Introduction: The Phoenix Mars Lander will begin a 90-sol mission in Mars’ north polar terrain on 25 May 2007. A Robotic Arm (RA) on the lander will dig one or more trenches, providing soil and ice samples to two deck chemistry instruments. Through the mission, a meteorology station (MET) and Lidar will measure pressure, temperature, and boundary layer properties. This abstract describes the multispectral science camera on Phoenix, the Surface Stereo Imager (SSI). The capabilities of the SSI respond to a number of constraints, both scientific and operational. SSI will be used to derive digital terrain maps used to guide the RA in digging and sampling operations; thus it requires stereo viewing capabilities. Selection of scientific targets for digging and sampling will be guided by images of the RA workspace: a Robotic Arm camera offers close-up detail views and SSI adds multispectral imaging. Documentation of sample material around the on-deck instruments requires special diopter filters for maximum resolution. SSI will monitor atmospheric optical depths both for studying polar weather and for understanding spacecraft performance in combination with solar panel data; thus neutral density filters capable of direct solar imaging are included. Phoenix includes a tell-tale for wind measurements, and SSI is used to monitor the tell-tale.

The cost and leadtime associated with beryllium has forced the MDA and other defense agencies to look for alternative materials with similar structural and thermal properties. The use of carbon-carbon material, specifically in optical components has been demonstrated analytically in prior SBIR work at San Diego Composites. Carbon-carbon material was chosen for its low in-plane and through-thickness CTE (athermal design), high specific stiffness, near-zero coefficient of moisture expansion, availability of material (specifically c-c honeycomb for lightweight substrates), and compatibility with silicon monoxide (SiO) and silicon dioxide (SiO2) coatings. Subsequent development work has produced shaped carbon-carbon sandwich substrates which have been ground, polished, coated and figured using traditional optical processing. Further development has also been done on machined monolithic carbon-carbon mirror substrates which have also been processed using standard optical finishing techniques.

Future space telescopes require primary mirrors that are much lighter than those currently being manufactured. They also must maintain optical tolerances while operating at cryogenic temperatures. We present a Mirror System Demonstrator for the Next Generation Space Telescope (NGST) that uses a thin glass facesheet with active control to achieve low mass and high surface quality. A 2-mm thick glass facesheet is controlled by miniature actuators and held together by a rigid carbon fiber frame. The 2-m diameter mirror system weighs only 13 kg/m2, including the glass, supports, actuators, support structure, and cabling. We present the status of the development and testing of this revolutionary mirror.

Fabrication of composite sandwich panel mirrors has advanced sufficiently in surface accuracy and thermal stability to consider a thin composite membrane supported by rigid active supports for a large space mirror. We are carrying out a technology development with a 0.5-meter diameter, 0.5-mm thick composite membrane on a 36-actuator support. Measurements will be made of the controlled figure at ambient and low temperatures to determine the figure accuracy and stability and the validity of the mathematical performance analysis.

Fabrication of composite sandwich panel mirrors has advanced sufficiently in surface accuracy and thermal stability to consider a thin composite membrane supported by rigid active supports for a large space mirror. We are carrying out a technology development with a 0.5-meter diameter, 0.5-mm thick composite membrane on a 36-actuator support. Measurements will be made of the controlled figure at ambient and low temperatures to determine the figure accuracy and stability and the validity of the mathematical performance analysis.

Recent developments in the design and fabrication of very light-weight all-composite mirrors have made possible extremely well balanced, thermally stable, structures which distort very little when cooled. One such mirror is the Composite Optics, Incorporated all-composite mirror, M4, which has a 45.7 cm diameter and 3 cm thickness and a spherical surface of radius-of-curvature 2.92 meters. Relative figure measurements of this mirror were made with the Steward Observatory Light Weight Mirror Low Temperature Test Chamber over a temperature range from 20 C to -60 C using a 10.6 μm interferometer. The measurements show a remarkably small increase in the rms figure departure from a spherical surface of fixed radius-of-curvature of 0.27 μm over the 80 C temperature change. The effective coefficient of thermal expansion over this temperature range derived from the focus change is 0.66 x 10-6/C, close to that of fused silica.

