Apollo Lunar Module

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Grumman Apollo LM
File:Apollo 16 LM.jpg
Apollo LM on lunar surface
Role: Lunar landing
Crew: 2; CDR, LM pilot
Height: 20.9 ft 6.37 m
Diameter: 14 ft 4.27 m
Landing gear span: 29.75 ft 9.07 m
Volume: 235 ft3 6.65 m3
Ascent module: 10,024 lb 4,547 kg
Descent module: 22,375 lb 10,149 kg
Total: 32,399 lb 14,696 kg
Rocket engines
LM RCS (N2O4/UDMH) x 16: 100 lbf ea 441 N
Ascent Propulsion System
(N2O4/Aerozine 50) x 1:
3,500 lbf ea 15.6 kN
Descent Propulsion System
(N2O4/Aerozine 50) x 1:
9,982 lbf ea 44.40 kN
Endurance: 3 days 72 hours
Aposelene: 100 miles 160 km
Periselene: surface surface
Spacecraft delta v: 15,390 ft/s 4,690 m/s
Apollo LM diagram
Apollo LM diagram (NASA)
Grumman Apollo LM

The Apollo Lunar Module was the lander portion of the Apollo spacecraft built for the US Apollo program to achieve the transit from Moon orbit to the surface and back. The module was also known as the LM from the manufacturer designation (yet pronounced "LEM" from NASA's early name for it, Lunar Excursion Module).

The module was designed to carry two crew in a 6.65 m³ space. The total module was 6.4 m high and 4.3 m across, resting on four legs. It consisted of two stages—the descent stage module and the ascent stage. The total mass of the module was 15,264 kg with the majority of that (10,334 kg) in the descent stage.


The Apollo Lunar Module came into being because NASA chose to reach the moon via a lunar orbit rendezvous (LOR) instead of a direct ascent or Earth orbit rendezvous (EOR) (see Choosing a mission mode for more information on the available rendezvous types). Both a direct ascent and an EOR would have involved the entire Apollo spacecraft landing on the moon; once the decision had been made to proceed using LOR, it became necessary to produce a separate craft capable of reaching the lunar surface.

The LM contract was given to Grumman Aircraft Engineering and a number of subcontractors. Grumman had begun lunar orbit rendezvous studies in late 1960 and again in 1962. In July 1962 eleven firms were invited to submit proposals for the LM. Nine did so in September, and Grumman was awarded the contract that same month. The contract cost was expected to be around $350 million. There were initially four major subcontractors - Bell Aerosystems (ascent engine), Hamilton Standard (environmental control systems), Marquardt (reaction control system) and Rocketdyne (descent engine).

The primary guidance, navigation and control system (PGNCS) on the LM was developed by the MIT Instrumentation Laboratory. The Apollo Guidance Computer was manufactured by Raytheon. A similar guidance system was used in the Command Module. A backup navigation tool, the Abort Guidance System (AGS), was developed by TRW.

To learn lunar landing techniques, astronauts practiced in the Lunar Landing Research Vehicle (LLRV), a flying vehicle that simulated the Lunar Module on earth.

Configuration freeze did not start until April 1963 when the ascent and descent engine design was decided. In addition to Rocketdyne a parallel program for the descent engine was ordered from Space Technology Laboratories in July 1963, and by January 1965 the Rocketdyne contract was cancelled. As the program continued there were numerous redesigns to save weight (including 'Operation Scrape'), improve safety, and fix problems. For example initially the module was to be powered by fuel cells, built by Pratt and Whitney but in March 1965 they were paid off in favor of an all battery design.

The initial design iteration had the LEM with three landing legs. It was felt that three legs, though the lightest configuration, was the least stable if one of the legs were damaged during landing. The next landing gear design iteration had five legs and was the most stable configuration for landing on an unknown terrain. That configuration was too heavy and the compromise was four landing legs.

The first LM flight was on January 22, 1968 when the unmanned LM-1 was launched on a Saturn IB for testing of propulsion systems in orbit. The next LM flight was aboard Apollo 9 using LM-3 on March 3, 1969 as a manned flight (McDivitt, Scott and Schweickart) to test a number of systems in Earth orbit including LM and CSM crew transit, LM propulsion, separation and docking. Apollo 10, which launched on May 18, 1969, was another series of tests, this time in lunar orbit with the LM separating and descending to within 10 km of the surface. From the successful tests the LM successfully descended and ascended from the lunar surface with Apollo 11.

In April 1970, the lunar module Aquarius played an unexpected role in saving the lives of the three astronauts of the Apollo 13 mission (Commander James A. Lovell Jr., CSM pilot John L. Swigert Jr., and LM pilot Fred W. Haise Jr.), after an electrical short circuit caused an oxygen tank in that mission's service module to overheat and explode. Aquarius served as a refuge for the astronauts during their return to Earth orbit, while its batteries were used to recharge the vital re-entry batteries of the command module that brought the astronauts through the Earth's atmosphere and to a safe spashdown on April 17, 1970. The LM's descent engine, designed to slow the vehicle during its descent to the moon, was used to accelerate the Apollo 13 spacecraft around the moon and back to Earth. After the accident, the LM's systems, designed to support two astronauts for 45 hours, actually supported three astronauts for 90 hours.

Lunar Module (LM) specifications

The LEM flight instrumentation panel and front windows. Credit: Alexandre Sabbatini

The Lunar Module was the portion of the Apollo spacecraft that landed on the moon and returned to lunar orbit. It is divided into two major parts, the Descent Module and the Ascent Module.

