No Scarcity of Desires: MSSR as MEM (1967-1968)

Scary experience: second stage and crew cabin of the Bellcomm minimal Mars Tour Module (MEM) ascent automobile. The unpressurized cabin would have included few shows and minimal communications. Picture credit score: Bellcomm/NASA.

The NASA Planetary Joint Motion Group (JAG) noticed the addition of the Mars Floor Pattern Returner (MSSR) probe to the piloted Mars/Venus flyby mission situations it studied in 1966 as a pivotal innovation. Earlier than the arrival of the MSSR, the piloted flyby mission seemed to be more and more threatened by profitable robotic flyby missions. The MSSR, members of the Planetary JAG contended, gave the piloted flyby mission an added functionality that might not be reproduced by an entirely robotic Mars mission.

The piloted flyby spacecraft would have launched the MSSR maybe 10 days earlier than Mars shut encounter. A rocket motor on the MSSR would have boosted it towards Mars, enabling it to achieve the planet and land at a preselected website a number of hours earlier than the piloted flyby spacecraft arrived. 

The crew on board the piloted flyby spacecraft would have used quite a lot of pattern collectors on board the MSSR to collect about two kilos of Mars floor materials and air by distant management because the planet grew ever bigger of their viewports. These would have been packed right into a three-stage ascent automobile and launched to the piloted flyby spacecraft. 

Partial cutaway of Mars Floor Pattern Returner (MSSR) probe. A = Mars intersect trajectory injection stage with toroidal propellant tank; B = pattern canister; C = ascent stage with three phases, every with a toroidal propellant tank; D = folded touchdown leg (one in all 4); E = aeroshell warmth protect; F = toroidal descent stage propellant tank; G = descent stage engine warmth protect cap. Picture credit score: NASA/DSFPortree.

The astronauts on board the piloted flyby spacecraft would have captured the pattern canister and ascent automobile third stage utilizing a boom-mounted docking ring and linked them to a port main right into a hermetically sealed organic laboratory. The MSSR probe would, it was anticipated, allow evaluation of Mars samples inside an hour of their assortment, serving to to make sure that any martian organisms they contained would nonetheless be alive. 

Part 1 of the Planetary JAG piloted flyby examine ended with distribution of an NASA report on 3 October 1966. The group then started work on Part 2 of its piloted flyby examine. Some members of the Planetary JAG foresaw a rosy future for the idea — they anticipated that MSSR examine contracts is likely to be awarded in Fiscal Yr 1968 and the piloted flyby mission would possibly turn into a NASA new begin undertaking in Fiscal Yr 1969.

Even earlier than the  AS-204/Apollo 1 fireplace (27 January 1967), NASA planning for missions past Apollo was on shaky floor. Neither the Administration of President Lyndon Baines Johnson nor the Congress supported formidable plans for post-Apollo spaceflight — for instance, a long-term lunar base or people on Mars. By late summer season 1967, the fireplace, racial and anti-war tensions throughout the U.S., issues in regards to the Federal price range deficit, and navy setbacks in Indochina had supplied opponents of an expansive U.S. future off the Earth with ample justification for curbing NASA efforts to outline its future.

Not all advance planning halted in August/September 1967, nonetheless. Bellcomm, NASA’s Washington, DC-based planning contractor, continued its efforts as a matter after all. Most Bellcomm research in 1967-1969 aimed to outline the form of the Apollo Program after the primary profitable piloted lunar touchdown, in addition to that of Apollo’s successor, the Apollo Software Program. Work towards extra formidable targets didn’t, nonetheless, cease fully.

In July 1967, Bellcomm planners D. Cassidy and H. London accomplished a brief technical memorandum by which they explored how the MSSR probe would possibly kind the idea for a piloted Mars Tour Module (MEM) lander. For his or her examine, Cassidy and London assumed a 15,000-pound MSSR with a two-stage ascent automobile able to launching 80 kilos to a passing piloted flyby spacecraft launched in 1975, 1977, or 1979 on a Mars Twilight flyby path. The “twilight” mission owed its identify to the geometry of its Mars flyby — closest strategy to Mars happened over the planet’s night time hemisphere close to the daybreak terminator, the road dividing pre-dawn darkness from daylight. 

Cassidy and London calculated that MSSR Mars ambiance entry velocity would attain 32,500 toes per second (fps) in 1975, 34,500 fps in 1977, and 39,000 fps in 1979. The automated MSSR would expertise deceleration equal to as much as 40 instances the pull of gravity on Earth’s floor (that’s, 40 Gs). To perform rendezvous with the passing piloted Mars flyby spacecraft, the MSSR ascent automobile must increase an 80-pound third stage and pattern container to 36,000 fps in 1975, 38,000 fps in 1977, and 42,500 fps in 1979. 

