the specimen, a 3D printed plastic version of the mating piece for the KB3X3 is attached for alignment when  stowed. A 3D printed version was used to minimize the mass at the tip of the specimen while still enforcing  good stow alignment.  Figure 4 also shows the location of some of the sensors used in the experiments. In the figure, the four  laser position sensors used to measure creep recovery are shown mounted to cold plates. In order to  achieve the temperature stability needed in the test chamber, the laser positions sensors needed to be  actively cooled. They were cooled using a Polyscience FF-12930-38 benchtop chiller set at 20.5 degrees  Celsius. Without this chiller, the temperature in the chamber would slowly increase over time due to the  heat released from the laser position sensors.   Test Instrumentation  Accurate and precise position measurements are critical for the deployment precision testing. Because of  the relatively small position range of interest, it was determined that only non-contact sensors could be  used. Sensors that contact the tests specimen would apply a small, unknown amount of load to the  specimen and most likely affect the precision measurements. After a survey of available precision, noncontact position sensors, laser displacement sensors were determined to be the best fit for this application.  These sensors can provide very accurate measurements from larger stand-off distances than capacitive  sensors, which was important for this application since we did not know how far from the nominal position  the specimens would be initially after deployment. The sensors chosen were Keyence LK-H027 1D laser  triangulation sensors. The specifications for this sensor are shown in Table 3. Based on these specifications  and the 0.1-degree Celsius worst-case temperature variation during a test, the RMS error for a 10-μm  measurement would be 63 nm. The Keyence LK-H027 were connected to a LK-G5001V controller unit. The  controller sampled data from the sensors at 1 kHz in the diffuse reflection mode. The sensor measurements  were then output from the unit as a moving mean of 4096 points. Four Keyence LK-H027 sensors were  used during this experiment, as indicated in Figure 4. Three sensors were used to obtain the piston, roll  and pitch of the mirror-mounting end of the specimen. The fourth sensor was used to measure axial  displacement.   Table 3. Keyence LK-H027 position sensor specifications  Specification Name Specification Value Laser output 655 nm at 0.95 mW  Spot size 25 µm by 1400 µm  Nominal stand-off 20 mm  Range ±3 mm  Linearity error ±1.2 µm  Precision error 20 nm  Temperature error 0.6 µm/C  The level of precision desired from the specimens is on the same order of magnitude of what might be seen  due to thermal expansion of many common materials in an unconditioned environment. Testing within the  thermal chamber achieves a maximum variation of 0.1 degree Celsius over 24 hours. In order to monitor  the temperatures of the test specimen, test apparatus and the test chamber, a number of temperature  measurements were made during each test. A custom temperature measurement system was acquired  from GEC Instruments to perform and acquire these measurements. The system is comprised of two 0.002degree Celsius precision thermistors and five 0.02-degree Celsius precision thermocouples. One thermistor  probe is located in the center of the optical breadboard and the second is located near the specimen root  end of the Invar reference plate. The five thermocouples are distributed around the Invar reference plate  and test specimen as shown in Figure 9. The specific location of each temperature sensors is described in  Table 3. This spatial distribution of temperature measurements provides a better understanding of the  temperatures at either end of the test specimen and at the sensor locations. The latter is important because  of the temperature sensitivity of the laser sensors as shown in Table 2. The maximum temperature  NASA/CP—2018-219887 422