Passive thermal control of the NGST

Abstract

Preliminary studies ofpassively cooling the Next Generation Space Telescope utilizing a lightweight deployable sunshield are described. The NGST mission concept of a passively-cooled large-aperture optical telescope is unique from any other mission flown to date. We show that achieving operational temperatures ofless than 50 K appears feasible by passive cooling alone through a combination of(i) operating the observatory far from the Earth so that the Sun becomes the only significant source ofenvironmental heating, (ii) selecting an observatory configuration that isolates all significant heat dissipation from the cold telescope, and (iii) employing a high performance sunshield to attenuate the incident solar radiation. The observatory configuration consists ofthe sunshield with cold telescope and instrument elements on the anti-sun side, and warm spacecraft avionics and propulsion elements on the sun-side of the sunshield. A sunshield thermal configuration trade study, preliminary telescope thermal analyses, and a mechanical concept for a lightweight deployable sunshield are presented. Also discussed are the remaining issues to be addressed.

Effects of Vacuum Ultraviolet Radiation on Thin Polyimide Films

“…The Next Generation Space Telescope (NGST) mission, whose purpose is to examine the origins of our universe by making measurements in the infrared portion of the spectrum, is anticipated to be launched by the National Aeronautics and Space Administration (NASA) in 2009. So that the telescope can operate at very low temperatures (less than 100 K), a halo orbit about the second Lagrangian point (L2) is being considered for NGST [1] as it is far from Earth and its reflected sunlight. The Sun-Earth L2 point is located 1.5 × 10 6 km from the Earth in the direction away from the Sun [1].…”

Simulated space vacuum ultraviolet (VUV) exposure testing for polymer films

“…2 While the typical polymer film thickness for thermal control materials ranges between 50 and 127 jim, trends continue toward use of large ultra-lightweight, inflatable or deployable structures requiring space-facing thin polymer films of 25 jam or less such as the sunshield proposed for use on the Next Generation Space Telescope. 3 These large area ultra-lightweight components will rely on the structural integrity of polymer films that are much thinner than have typically been used in the past for thermal control. Thinner materials will be more susceptible to radiation damage such as that provided by 1 American Institute of Aeronautics and Astronautics electrons, vacuum ultraviolet (VUV), and soft x--rays, because these radiation species can deposit significantly more energy in the polymer surface and deposited energy diminishes through the bulk of the material.…”

“…Some very large proposed spacecraft components, such as sunshields and inflatable structures, will require the thin polymer to be seamed, folded, and durable to stresses imposed by the deployed configuration. 3 These demands pose a number challenges in the area of space environmentally durable polymer films.…”

Improving active space telescope wavefront control using predictive thermal modeling

“…Since a typical observation lasts a few hours, there is insufficient time for a cryogenic shielded telescope to equilibrate before the next slew; the thermal time constant for typical designs is on the order of days. [16][17][18] As a result, the thermal state of the telescope is not a simple function of attitude, but rather a complex function of attitude history. As the thermal state changes during a mission, the thermally induced deformations in the observatory structures also vary, causing perturbations in the WFE (Fig.…”