Sine Test  There were a total of six different test input levels of 0.25 g's initial, 2.5 g's, 7.5 g's, 12 g's, 16.25 g's and  finally 0.25 g's. The input at the base was limited for the 7.5 g's, 12 g's, and 16.25 g's to achieve a peak  response at the payload mass of 16.25 g's. The mass responses for the 0.25 g's and 2.5 g's test levels  are not limited. Reviewing the mass response provides an indication of the affect of the isolator structural  modes on the payload mass. It is best to determine the performance of the isolators by reviewing the  transfer function of the isolator which is a ratio of the response relative to the input. Using the Transfer  function the different input levels can be compared to each other.  Sine Test Transmissibilitv Data (Transfer function)  Prior to performing the vibration test, we identified which response channels we wanted to compare to the  reference channels so that the transmissibility of the isolator could be evaluated without consideration to  the input level. For the purposes of this paper, we will discuss the calculated transmissibility of mass  response accelerometer, channel 8, to the bipod base.  The transfer function for all the base input different levels is plotted in Figure 9. In this plot, the bipod  break frequency is shown, the lateral mode of both of the isolators can be clearly identified, the spring  body surge mode with its very high response can be clearly identified, and there are modes above 1000  Hz that are evident.  In order to evaluate the mass response and the bipod structural modes, we will break the plot in Figure 9  up into three different ranges, 10 Hz to 100 Hz, 100 Hz to 1000 Hz, and 1000 Hz to 2000 Hz. First, we will  examine the break frequency of the bipod shown in the plot from 10 Hz to 100 Hz. The bipod break  frequency shows shifts with the change in the base input level. Care was taken to ensure that the  temperature of the isolator was at room temperature before the start of each test. The break frequency  and calculated transmissibility changed slightly as the input level increased. This is consistent with the  theory for the isolator. An explanation of the three parameter isolator theories that predict shift in  frequency and change the isolator break frequency and damping is included in Reference *. The isolator  design is such that as the damping (Ca) decreases because of the heating of the isolator, the isolator is  more closely tuned to the input level which slightly decreases the break frequency and the isolator  calculated transmissibility. We measured the temperature rise of the damper housing during the 16.25 g  test and the increase in temperature was 18.8 "C (34 OF). The effect of the temperature change is clear in  Figure 9.  In the frequency range from 100 Hz to 1000 Hz we see that there is a lateral mode of both of the isolators  in the bipod at 21 5 Hz and the isolator spring body modes at 615 Hz. This data is consistent with the data  collected in previous testing. The 615-Hz mode can be used to evaluate the transmissibility of the main  spring surge mode. The worst-case transfer function peak of the 615-Hz mode is approximately 0.9. If  there was no mode at this location, the mass response should be approximately 0.02 therefore, the  calculated transmissibility of the mass response due to the spring surge mode is approximately 45. This is  likely an optimistic estimate since this measurement is not in-line with the isolator.  In the frequency range from 1000 Hz to 2000 Hz, there are some structural modes of interest in the  payload mass response transfer function. The first mode of interest is at 1 190 Hz. The transfer function  approaches a calculated transmissibility of 0.12 or a factor of 8 below bipod base input. There are  additional modes above 1 190 Hz but there levels are even lower. Evaluation of the higher modes is still in  progress.  147