM) are added to minimize
         the amount of joint opening during motor pressurization.  The
         joint also incorporates adhesively bonded insulation surfaces, a
         shaped relief slot and an added Viton "wiper" O-ring designed to
         keep the adhesive on the insulation surfaces during assembly.
              A standard aft skirt is fitted to the motor. For the TPTA
         tests the aft skirt is attached to actual launch pad hold-down
         posts.

         What Happens During the Test
              During the TPTA test, pressure is produced by a standard
         solid rocket motor igniter and about 400 pounds of propellant to
         duplicate the maximum pressure rise of the motor. Maximum
         expected pressure is achieved in about six-tenths (0.6) of a
         second and the pressure decay to ambient (outside air) conditions
         occurs in about 90 seconds.
              During the pressure cycle, dynamic strut loads will be
         applied to the motor from a specially designed external tank
         attach (ETA) load tower.  Three connecting load lines will induce
         loads which will simulate the three struts that attach the SRM to
         the Shuttle's external tank at the base of the motor.
              At the same time, the test article is subjected to a million
         pound weight attached above the forward segment.  This weight
         simulates the remainder of the Shuttle elements on the launch
         pad.  The strut loads are synchronized with the ignition pressure
         transient to recreate joint loading conditions that occur after
         ignition when the pressure in the motor jumps causing the case to
         bulge and rotate.
              The TPTA  will be fitted with 1500 instruments to measure
         strain, deflection, temperature, pressure data and other
         conditions.
              The first test will be a nominal verification test of the
         TPTA configuration (no flaws).  In subsequent tests flaws will be
         built into the J-seals and/or O-rings.
              Upon completion of each test, the test article will be
         refurbished in a facility adjacent to the test stand.  A huge
         crane will destack segments from the test stand and place them in
         the refurbishment facility.  Each test motor will be taken apart,
         inspected, refurbished and new propellant added before being
         fired again.

         TPTA Test Objectives
              The six primary test objectives are:
              o  Simulate the SRM maximum pressure rise rate.
              o  Simulate external loading influences on the sealing
                 capability of the redesigned SRM joint.
              o  Provide high temperature gas to demonstrate no evidence
                 of blowby or erosion of O-rings.
              o  Obtain reliable, repeatable SRM joint deflection data.
              o  Verify static and dynamic models of the field and
                 case-to-nozzle joints.
              o  Demonstrate design solutions for the field and nozzle
                 joints.

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