Apollo Lunar Module
(Redirected from Lunar module)
Apollo 16 LM Orion on the lunar surface
Grumman Aircraft
Thomas J. Kelly
Manned lunar landing
Design life
75 hours (Extended)
Launch mass
33,500 pounds (15,200 kg) initial
36,200 pounds (16,400 kg) Extended
Crew capacity
17.9 feet (5.5 m) high
14.0 feet (4.3 m) wide
13.3 feet (4.1 m) deep
235 cubic feet (6.7 m3)
Lunar orbit
First launch
Last launch
Last retirement
Apollo LM diagram
The Apollo Lunar Module (LM), originally designated the Lunar Excursion Module (LEM), was the lander portion of the Apollo spacecraft built for the US Apollo program by Grumman Aircraft to carry a crew of two from lunar orbit to the surface and back. Designed for lunar orbit rendezvous, it consisted of an ascent stage and descent stage, and was ferried to lunar orbit by its companion Command and Service Module (CSM), a separate spacecraft of approximately twice its mass, which also took the astronauts home to Earth. After completing its mission, the LM was discarded. It was capable of operation only in outer space; structurally and aerodynamically it was incapable of flight through the Earth's atmosphere. The Lunar Module was the first, and to date only, manned spacecraft to operate exclusively in the airless vacuum of space.
Six such craft successfully landed on the Moon between 1969 and 1972. A seventh provided propulsion and life support for the crew of Apollo 13 when their CSM was disabled by an oxygen tank explosion en route to the Moon.
The LM's development was plagued with problems which delayed its first unmanned flight by about ten months, and its first manned flight by about three months. Despite this, the LM eventually became the most reliable component of the Apollo/Saturn space vehicle, the only component never to suffer a failure that significantly impacted a mission.[1] It holds the distinction of being the first, and to date only, manned vehicle to either land on or take off from a natural object in the solar system other than the Earth.
1 Operational profile
2.1 Contract letting
2.2 Design phase
2.3 Astronaut training
2.4 Development flights
2.5 Production flights
2.6 Extended J Class Missions
3.1 Ascent stage
3.2 Descent stage
4 Lunar Modules produced
5 Proposed derivatives
5.1 Apollo Telescope Mount
5.2 LM Truck
6 Depiction in film and television
7 Media
Operational profile[edit]
The lunar module of Apollo 11 seen in orbit above the Moon. Earth is visible in the far distance.
At launch, the Lunar Module sat directly beneath the Command/Service Module (CSM) with legs folded, inside the Spacecraft-to-LM Adapter (SLA) attached to the S-IVB third stage of the Saturn V rocket. There it remained through earth parking orbit and the Trans Lunar Injection (TLI) rocket burn to send the craft toward the Moon.
Soon after TLI, the SLA opened and the CSM separated, turned around, came back to dock with the Lunar Module, and extracted it from the S-IVB. During the flight to the Moon, the docking hatches were opened and the LM Pilot entered the LM to temporarily power up and test its systems (except for propulsion). Throughout the flight, he performed the role of an engineering officer, responsible for monitoring the systems of both spacecraft.
After achieving a lunar parking orbit, the Commander and LM Pilot entered and powered up the LM, replaced the hatches and docking equipment, unfolded and locked its landing legs, and separated from the CSM, flying independently. The Commander operated the flight controls and engine throttle, while the Lunar Module Pilot operated other spacecraft systems and kept the Commander informed on systems status and navigational information. After visual inspection of the landing gear by the Command Module Pilot, the LM was withdrawn to a safe distance, then the descent engine was pointed forward into the direction of travel to perform the 30 second Descent Orbit Insertion burn to reduce speed and drop the LM's perilune to within approximately 50,000 feet (15 km) of the surface,[2] about 260 nautical miles (480 km) uprange of the landing site.
