MEM Credit - NASA Media Gallery

Von Braun's final vision for a manned expedition to Mars was a robust plan that eliminated much of the risk of other scenarios. Two ships would fly in convoy from earth orbit to Mars and back. They were entirely reusable for future expeditions, the only element being expendable being the Mars Excursion Module used to visit the planet's surface. This was Von Braun's last attempt to convince the American government to finance his dream. Five months later he would be sidelined to a dead-end headquarters job at NASA, and leave the Agency two years after that.

The successful landing on the moon of Apollo 11 brought a brief period of political enthusiasm for manned spaceflight. A new Space Task Group was formed to recommend a post-Apollo manned space program. On 4 August 1969 NASA Administrator Paine briefed the Space Task Group, with Vice President Agnew chairing, on Marshall's proposed post-Apollo integrated plan. Von Braun briefed the plan for a manned expedition to Mars as a follow-on to Apollo. The Integrated Plan foresaw first flight of a manned space shuttle by 1975, an earth orbit space station soon thereafter, with production and improvement of the Saturn V continuing, and the NERVA nuclear thermal upper stage completing development. All of these projects would mean a Mars spacecraft like that proposed by Boeing in 1969 could be developed, with the only new unique hardware being the Mars Excursion Module (the Mission Module would be one of the modules already proven on the earth orbit station). Testing in earth orbit of the first Mars Excursion Module would begin in 1978, with the first Mars landing coming in 1982.

Von Braun had tweaked his original Mars Expedition scenario between 1952 and 1956 to halve the size of his original Mars expedition spacecraft. He used the same methods in 1969 to come up with Mars spacecraft under half the mass of Boeing's 1968 IMIS. This allowed two Mars expedition spacecraft to travel in convoy on the mission together, providing Von Braun's preferred mutual support and back-up. The Nuclear Shuttles used for propulsion were essentially the same as Boeing's Primary Propulsion Modules, and had 38 metric tons less propellant. But due to lower delta-V's at Mars orbit, only three of the NERVA Primary Propulsion Modules (now called Nuclear Shuttles) were needed per spacecraft as opposed to five in Boeing's study. The spacecraft consists, from fore to aft:

• Two lateral PPM's. These were only partially fuelled, enough for the necessary delta-V to set the spacecraft toward Mars on 12 November 1981. They then separated, and maneuvered back to rendezvous and docking with the earth orbit station. There they were refueled and reused for earth-moon shuttle service or a future Mars expedition.
• A central PPM. This provided all of the remaining delta-V for the mission - insertion into Mars orbit, trans-Earth injection, and a braking maneuver back into earth orbit at the end of the mission. Significant savings were obtained by braking into and leaving a high-altitude elliptical Mars orbit rather than a low-altitude circular orbit.
• A Planetary Mission Module. This was the result of Phase B studies to identify a module that could be used for both earth and lunar space stations and interplanetary flights. It provided six crew with quarters during the mission. It had sufficient consumables that 12 crew could be supported in case one of the spacecraft had to be abandoned anywhere along the route.
• Mars Excursion Module. The variation for this mission had a mass of 43 metric tons. It could descend from the high elliptical orbit, and support three crew on the surface for up to sixty days. Since two ships were in convoy, the two MEM's could land near each other and provide mutual support. All six surface crew could return in one of the MEM's ascent stages if needed.
• 16 unmanned probes. 12 would return samples from various sites on the Martian surface to the orbiting PMM. Four would be dropped into the atmosphere of Venus during the swingby of that planet on the return home.

The mission profile was as follows:

• 12 November 1981: Trans-Mars injection. Each spacecraft had a starting mass in low earth orbit of 727 metric tons. After the 3.8 m/s maneuver, the two lateral PPM's would separate, leaving the single PPM, PMM, MEM, and probes with a total mass of 614 metric tons.
• 9 August 1982: Mars orbit insertion. The spacecraft entered an elliptical Mars orbit. This requires a delta-V of only 2.2 km/s, only 1/3 to 1/8 the amount Boeing assumed in their study for obtaining a circular orbit. This was a huge driver in reducing the total expedition mass. Mass before the maneuver was 295 metric tons, and afterwards around 226 metric tons.
• The MEM's separate and headed for the surface. Meanwhile, the three crew left aboard each PMM drop the 12 sample-return probes and survey the Martian surface and moons from orbit.
• 28 October 1982: Trans-Earth Injection. Having shed the MEM and probes, the mass at the start of the maneuver was 172 metric tons.
• 28 February 1983: Venus swingby. This reduces the velocity at the return to earth, and provided an additional science opportunity. Four probes were dropped into the atmosphere of Venus.
• 14 August 1983: Earth Orbit Insertion. The PPM fired one last time to brake the spacecraft into low earth orbit. It docked with the earth orbiting space station and the crews and their samples were placed in quarantine. Final mass of each ship was 72.6 metric tons. Von Braun preferred this approach to a direct return to earth in an Apollo Command Module. His mission profile made the propellant available for it, and the risk of contamination of the earth by Martian organisms was eliminated.

