The Apollo Lunar Module (LM /ˈLEM), originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon’s surface during the United States’ Apollo program. It was the first crewed spacecraft to operate exclusively in the airless vacuum of space, and remains the only crewed vehicle to land anywhere beyond Earth.
Everyone called the vehicle the ‘LEM’ throughout most of its development life until May 1966 when a memo from the NASA Project Designation Committee officiously changed the name simply to ‘LM’.
Structurally and aerodynamically incapable of flight through Earth’s atmosphere, the two-stage Lunar Module was ferried to lunar orbit attached to the Apollo command and service module (CSM), about twice its mass. Its crew of two flew the Lunar Module from lunar orbit to the Moon’s surface. During takeoff, the spent descent stage was used as a launch pad for the ascent stage which then flew back to the command module, after which it was also discarded.
In November 1962 Grumman won the contract for the Lunar Module. Overseen by Grumman, the LM’s development was plagued with problems that delayed its first uncrewed flight by about ten months and its first crewed flight by about three months. Regardless, the LM became the most reliable component of the Apollo–Saturn space vehicle. The total cost of the LM for development and the units produced was $21.65 billion in 2016 dollars, adjusting from a nominal total of $2.29 billion using the NASA New Start Inflation Indices.
Ten lunar modules were launched into space. Of these, six were landed by humans on the Moon from 1969 to 1972. The first two flown were tests in low Earth orbit: Apollo 5, without a crew; and Apollo 9 with a crew. A third test flight in low lunar orbit was Apollo 10, a dress rehearsal for the first landing, conducted on Apollo 11. The Apollo 13 lunar module functioned as a lifeboat to provide life support and propulsion to keep the crew alive for the trip home, when their CSM was disabled by an oxygen tank explosion en route to the Moon.
The six landed descent stages remain at their landing sites; their corresponding ascent stages crashed into the Moon following use. One ascent stage (Apollo 10’s Snoopy) was discarded in a heliocentric orbit after its descent stage was discarded in lunar orbit. The other three LMs were destroyed during controlled re-entry in the Earth’s atmosphere: the four stages of Apollo 5 and Apollo 9 each re-entered separately, while Apollo 13’s Aquarius re-entered as a unit.
Height: 9 ft 3.5 in (2.832 m)
Width: 14 ft 1 in (4.29 m)
Depth: 13 ft 3 in (4.04 m)
Mass, dry: 4,740 lb (2,150 kg)
Mass, gross: 10,300 lb (4,700 kg)
Crew cabin volume: 235 cu ft (6.7 m3)
Habitable volume: 160 cu ft (4.5 m3)
Crew compartment height: 7 ft 8 in (2.34 m)
Crew compartment depth: 3 ft 6 in (1.07 m)
Atmosphere: 100% oxygen at 4.8 psi (33 kPa)
Water: two 42.5 lb (19.3 kg) storage tanks
Coolant: 25 pounds (11 kg) of ethylene glycol / water solution
Thermal Control: one active water-ice sublimator
RCS propellant mass: 633 lb (287 kg)
RCS thrusters: Sixteen × 100 lbf (440 N) in four quads
RCS propellants: Aerozine 50 fuel / Dinitrogen tetroxide (N2O4) oxidizer
RCS specific impulse: 290 s (2.8 km/s)
APS propellant mass: 5,187 lb (2,353 kg) stored in two 36-cubic-foot (1.02 m3) propellant tanks
APS engine: Bell Aerospace LM Ascent Engine (LMAE) and Rocketdyne LMAE Injectors
APS thrust: 3,500 lbf (16,000 N)
APS propellants: Aerozine 50 fuel / Dinitrogen Tetroxide oxidizer
APS pressurant: Two 6.4 lb (2.9 kg) helium tanks at 3,000 pounds per square inch (21 MPa)
APS specific impulse: 311 s (3.05 km/s)
APS delta-V: 7,280 ft/s (2,220 m/s)
Thrust-to-weight ratio at liftoff: 2.124 (in lunar gravity)
Batteries: Two 28–32 volt, 296 ampere hour Silver-zinc batteries; 125 lb (57 kg) each
Power: 28 V DC, 115 V 400 Hz AC
Crew: 2
All Aero 