September-October 1982:JPL space report

IRAS

The first satellite survey of the celestial sphere in the infrared portion of the spectrum will be accomplished by IRAS, a cryogenic satellite scheduled for launch into a 900 km, Sun-synchronous orbit late this year. The project is an international endeavour, with JPL managing the US half, The Netherlands managing the European half, and the UK supplying the tracking station and associated support at the Rutherford and Appleton Laboratories near Chilton, England.

Data taken by the 60 cm telescope (sensitive in the 8 to 120 micron range) will be stored on a tape recorder and dumped twice per day during passes over the Chilton station. These data are electronically transferred to JPL and processed by the Scientific Data Analysis System (SDAS), which is based upon a highly sophisticated set of computer programmes designed specifically for IRAS data processing.

The basic processing will be accomplished on an IBM 3032 and the primary product will be a catalogue of infrared point sources, primarily stars and galaxies. Somewhere between 250,000 to 1,000,000 such sources are expected. This catalogue should serve generations of astronomers as a guide to the infrared sky and as a research tool to assist in identifying interesting objects suitable for more detailed study.

Although the telescope does not directly produce photographic products, SDAS processing will yield photographic¬ like representations of large regions of the sky in order to show bulk distribution of stars, dust, and gas. After an initial “shakedown” period of two to three months following launch, SDAS will process data within a few days of receipt at the ground station. This prompt analysis will assist mission planners in their assessment of mission progress, and may result in changes to the strategy of sky coverage.

The JPL project manager for IRAS is Gerald M. Smith. John H. Duxbury manages SDAS, and Dr. B. T. Soifer of Caltech is the principal science advisor for SDAS matters.

LOW-COST PLANETARY MISSIONS

The Mariner Mark II project (MMII) was initiated recently at JPL in order to develop a set of planetary missions which will allow continued exploration of the Soiar System under very tight budget constraints. The central idea is to design the mission “set" so that a relatively constant yearly expenditure suffices. The fiscal target is a cost of about $100 million (1982 dollars) per year for the funding of four to five missions launched in the 1989 to 1998 period. Focussed science, reduced complexity, and maximised inheritance (hence the Mariner Mark II designation) are key to achieving the MMII goals.

The mission set for MMII is still under study but several mission types are being considered:

1. Comet rendezvous

2. Comet intercept/sample return

3. Asteroid rendezvous (near Earth and main belt)

4. Mars orbiter

5. Titan flyby/Titan probe

6. Saturn orbiter/Titan mapper

The indicated launch vehicle for these missions is the STS/IUS 2-stage with or without the STAR-48 kick stage.

SHUTTLE EXPERIMENTS

Two of the seven experiments aboard the Space Shuttle Columbia were designed by JPL for the scientific payload flown 12-14 November 1981.

The Shuttle Imaging Radar-A (SIR A) represents a natural outgrowth from a JPL technological base for synthetic aperture radars (SAR), one of which was employed on the 1978 Seasat oceanographic satellite. The SAR technology also played a prominent role in the design of the Venus Orbiting Imaging Radar mission (VOIR), now cancelled due to budgetary constraints.

SIR-A obtained eight hours of data covering ten million square kilometers of Earth, including a 45 minute swath from Spain, through the Mediterranean, and out to India and Australia.

The primary advantage of SAR observations over more conventional optical images is that the SAR supplies its own microwave illumination and is not limited by the presence of clouds or the lack of sunlight. After processing, the SIR-A system can yield a spatial resolution of 40 m. This resolution is obtained using an antenna which measures 9.35 by 2.0 m.

The failure of a fuel cell onboard Columbia necessitated an early return to Earth and a resultant disruption of the original mission design for the SIR-A experiment. However, using a microcomputer equipped with an advanced graphical software package. Henry Harris (team leader) and Joan Pojman of JPL rapidly redesigned the experimental procedures, and a new set of commands was sent to the crew in time to successfully obtain the data.

The Principal Investigator for the SIR A experiment was Charles Elachi of JPL.

The second experiment, the Shuttle Multispectral Infrared Radiometer (SMIRR), was flown in order to investigate Earth resources.

The spectral reflectance of rocks and soil on the surface of the Earth permits inferences to be made concerning the composition of surface materials or possible petroleum deposits below the surface. The system consists of a 17.8 cm telescope (derived from a telescope flown on the 1973 Mariner 10 Mission to Venus and Mercury), filters, detectors, and other supporting equipment. Ten bands within the 1.0 to 2.5 micron portion of the infrared were tested for effectiveness in providing clues to surface composition. Since the SMIRR is not an imaging device, two cameras (one colour and one black and white) were aligned with the SMIRR telescope to provide images which can be correlated with the SMIRR data.

Initial results obtained from analysis of the data from this instrument were announced at a meeting of the American Society of Photogrammetry in Denver. Colorado in March 1982. In one case the SMIRR appears to have surpassed normal field techniques in the ability to differentiate between minerals!

The Principal Investigator was Dr. Alexander Goetz of JPL.