The Space Task Group made its final report on 15 September 1969, recommending the whole vast infrastructure envisioned by Von Braun. It was not to be -- every element of the NASA plan, except for a much-compromised space shuttle design, would be stripped away by Nixon's budget office. There was no public support for such a grand scheme. The view of Mars as a seemingly barren, lifeless, and uninteresting world in any case was reinforced by the Mariner 7 mission which flew by the planet the day after Von Braun's presentation was made. His ultimate dream crushed, Von Braun was sidelined to a headquarters post at NASA seven months later. He left NASA in 1972 and died in 1977.

• Summary: Final NASA/Von Braun design for a manned expedition to Mars using nuclear thermal rockets.
• Propulsion: Nuclear thermal
• Braking at Mars: propulsive
• Mission Type: opposition
• Venus swingby: yes
• Split or All-Up: all up
• ISRU: no ISRU
• Launch Year: 1981
• Crew: 12
• Mars Surface payload-metric tons: 5
• Outbound time-days: 270
• Mars Stay Time-days: 80
• Return Time-days: 290
• Total Mission Time-days: 640
• Total Payload Required in Low Earth Orbit-metric tons: 1452
• Total Propellant Required-metric tons: 1088
• Propellant Fraction: 0.74
• Mass per crew-metric tons: 121
• Launch Vehicle Payload to LEO-metric tons: 249
• Number of Launches Required to Assemble Payload in Low Earth Orbit: 6
• Launch Vehicle: Saturn V-25(S)U

Design Life: Ten years. Length: 82.00 m (269.00 ft). Basic Diameter: 10.06 m (33.00 ft). Maximum Diameter: 31.00 m (101.00 ft). Mass: 726,000 kg (1,600,000 lb). Main Engine: NERVA. Main Engine Thrust: 1,733.800 kN (389,774 lbf). Main Engine Propellants: Nuclear/hydrogen. Main Engine Propellants: 544,000 kg (1,199,000 lb). Main Engine Isp: 850 sec.

• PPM.  Other Designations: Primary Propulsion Module. Class: Tug. Destination: Mars. Nation: USA. Manufacturer: Boeing.

  The Primary Propulsion Module was the definitive 1960's design for a nuclear thermal rocket stage suitable for interplanetary operations. The basic NERVA stage was modified to allow for docking and assembly in orbit, storage and reliquefaction of its liquid hydrogen propellant for periods of up to three years on long voyages to Mars and Venus, and to feed propellant to lower stages as needed.

  Detailed mass breakdown was as follows:

  • Liquid hydrogen propellant: 174,600 kg
  • NERVA nuclear thermal engine system: 14,500 kg
  • Propellant tank: 22,700 kg
  • Stage equipment: 2700 kg
  • Meteoroid shield: 19,000 kg
  • Interstage structures: 5200 kg
  • 11% growth and contingency allowance: 6800 kg

  Design Life: 1100. Length: 48.20 m (158.10 ft). Basic Diameter: 10.06 m (33.00 ft). Maximum Diameter: 10.06 m (33.00 ft). Mass: 245,600 kg (541,400 lb). Main Engine: NERVA. Main Engine: 14,500 kg (31,900 lb). Main Engine Thrust: 866.900 kN (194,887 lbf). Main Engine Propellants: Nuclear/hydrogen. Main Engine Propellants: 174,600 kg (384,900 lb). Main Engine Isp: 850 sec.

• Planetary Mission Module.  Class: Manned. Type: Mars Orbiter. Destination: Mars. Nation: USA. Agency: NASA. Manufacturer: North American, McDonnell.

  NASA had the long range goal of sending men to explore the planet Mars. To assure that the developments undertaken as part of the Space Station program contributed to this long term goal without undue increase in program cost or complexity, an assessment was made to determine where common or near common requirements existed. Two manned Mars missions, a 1981 opposition class mission and a 1986 conjunction class mission, were selected as representative types about which to develop total vehicle and operational concepts. These concepts involved the use of two Nuclear Shuttles for Earth departure and a third Shuttle to accompany the planetary spacecraft for use in braking into Mars orbit, in Mars orbit departure and in braking into a highly elliptic Earth orbit.

  Although complete spacecraft concepts with Mars excursion modules and probes were laid out by both Phase B contractors, the principal effort was devoted to the so-called mission module which housed the living quarters, command and control, and laboratories. These were 10 m in diameter, utilized isotope Brayton power generation systems, and had centrally-located radiation shelters. Both contractor design teams concluded that substantial commonality could exist between the postulated planetary mission and the Earth orbital mission, particularly in habitability and long life system approaches.

  Non-commonalties of station and planetary mission module (PMM) were based on several unique interplanetary mission characteristics or requirements. The long mission duration, with no practical feasibility of resupply, demands larger storage volumes in the PMM. Maintenance philosophy, in the interest of weight constraints, emphasized repair over throw-away and replacement from spares supply; while at the same time requiring considerable spares storage. The fact that the planetary spacecraft may approach the Sun as closely as 0.5 A.U. requires resized of the environmental control system radiator to operate satisfactorily at 4 times the solar constant near Earth.

