470 Testing Results & Data Analysis for Each Generation 

First Generation   The primary intention of the first round of testing was to verify our assumptions about the electrical and  thermal aspects of the concept. The device would eventually reach the temperature we calculated was required for separation (approximately a 70°C delta), but we learned that a single 30-W device was insufficient in both power handling capacity and output power. The power output was considered   insufficient because it took several minutes for the device to change temperature. We theorized that more power input would reduce the delta-T of the low CTE plug part, as increasing the temperature of the high CTE part faster would provide less time for heat transfer to the low CTE part. This would, in turn, require a lower delta-T in the high CTE part to achieve separation. This was proven later in modifications implemented in the third generation device. We consulted with electrical component engineers who  helped us pick parts using appropriate levels of part de-rating. Before this, we failed a few resistors by running them above their current-temperature curves. Using appropriate de-rating guidelines, we increased the resistance to 5.6 Ω, doubled the number of resistors, and switched from 30-W parts to   50-W parts. After the intial thermal and electrical tests were complete, we verified that concept would work, as we were able  to expand the aluminum part to the point that we were able to assemble the unit.  When we performed the first simulated actuation by removing the plug from the actuator at ambient pressure, we realized we had forgotten a vent hole in the actuator body. We also learned that we couldn’t make the parts on a manually operated lathe. We needed a CNC lathe to achieve the required tolerances for consistent device operation. The first generation test rig is depicted in Figure 5.   Figure 5 - First generation device shown in a bell jar type vacuum chamber. Striped wires are  power, white wires are temperature sensors.  Second Generation  The second generation of the actuator was subjected to the tests listed below.  Static load testing was  conducted prior to functional testing on the actuator, and a load of 334 N (75 lb) was maintained for 15 minutes. Following static load testing, we performed several separations at ambient conditions with 2 A of current. As expected, it took a long time to separate (236 sec). The delta-T to separate was low, 66°C, which we think can be attributed to the virgin state of the actuator (blemishes accrue with uncoated parts). Initial functional testing at vacuum was then successfully completed (separations 4 and 5). Lastly, 12 separations were conducted in vacuum under flight conditions, with the results summarized in Table 2.  Run 15 was a scrub. Power was cut off before the full actuation occurred. Note 4 indicates a smooth plug insertion. Note 5 indicates a rough plug insertion. Nine of the twelve separations can be considered to be in family with the majority of the sample population. There were three separations that were out of family. We think these three separations took longer because the insertion of the plug into the cup for these runs was rougher. The rough insertions likely were due to a misalignment of the parts. As the number of cycles increased, we noted some wear marks forming on the uncoated  titanium part, indicating that some galling  took place, primarily during insertions, but during ejection, as well.