The Submillimeter High Angular Resolution Camera II (SHARC-II) is a 32 x 12 pixel submillimeter camera that is used with the ten-meter diameter Caltech Submillimeter Observatory (CSO) on Mauna Kea. SHARC-II can be operated at either 350 or 450 microns. We are developing an optics module that we will install at a position between the SHARC-II camera and the focus of the CSO's secondary mirror. With our module installed, SHARC-II will be converted into a sensitive imaging polarimeter. The basic idea is that the module will split the incident beam coming from the secondary into two orthogonally polarized beams which are then re-imaged onto opposite ends of the “long and skinny” SHARC-II bolometer array. When this removable polarimetry module is in use, SHARC-II becomes a dual-polarization 12 x 12 pixel polarimeter. (The central 12 x 8 pixels of the SHARC-II array will remain unused.) Sky noise is a significant source of error for submillimeter continuum observations. Because our polarimetry module will allow simultaneous observation of two orthogonal polarization components, we will be able to eliminate or greatly reduce this source of error. Our optical design will include a rotating half-wave plate as well as a cold load to terminate the unused polarization components.
The Stratospheric Observatory for Infrared Astronomy (SOFIA) will carry a 2.5 meter effective aperture telescope onboard a Boeing 747SP aircraft to altitudes of 41,000 to 45,000 ft, above most of the atmosphere's IR-absorbing water vapor. SOFIA will start its astrophysical observations in early 2005, flying from Moffett Field, California with a suite of specialized cameras and spectrometers covering wavelengths between 0.3 and 600 m. A high-speed visible range CCD camera will use the airborne observatory to chase the shadows of celestial bodies during occultations. The SOFIA telescope was designed and built in Germany and has been delivered to the U.S. in September 2002. Its integration into the B747SP is well advanced so flight-testing will start in mid of 2004. After an initial test phase dedicated to the re-certification of the modified aircraft, functional and performance tests of the telescope and other scientific systems will commence. At NASA's Ames Research Center the ground support facilities for the observatory are being prepared.
The SOFIA Airborne Observatory will operate a 2.5 m aperture telescope with the goal of obtaining over 960 successful science hours per year at a nominal altitude of 12.5 km and covering a wavelength range from 0.3 mm to 1.6 mm. The observatory platform is comprised of a Boeing 747SP with numerous significant modifications. The ground and flight mission operations architectures and plans are tailored to keep the telescope emissivity low and achieve high observing efficiency.
A brief introduction to SOFIA will be given with an outline of its planned investigator program, followed with a summary of the expected performance capabilities of SOFIA at first light. The remainder of the paper will then give examples of SOFIA science to be expected from science instruments to be commissioned on the observatory within the first year os operation.
This paper will summarize the stray-light study commissioned by USRA from BRO (Breault Research Organization) to estimate the level of dynamic background that might be observable at SOFIA's focal plane. This dynamic background is due to cavity and aircraft motions with respect to the inertially fixed telescope. BRO used their ASAP program to trace rays emitted from the Earth, aircraft engines, and telescope cavity to the focal plane through reflection and scatter off a number of surfaces (including Level 500 contaminated optics).
The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is a direct detection, imaging, submillimeter spectrometer. The spectral resolving elements are a pair of cryogenic, scanning Fabry-Perot interferometers which use a free- standard Ni mesh for the etalon mirrors. The detectors for SPIFI are a 5 X 5 array of bolometers coupled to the focal plane with Winston cones. An adiabatic demagnetization refrigerator cools the bolometers to approximately 60 mK while a 3He system operates simultaneously as a thermal guard. SPIFI is intended to operate on the ASO/RO submillimeter telescope at the South Pole and on the JCMT telescope on Mauna Kea and will be used to study the gas- phase reservoirs of carbon in star-forming regions in our own and near-by galaxies. SPIFI takes advantage of three things: (1) Advanced bolometers that achieve background limited performance at very high resolving powers. (2) The imaging capability and high spectral resolving power of Fabry-Perot interferometers. (3) The superb atmospheric transmission in submillimeter bands possible from the South Pole. The SPIFI uses state-of-the-art monolithic silicon bolometers fabricated at the NASA Goddard Space Flight Center. The cryogenic, scanning Fabry-Perots in SPIFI were designed and built at Cornell and are an evolution of the design used with great success for the Kuiper Wide Field Camera. The 1.7 m Antarctic Submillimeter Telescope/Remote Observatory exploits what is thought to be the best submillimeter observing site in the world.
The joint US and German SOFIA project to develop and operate a 2.5 meter IR airborne telescope in a Boeing 747-SP is now in its second year. The Universities Space Research Association , teamed with Raytheon E-Systems and United Airlines, is developing and will operate SOFIA. The 2.5 meter telescope will be designed and built by a consortium of German companies led by MAN. Work on the aircraft and the preliminary mirror has started. First science flights will begin in 2001 with 20 percent of the observing time assigned to German investigators. The observatory is expected to operate for over 20 years. The sensitivity, characteristics, US science instrument complement, and operations concept for the SOFIA observatory, with an emphasis on the science community's participation are discussed.