SNAP-III--THERMOELECTRIC GENERATOR ENVIRONMENTAL TEST. VOLUME III

The results of tests on four thermoelectric generators (two each of two different configurations) of the Snap III type to both the J.P.L. and the L.M.S.D. specifications for shock, vibration. and acceleration test are reported. The simulated levels were based on the anticipated environments of the Vega (J.P.L.) and WS117L (L.M.S.D.) systems. All four generators exhibited the same characteristic behavior pattern throughout the vibration portion of the test prograna, showing a d-c ripple in the generator output only in the Y place. This behavior of the generator is attributed to the oscillatory change in internal resistance resulting from vibratory elastic deformation of the thermoelectric elements. This produces a transient in the electrical output with a resultant reduction in generator efficiency. The maximum reduction in efficiency was noted in the 700 cps region. A resonance on the generator shell at 1845 cps was noted, but generator electrical output and efficiency were not affected. Upon discontinuance of the induced vibration, the generators returned to normal operating conditions. While undergoing shock test, a d-c transient was noted at the time of impact, resulting in a slight decrease in effi ciency. The generators immediately returned to their normal operating efficiency. In the acceleration portion of the test no d-c transient was evident in any of the three planes, therefore the generator efficiency remained constant. Steady state conditions were re-established at the start of each new test phase (i.e., changing planes of excitation, changing from shock to vibration, etc.). Thus, any variation from pretest efficiency was attributed to the external load resistance becoming umnatched due to the change in internal resistance. The important result is that complete generator recovery was consistent in all cases and normal operation continued The generator, shell, internal structure and pressure, and the hot and cold junction temperature were not affected during the test. As a result of this test program, it was concluded that the Snap III thermoelectric generator will operate reliably in the enviromnents associated with the Vega and WS117L vehicles. (auth