The accurate measurement of the orientation of optica l parts and systems is a pressing problem for upcoming space m issions, such as stellar interferometers, requiring the know ledge and maintenance of positions to the sub-arcsecond level. Theodo lites, the devices commonly used to make these measurements, cannot provide the needed level of accuracy. This paper describes the design, construction, and testing of an interferometer system to fill the w idening gap between future requirements and current capabi lities. A Twyman-Green interferometer mounted on a 2 degree of freedom rotation stage is able to obtain sub-arcsecond , gravity-referenced ti It measurements of a sample al ignment cube. Dubbed a 'theoferometer,' this device offers greater ease-of-use, accuracy, and repeatability than conventional methods, making it a suitable 2 1 st-century replacement for the theodol ite.

The increasing difficulty of metrology requirements on projects involving optics and the alignment of instrumentation on spacecraft has reached a turning point. Requirements as low as 0.1 arcseconds for the static, rotational alignment of components within a coordinate system cannot be met with a theodolite, the alignment tool currently in use. A "theoferometer: is an interferometer mounted on a rotation stage with degrees of freedom in azimuth and elevation for metrology and alignment applications. The success of a prototype theoferometer in approaching these metrology requirements led to a redesign stressing mechanical, optical, and software changes to increase the sensitivity and portability of the unit. This paper covers the improvements made to the first prototype theoferometer, characteristic testing, and demonstration of the redesigned theoferometer's capabilities as a "theodolite replacement" and low-uncertainty metrology tool.

The Infrared Multi-Object Spectrograph (IRMOS) is a facility instrument for the Kitt Peak National Observatory Mayall Telescope (3.8 meter). IRMOS is a low-to mid-resolution (R X/AX 300-3000), near-JR (0.8-2.5 rim) spectrograph that produces simultaneous spectra of -100 objects in its 2.8 x 2.0 arcmin field of view using a commercial MEMS multi-mirror array device. The instrument operating temperature is '-8O K and the design is athermal. The optical bench and minors are machined from aluminum 6061-T65 1.In spite of its baseline mechanical stress relief, aluminum 606 1-T65 1 harbors some residual stress, which, unless relieved during fabrication, may distort mirror figure to unacceptable levels at the operating temperature (8O K). Other cryogenic instruments using aluminum minors for both ground-based and space JR astronomy have employed a variety of heat treatment formulae, with mixed results.We present the results of a test program designed to empirically determine the best stress relief procedure for the IRMOS mirrors. Identical test minors with spherical and flat optical prescriptions are processed with five different stress relief formulae from the literature and institutional heritage and compared to samples without any additional processing. After figuring via diamond turning, the mirrors are tested for figure error and radius of curvature at room temperature and at -8O K for three thermal cycles. The heat treatment procedure for the mirrors that yielded the least and most repeatable change in figure error is applied to the IRMOS mirror blanks. We correlate the results of our optical testing with heat treatment and metallographic data.

We present the results of an on-going test program designed to empirically determine the effects of different stress relief procedures for aluminum mirrors used in cryogenic applications. Earlier test results identified a preferred heat treatment for flat and spherical mirrors diamond turned from blanks cut out of Al 6061-T651 plate stock 1 . Further tests were performed on mirrors from forged stock to measure the effect of this variable on cryogenic performance. The mirrors are tested for figure error and radius of curvature at room temperature and at 80 K for at least three thermal cycles. We correlate the results of our optical testing with heat treatment and metallographic data.

The Earth Atmospheric Solar-Occultation Imager (EASI) is a proposed interferometer with 5 telescopes on an 8-meter boom in a 1D Fizeau configuration. Placed at the Earth-Sun L2 Lagrange point, EASI would perform absorption spectroscopy of the Earth's atmosphere occulting the Sun. Fizeau interferometers give spatial resolution comparable to a filled aperture but lower collecting area. Even with the small collecting area the high solar flux requires most of the energy to be reflected back to space. EASI will require closed loop control of the optics to compensate for spacecraft and instrument motions, thermal and structural transients and pointing jitter.The Solar Viewing Interferometry Prototype (SVIP) is a prototype ground instrument to study the needed wavefront control methods. SVIP consists of three 10 cm aperture telescopes, in a linear configuration, on a 1.2-meter boom that will estimate atmospheric abundances of O 2 , H 2 O, CO 2 , and CH 4 versus altitude and azimuth in the 1.25 -1.73 micron band. SVIP measures the Greenhouse Gas absorption while looking at the sun, and uses solar granulation to deduce piston, tip and tilt misalignments from atmospheric turbulence and the instrument structure. Tip/tilt sensors determine relative/absolute telescope pointing and operate from 0.43 -0.48 microns to maximize contrast. Two piston sensors, using a robust variation of dispersed fringes, determine piston shifts between the baselines and operate from 0.5 -0.73 microns. All sensors are sampled at 800 Hz and processed with a DSP computer and fed back at 200 Hz (3 dB) to the active optics. A 4 Hz error signal is also fed back to the tracking platform. Optical performance will be maintained to better than λ/8 rms in closed-loop.