SKYLAB TESTING PROGRAM The Skylab testing program cosists of three phases: the first deals with the Orbital Workshop, a cylinder approximately 22 feet in diameter and 43 feet long, a portion of the Saturn booster converted into a laboratory; the second is the Payload Assembly, with the same major diameter and some 75 feet high, which houses much of the equipment to be deployed in space; and the third is the Orbital Configuration which contains the deployable equipment in the Payload Assembly, a docked modified Apollo Command and Service Module, and a docked portion of the Orbital Workshop. The major objectives of the program are identified in figure 6. Note that both the first two phases (concerning the Orbital Workshop and the Payload Assembly) require both acoustic and vibration testing, the third phase (pertaining to the Orbital Configuration) requires vibration testing only. The test specifications stated that the mode of acoustic excitation be impingement of essentially uniform reverberant energy over the vehicles to levels higher than attainable in the Spacecraft Acoustic Laboratory. Accordingly, a study was made which resulted in a proposal to erect a reverberant chamber with reinforced concrete walls within the Spacecraft Acoustic Laboratory; the resultant chamber can be seen in the cut-away view in figure 7. Checkout tests with dummy vehicles subsequently demonstrated that the desired acoustic levels could be attained. PHASE I-SKYLAB ORBITAL WORKSHOP Some of the special features associated with the testing of the Orbital Workshop are shown in figure 8. The acoustic tests began in late December and have been completed; a photograph of the test article in the new reverberant chamber is shown in figure 9. Two different acoustic spectrums, lift-off and aerodynamic buffet, were applied For each, one reduced level test was performed to check all systems and instrumentation, then a full level test was made and the data reviewed, and finally another full-level was performed (any anomalies could be check by this test run). The 220 response measurements were in the form of accelerations of equipment hardware and structure to check on the validity of the vibration levels used for component qualification. Upon successful completion of the acoustic tests, the OWS was moved to the vibration tower and set up for excitation in the vertical or longitudinal axis. Figure 10 shows the entire vibration test setup. A somewhat more detailed view of the test setup can be seen in figure 11. When the vertical excitation tests have been completed, the shakers utilized to impart the driving force will be attached to the vertical numbers of the ring to excite the base horizontally, first in one axis and later in a perpendicular horizontal axis. Tests in each of the 3 axes consist of slowly exciting the vehicle by sinusoidally changing forces through a frequency range of 3 to 50 cycles per second (Hz) in order to identify the resonant (natural frequency) conditions of the vehicle. When these have been established, the vibration forces will be applied at these frequencies to determine precisely how the structure and all major mass items respond, or in other words, the mode shape at that frequency, and then the structural damping. This information is needed, to a high degree of accuracy, to predict how the vehicle will respond to any and all types of loading and for guidance and control purposes. PHASE II-PAYLOAD ASSEMBLY As can be seen from figure 12, the testing of the Payload Assembly (PA) very closely follows the testing pattern of the Orbital Workshop. The objectives of both phases are essentially identical. The configuration shown is that for the vibration tests; for the acoustic tests the air springs (shown schematically at the sides) and the shakers (indicated by the arrows) will not be required. Since the PA sits on top of the OWS, its lift-off acoustic level is slightly lower then for the OWS, but in flight its Aerodynamic Buffet level is therefore somewhat higher. Testing of the Payload Assembly will occur during the summer of 1971. |