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Prelude to Mars Sample Return: The Mars 1984 Mission (1977)
19 August 2017


The Viking 2 rover on the frosty plain at Utopia. Image credit: Pat Rawlings/NASA

Even before Viking 1 landed on Mars (20 July 1976), NASA and its contractors studied post-Viking robotic Mars missions. Prominent among them was Mars Sample Return (MSR), considered by many to be the most scientifically significant robotic Mars mission.

The Viking missions reinforced this view of MSR, and also revealed the perils of making too many assumptions when planning costly and complex Mars exploration missions. The centerpiece of the $1-billion Viking mission, a briefcase-sized package of three biology experiments, yielded more questions than answers. Most scientists interpreted their data as evidence of previously unsuspected reactive soil chemistry, not biology. The truth, however, was that no one could be certain what the Viking biology experiment results meant.

With that unsatisfying experience in mind, A. G. W. Cameron, chair of the National Academy of Sciences Space Science Board, wrote in a 23 November 1976 letter to NASA Administrator James Fletcher that

[to] better define the nature and state of Martian materials for intelligent selection for sample return, it is essential that precursor investigations explore the diversity of Martian terrains that are apparent on both global and local scales. To this end, measurements at single points. . .should be carried out as well as intensive local investigations of areas 10-100 [kilometers] in extent.

Soon after Cameron wrote his letter, NASA Headquarters asked the Jet Propulsion Laboratory (JPL) to study a 1984 MSR precursor mission. The JPL study, results of which were due by July 1977, was meant to prepare NASA to request "new start" funds for the 1984 mission in Fiscal Year 1979. NASA also created the Mars Science Working Group (MSWG) to advise JPL on the mission's science requirements. The MSWG, chaired by Brown University's Thomas Mutch, included planetary scientists from several NASA centers, the U.S. Geological Survey (USGS) Astrogeology Branch, and Viking contractor TRW.

The MSWG's July 1977 report called the Mars 1984 mission the "next logical step" in "a continuing saga" of Mars exploration and a "required precursor" for an MSR mission, which it targeted for 1990. Mars 1984 would, it explained, provide new insights into the planet's internal structure and magnetic field, surface and sub-surface chemistry and mineralogy ("especially as related to the reactive surface chemistry observed by Viking"), atmosphere dynamics, water distribution and state, and geology of major landforms.

The Mars 1984 mission would also seek answers to "The Biology Question." The MSWG declared that

on-going exploration of Mars must address the issue of biology. Although there does not appear to be active biology at the two Viking landing sites, there may be other localities with special environments conducive to life. Life-supportive aspects of the Martian environment must be defined in greater detail. The characterization of former environments [and] a search for fossil life. . .should be conducted.

Mars 1984 would begin in December 1983-January 1984 with two Space Shuttle launches no less than seven days apart. The piloted, reusable Space Shuttle Orbiters would each place into low-Earth orbit a Mars 1984 spacecraft comprising one 3683-kilogram orbiter based on the Viking Orbiter design, three penetrators with a combined mass of 214 kilograms, and one 1210-kilogram lander/rover combination housed in an extended Viking bioshield/aeroshell. Together with an adapter linking it to a two-stage Intermediate Upper Stage (IUS), each Mars 1984 spacecraft would weigh a total of 5195 kilograms.


A Viking orbiter releases an aeroshell containing a Viking Mars lander. The Mars 1984 orbiter would have a similar design; the aeroshell, however, would stand taller to provide sufficient room for the lander/rover combination within it.

Viking aeroshell (left) and Mars 1984 aeroshell. Image credit: Martin Marietta

The Shuttle Orbiters would each deploy a spacecraft/IUS combination from its payload bay, then would maneuver away before IUS first-stage ignition. The MSWG calculated that the IUS would be capable of placing 5385 kilograms on course for Mars on 2 January 1984, near the middle of a launch opportunity spanning 28 days.

The twin Mars 1984 spacecraft would reach Mars from 14 to 26 days apart between 25 September and 18 October 1984, after voyages lasting a little more than nine months. Each would perform a final course-correction rocket burn using attitude control thrusters a few days before planned Mars Orbit Insertion (MOI). Their penetrators would separate two days before MOI and fire small solid-propellant rocket motors to steer toward their target impact sites on Mars. The motors would then separate from the penetrators.

During MOI, each spacecraft would fire a solid-propellant braking rocket motor, then the orbiter's liquid-propellant maneuvering engine would ignite to place it into a 500-by-112,000-kilometer "holding" orbit with a five-day period. Spacecraft #1's orbit would be near-polar, while spacecraft #2 would enter an orbit tilted from 30° to 50° relative to the martian equator. MOI completed, flight controllers would turn the orbiter's cameras toward Mars to assess weather conditions ahead of lander separation.


