The Lockheed Martin/Advanced Technology Center (LM/ATC) developed a lightweight, compact, high-load capable and yet high precision latch for use on deployable optical systems such as the Next Generation Space Telescope (NGST). The design allows precise self-centering and control of the stiffness at the latch interface. It also incorporates unique capabilities to evaluate the effects of gravity loads, latch preload level, creep, and very low vibration loads on the dynamics and microdynamics of the deployed instrument.
The stiffness, nonlinearity and hysteresis characteristics of the latch and its catch flexure assembly were thoroughly tested in 6 axes down to the nanometer level at room temperature using the LM/ATC Compliance Measurement Device. The latch is stiff enough to hold an NGST-size mirror segment cantilevered against gravity allowing only small gravity sag when the primary mirror is horizontal, thus enabling end-to-end performance verification in 1-G in that orientation. The latch hysteresis is less than 1.0 nm/N under mechanical loads less than 25 N, which meets the NGST stability requirements with significant margin (20 nm at the tip of the petal in space environment).
Several of these latches were integrated and demonstrated at the petal assembly level on a Single Petal Test-bed and the experimental results obtained on that test-bed are consistent with the component level results described in this report.
We experimentally demonstrated that the latch engagement performance is not affected by exposure to cryogenic temperatures down to 20K, as required for use of the device on cryogenic infrared optical instruments such as NGST.
A structural model of the latch was developed using Finite Element Analysis. Good correlation was obtained between the linear components of the analytical and of the experimental results: the model can therefore reliably be used in future NGST or other mission design efforts.
This paper includes a brief description of the LM/ATC latch hardware and its principle of operation as well as the results of the modeling and the experimental characterization work performed on that hardware in the NGST Phase I formulation.