Session
Technical Session VII: Instruments & Sensors
Abstract
Cryogenically cooled components in infrared instruments designed by Utah State University's Space Dynamics Laboratory traditionally have been mounted on glass-epoxy composite (G-10) cylinders for thermal isolation. Ensuring adequate mechanical stiffness to withstand typical launch loads often compromises the desired thermal isolation and conduction parasitic heat loads become a concern. Beginning with a senior design project in the Mechanical and Aerospace Engineering Department, a new approach to rigidly supporting cold components using high performance fibers in tension was initiated. The development effort included consideration of several candidate fibers for tensile strength, shear strength, creep, and thermal conductivity as well as a technique for attaching and tensioning the support strands. A support system designed, fabricated and tested for application on the SABER instrument utilizes strands of Kevlar 49 in a bicycle wheel-spoke like arrangement to support a focal plane assembly (FPA) cooled by a miniature pulse tube refrigerator. The first resonant frequency of the Kevlar supported assembly has been measured to be greater than 600 Hz in all axes. This compares with typical values of 50 to 70 Hz for a similar assembly supported by concentric G-10 cylinders. In addition to an order of magnitude increase in the mechanical stiffness, the Kevlar system reduced parasitic conduction heat loads by almost two orders of magnitude. Calculated conduction loads through the Kevlar strands total less than 1 mW as compared to 85 mW for the G- 10 supports. This dramatic reduction brought total parasitic heat loads to within the limited cooling capacity of the miniature refrigerator and made possible the SABER instrument with its very stringent power and mass constraints. Further applications for this technology are currently being designed.
Applying Fiber Support Technology to Small Satellite Systems
Cryogenically cooled components in infrared instruments designed by Utah State University's Space Dynamics Laboratory traditionally have been mounted on glass-epoxy composite (G-10) cylinders for thermal isolation. Ensuring adequate mechanical stiffness to withstand typical launch loads often compromises the desired thermal isolation and conduction parasitic heat loads become a concern. Beginning with a senior design project in the Mechanical and Aerospace Engineering Department, a new approach to rigidly supporting cold components using high performance fibers in tension was initiated. The development effort included consideration of several candidate fibers for tensile strength, shear strength, creep, and thermal conductivity as well as a technique for attaching and tensioning the support strands. A support system designed, fabricated and tested for application on the SABER instrument utilizes strands of Kevlar 49 in a bicycle wheel-spoke like arrangement to support a focal plane assembly (FPA) cooled by a miniature pulse tube refrigerator. The first resonant frequency of the Kevlar supported assembly has been measured to be greater than 600 Hz in all axes. This compares with typical values of 50 to 70 Hz for a similar assembly supported by concentric G-10 cylinders. In addition to an order of magnitude increase in the mechanical stiffness, the Kevlar system reduced parasitic conduction heat loads by almost two orders of magnitude. Calculated conduction loads through the Kevlar strands total less than 1 mW as compared to 85 mW for the G- 10 supports. This dramatic reduction brought total parasitic heat loads to within the limited cooling capacity of the miniature refrigerator and made possible the SABER instrument with its very stringent power and mass constraints. Further applications for this technology are currently being designed.
