A report describes the development of a mechanism that automatically clamps upon warming and releases upon cooling between temperature limits of ~180 K and ~293 K.
The mechanism satisfied a need specific to a program that involved repeated excursions of a spectrometer between a room-temperature atmospheric environment and a cryogenic vacuum testing environment. The mechanism was also to be utilized in the intended application of the spectrometer, in which the spectrometer would be clamped for protection during launch of a spacecraft and released in the cold of outer space to allow it to assume its nominal configuration for scientific observations. The mechanism is passive in the sense that its operation does not depend on a control system and does not require any power other than that incidental to heating and cooling. The clamping and releasing action is effected by bolt-preloaded stacks of shape-memory-alloy (SMA) cylinders. In designing this mechanism, as in designing other, similar SMA mechanisms, it was necessary to account for the complex interplay among thermal expansion, elastic and inelastic deformation under load, and SMA thermomechanical properties.
This work was done by David Rosing and Virginia Ford of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category.
NPO-40541
This Brief includes a Technical Support Package (TSP).
Temperature-Controlled Clamping and Releasing Mechanism
(reference NPO-40541) is currently available for download from the TSP library.
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Overview
The document is a technical support package from NASA's Jet Propulsion Laboratory detailing the development and implementation of a Temperature-Controlled Clamping and Releasing Mechanism, specifically for the Tropospheric Emission Spectrometer (TES) instrument. The TES is designed to measure atmospheric gases, particularly ozone, from space, contributing to our understanding of global climate change.
The core of the document discusses the use of Shaped Memory Alloys (SMAs) in the clamping mechanism, which is crucial for maintaining the optical alignment of the TES optics bench during launch and operational phases. The optics bench, made of cyanate-ester composite, is cooled to 177K during operations and contains essential optical components such as beamsplitters and detectors. The challenge faced was that the optical alignment was significantly altered when the bench was installed in the main structure frame, due to over-constrained mounting conditions.
To address this, a passive release system was developed that would allow the optics bench to remain aligned while also accommodating thermal expansion and contraction during operation. The system needed to maintain a minimum preload during launch and vibration testing, and it had to release completely when the instrument reached its operational temperature. The design included a mechanism that would ensure the bench could be reset to its original alignment after periodic thermal cycles, which were expected to occur frequently over the mission's five-year lifespan.
Extensive testing validated the effectiveness of the SMA system, demonstrating that it could reliably maintain optical alignment and perform to specifications. The successful implementation of this technology not only allowed the TES instrument to be delivered on time for installation on the Aura spacecraft but also showcased the potential for broader applications in aerospace technology, particularly in environments requiring thermal isolation and precise mechanical control.
In conclusion, the document highlights the innovative use of SMAs in aerospace applications, emphasizing their reliability and effectiveness in maintaining critical optical alignments in challenging conditions. The collaboration with Intrinsic Devices, Inc. was crucial for the rapid production of the SMA devices, underscoring the importance of partnerships in advancing aerospace technology.