The Bendix Mars penetrator was designed to enter Mars's atmosphere directly from an interplanetary trajectory and embed itself in solid rock. A = radio antenna; B = meteorology package and magnetometer; C = isotope heater; D = aft body electronics; E = Aft body/fore body separation plane; F = cable linking aft body and fore body; G = accelerometer and neutron detector; H = fore body electronics; I = drill assembly; J = sampling drill bit; K = geochemical analysis package; L = seismometer; M = batteries; N = radioisotope thermal generator. Image credit: Bendix Corporation

At about the time the twin spacecraft entered their respective holding orbits, the six penetrators would impact at widely scattered points. Each would split at impact into two parts linked by a cable. The aft body, which would include a weather station and an antenna for transmitting data to the orbiters, would protrude from the martian surface after impact. The fore body would include a drill for sampling beneath Mars's surface and a seismometer. According to the MSWG, penetrators were "the only economic means" of establishing a Mars-wide sensor network. Establishing a network of widely scattered seismometers was considered vital for charting the planet's interior structure.

After several months in holding orbit, spacecraft #2 would move to a 300-by-33,700-kilometer "magneto orbit," where it would explore Mars's magnetospheric bow wave and tail. It would then maneuver to a 500-by-33,500-kilometer "landing orbit" with a period of one martian day (24.6 hours). During a one-month landing site certification period, scientists and engineers would closely inspect orbiter images of the candidate landing site. Spacecraft #1, meanwhile, would proceed directly from holding orbit to landing orbit.


The Mars 1984 landing system for delivering the Mars 1984 rover to the surface would include five main parts. 1= top bioshield for protecting the sterilized lander and rover from contamination; 2 =  top aeroshell for protecting the lander from reentry heating; 3 = folded lander (rover not displayed); 4 = bottom aeroshell with attitude control/deorbit thrusters and propellant tanks; 5 = bottom bioshield/heat shield. Landing would occur as follows: the top bioshield would be left behind on the Mars 1984 orbiter and the rest of the lander moved away; motors on the bottom aeroshell would ignite; the top aeroshell would deploy a single large parachute; the bottom aeroshell/heat shield would fall away; and the lander would fall free of the top aeroshell and ignite its landing motors for final descent. Image credit: Martin Marietta

The landers would have one purpose: to deliver the Mars 1984 rovers to Mars's surface. Lander #2 would set down first at a high latitude and lander #1 would land near Mars's equator at least 30 days later. JPL estimated that imaging data from the Viking orbiters would enable each Mars 1984 lander to set down within a safe "error ellipse" 40 kilometers wide by 65 kilometers long (for comparison, Viking's landing ellipse measured 100 kilometers wide by 300 kilometers long).

The Mars 1984 landers, based on a Martin Marietta design, would each include a "terminal site selection system." This would steer them away from boulders and other hazards as they descended the final kilometer to the martian surface. In other respects, their deorbit and landing systems would closely resemble those of the Vikings.

After lander separation, orbiter #1 would maneuver to a 500-kilometer circular orbit and orbiter #2 would move to a 1000-kilometer circular orbit. Orbiter #1's low near-polar orbit would permit global mapping at 10-meter resolution, while orbiter #2's higher near-equatorial orbit would enable it to map the equatorial region at 70-meter resolution. Orbiter #1 would serve as the radio relay for data from the six penetrators, while orbiter #2 would relay signals to and from the twin rovers.

The MSWG expected that most orbiter science operations would require minimal planning, since they would "be highly repetitive with most instruments acquiring data continuously and sending it to Earth in real time without tape recording." The exception would be imaging operations, since imaging data would be "acquired at a rate many times too great for real-time transmission." The MSWG suggested that the orbiters relay to Earth about 80 images of Mars per day.


Mars 1984 rover. A = antenna for signal relay through orbiter #2; B = antenna for direct transmission to and from Deep Space Network antennas on Earth; C = optics port cluster and strobe light (1 of 2); D = imaging/laser rangefinder mast (1 of 2); E = selenide radioisotope thermal generator (cover removed to display cooling vanes); F = rover chassis; G = manipulator arm with sampling drill (folded in travel position); H = sample-analysis inlet port; I = hazard detectors; J = loopwheel mobility system (1 of 4).


