Encyclopedia Astronautica
Mars Direct



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Mars Direct
Credit: NASA
American manned Mars expedition. Study 1991. In 1991 Martin Marietta and NASA Ames (Zubrin, Baker, and Gwynne) proposed 'Mars Direct' - a Mars expedition faster, cheaper, and better than the standard NASA plan.

Key features included:

  • Direct flight to and from the Martian surface. Artificial gravity provided en route. No earth orbit or lunar orbit rendezvous; no zero-G assembly operations or crewed monitoring of spacecraft in Mars orbit.

  • Fuelling of the Earth Return Vehicle using propellant generated on Mars from the atmosphere.

  • Extended operations on the Martian surface (555 days) as opposed to the 20 days for NASA 'fast' missions.

Mars Direct would be completed in two launches of the proposed Ares heavy lift booster. The first launch would deliver an unfuelled and unmanned Earth Return Vehicle (ERV) to the Martian surface. After landing an on-board production plant would generate methane/oxygen propellants. A second launch would deliver the four-person crew. Following eighteen months of extensive exploration of the surface, they would enter the ERV and return directly to Earth. The same launch vehicles and spacecraft developed for Mars Direct could also support a lunar base.

Launch 1: In December 1996, a single Ares launch vehicle would place an unmanned 40 metric ton payload onto a direct trans-Mars trajectory. The payload would consist of:

  • ERV - Earth return vehicle. This unfuelled, unmanned vehicle would eventually be used by the manned crew to ascend from the Martian surface and return to earth
  • Automated chemical processing unit and set of compressors. This would manufacture rocket propellant for the ERV using the Martian atmosphere.
  • 100 kWe nuclear reactor mounted on a methane/oxygen propelled light truck. This would power the chemical processing unit. After the ERV propellant was generated it would provide power to the base.
  • 6 metric tons of liquid hydrogen. This would be catalytically reacted by the processing plant with Martian atmospheric carbon dioxide to produce methane and water. The water would then be electrolyzed to produce oxygen and more hydrogen, which would be recycled through the plant. The process would provide 24 metric tons of methane and 48 metric tons of oxygen rocket propellants. An additional 36 metric tons of oxygen would be produced through direct reduction of Martian carbon dioxide. The total propellant produced was to be 107 metric tons - 96 metric tons for the ERV and 11 metric tons to fuel surface vehicles.
  • Small scientific rovers
  • Aerobrake/landing engine assembly

Launch 2: In 1999 an Ares would launch a manned 80 metric ton payload. This would consist of:

  • Habitation module with a crew of four and supplies for three years. Artificial gravity would be provided for the crew during the coast to Mars by unreeling a tether between the spacecraft and the spent Ares third stage. The habitation module was 8.4 m in diameter, 4.9 m tall, and consisted of two floors: the lower floor, with cargo and the ground rover; and the upper floor, with the crew quarters. Total mass was 35 metric tons.
  • Pressurized methane/oxygen driven ground rover. This was to be fuelled with a one-way surface range of up to 1000 km. If for any reason the crew landed far from the ERV, it could be used to reach it for the return home. Normally it would be refueled from the propellants at the ERV site.
  • Aerobrake/landing engine assembly. This would be used to land at the Launch 1 site, guided by a beacon on the ERV.

These two launches would constitute the main Mars Direct expedition. But a backup return vehicle would be available, since in 1999 a payload identical to Launch 1 would also be put on a trans-Mars trajectory. If for any reason the Launch 1 ERV was unusable, this payload would provide a backup for the Launch 2 crew. If all went well, it would be used as the return vehicle for the next crew, to be launched in 2001. In this way two ERV's would always available for crew return as missions were sent out every two years. During the eighteen months on the Martian surface, the crew would use the ground vehicle to traverse 22,000 kilometers of Martian terrain within 500 km from the base.

The same equipment could be used to establish a lunar base - in fact it could be tested comprehensively on the moon before committing to the Mars expedition. In the lunar scenario the Ares booster could launch a 59 metric ton payload consisting of the standard Habitation Module with a Lunar orbital capture and lunar descent (LOC/LD) stage. The LOC/LD stage would land the Habitation Module on the Moon. A crew could then be flown to the Moon using an ERV with an LOC/LD stage. This ERV used only the second stage of the Mars ERV for Earth return direct from the lunar surface.

Use of a nuclear thermal rocket (NTR) third stage on the Ares would increase trans-Mars payload by 50%. The NTR stage would have a specific impulse of 900 s, a power of 900 MWth, and a thrust of 45,000 lb. Use of a NIMF (Nuclear rocket using Indigenous Martian Fuel) stage on the lander would provide the Habitation Module with the capability of leaping from one location on the Martian surface to another, using compressed Martian carbon dioxide from the atmosphere as propellant. This would allow 18 sites on the surface to be visited within the 550 days of surface time, as opposed to just one for the baseline expedition.

