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.
Ball Aerospace has constructed a new collimator for interferometric and image quality testing of meter scale optical
systems under cryogenic, vacuum conditions. Termed the Vertical Collimator Assembly (VCA), it features 1.5 m
diameter off-axis parabolic and calibration flat mirrors. In order to preserve as large a volume as possible for the unit
under test, the main platform is suspended inside its vacuum chamber by a hexapod, with the parabolic mirror mounted
overhead. A simultaneous interferometer facilitates collimator alignment and monitoring, as well as wavefront quality
measurements for the test unit. Diffusely illuminated targets may be employed for through-focus image quality
measurements with pinholes and bar targets. Mechanical alignment errors induced by thermal and structural
perturbations are monitored with a three-beam distance measuring interferometer to enable mid-test compensation.
Sources for both interferometer systems are maintained at atmospheric pressure while still directly mounted to the main
platform, reducing vibration and stability problems associated with thermal vacuum testing. Because path lengths inside
the ambient pressure vessels are extremely short, problems related to air turbulence and layering are also mitigated. In-chamber
support equipment is insulated and temperature controlled, allowing testing while the chamber shrouds and test
unit are brought to cryogenic temperatures.
The Wide Field Camera 3 (WFC3) instrument was designed and built to replace the Hubble Space Telescope (HST) instrument Wide Field and Planetary Camera 2 (WF/PC2) and to provide improved ultra-violet through near infrared imaging capability over the extended HST mission. We describe the optical component integration, alignment, and performance testing of the optical bench assembly.
The space telescope imaging spectrograph (STIS) instrument is due to be installed on board the Hubble Space Telescope (HST) in 1997. STIS uses 20 filters located on a wheel that can rotate any one of 88 apertures or combination filter/aperture in to the beam path. The instrument incorporates a continuous range of spectral response from the VUV (115.0 nm) to 1 micrometer. Therefore, filters that perform in the VUV are discussed as well as filters that operate in the near infrared. Neutral density filters are also being used for on-board calibration from 300 nm to Lyman-Alpha (121.6 nm).
To facilitate the accurate placement and alignment of the corrective optics space telescope axial replacement (COSTAR) structure, mechanisms, and optics, the COSTAR Alignment System (CAS) has been designed and assembled. It consists of a 20-foot optical bench, support structures for holding and aligning the COSTAR instrument at various stages of assembly, a focal plane target fixture (FPTF) providing an accurate reference to the as-built Hubble Space Telescope (HST) focal plane, two alignment translation stages with interchangeable alignment telescopes and alignment lasers, and a Zygo Mark IV interferometer with a reference sphere custom designed to allow accurate double-pass operation of the COSTAR correction optics. The system is used to align the fixed optical bench (FOB), the track, the deployable optical bench (DOB), the mechanisms, and the optics to ensure that the correction mirrors are all located in the required positions and orientations on-orbit after deployment. In this paper, the layout of the CAS is presented and the various alignment operations are listed along with the relevant alignment requirements. In addition, calibration of the necessary support structure elements and alignment aids is described, including the two-axis translation stages, the latch positions, the FPTF, and the COSTAR-mounted alignment cubes.
The corrective optics space telescope axial replacement (COSTAR) configuration contains mechanisms in each science instrument channel that allow for on-orbit correction for image plane focus and for lateral and axial mapping of the Hubble Space Telescope (HST) primary mirror onto the aspheric corrector mirrors. The optical alignment of the COSTAR optics is accomplished in two phases. In Phase I, the mirror bezel tilts and lateral positions are determined through the use of surrogate flat mirrors with the mechanism's positions held at the mid-range of their travel. The Phase I alignment is followed by Phase II interferometric optimization of all five optical channels. At the conclusion of the Phase I alignment, the optics are positioned accurately enough to allow simultaneous correction of most channels on orbit through the use of the mechanism compensation and telescope fine-pointing control. Individual mirror positions and orientations are determined through the use of alignment telescopes, theodolites, alignment lasers, and reference fiducials incorporated into the COSTAR Alignment System (CAS).