Optical testing of the Kepler Photometer in a thermal vacuum environment at Ball Aerospace

Abstract

The Kepler spacecraft and telescope were designed, built and tested at Ball Aerospace & Technologies Corporation in Boulder, Colorado. The Kepler spacecraft was successfully launched from NASA's Kennedy Space Center on March 6, 2009. In order to adequately support the Kepler mission, Ball Aerospace upgraded its optical testing capabilities. This upgrade facilitated the development of a meter-class optical testing capability in a thermal vacuum (TVAC) environment. This testing facility, known as the Vertical Collimator Assembly (VCA), was used to test the Kepler telescope in 2008. Ball Aerospace designed and built the VCA as a 1.5m, f/4.5 collimator that is an un-obscured system, incorporating an off-axis parabola (OAP) and test flat coated for operations in the VIS-IR wavelength region. The VCA is operated in a large thermal vacuum chamber and has an operational testing range of 80 to 300K (-315 to 80°F). For Kepler testing, the VCA produced a 112nm rms wavefront at cryogenic temperatures. Its integral autocollimation and alignment capabilities allowed knowledge of the collimated wavefront characteristics to <5nm rms during final thermal vacuum testing. Upcoming modifications to the VCA optics will bring the VCA wavefront to <20nm rms. The VCA optics are designed and mounted to allow for use in either a vertical or horizontal orientation without degradation of the collimated optical wavefront.