Engineering topics
Publications and source records attributed to Irace, W. R..
This paper will provide an overview of the SIRTF mission, telescope, cryostat, instruments, spacecraft, orbit, and operations in preparation for an accompanying set of detailed technical presentations.
A study was carried out at JPL during the first quarter of 1985 to develop a system concept for NASA's LDR. Major features of the concept are a four-mirror, two-stage optical system; a lightweight structural composite segmented primary reflector; and a deployable truss backup structure with integral thermal shield. The two-stage optics uses active figure control at the quaternary reflector located at the primary reflector exit pupil, allowing the large primary to be passive. The lightweight composite reflector panels limit the short-wavelength operation to approximately 30 microns but reduce the total primary reflector weight by a factor of 3 to 4 over competing technologies. On-orbit thermal analysis indicates a primary reflector equilibrium temperature of less than 200 K with a maximum gradient of about 5 C across the 20-m aperture. Weight and volume estimates are consistent with a single Shuttle launch, and are based on Space Station assembly and checkout.
The Infrared Astronomical Satellite (IRAS) was launched on January 25, 1983, and has provided astronomers with their first extended views of the universe in the 8 to 120 micron wavelength region. The infrared telescope system is one of several United States contributions to this international project sponsored by the U.S.A., The Netherlands, and the U.K. This telescope employs four bands of detectors cooled to 2.4 K to achieve a noise equivalent flux density in the 10 to the -18th to 10 to the -19th watts/sq cm range and will operate for approximately eleven months before depletion of its supply of superfluid helium. This paper describes major problems, early flight results, and technical lessons learned during the course of the telescope's development and flight operations.
The Infrared Astronomical Satellite, to be launched in August 1981, will perform an all-sky survey in the 8-120 micron wavelength region. High sensitivity to thermal radiation and the low operating temperature of optics and thermal control surfaces make the IRAS telescope extremely vulnerable to contamination. Four special topics of importance are discussed in this paper: (1) deposition of atmospheric gases; (2) sighting of particles released from the satellite; (3) functions of a deployable aperture cover; and (4) degradation of a radiatively cooled sunshade from spacecraft outgassing. These topics demonstrate how mission strategy, ground cleaning and handling, and hardware design are used to avoid contamination which would degrade telescope performance.
The feasibility of developing a solar electric multimission spacecraft (SEMMS) is examined with emphasis on understanding the effect of solar electric propulsion elements on a spacecraft system design. The applicability of Mariner, Viking, and thermoelectric outer planet spacecraft (TOPS) technologies to postulated mission/science objectives is investigated. A Mariner/Viking-based, modular spacecraft evolves which, with minimum modifications, is capable of performing a variety of interplanetary missions, including comet and asteroid rendezvous and orbit of Mercury, Jupiter, and Saturn. An early technology-evaluation flight is recommended to minimize the risk in subsequent missions.