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The Soviet Union eventually dissolved and the balloons were removed from the Russian mission that had been delayed from its 1992 launch, first to 1994 and finally to 1996. Meanwhile, the first MR system was placed aboard the 1992-launched US Mars Observer spacecraft, which was lost in 1993. A second MR was delivered by CNES for the Mars Global Surveyor spacecraft. The Russian Mars mission failed shortly after launch in November 1996, but the MR antenna became the critical means for retrieving data from the Deep Space 2 Microprobes that were launched with Mars Polar Lander in January 1999. With the loss of Mars Climate Orbiter, plans were developed that called for the Mars Global Surveyor MR to be available as a relay system for the Mars Polar Lander (MPL). The loss of both the DS-2 probes and MPL in December 1999 without any indication of what failed led NASA to require that all future missions insure communications during critical events. For the Mars Exploration Rovers, MGS and its relay will be used to collect critical data during the descent and landing, and will also play a key role in returning science data to Earth.
A French Proposal: In 1987, Dr. Jacques Blamont of the French Centre National d'Etudes Spatiales (CNES) proposed an international collaboration between France, the Soviet Union, and the United States in exploring Mars. The Soviet Union was working on a mission to send a large orbiter, several small landers, and a pair of French-made balloons, to Mars at the same time that the U. S. was to be flying its Mars Observer (MO) spacecraft in Mars orbit. Because the MO spacecraft was in a much better orbit to provide radio relay support to the small landers and balloons than the Soviet orbiter, Blamont proposed that the French provide a radio system to fly on the U.S. spacecraft.
Getting MOC Involved: The primary problem with the French proposal was that the MO spacecraft could not accept data from the relay at the rates at which the landers and balloons would be transmitting. Cooperatively with Mars Observer Camera (MOC) Principal Investigator Mike Malin, Blamont noted that the large computer memory in the camera could be used to buffer data between the high data rate relay and the low data rate spacecraft, much as it is used internally by the camera for its own data. After discussions of both the technical and political issues, NASA and CNES signed a memorandum of understanding and the Mars Observer Project provided resources for redesign of the camera to accommodate and act as the data interface between the relay and the MO spacecraft.
Times A-Changin': Many changes occurred after the initial agreement was in place. Owing to financial issues associated with the breakup of the Soviet Union into independent states, Soviet/Russian missions to Mars planned for the 1992 and 1994 launch opportunities never materialized. However, the French continued to work on, and deliver, the hardware for the Mars Balloon Relay (MBR) with the expectation that one or more surface or atmosphere vehicles would ultimately fly to Mars. The MBR was on-board Mars Observer (MO) when it launched on September 25, 1992. It was shown to be operational after launch during a payload checkout period early in the cruise to Mars. After an uneventful flight, the MO spacecraft disappeared without a trace 3 days before arrival at Mars (the likely failure was ignition of propellant within the fuel lines).
Mars Global Surveyor Emerges: In the aftermath of this loss, NASA developed a more comprehensive program to explore Mars with a series of smaller, less-expensive spacecraft. The first of this series was the single Mars Global Surveyor (MGS), designed to recover a significant fraction of the Mars Observer science objectives by flying five of the MO instruments (the camera, the Thermal Emission Spectrometer, the Mars Orbiter Laser Altimeter, the Magnetometer/Electron Reflectometer, and the ultra-stable oscillator portion of the Radio Science experiment) and the spare Mars Relay (MR) equipment. This mission began development in 1994 and launch occurred on November 7, 1996.
Russian Mars '96: A Mars mission was also planned and developed by Russia for launch in 1996. Although this spacecraft did not include the French balloon experiment, it did include small landers. Thus, the relay on-board MGS was re-named the Mars Relay. The Mars '96 spacecraft was launched on November 16, 1996, but experienced a launch-phase failure. Owing to financial constraints following this loss, both the French and Russians were unable to participate further in the MGS mission.
Mars Surveyor '98: The mission following MGS to Mars (Mars Surveyor '98) consisted of two spacecraft--the Mars Climate Orbiter (MCO), launched December 11, 1998 and the Mars Polar Lander (MPL), launched January 3, 1999. Although the original concept for communicating with MPL assumed that MGS would provide initial support while MCO attained its planned orbit, the MCO mission was changed during development to provide the primary communications route for the lander throughout its mission. A powerful direct-to-Earth capability was also added to the lander, and MGS support was considered secondary.
Deep Space 2: As the Mars Surveyor '98 mission was being developed, the Jet Propulsion Laboratory was also developing an engineering test mission called Deep Space 2 (DS-2). DS-2 bought a piggy-back ride to Mars on-board the MPL, and based its ability to return data on the use of the MGS MR relay. DS-2 consisted of two very small landers with a lifetime limited by newly-designed batteries.
Climate Orbiter Lost: On September 23, 1999, during the Mars Orbit Insertion manueuver, the Mars Climate Orbiter spacecraft dipped too deeply into the martian atmosphere and was destroyed. After this loss, planning focused primarily on use of the direct-to-Earth communications link for the Mars Polar Lander mission. However, there were strong technical and scientific reasons to use the MR, and MGS/MR support for MPL was planned to begin after the first 6-9 days on Mars.
Loss of MPL and DS-2: On December 3, 1999, the two DS-2 probes
were released from the MPL carrier vehicle, followed shortly
thereafter by the separation of the cruise stage and lander. The last
communications with MPL showed all was working prior to entry.
Nothing was ever heard from either of the three vehicles again. The
MR was used extensively for several months, looking for faint signals
from the DS-2 probes for the first two weeks of December, and then for
signals from MPL as various commands were sent "in the blind" to try
to turn on MPL's transmitters (if it were listening). By late January
2000, all branches of the "fault tree" were explored and the
spacecraft were officially declared lost. The Mars Surveyor 1998
mission was a total failure, with the loss of the Orbiter in September
and the Lander in December.