We have achieved reliable, repeatable coatings of solgel-deposited glass on Carbon Fiber Reinforced Plastic (CFRP) sandwich panel mirrors of sizes 10 to 90 cm. Very lightweight CFRP panels up to 2 meter size have been produced with high thermal and temporal stability, but replicated surface accuracy limited to millimeter and sub-millimeter applications. The solgel coatings of 20 to 200 mu m thickness provide a surface which can be optically ground, polished, and figured to provide infrared and optical quality mirrors. We have demonstrated this with both flat and concave spherical mirrors.

We have been able to utilize silicon monoxide (SiO) as a refractory coating to improve on the replicated figure of composite optics made from carbon fiber reinforced plastic (CFRP) sandwich panels. We apply an evaporative coating of SiO to the surface of the mirror and polish that coating to obtain the desired figure for the complete mirror. We have developed this technique to allow the use of CFRP optics which are both stable and have a low areal density. This represents a novel use of thin film vacuum coating to produce an optical substrate rather than a simple reflective or protective overcoating and represents an advance in producing thick SiO coatings (10 - 40 micrometers) over large areas (25 - 60 cm).

We have been able to utilize silicon monoxide (SiO) as a refractory coating to improve on the replicated figure of composite optics made from Carbon Fiber Reinforced Plastic (CFRP) sandwich panels. We apply an evaporative coating of SiO to the surface of the mirror and polish that coating to obtain the desired figure for the complete mirror. We have developed this technique to allow the use of CFRP optics which are both stable and have a low areal density. This represents a novel use of thin Nm vacuum coating to produce an optical substrate rather than a simple reflective or protective overcoating and represents an advance in producing thick SiO coatings (10-40 mu m) over large areas (25-60 cm).

Since 1984, low temperature optical tests were made of very lightweight mirror panels for use in balloon and space infrared and submillimeter telescopes. In order to accomplish this testing, an ambient pressure 0.5 meter test chamber operating from 20 to -80 C, developed techniques for measuring non-optical quality mirrors with phase modulation 10.6 micron interferometry, and created the interferogram reduction program. During the course of the program, nineteen mirrors from four manufactures were tested: carbon fiber reinforced plastic (CFRP) aluminum honeycomb sandwich panel mirrors, a CFRP sandwich panel with an added glass facesheet, and carbon fiber reinforced glass panels. The results of the panel development and test program are summarized.

As part of a design study for a balloon-borne 3-m telescope for far-infrared and submillimeter astronomy, it has been necessary to test and evaluate the state-of-the-art for ultra lightweight primary mirror material candidates. In addition to being ultra lightweight (I0kg/m2), the primary mirror of this telescope must operate at -50°C with 300 diffraction limited performance. Evaluating the performance of mirror candidates has required cooling them in a low temperature test chamber while remotely monitoring the surface figure changes at several different temperatures. Some of the test panels were constructed with surfaces not smooth enough to provide recognizable 10p fringes suitable for analysis by standard Fringe techniques. To deal with this problem, we have successfully developed an analysis technique and software for a microcomputer which reliably generates surface maps from pathological interferograms. The programs operate rapidly and can provide a variety of outputs such as surface map averages, differences, Zernike polymonial coefficients, and RMS residuals during the tests. The system can also compensate for camera and test optics field distortions.

Development of carbon fiber reinforces plastic (CFRP) panel overcoating and polishing is structured in two parts. The first part utilized a short series of experiments to determine the feasibility of overcoating and polishing CFRP panels, and the second part employes a systematic approach to optimize techniques learned. Questions which required answers in the initial investigation are summarized. Tests were performedin the Steward Observatory's 2.2 Meter Vacuum Coating Chamber and began with 3 cm square pieces of CFRP facesheet material. Next, a 10 cm square and one-inch-thick CFPR-Aluminum core panel was tested. Tests were then conducted on a 0.5-meter-square Dornier panel (QUAD 4) with CFRP facesheets on two-inch aluminum Flexcore. To complete the initial study, a previously characterized 0.5 m Dornier panel (QUAD 23) was coated and hand polished. The mirror's optical performance was not affected by the SiO coating.