The Descent Modules contains the landing gear, landing radar antenna, descent rocket engine, and fuel to land on the moon. It also had several cargo compartments used to carry among other things, the Apollo Lunar Surface Experiment Packages ALSEP, Mobile Equipment Cart (a hand pulled equipment cart—Apollo 14), the Lunar Rover (moon car)—Apollo 15, 16 and 17), surface television camera, surface tools and lunar sample collection boxes. Also, on the ladder of the descent stage is attached a plaque.

The Ascent Module contains the crew cabin, instrument panels, overhead hatch/docking port, forward hatch, reaction control system, radar and communications antennas, ascent rocket engine and fuel to return to lunar orbit and rendezvous with the Apollo Command and Service Modules.

  • Specifications: (Baseline LM)
    • Ascent Stage:
      • Crew: 2
      • Crew cabin volume: 6.65 m³ (235 ft³)
      • Height: 3.76 m (12.34 ft)
      • Diameter: 4.2 m (13.78 ft)
      • Mass including fuel: 4,670 kg (10,300 lb)
      • Atmosphere: 100% oxygen at 250 mmHg (33 kPa)
      • Water: two 19.3 kg (42.5 lb) storage tanks
      • Coolant: 11.3 kg (25 lb) of ethylene glycol/water solution
      • RCS (Reaction Control System) Propellant mass: 287 kg (633 lb)
      • APS Propellant mass: 2,353 kg (5,187 lb)
      • RCS thrusters: 16 x 445 N; four quads
      • RCS propellants: N2O4/UDMH
      • RCS specific impulse: 2.84 kN·s/kg
      • APS thrust: 15.6 kN (3,500 lbf)
      • APS propellants: N2O4/Aerozine 50 (UDMH/N2H4)
      • APS pressurant: 2 x 2.9 kg helium tanks at 21 MPa
      • Engine specific impulse: 3.05 kN·s/kg
      • Thrust-to-weight ratio: 0.34 lbf/lb (3.3 N/kg)
      • Ascent stage delta V: 2,220 m/s (7,280 ft/s)
      • Batteries: 4 x 400 A·h silver-zinc batteries
      • Power: 26-32 V DC buses

Thus the thrust was less than the weight on Earth, but enough on the Moon.

    • Descent Stage:
      • Height: 3.2 m (10.5 ft)
      • Diameter: 4.2 m (13.8 ft)
      • Landing gear diameter: 9.4 m (30.8 ft)
      • Mass including fuel: 10,334 kg (22,783 lb)
      • Water: 1 x 151 kg storage tank
      • Power: 2 x 296 A·h silver-zinc batteries (secondary system)
      • Propellants mass: 8,165 kg (18,000 lb)
      • DPS thrust: 45.04 kN (10,125 lbf), throttleable to 4.56 kN (1025 lbf)
      • DPS propellants: N2O4/Aerozine 50 (UDMH/N2H4)
      • DPS pressurant: 1 x 22 kg supercritical helium tank at 10.72 kPa.
      • Engine specific impulse: 3050 N·s/kg
      • Descent stage delta V: 2,470 m/s (8,100 ft/s)
      • Batteries: 2 x 296 A·h silver-zinc batteries

File:Lunar Module diagram.jpg
Apollo Spacecraft: Apollo Lunar Module Diagram.
File:LM illustration 02.jpg
Apollo Lunar Module

Lunar Modules produced

Serial number Use Launch date Current location
LM-1 Apollo 5 January 22, 1968 Reentered Earth's atmosphere
Not flown
On display at the National Air and Space Museum, Washington, DC. (photo).
LM-3 Spider Apollo 9 March 3, 1969 Reentered Earth's atmosphere
LM-4 Snoopy Apollo 10 May 18, 1969 Descent stage impacted Moon; Ascent stage in solar orbit
LM-5 Eagle Apollo 11 July 16, 1969 Lunar surface*
LM-6 Intrepid Apollo 12 November 14, 1969 Lunar surface*
LM-7 Aquarius Apollo 13 April 11, 1970 Reentered Earth's atmosphere over Fiji
LM-8 Antares Apollo 14 January 31, 1971 Lunar surface*
Not flown
On display at the Kennedy Space Center (Apollo/Saturn V Center)
LM-10 Falcon Apollo 15 July 26, 1971 Lunar surface*
LM-11 Orion Apollo 16 April 16, 1972 Lunar surface*
LM-12 Challenger Apollo 17 December 7, 1972 Lunar surface*
Not flown (meant for later Apollo flights)
Partially completed by Grumman; restored and on display at Cradle of Aviation, Long Island, New York
Not flown (meant for later Apollo flights)
Never completed; unconfirmed reports claim that some parts (in addition to parts from LTA-3) are included in LM on display at the Franklin Institute, Philadelphia
Not flown (meant for later Apollo flights)

(* See List of artificial objects on the Moon for location.)

External links


  • Kelly, Thomas J. (2001). Moon Lander: How We Developed the Apollo Lunar Module (Smithsonian History of Aviation and Spaceflight Series). Smithsonian Institution Press. ISBN 156098998X.
  • Baker, David (1981). The History of Manned Space Flight. Crown Publishers. ISBN 051754377X
  • Brooks, Courtney J., Grimwood, James M. and Swenson, Loyd S. Jr (1979) Chariots for Apollo: A History of Manned Lunar Spacecraft NASA SP-4205.
  • Sullivan, Scott P. (2004) Virtual LM: A Pictorial Essay of the Engineering and Construction of the Apollo Lunar Module. Apogee Books. ISBN 1894959140
  • Stoff, Joshua. (2004) Building Moonships: The Grumman Lunar Module. Arcadia Publishing. ISBN 0738535869

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