An MSSR-derived MEM launched throughout piloted Mars orbiter strategy to Mars — that’s, earlier than the orbiter fired its rocket motors to decelerate in order that Mars’s gravity may seize it into an elliptical orbit with a one-day interval — would, then again, in 1978, 1982, 1984, 1985, and 1986 enter the martian ambiance shifting at between 20,000 fps and 25,000 fps. It might decelerate at about 10 Gs, which Cassidy and London judged to be acceptable for an astronaut. 

MSSR-derived minimal MEM. Picture credit score: Bellcomm/NASA.
Two methods of touchdown on Mars: Direct Entry Mode would see a pair of minimal Mars Tour Modules (MEMs) and a shelter deployed from a Mars orbiter (labelled “S/C”) throughout strategy to Mars. The orbiter would then fireplace rocket motors to seize into an elliptical Mars orbit. If the orbiter couldn’t seize into orbit, the dual MEMs would abort their touchdown, fly previous Mars, and rendezvous with the orbiter. Entry from Elliptical Orbit would see minimal MEM and shelter separation after the Mars orbiter captured efficiently into Mars orbit. Picture credit score: Bellcomm/NASA.

An equal MEM launched in Mars orbit would enter extra slowly and topic its occupant to a lowered G load whereas additionally enabling extra exact touchdown website concentrating on. The MSSR-derived MEM ascent stage may increase a 900-pound third stage and crew capsule containing a single astronaut to a velocity of 18,000 fps to a rendezvous with the piloted orbiter in an elliptical Mars orbit with a interval of in the future. 

Cassidy and London wrote {that a} separate Bellcomm examine had decided {that a} minimal one-person MEM with a crew capsule weighing as little as 600 kilos with out an astronaut on board is likely to be attainable. Such a MEM would carry solely sufficient life help consumables to stay on Mars for a short while and no scientific exploration tools. They envisioned that an prolonged piloted Mars touchdown mission would make use of three MSSR-derived landers: a pair of minimal MEMs, every carrying one astronaut, and an automatic one-way cargo automobile able to delivering 5,500 kilos of life help provides and scientific tools to the floor of Mars.

The examine of a 600-pound MEM crew capsule Cassidy and London referenced was carried out by M. Skeer in session with Cassidy and McDonnell Plane engineers. Skeer, a newcomer to Bellcomm in 1966, summed up outcomes of his examine in a technical memo dated two months after the Cassidy and London examine.

In contrast with the MSSR-derived MEM ascent automobile, the Mercury capsule was massive, heavy, and sophisticated. Picture credit score: NASA.

In his memo, Skeer explored whether or not the design of the one-man McDonnell-built Mercury capsule, which carried six astronauts on suborbital and orbital missions in 1961-1963, would possibly include weight-saving classes for designers of an MSSR-derived MEM ascent automobile. The 4600-pound Mercury capsule, he defined, was a sensible choice for his examine as a result of, just like the minimum-mass MEM ascent automobile, it had comparatively easy mission goals in contrast with the Gemini or Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft.

The minimal MEM would descend from a spacecraft in a extremely elliptical Mars orbit with a interval of from 24 to 48 hours. A spacecraft in such an orbit can be certain loosely by Mars’s gravity, so would require minimal propellant expenditure to depart the planet when the time got here to return to Earth. Descent from the extremely elliptical orbit to the floor of Mars would final about six hours and return from the floor of Mars to extremely elliptical orbit would require about two hours. 

Skeer eradicated 47% of Mercury’s weight instantly by deleting the 1119-pound launch escape tower, 315-pound warmth protect, 317-pound retrograde propulsion system (used to deorbit the Mercury capsule), touchdown techniques and restoration gear collectively weighing 343 kilos, and 51 kilos of experiments. He then handled remaining Mercury techniques intimately. He wrote, for instance, that McDonnell engineers had informed him that the 75-pound Mercury sofa may very well be trimmed to fifteen kilos. Skeer arrived at a complete MEM ascent stage weight of 738 kilos together with a 170-pound astronaut. 

Minimal MEM entry and touchdown. Picture credit score: Bellcomm/NASA.
Helpful payload: two-stage minimal MEM ascent automobile. Picture credit score: Bellcomm/NASA.
Minimal MEM liftoff, ascent, and orbital insertion. After rendezvous in Mars orbit the only astronaut would fly the capsule right into a hangar on the Mars orbiter or would abandon the capsule and enter the Mars orbiter by spacewalking. Picture credit score: Bellcomm/NASA.
The MEM cabin would offer simply 92 cubic toes of quantity for the astronaut — 26 cubic toes lower than the cosy Mercury cabin. A “plastic shroud” measuring simply 30 inches huge by 60 inches lengthy, it might be neither pressurized nor insulated. Skeer estimated that it may weigh as little as 200 kilos, about 415 kilos lower than the Mercury cabin construction. The cabin’s small quantity would stop the astronaut would shifting a lot; Skeer argued that astronaut immobility would simplify ascent stage steerage and management by avoiding center-of-gravity shifts. 

