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.