ERV Mass Breakdown - total 28,500 kg landed on Martian surface:

  • ERV Cabin structure: 3,000
  • Life support system: 1,000
  • Consumables: 3,400
  • Solar array (5 kWe): 1,000
  • Reaction control system: 500
  • Communications and information management: 100
  • Furnishings: 500
  • 4 space suits: 400
  • Spares and 16% growth: 1,600
  • Earth return aeroshell: 1,800
  • Rover: 500
  • Hydrogen feedstock: 6,300
  • ERV propulsion stages: 4,500
  • Propellant production plant: 500
  • Nuclear reactor (100 kWe): 3,500

Habitat Mass Breakdown - total 25,200 kg landed on Martian surface:

  • Habitat structure: 5,000
  • Life support system: 3,000
  • Consumables: 7,000
  • Solar array (5 kWe): 1,000
  • Reaction control system: 500
  • Communications and information management: 200
  • Furnishings: 1,000
  • 4 space suits: 400
  • Spares and 16% growth: 3,500
  • Pressurized rover: 1,400
  • 2 Open rovers: 800
  • Lab equipment: 500
  • Field science equipment: 500
  • Crew: 400

Mars Direct Nuclear Thermal Mission Summary:

  • Summary: Low cost; no orbital rendezvous or assembly; dependent upon ISRU propellant production for return; Chemical and NTR options
  • Propulsion: Nuclear thermal
  • Braking at Mars: aerodynamic
  • Mission Type: conjunction
  • Split or All-Up: split
  • ISRU: ISRU
  • Launch Year: 1997
  • Crew: 4
  • Mars Surface payload-metric tons: 30
  • Outbound time-days: 100
  • Mars Stay Time-days: 550
  • Return Time-days: 130
  • Total Mission Time-days: 780
  • Total Payload Required in Low Earth Orbit-metric tons: 220
  • Mass per crew-metric tons: 55
  • Launch Vehicle Payload to LEO-metric tons: 105
  • Number of Launches Required to Assemble Payload in Low Earth Orbit: 2
  • Launch Vehicle: Ares

Mars Direct Chemical Mission Summary:

  • Summary: Low cost; no orbital rendezvous or assembly; dependent upon ISRU propellant production for return; Chemical and NTR options
  • Propulsion: LOX/LH2
  • Braking at Mars: aerodynamic
  • Mission Type: conjunction
  • Split or All-Up: split
  • ISRU: ISRU
  • Launch Year: 1997
  • Crew: 4
  • Mars Surface payload-metric tons: 30
  • Outbound time-days: 180
  • Mars Stay Time-days: 640
  • Return Time-days: 60
  • Total Mission Time-days: 880
  • Total Payload Required in Low Earth Orbit-metric tons: 220
  • Total Propellant Required-metric tons: 150
  • Propellant Fraction: 0.68
  • Mass per crew-metric tons: 55
  • Launch Vehicle Payload to LEO-metric tons: 105
  • Number of Launches Required to Assemble Payload in Low Earth Orbit: 2
  • Launch Vehicle: Ares Mars Direct

Crew Size: 4.

Gross mass: 160,000 kg (350,000 lb).

More... - Chronology...


Associated Countries
See also
  • Mars Expeditions Since Wernher von Braun first sketched out his Marsprojekt in 1946, a succession of designs and mission profiles were seriously studied in the United States and the Soviet Union. By the late 1960's Von Braun had come to favour nuclear thermal rocket powered expeditions, while his Soviet counterpart Korolev decided that nuclear electric propulsion was the way to go. All such work stopped in both countries in the 1970's, after the cancellation of the Apollo program in the United States and the N1 booster in the Soviet Union. More...

Associated Launch Vehicles
  • Ares Mars Direct American orbital launch vehicle. The Ares launch vehicle was designed for support of Zubrin's Mars Direct expedition. It was a shuttle-derived design taking maximum advantage of existing hardware. It would use shuttle Advanced Solid Rocket Boosters, a modified shuttle external tank for handling vertically-mounted payloads, and a new Lox/LH2 third stage for trans-Mars or trans-lunar injection of the payload. Ares would put 121 tonnes into a 300 km circular orbit , boost 59 tonnes toward the moon or 47 tonnes toward Mars. Without the upper stage 75 tonnes could be placed in low earth orbit. More...

Associated Manufacturers and Agencies
  • NASA American agency overseeing development of rockets and spacecraft. National Aeronautics and Space Administration, USA, USA. More...
  • Martin American manufacturer of rockets, spacecraft, and rocket engines. Martin Marietta Astronautics Group (1956), Denver, CO, USA. More...

Bibliography
  • Zubrin, Robert, Baker, David A, and Gwynne, Owen, Mars Direct: A Simple, Robust, and Cost Effective Architecture for the Space Exploration Initiative, AIAA-91-0328, 1991. Web Address when accessed: here.
  • Portree, David S. F., Humans to Mars: Fifty Years of Mission Planning, 1950 - 2000, NASA Monographs in Aerospace History Series, Number 21, February 2001.
  • Griffin, Brand; Thomas, Brent; Vaughan, Diane, A Comparison of Transportation Systems for Human Missions to Mars, AIAA 2004-3834, 40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit ,11-14 July 2004.

Mars Direct Chronology


1991 During the Year - .
  • Mars Direct - . Nation: USA. Spacecraft: Mars Direct. Summary: Martin Marietta and NASA Ames (Zubrin, Baker, and Gwynne) proposed 'Mars Direct' - a Mars expedition faster, cheaper, and better than the standard NASA plan..

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