The first step in implementing the capability to test sensitive launch vehicle instruments in a combined environment has been completed. The test environment consists of specific vibration spectra induced under sustained Gs, using NASTAR’s ATFS-400 centrifuge. Fixtures allow mounting of the device under test (DUT) to a vibrational shaker in a centrifuge for generating moderate G-loading (1.4 to 9G) such that the vibrational shaker’s capabilities are only slightly affected by the G-loads applied during testing. Two configurations were designed, with the vibrational load parallel to the G-loads, and with the vibration loads transverse (at right angles) to the G-loads. The results are extremely encouraging, and demonstrate the potential of the NASTAR centrifuge to perform this kind of combined testing in a controlled, calibrated, and repetitive manner.

In addition to the main centrifuge, the test equipment comprised an electrodynamic shaker system. The test consisted of rigging the shaker and amplifier in a special test module that was then installed in the centrifuge. Due to the unique design of the NASTAR centrifuge, which consists of a gondola “shell” in which modules with different configurations can be installed, the module could be prepared “offline” while the centrifuge was used for other activities.

Control and feedback signals were routed using the available coaxial line from the amplifier and accelerometer to the centrifuge control room, where the laptop and controller were wired to close the loops. The LDS Shaker Control Software was programmed to inject the NASA GEVS Qualification profile, which is considered to represent a worst-case scenario because it contains the conceivable profiles associated with launch vehicle exposure. The centrifuge was programmed for different sustained G levels (3G, 5G, 7G, and 9G), and the qualification vibration profile was injected into the payload for 1 minute. The test verified not only that the centrifuge transmission lines are adequate for this type of signal feedback, opening the way for tests with higher payloads, but also that the controller can dynamically adapt to the increased G level to which the payload is subjected.

This work was done by John Littlefield of American Aerospace Advisors, Inc. for Kennedy Space Center. KSC-13783

Motion Control & Automation Technology Magazine

This article first appeared in the August, 2014 issue of Motion Control & Automation Technology Magazine.

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