Advanced thermo-structural technologies for the NASA terrestrial planet finder mission

Abstract

The primary objective of the NASA Terrestrial Planet Finder flight missions will be to detect and characterize Earth-like planets around nearby stars. Because of the complexity of the design concepts, the project will rely heavily on the use of analytical simulations to predict on-orbit performance. Furthermore, current understanding of these missions indicates that the 3-8 m class optical systems need to be as stable as picometres in wavefront and sub-milli arcsec in pointing. These extremely small requirements impose on the models a level of predictive accuracy heretofore never achieved, especially in the area of microgravity effects, material property accuracy, thermal solution convergence, microdynamic stability and all other second-order modelling effects typically ignored. New modelling tools and analysis paradigms are developed which emphasize computational accuracy and fully integrated analytical simulations. The process is demonstrated on sample problems using a TPF Coronagraph design concept. The TPF project is also planning a suite of testbeds through which various aspects of the models and simulations will be verified.as it existed only a few hundred million years after the Big Bang, the event which is believed to have created the Universe about 13.5 billion years ago.Since the time of the ancient Greeks, philosophers and scientists have speculated about the possibility that other Earth-like planets may be orbiting other stars in our Universe. The first discovery of a planet orbiting another star was made in 1995 by astronomers observing the Doppler shift of the star's spectrum caused by the gravitation tug of the orbiting planet. By the time of this writing, about 150 planets have been found in this way, although the technology is not yet capable of detecting planets as small as Earth. NASA envisions the development of telescopes within the next decade that will indirectly detect Earth-size planets orbiting nearby stars. These missions will be followed by two missions collectively called the terrestrial planet finder (TPF). TPF will directly image Earth-like planets around nearby stars, and characterize their atmospheres searching for water, oxygen, and signs of life. The TPF missions include a visible light coronagraph (TPF-C) that will use advanced techniques to block the light from the star and thereby reveal faint orbiting planets, and a midinfrared interferometer (TPF-I) that will combine light from a formation of independent spacecraft.Imaging Earth-like planets around nearby stars is a staggeringly challenging measurement because the planets are a billion times fainter than the star, and are separated from the star by an angle only few hundredths of an arc-second in size as seen from Earth. The TPF-C observatory must employ a telescope much larger than Hubble, but with optical quality many thousands of times more precise. While TPF-C will be operating at or near room temperatures but at stability levels exceeding milli Kelvins, TPF-I will be operating at cryogenic temperatures of about 40 K. I...