Mars 1984 rover and lander folded within their aeroshell and bioshield. A = folded landing leg (1 of 3); B = Viking-type landing footpad (1 of 3); C = lander body; D = Viking-type terminal descent engine (1 of 3); E = Viking-type parachute canister with deployment mortar; F = terminal site selection system sensors; G = folded rover ramp (1 of 2); H = folded loopwheel mobility system (2 of 4); I = stowed imaging/laser rangefinder mast (1 of 2); J = folded antenna for direct communication with Earth; K = rover chassis; L = radioisotope thermal generator; M = outer surface of aeroshell (tanks and thrusters not shown); N = outer surface of bioshield (heat shield not shown); O = attachment point linking bioshield to Mars 1984 orbiter. Image credit: Martin Marietta

The MSWG envisioned that the Mars 1984 rovers would be "substantial vehicles" capable of traveling up to 150 kilometers in two years at a rate of 300 meters per day. They based their rover concept on a Jet Propulsion Laboratory (JPL) design. Each would include four "loop-wheel" treads on articulated legs, a radioisotope thermal generator providing heat and electricity, laser range-finders for hazard avoidance, an "improved Viking-type manipulator" arm, twin cameras for stereo imaging, a microscope, a percussion drill for sampling rocks to a depth of 25 centimeters, and a sample processor for distributing martian materials to an on-board automated laboratory for analysis.

The MSWG acknowledged that a costly automated lab on an MSR precursor mission might be hard to justify, given that the MSR mission meant to follow it was intended to return samples to well-equipped labs on Earth for detailed analysis. The group argued, however, that clues to the nature of the reactive soil chemistry found by the Vikings might "reside in loosely bound complexes or interstitial gases" that "would be extraordinarily difficult to preserve in a returned sample." The scientists might also have worried that the planned MSR mission would be postponed or cancelled, leading them to attempt to exploit every opportunity for acquisition of new data.

The rovers would hold particularly interesting samples for collection during the MSR mission and test the effects of Mars's reactive soil chemistry on MSR sample container materials. They would also drop off three seismometer/weather stations each as they moved over the surface to create a pair of 20-kilometer-wide regional sensor networks.

The rovers would employ three Mars surface operation modes. The first, Site Investigation Mode, would enable "intensive investigation of a scientifically interesting site." The rover would be fully controlled from Earth.

In Survey Traverse Mode, the second mode, the rover would operate nearly autonomously in a "halt-sense-think-travel-halt" cycle. Each survey/traverse cycle would last about 50 minutes and move the rover forward from 30 to 40 meters. Science operations would occur during the "halt" portion and while the rover was parked at night. Flight controllers would update rover commands once per day. The rover would cease autonomous operations and alert Earth when it encountered a hazard or a feature of scientific interest.

The third mode, Reconnaissance Traverse Mode, would occur when the terrain was sufficiently smooth (and scientifically dull) to allow the rover to move at its top speed of 93 meters per hour. The rover would make few science stops and would travel both by day and by night.


Valles Marineris with Mars 1984 landing ellipses marked in red and labeled. Image credit: NASA

To conclude its report, the MSWG drew on USGS studies based on Mariner 9 and Viking orbiter data to offer two candidate landing sites for the Mars 1984 landers. Capri Chasma, at the eastern end of near-equatorial Valles Marineris, included heavily cratered (thus ancient) highlands terrain, lava flows of different ages, lava channels, and possible water-related channels and deposits. Candor Chasma, a north-central branch of Valles Marineris, included at least two rock types in its four-kilometer-high canyon walls. The group expected that a Mars 1984 rover might find ancient crystalline rocks on the canyon floor.

New Mars missions stood little chance of acceptance in the late 1970s, when NASA's limited resources were largely devoted to Space Shuttle development and public enthusiasm for the Red Planet was (thanks the equivocal Viking biology results) at a nadir. Though MSR remained a high scientific priority (as it does today), the planetary science community opted to seek support for missions to other destinations: for example, the Jupiter Orbiter and Probe mission, later renamed Galileo, got its start in NASA's Fiscal Year 1978 budget.

NASA's next Mars spacecraft, the Mars Observer orbiter, was approved in 1985 for a 1990 launch; launch was subsequently postponed until September 1992, then the spacecraft failed during Mars orbit insertion in August 1993. NASA would return successfully to Mars for the first time since Viking in July 1997, when the 264-kilogram Mars Pathfinder spacecraft landed in Ares Valles bearing the 10.6-kilogram rover Sojourner.

Sources

Post-Viking Biological Investigations of Mars, Committee on Planetary Biology and Chemical Evolution, Space Science Board, National Academy of Sciences, 1977

Mars '84 Landing System Definition: Final Report, "Technical Report," Martin Marietta, April 1977

A Mars 1984 Mission, NASA TM-78419, "Report of the Mars Science Working Group," July 1977

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Source: Prelude to Mars Sample Return: The Mars 1984 Mission (1977)