In 1986, NASA's Solar System Exploration Committee (SSEC) published its report Planetary Exploration through Year 2000: An Augmented Program. Leading the pack of proposed advanced robotic planetary missions was Mars Rover Sample Return (MRSR), a mission NASA and contractor scientists and engineers had studied in 1984-1985 at the request of the SSEC. At the same time, enthusiasm was building in Congress for joint U.S.-Soviet space ventures.
NASA's Mars Exploration Strategy Advisory Group created the Mars Study Team (MST) in the autumn of 1986 to look at "a potential opportunity not previously examined; namely, a Mars Rover/Sample Return (MRSR) mission which would involve a significant aspect of international cooperation" with "minimum technology transfer, maximum sharing of scientific results, and independent credibility of each mission role." The MST included many participants from the 1984-1985 MRSR studies, as well as scientists and engineers from NASA Headquarters, the U.S. Geological Survey Astrogeology Branch in Flagstaff, Arizona, and NASA Ames Research Center.
The MST assumed that NASA would provide the mission's large sample-collection rover and an unnamed "international partner" would provide the spacecraft that would convey the Mars samples to Earth. This division of labor reflected the institutional preference of the Jet Propulsion Laboratory in Pasadena, California, the home of NASA's robotic planetary program. In addition to the Rover and its lander, the NASA spacecraft would include a Rover Support Orbiter (RSO) which would image Rover traverse routes and relay radio signals from the Rover to Earth. The RSO would image objects on the surface smaller than 1.5 meters wide using a telescopic camera with a one-meter aperture.
The international MRSR mission would commence in 1996 with up to three launches to Earth orbit. The launch vehicles used would depend on the mission design selected; if, for example, the NASA spacecraft entered Mars orbit by aerocapture ("the preferred option"), then its mass would be low enough (2709 kilograms) that a solid-propellant Inertial Upper Stage could push it out of Earth orbit toward Mars. This in turn meant that it could reach Earth orbit on board a Space Shuttle orbiter.
If, on the other hand, the NASA spacecraft fired a rocket motor to slow down so that Mars's gravity could capture it into orbit, the braking propellant it would need would boost its mass to 3571 kilograms. The 1984-1985 MRSR studies had tapped the powerful liquid-propellant Centaur G' upper stage for Earth-orbit departure. The Centaur G', a variant of the U.S. Air Force Centaur G, was designed to reach orbit in the Shuttle payload bay. Citing safety concerns in the wake of the January 1986 Challenger Shuttle accident, however, NASA had in June 1986 banned Centaur G' from the Shuttle. The NASA MRSR spacecraft and its Centaur upper stage would thus use a Titan IV or other large expendable rocket to attain Earth orbit.
The international partner MRSR spacecraft would comprise the orbiter/Earth Return System (ERS) and the lander/Sample Return System (SRS). In the MST's scenario, the international partner spacecraft would have about three times the mass of its NASA counterpart. The team acknowledged that this might "exceed the near-term, single launch capability of any international partner." It suggested that the international partner might launch its spacecraft and Earth-departure upper stage separately on a pair of rockets and link them together in Earth orbit.
Launch from Earth orbit on the nominal departure date of 17 November 1996, would see the two MRSR spacecraft arrive at Mars on 17 September 1997, after an Earth-Mars transfer lasting 302 days. The NASA lander/Rover/RSO combination would capture into an elliptical Mars orbit with a period of one martian day and the international partner spacecraft would enter a low circular orbit. The two orbiters would then certify landing site safety through "coordinated orbital reconnaissance."
The MST noted that the dust storm season would begin shortly after the two MRSR spacecraft reached Mars, and that this might delay the MRSR landings. After clearance was given to land on Mars, the SRS would separate from the ERS, land, and activate its radio beacon. The Rover on its lander would then separate from the RSO and home in on the beacon to land close by.
The MST's agile Rover, which it called "one of the most complex elements of the MRSR mission," would be scaled to negotiate rocks and other obstacles up to 1.5 meters high (image at top of post). The 606.5-kilogram vehicle would comprise three "cabs," each with two wheels, linked by "passive axial flexural ties which [would] permit yaw, pitch, and roll motions."
The front cab would carry two robotic arms capable of brandishing a variety of sampling tools, plus a sampling drill and 90 kilograms of sample science equipment. A steerable binocular vision system would be mounted on a stalk on top of the center cab, and an antenna linking the Rover to the RSO would be mounted on top of the vision system. The aft cab would include the radioisotope thermal generator that would power the Rover.
Based on analysis of Viking Orbiter images, the MST proposed 11 candidate MRSR landing sites. Of these, the near-equatorial east Mangala Valles site was most thoroughly characterized. Mangala Valles consists of overlapping channels of different ages and characteristics, the most extensive of which is 80 kilometers long. The Rover would conduct four traverses with a total of 28 sampling stops. Each traverse would start and end at the SRS. The first and shortest traverse would measure seven kilometers long and include three sampling stops, while the last and longest would cover 86 kilometers and have seven stops. After each traverse, the Rover would hand its samples to the SRS, which would place them into a sample canister. In all, it would collect about five kilograms of martian rock, sand, dust, and other materials.
After handing over the last of its samples, the Rover would move a safe distance away from the SRS. The SRS ascent vehicle would then carry the sample canister into Mars orbit. The ERS would then rendezvous with it and take it on board. The Rover, meanwhile, would begin an open-ended extended mission lasting at least two years.
On 14 August 1998, after 332 days near Mars, the ERS would fire its rocket motors to depart Mars orbit for a 357-day trip to Earth. The Mars samples would arrive in Earth orbit on 6 August 1999, where they would be retrieved and transferred to an Earth-orbiting space station for preliminary analysis and planetary protection quarantine.
The MST envisioned a second MRSR mission overlapping the first. The second mission would begin in late 1998 and would reach Mars at the end of 1999 (in the midst of another martian dust storm season). After a 489-day stay at Mars, the second mission's ERS would depart Mars for Earth in early 2001. Its samples would reach Earth orbit late in that year. The second Rover's extended mission would last until at least late 2003.
The MST's "very preliminary" cost estimate for the NASA portion of the 1996 and 1998 MRSR missions was between $2 billion and $2.2 billion. The team called its international MRSR mission "technically feasible," though it cautioned that "[a]ll technical issues need to be addressed again in greater depth" before a decision to proceed could be made. Studies planned for 1987-1988 would, the MST explained, add further detail to the scenario of an international mission with a NASA lander/Rover. They would also examine an international scenario in which NASA contributed the lander/SRS and orbiter/ERS spacecraft, as well as a NASA-only scenario. "NASA intends to be prepared for any opportunity that may arise regarding Mars sample return," the MST declared.
Reference
A Preliminary Study of Mars Rover/Sample Return Missions, The Mars Study Team, Solar System Exploration Division, NASA Headquarters, January 1987.
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