December 1982:JPL space report

VENUS RADAR MAPPER MISSION

The Venus Orbiter Imaging Radar (VOIR) mission was cancelled by the Reagan administration in January 1982 for budgetary reasons. JPL mission designers reviewed the remaining Venus-exploration options and came to the conclusion that ellipses are cheaper than circles. The VOIR mission would have placed a synthetic-aperture radar (SAR) 250 km above the planet in a circular, near-polar orbit, with the intention of mapping most of the planet to a resolution of about 600 m. The Venus Radar Mapper (VRM) mission would place a SAR-equipped spacecraft in orbit about Venus for global mapping at about 1 km resolution but would not cir cularise the orbit.

Eliminating the need to circularise the orbit, which would have been done by mass expulsion or aerobraking, results in a simpler, less expensive spacecraft design. Since mission costs are almost always dominated by the expense of the spacecraft, it is clear that significant cost savings might result. In fact, the total mission cost has been cut approximately in half, to under a run-out cost of $300 million dollars. In order to achieve these savings some atmospheric science which was planned for VOIR had to be excluded from VRM.

Despite previous missions to Venus by the United States and Russia. Venus is the only terrestrial planet which has not been characterised geologically. The status of exploration of the second planet has been likened to that of the United States in the early 1800’s when the gross physiography was known, but not the geologic processes which shaped it. The smaller terrestrial planets (Moon, Mercury and Mars) have been fashioned by two major geologic processes: impact cratering and vulcanism. In addition, they are one-plate planets with a single, global lithospheric plate. They also possess ancient surfaces, over 2.5 thousand million years old, which aredargely unmodified since the time of the early Solar System. These planets are in distinct contrast to the Earth, and a primary question is how Venus fits into this geological dichotomy.

The basic mission plan for VRM consists of an April 1988 launch from the Shuttle with a Centaur upper stage and an arrival at Venus in July 1988. The nearly 900 kg spacecraft will be inserted into a 3.7 hour elliptical orbit inclined at 83 degrees to the Venusian equator.

The mapping strategy will employ the same antenna for collecting data (at a rate of over 600 kilobits per second) that will be used to transmit the science data to Earth, at 230 kilobits per second. On every orbit, the planet will be mapped by the SAR at 71 degrees on each side of periapsis, about 41 minutes total time per orbit, and the antenna will then be reoriented toward Earth for playback of the tape-recorded data. This mode of operation results in the planet being mapped at a range which varies from 250 km at periapsis to 1900 km at ±71 degrees true anomaly.

The side-looking radar will map 92 percent of the surface of Venus at 1 km resolution if all goes according to plan. Only small polar caps in the north and south will be excluded; they may be included in the map but at lower resolution. The total mission requires eight months in orbit, with the mapping being completed just as Venus enters into solar conjunction.

The project manager for VRM is John Gerpheide, who played a key role as spacecraft manager in the highly successful Seasat mission which first demonstrated the value of the SAR as a planetary-mapping device. A second application of SAR technology took place with the SIR-A experiment on the third flight of the Shuttle. It is clear that the SAR technology would not only be useful in penetrating the cloud cover of Venus but could also provide that service for a Titan mapper mission or a search for sand-buried water features on Mars (SIR-A traced out ancient drainage patterns under the dry sands of the Sahara).

The VRM mission has been presented to NASA with the intent that it be formally initiated as a project as early as October 1983, pending approval by NASA, the Reagan administration and Congress.

NEW DIRECTOR FOR JPL

Dr. Lew Allen, Jr. assumed the post as Director of JPL in October. In addition to the lead role at JPL, Allen was also named as a Vice President of the California Institute of Technology, which operates JPL. Until his retirement from the US Air Force last June, Allen held the rank of general and was the Air Force’s Chief of Staff and a member of the Joint Chiefs of Staff. He has a Ph.D. in physics from the University of Illinois.

With the selection of Allen it is clear that Caltech and JPL plan to move actively and aggressively to meet the challenges to the Laboratory that have been posed by the erosion of its traditional market: interplanetary missions for NASA. The new director brings three obvious strengths to the Laboratory: administrative ability demonstrated by leading a combined military and civilian workforce of nearly one million people, experience in space systems acquired by heading several of the Air Force’s top satellite and missile programmes, and an insider’s knowledge of Washington and the military. JPL may devote up to 30 per cent of its activity to military projects in the future.

The basic commitment of JPL to the exploration of space for scientific purposes was underscored by Allen’s appointment as a Vice President of Caltech. In addition he has stated, “JPL has done magnificant things in planetary exploration. I intend to seek the support of space scientists and do the best I can to continue that record of achievement.”

Lew Allen was born on 30 September 1925 in Gainesville, Texas. He graduated in 1946 from the US Military Academy at West Point and received his Ph.D. in physics in 1954 from the University of Illinois. He worked as a research physicist at Los Alamos Scientific Laboratory and, in 1957, became science adviser to the Physics Division of the Air Force Special Weapons Center. In 1962 he worked in the Space Technology Office of the Secretary of Defense. From 1965 to 1973 he served in the Office of the Secretary of the Air Force in several roles, including that of Director of Space Systems at the Pentagon, and Director of the Space and Missile Systems Organization. From 1973 to 1977 he held several national security posts and in 1977 was named as commander of the Air Force Systems Command.