  Maximum solar distance may be as large as 1.8 AU This rendered solar cell arrays unsuitable, considering a required power level of 25 kW. It also necessitated greater meteoroid protection. The consequences concerning solar flare exposure outside the geomagnetic shield created the need for a radiation shelter arrangement. The use of a two-vehicle buddy system for mutual self-rescue and survive required that each PMM store provisions for a crew of 12 while housing 6 under nominal conditions, thus providing still more ample shielding. The planetary mission plan called for the use of Mars Surface Sample Returners (MSSR) and manned Mars Excursion Modules (MEM). The resulting exposure to Mars material required special provisions to avoid possible backward contamination.

  Crew Size: 6. Design Life: 3 years. Typical orbit: 456 km x 456 km at 55 degrees inclination. Length: 33.50 m (109.90 ft). Basic Diameter: 6.70 m (21.90 ft). Maximum Diameter: 16.50 m (54.10 ft). Span: 10.00 m (32.00 ft). Habitable Volume: 930.00 m3. Mass: 100,000 kg (220,000 lb). Electrical System: Nuclear. Electric System: 25.00 average kW.

• MEM.  Other Designations: Mars Excursion Module. Class: Manned. Type: Mars Lander. Destination: Mars. Nation: USA. Manufacturer: North American Rockwell.

  The Mars Excursion Module was designed by North American for the Marshall Spaceflight Center in an October 1966-August 1967 study. This lander design was the first to incorporate the Mariner 4 findings on the tenuous nature of the Martian atmosphere.

  The lander followed the aerodynamic form of the Apollo Command Module, a configuration that was completely understood. The crew would endure 7 G's on Mars atmospheric entry. The heat shield was designed to allow re-entry into both the earth and Martian atmospheres so that it could be thoroughly tested from earth orbit prior to any Mars mission. After slowing to near-supersonic speed, the capsule would be stabilized by a drag chute, then a ballute. At 3 km over the surface, the ballute would be jettisoned and the main engine, using liquid oxygen/liquid methane propellants, would fire to bring the capsule to a soft landing on the surface. Enough propellant was available for a two minute hover. Six landing legs could handle slopes of up to 15 degrees.

  The design was modular, so that by deleting ascent propellant and internal compartments and surface supplies, total lander mass could be between 30.0 and 49.4 metric tons. The lighter stripped lander, departing from and returning to a low-earth orbit Mars orbiter, could support only two crew for four days on the surface. The heavier all-up version could support four crew for thirty days and had enough delta-V to reach an orbiter in a higher Mars elliptical orbit. Variations of internal equipment fit and propellant between these extremes could accommodate a variety of missions.

  After exploring the Martian surface and taking samples, a separable ascent stage would bring the crew and their samples back to the mother ship in Mars orbit. Up to eight strap-on propellant tanks fuelled the same engine during ascent and were jettisoned as the propellant was depleted. The propellant remaining in the core was used to achieve orbit and dock with the waiting mother ship in Mars orbit.

  North American estimated that development would have to start in 1971 in order to support a 1982 landing on Mars. Before the main landing mission, flight tests would take place in earth orbit, using six test articles. Three two-stage Saturn V vehicles and three Saturn I boosters would put the test articles on suborbital and orbital trajectories. In the final 1979 test a MEM and manned Apollo CSM would be placed in earth orbit. The Apollo CSM would separate, transpose, and dock with the MEM. The crew would enter the MEM and ride it to a landing on the earth's surface.

  Development Cost $: 4,100.000 million. Cost Notes: 1967 dollars. Crew Size: 4. Design Life: 30. Length: 9.00 m (29.50 ft). Basic Diameter: 9.00 m (29.50 ft). Maximum Diameter: 9.00 m (29.50 ft). Habitable Volume: 4.00 m3. Mass: 49,400 kg (108,900 lb). Main Engine Propellants: Liquid oxygen/methane. Electrical System: Fuel cells.

• 1966 April 15 - NASA said to need a manned space flight goal other than "using Apollo hardware" - a Mars flyby or landing mission. -

  MSC Director Robert R. Gilruth summarized Houston's position expressed during discussions with Associate Administrator for Manned Space Flight George E. Mueller two days earlier. Gilruth cited NASA s need for a manned space flight goal other than 'using Apollo hardware' (and suggested a Mars flyby or landing mission as an in-house focus for planning.) Also, he repeated his concern over the imbalance between AAP goals and resources, as well as the extent of engineering redesign and hardware modification that had been forced upon the project. Though expressing his and MSC's desire to contribute to and be a part of AAP, Gilruth voiced concern that 'the future of manned space flight . . . is in jeopardy because we do not have firm goals, and because the present approach appears to us to be technically unsound.'

• Portree, David S. F., Humans to Mars: Fifty Years of Mission Planning, 1950 - 2000, NASA Monographs in Aerospace History Series, Number 21, February 2001. Excellent overview of American plans for sending men to Mars.

• Miller, Ron, The Dream Machines, Krieger, Malabar, Florida, 1993. ISBN: 0894640399. Sensational chronological roundup of text, photos, and sketches of virtually every spacecraft and launch vehicle design every conceived but never built. A gold mine for space-struck baby boomers. More at amazon.com...