Mariner Mark Ii Spacecraft

Mariner Mark Program

The Mariner Mark II spacecraft is designed specifically to carry out deep space missions to comets, asteroids, and the outer planets. The spacecraft will theretore be equipped to meet a multiplicity of demands imposed by the nature of these missions, including the need to provide electrical power at great distances from the Sun. to transmit large amounts of data to Earth over these vast distances, and to provide highly accurate pointing for the precise aiming and/or delivery ol penetrators, probes, and remote-sensing instruments, as well as for the proper orientation of high-gain antennas. Of equal significance is the need for a high degree ol autonomous operation and reliability.

At the same time, the cost of the missions must be minimized without compromising quality. The Mariner Mark II Program will meet this challenge by making the spacecraft lor its various missions as nearly uniform in design as possible. For CRAF and Cassini. each spacecraft will be designed to carry either set ol instruments as well as to power these instruments, point them, and store and transmit their data with the lewest possible changes in spacecraft design. Where detailed requirements dilfer, the final design will be driven by the requirements of the more demanding mission. The size of the propellant tanks, for example, is determined by CRAF's requirements; Cassini will use the same tanks, bul they will not be completely filled with fuel

July 2001

CRAF Peneliaior Delivery

October 2002

Cassmi Arrival i\ Saturn

December 2002

Cornel Kopif al Perihelion

As another example, the size ot the antenna is delined by the distance between Saturn and Earth; a smaller antenna would be sufficient for the CRAF mission, The cost of overdesigning for the mission with the less stringent requirements is more than compensated by savings derived from the design, construction, testing, and operation of identical subsystems on both missions,

Computer-generated drawings of fhe two spacecraft, complete with their scientific instruments, are shown at left The principal common features are the central 10-sided spacecraft bus that holds most of Ihe electronics, the large propulsion subsystem (fuel tanks, rocket engine, and structure) below the bus. the high-gain antenna and radio feeds above the bus, fhe two nuclear-powered radioisotope thermoelectric generators on a boom behind the bus, and the booms on which experiments are mounted. In the foreground, the figures show CRAF's penetrator and Cassini's Titan probe at Ihe same location on each of these versatile multimission spacecraft

The spacecraft will fly with their high-gain antennas pointed toward Earth. On CRAF, two instrument-laden platforms will keep fhe telescopes and other sensors trained on the target under study. Cassini will use one of Ihe CRAF platforms for its cameras and spectrometers, but the other will be replaced by a turntable that will create ever-changing maps of the dust, plasma, and energetic particles arriving from all parts of the sky.

Both spacecraft are being designed and built by NASA, the Titan probe by the European Space Agency, and Ihe CRAF propulsion subsystem by the Federal Republic of Germany. Scientific instruments will be provided by all of the international pariners Both the CRAF and Cassini missions will be launched on the expendable Titan IV/Centaur G; CRAF in 1995 and Cassini in 1996.

Facing page:

The CRAF spacecraft (top) with the penetrator in the foreground. The Cassini spacecraft (bottom) immediately after release of the probe.

Facing page:

The CRAF spacecraft (top) with the penetrator in the foreground. The Cassini spacecraft (bottom) immediately after release of the probe.

Above:

Mosaic of Viking images of the

Martian moon Phobos, which may be a captured asteroid.

January 2003

March 2003

February 2006

Cassini Tiian Probe Delivery

CRAF End ol Mission

Cassini High-lnclinasion OiDHs

SUMMARY

Above:

Artist's view of the solar nebula before the planets formed.

(Painting by Dor Davis. ©1945 Time-Life Books Inc.

All rights reserved. Reprinted by permission from Time-Life Books Inc.)

What we will learn from the CRAF/ Cassini initiative will greatly enhance what we have already discovered about the outer solar system through ground-based observations and through our previous missions—Pioneer 10 and 11 and the Voyager encounters ot Jupiter, Saturn, Uranus, and, soon. Neptune. CRAF will help us explain the intriguing glimpses into the mysteries ol a comet nucleus that were first offered by the international flotilla of spacecraft that flew by Comet Halley. Cassini will provide a thorough investigation of the Saturnian system

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