Method of making ultralight primary mirrors
Abstract
Space vehicle weight limitations require space telescope components to be as light as possible. This is particularly important for multimirror designs where the weight of mirror segments alone can be very large. In this paper, the fabrication of ultralight mirror segments is described. The mirrors are made from HTP (high thermal performance material), better known as a third generation derivative of the space shuttle heat shield tile. The HTP material has a density of only about 9.14 gms/cc and is made from tangled fibers of aluminum oxide and silicon dioxide sintered together as a non-isotropic material. HTP material is also stiff, and undergoes very small shrinkage and expansion due to thermal effects (coefficient of expansion equals 3.5 to 44.0 X 10-7 in/in-F0). When one side of an HTP surface is coated with a suitable glassy substance, such as a fused silica, fine mirrors can be made. HTP material also outgasses quickly, thereby preventing annoying virtual leaks that can result in condensation of gaseous species onto optical surfaces. Experiments have shown that a one centimeter thick specimen of HTP material will outgas from one atmosphere pressure down to the ambient pressure at low Earth orbit in 8 minutes when the pumping rate is 200 liters/sec.
- Publication:
-
Space Astronomical Telescopes and Instruments
- Pub Date:
- September 1991
- DOI:
- 10.1117/12.46746
- Bibcode:
- 1991SPIE.1494..491Z
- Keywords:
-
- Aluminum Oxides;
- Mirrors;
- Silicon Dioxide;
- Sintering;
- Spaceborne Telescopes;
- Weight Reduction;
- Earth Orbital Environments;
- High Temperature Environments;
- Refractory Materials;
- Thermal Expansion;
- Mechanical Engineering