Michael D. Hill

Mirror Technology Development for the International X-ray Observatory Mission

The International X-ray Observatory mission is a collaborative effort of NASA, ESA, and JAXA. It will have unprecedented capabilities in spectroscopy, imaging, timing and polarization measurement. A key enabling element of the mission is a flight mirror assembly providing unprecedented large effective area (3 m2) and high angular resolution of (5 arcseconds half-power diameter). In this paper we outline the conceptual design of the mirror assembly and development of technology to enable its construction.

Optical Alignment and Test of the James Webb Space Telescope Integrated Science Instrument Module

The James Webb Space Telescope (JWST) is a 6.6 m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40 K). The JWST observatory architecture includes the optical telescope element (OTE) and the integrated science instrument module (ISIM) element that contains four science instruments (SI) including a guider. The SIs and Guider are mounted to a composite metering structure with outer dimensions of 2.1 times 2.2 times 1.9 m. The SI and guider units are integrated to the ISIM structure and optically tested at NASA/Goddard Space Flight Center as an instrument suite using an OTE SIMulator (OSIM). OSIM is a high-fidelity, cryogenic JWST telescope simulator that features a 1.5 m diameter powered mirror. The SIs are aligned to the structures coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. Temperature-induced mechanical SI alignment and structural changes are measured using a photogrammetric measurement system at ambient and cryogenic temperatures. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors in six degrees of freedom. SI performance, including focus, pupil shear and wavefront error, is evaluated at the operating temperature using OSIM. We describe the ambient and cryogenic optical alignment, test and verification plan for the ISIM element.

Alignment measurements of the Microwave Anisotropy Probe (MAP) instrument in a thermal/vacuum chamber using photogrammetry

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a 2001 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (< 0.3 degree(s) at 90 GHz) map of the cosmic microwave background radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the hardware and methods used to validate the displacement/deformation predictions of the reflectors and the microwave feed horns during thermal/vacuum testing of the reflectors and the microwave instrument. The smallest deformations to be resolved by the measurement system were on the order of +/- 0.030 inches (0.762 mm).

Photogrammetric Metrology for the James Webb Space Telescope Integrated Science Instrument Module

The James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). The JWST Observatory architecture includes the Optical Telescope Element and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SI) including a Guider. The ISIM structure must meet its requirements at the ~40K cryogenic operating temperature. The SIs are aligned to the structures coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. The ISIM structure is thermally cycled for stress relief and in order to measure temperature-induced mechanical, structural changes. These ambient-to-cryogenic changes in the alignment of SI and OTE-related interfaces are an important component in the JWST Observatory alignment plan and must be verified. We report on the planning for and preliminary testing of a cryogenic metrology system for ISIM based on photogrammetry. Photogrammetry is the measurement of the location of custom targets via triangulation using images obtained at a suite of digital camera locations and orientations. We describe metrology system requirements, plans, and ambient photogrammetric measurements of a mock-up of the ISIM structure to design targeting and obtain resolution estimates. We compare these measurements with those taken from a well known ambient metrology system, namely, the Leica laser tracker system.

Microwave anisotropy probe scientific instrument metrology

The Wilkinson Microwave Anisotropy Probe (WMAP) measures anisotropy or temperature differences in the Cosmic Microwave Background (CMB) radiation with high angular resolution and sensitivity, yielding unprecedented accuracy. To achieve this measurement, WMAP’s back-to-back Gregorian telescopes focus microwave radiation into 20 feed horns connected to 10 differential microwave radiometers. Proper alignment of the telescope reflectors, feed horns, and radiometers at flight temperatures was essential to the mission success. This paper will present the WMAP instrument metrology requirements and associated challenges, discuss the opto-mechanical tooling utilized to accomplish these objectives, and then give an overview of the metrology effort. The WMAP instrument integration effort included the following key metrology tasks: alignment and clocking of 20 microwave feed horns and mating microwave differencing assemblies within a focal plane assembly; alignment of a pair of primary and secondary reflectors composing back-to-back Gregorian telescopes; and the placement of the focal plane assembly and reflector system relative to each other, and as a unit on the spacecraft. WMAP environmental test metrology efforts included: reflector and truss thermal stability at 80 K; reflector and feed horn position verification at 90 K, and pre and post vibration and acoustic test reflector and feed horn position verification. The WMAP instrument integration and test objectives required the use of a photogrammetric camera, a laser tracker, a portable coordinate measuring machine (PCMM), and theodolites utilizing an electronic theodolite metrology system (ETMS) and autocollimation. The synergy of these metrology systems facilitated the successful characterization of the WMAP scientific instrument mechanical performance data at room temperature and flight temperatures, and correlation of the data to the analytical model. WMAP was launched on July 1, 2001, and flight data has confirmed the proper on-orbit instrument alignment was achieved.

Photogrammetrically measured distortions of a composite microwave reflector system in vacuum at ~90 K

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a 2001 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (< 0.3 degree(s) at 90 GHz) map of the cosmic microwave background radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the methods and analysis used to validate the in-flight position and shape predictions for the reflectors based on photogrammetric metrology data taken under vacuum with the reflectors at approximately 90 K. Contour maps showing reflector distortions were generated. The resulting reflector distortion data are shown to be crucial to the analytical assessment of the MAP instruments microwave system in- flight performance.