Encyclopedia Astronautica

Apolo LM
Credit: © Mark Wade
American manned Mars expedition. Study 1966.

A Mars expedition concept where the lander would separate from a manned Mars flyby spacecraft, aerobrake directly into the Martian atmosphere, land on the surface, and then place itself into solar orbit, and rendezvous and dock with the flyby spacecraft. Since the main spacecraft would not have to brake into and out of Mars orbit, huge propellant savings were possible, making a manned Mars landing expedition possible in a single Saturn V launch.

FLEM was described in a 30 June 1966 report by R R Titus, an engineer at United Aircraft. This Flyby-Landing Excursion Module could separate from the a manned Mars flyby spacecraft 60 days before reaching the planet, and thrust into a faster trajectory. FLEM would have enough propellant to brake into Mars orbit, select an acceptable landing point, enter the Martian atmosphere, land, and then boost itself to solar orbit. This would allow it to reach Mars and spend 19 days on the surface before it would have to rocket back into solar orbit to rendezvous and dock with the Mars flyby spacecraft. A separation 30 days before the flyby would give it 9 days on the surface. Titus calculated that using FLEM with a nuclear thermal upper stage, the total spacecraft mass for a manned landing expedition could be kept to 118 metric tons, meaning a single Saturn V launch could mount a Mars landing mission. An unmanned version of FLEM was dubbed MSSR and was proposed as a surface-sample return vehicle in the NASA Planetary Joint Action group flyby plan of 1966-1967.

FLEM Mission Summary:

  • Summary: Flyby-rendezvous spacecraft design.
  • Propulsion: Nuclear thermal
  • Braking at Mars: flyby-rendezvous
  • Mission Type: Crocco
  • Split or All-Up: split
  • ISRU: no ISRU
  • Launch Year: 1985
  • Crew: 3
  • Outbound time-days: 130
  • Mars Stay Time-days: 19
  • Return Time-days: 560
  • Total Mission Time-days: 690
  • Total Payload Required in Low Earth Orbit-metric tons: 118
  • Mass per crew-metric tons: 39
  • Launch Vehicle Payload to LEO-metric tons: 118
  • Number of Launches Required to Assemble Payload in Low Earth Orbit: 1
  • Launch Vehicle: Saturn MLV-V-1


Crew Size: 3.

Gross mass: 118,000 kg (260,000 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 Manufacturers and Agencies
Associated Propellants
  • Nuclear/LH2 Nuclear thermal engines use the heat of a nuclear reactor to heat a propellant. Although early Russian designs used ammonia or alcohol as propellant, the ideal working fluid for space applications is the liquid form of the lightest element, hydrogen. Nuclear engines would have twice the performance of conventional chemical rocket engines. Although successfully ground-tested in both Russia and America, they have never been flown due primarily to environmental and safety concerns. Liquid hydrogen was identified by all the leading rocket visionaries as the theoretically ideal rocket fuel. It had big drawbacks, however - it was highly cryogenic, and it had a very low density, making for large tanks. The United States mastered hydrogen technology for the highly classified Lockheed CL-400 Suntan reconnaissance aircraft in the mid-1950's. The technology was transferred to the Centaur rocket stage program, and by the mid-1960's the United States was flying the Centaur and Saturn upper stages using the fuel. It was adopted for the core of the space shuttle, and Centaur stages still fly today. More...

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

Home - Browse - Contact
© / Conditions for Use