The astronaut packed into the coffin-like MEM cabin would rely for all times help on a 40-pound house swimsuit with a 100-pound life help backpack containing adequate life help consumables for 12 hours of operations. This mix would substitute a Mercury cabin life help system weighing 248 kilos. 

Skeer briefly examined a two-person minimal MEM with a descent stage not based mostly instantly on the piloted flyby MSSR. This is able to, he wrote, have a complete weight of lower than 35,000 kilos. Of this, 1360 kilos would comprise the MEM ascent stage and crew. He clearly favored the single-person minimal MEM, nonetheless. 

Skeer subsequently carried out a pair of follow-on research of MSSR-derived piloted spacecraft. The primary, accomplished on 8 Might 1968, checked out a 4064-pound MSSR-derived two-person floor shelter that may allow a two-week Mars floor keep by astronauts landed individually in a pair of MSSR-derived minimal MEMs. Expendables supporting the two-week keep — principally for all times help and energy era — would account for 1053 kilos of the shelter’s weight.

Cutaway view of MSSR-derived Mars floor shelter. Picture credit score: Bellcomm/NASA.
Plan view of MSSR-derived Mars floor shelter. Picture credit score: Bellcomm/NASA.

The 575-cubic-foot shelter would come with a 60-cubic-foot airlock accessed from the martian floor by a “hoist” (apparently a one-person open elevator platform). A pair of 25-cubic-foot compartments accessed from throughout the shelter (not from the airlock) contained 4 full house fits so every crewmember may have a spare. A laboratory space accounted for 50 cubic toes of the shelter’s quantity.

Scientific exploration tools accounted for 1460 kilos of the shelter’s weight. This included a single 367-pound one-person floor rover or flyer with a complete vary of 420 kilometers, 77 kilos of multiband images/radiometry tools, a 107-pound shelter-mounted drill able to reaching a depth of 30 meters, 100 kilos of “surveying instruments,” a 250-pound “Emplaced Science Station” and three “satellite tv for pc science stations” (whole weight 140 kilos) meant to be left behind on the martian floor, and “native sampling and environmental tools” weighing a complete of 395 kilos. The shelter’s pressurized cabin would include 50 kilos of kit for geologic evaluation. (Skeer made no reference to return of samples within the two minimal MEM automobiles; presumably pattern evaluation on Mars was meant to switch return of samples to Earth.)

Skeer’s second follow-on examine, a extra detailed examination of the minimal MEM ascent stage dated 8 July 1968, sought to determine “fruitful areas of technological analysis and improvement wanted for analysis and future program planning choices.” He argued for improvement of latest propulsion techniques able to burning new high-energy propellants (for instance, fluorine-LOX/methane), compact and light-weight refrigeration techniques for long-term storage of such propellants, and improvement of latest light-weight supplies to allow additional minimal MEM weight discount. 

He additionally famous that flights of MSSR probes throughout piloted flyby missions may very well be seen as take a look at flights of minimal MSSR know-how. Sadly, by the point Skeer accomplished his second follow-on examine, work throughout the NASA Planetary JAG towards a piloted flyby with MSSR probe had been largely deserted for almost a yr.


“MSSR/MEM Commonality – Case 233,” D. E. Cassidy and H. S. London, Bellcomm, Inc., 19 July 1967.

“Preliminary Sizing of a Mars Tour Module Ascent Capsule Based mostly on Mercury Spacecraft Design – Case 233,” M. H. Skeer, Bellcomm, Inc., 25 September 1967.

“Preliminary Mars Tour Module Shelter Design – Case 730,” M. H. Skeer, Bellcomm, Inc., 8 Might 1968.

“Mars Tour Module Ascent Propulsion Stage Design,” M. H. Skeer, Bellcomm, Inc., 8 July 1968.

Extra Data

A New Step in Spaceflight Evolution: To Mars by Flyby-Touchdown Tour Mode (1966)

NASA’s Planetary Joint Motion Group Piloted Flyby Research (1966)

Triple-Flyby: Venus-Mars-Venus Piloted Missions within the Late Nineteen Seventies/Early Eighties (1967)

Flyby’s Final Gasp: North American Rockwell’s S-IIB Interplanetary Booster (1968)

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