The most recent study of the Wide Field Infrared Survey Telescope (WFIRST) mission is based on reuse of an
existing 2.4m telescope. This study was commissioned by NASA to examine the potential science return and cost
effectiveness of WFIRST by using this significantly larger aperture telescope. We review the science program
envisioned by the WFIRST 2012-2013 Science Definition Team (SDT), an overview of the mission concept, and
the telescope design and status. Comparisons against the previous 1.3m and reduced cost 1.1m WFIRST design
concepts are discussed. A significant departure from past point designs is the option for serviceability and the
geostationary orbit location which enables servicing and replacement instrument insertion later during mission
life. Other papers at this conference provide more in depth discussion of the wide field instrument and the optional
exoplanet imaging coronagraph instrument.
SAFIR is a 10-meter, 4 K space telescope optimized for wavelengths between 20 microns and 1 mm. The combination of aperture diameter and telescope temperature will provide a raw sensitivity improvement of more than a factor of 1000 over presently-planned missions. The sensitivity will be comparable to that of the JWST and ALMA, but at the critical far infrared wavelengths, where much of the universe's radiative energy has emerged since the origin of stars and galaxies. We examine several of the critical technologies for SAFIR which enable the large cold aperture, and present results of studies examining the spacecraft thermal architecture. Both the method by which the aperture is filled, and the overall optical design for the telescope can impact the potential scientific return of SAFIR. Thermal architecture that goes far beyond the sunshades developed for the James Webb Space Telescope will be necessary to achieve the desired sensitivity of SAFIR. By optimizing a combination of active and passive cooling at critical points within the observatory, a significant reduction of the required level of active cooling can be obtained.
The Dual Anamorphic Reflector Telescope (DART) is an architecture for large aperture space telescopes that enables the use of membranes. A membrance can be readily shaped in one direction of curvature using a combination of boundary control and tensioning, yielding a cylindrical reflector. Two cylindrical reflectors (orthogonal and confocal) comprise the 'primary mirror' of the telescope system. The aperture is completely unobstructed and ideal for infrared and high contrast observations. The DART high precision testbed researches fabrication, assembly, adjustment and characterization of 1 meter cylindrical membrane reflectors made of copper foil or kapton. We have implemented two metrology instruments: a non-contacting, scanning profilometer and an infrared interferometer. The profilometer is a laser confocal displacement measuring unit on an XYZ scanning stage. The infrared interferometer used a cylindrical null lens that tests a subaperture of the membrane at center of curvature. Current surface figure achieved is 25 μm rms over a 50 cm diameter aperture.
A 2-meter by 4-meter aperture DART (dual anamorphic reflector telescope) system has been designed and fabricated using thin stretched mesh reflectors. The system concept consists of a pair of single curvature reflectors with curvature in orthogonal directions relative to each other and is being developed for future ultra-lightweight space applications. The current design is an extension of a 1-meter aperture system previously prototyped and successfully tested in the FarIR. The 2m x 4m system is a laboratory prototype with areal density of less than 10kg/m2 for each reflector. The new design demonstrates the advantageous scaling properties of the single curvature reflector concept. The 2m x 4m system was configured and tested in the RF over several frequencies from 5.8 - 8.2 GHz. This paper documents the structural configuration, test preparation, test results, and analysis correlation. Test results show the DART system to be a high directivity antenna (46.5 dB), very low cross-polarization (-33 dB), and good off-axis properties. Test results were in good agreement with analytical predictions of the performance. Generally, the DART system easily achieves the surface accuracy requirements at 8.2 GHz.
Damping of axial and bending mode vibrations in giant magnetoelastic polycrystalline TbDy alloys was studied at cryogenic temperatures. All specimens of TbDy were arc-melted in the proper composition ratio and dropped into a chilled copper mold. Additional treatments consisted of cold plane-rolling to induce crystallographic texture and then heat-treating to relieve internal stress. Mechanical hysteretic losses were measured at various strains, frequencies, and loading configurations down to 77 K. Both as-cast and textured polycrystalline TbDy samples were tested along with an aluminum specimen for comparison. Loss factors at multiple natural vibration frequencies of the samples were measured for axial modes. Larger damping rates were measured for axial mode vibrations than for bending mode vibrations, possibly reflecting the larger specimen volume contributing to magnetoelastic damping. At LN2 temperatures TbDy materials demonstrated η > 0.05 at 0.01 Hz and η > 0.1 at higher frequencies from 0.6-1.5 kHz.
A 1.2-meter prototype Dual Anamorphic Reflector Telescope (DART) system has been built and tested. The key design feature of the telescope is a pair of membrane mirrors stretched to single curvature parabolic cylindrical sections. The parabolic figure of the mirrors is controlled by a pair of edge rails at two opposing ends of the membrane. The flexible edge rails are adjusted to parabolic to very high accuracy and can potentially be easily refigured on-orbit. The prototype telescope is lightweight and has demonstrated excellent optical performance for the farIR. The design is readily scalable to larger apertures and for operation at shorter wavelengths. Design and test results are discussed.
NASA's Space Infrared Telescope Facility (SIRTF) is a 1- meter class cryogenically-cooled space observatory. The constituent sub-assemblies are currently in their assembly and verification phase. To facilitate the assembly and verification of the telescope, the Space Telescope Test Facility (STTF) has been built at the Jet Propulsion Laboratory. The STTF allows for the assembly, alignment, and optical characterization of individual components, as well as the telescope assembly with its cryogenic mechanism, at temperatures from 300 to 5 K in a chamber with interior diameter of 1.4 m, and a height of 2.3 m. The chamber is surrounded by a class 10,000 or better clean room. This paper reports on the functional and operational capabilities of this facility.