At this point, the engine was started again for Powered Descent Initiation. During this time the crew flew on their backs, depending on the computer to slow the craft's forward and vertical velocity to near zero. Control was exercised with a combination of engine throttling and attitude thrusters, guided by the computer with the aid of landing radar. During the braking phase altitude decreased to approximately 10,000 feet (3.0 km), then the final approach phase went to approximately 700 feet (210 m). During final approach, the vehicle pitched over to a near-vertical position, allowing the crew to look forward and down to see the lunar surface for the first time.[3] Finally the landing phase began, approximately 2,000 feet (0.61 km) uprange of the targeted landing site. At this point manual control was enabled for the Commander, and enough fuel reserve was allocated to allow approximately two minutes of hover time to survey where the computer was taking the craft and make any necessary corrections. (If necessary, landing could have been aborted at almost any time by jettisoning the descent stage and firing the ascent engine to climb back into orbit for an emergency return to the CSM.) Finally, 66 inch (1676 mm) long probes extending from three footpads of the lander touched the surface, activating the contact indicator light which signaled time for descent engine cutoff, allowing the LM to settle on the surface.
When ready to leave the Moon, the LM would separate the descent stage and fire the ascent engine to climb back into orbit, using the descent stage as a launch platform. After a few course correction burns, the LM would rendezvous with the CSM and dock for transfer of the crew and rock samples. Having completed its job, the LM was separated and sent into solar orbit or to crash into the Moon.
A 1962 model of the first LEM design, docked to the Command / Service Module, is held by Dr. Joseph F. Shea
The Lunar Module (originally designated the Lunar Excursion Module, known by the acronym LEM) was designed after NASA chose to reach the Moon via Lunar Orbit Rendezvous (LOR) instead of the direct ascent or Earth Orbit Rendezvous (EOR) methods. Both direct ascent and EOR would have involved landing a much heavier, complete Apollo spacecraft 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 and ascending back to lunar orbit.
Contract letting[edit]
In July 1962, eleven firms were invited to submit proposals for the LEM. Nine companies responded in September, answering 20 specific questions posed by the NASA RFP in a 60-page limited technical proposal. Grumman Aircraft was awarded the contract two months later. Grumman had begun lunar orbit rendezvous studies in the late 1950s and again in 1961. 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) 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.
Design phase[edit]
This 1963 model depicts the second LEM design, which gave rise to informal references as "the bug".
The Lunar Module was chiefly designed by Grumman aerospace engineer Thomas J. Kelly.[4] The first LEM design looked like a smaller version of the Apollo Command/Service Module (a cone-shaped cabin atop a cylindrical propulsion section) with folding legs. The second design invoked the idea of a helicopter cockpit with large curved windows and seats, to improve the astronauts' visibility for hover and landing. This also included a second, forward docking port, allowing the LEM crew to take an active role in docking with the CSM.
As the program continued, there were numerous redesigns to save weight, improve safety, and fix problems. First to go were the heavy cockpit windows, and the seats; the astronauts would stand while flying the LEM, supported by a cable and pulley system, with smaller triangular windows giving them sufficient visibility of the landing site. Later, the redundant forward docking port was removed, which meant the Command Pilot gave up active control of the docking to the Command Module Pilot; he could still see the approaching CSM through a small overhead window. These changes resulted in significant weight savings. Egress while wearing bulky Extra-Vehicular Activity (EVA) spacesuits was also facilitated by a simpler-opening forward hatch (32 x 32 inches).
A configuration freeze did not start until April 1963, when the ascent and descent engine designs were decided. In addition to Rocketdyne, a parallel program for the descent engine was ordered from Space Technology Laboratories (TRW) in July 1963, and by January 1965 the Rocketdyne contract was canceled.
Power was initially to be produced by fuel cells built by Pratt and Whitney similar to the CSM, but in March 1965 these were discarded in favor of an all-battery design.[5]
The initial design had three landing legs. As any particular leg would have to carry the weight of the vehicle if it lands at any significant angle, three legs was the lightest configuration. However, it would be 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, however, was too heavy and the designers compromised on four landing legs.[6]
In June 1966, the name was changed to Lunar Module (LM), eliminating the word "excursion".[7][8] According to George Low, Manager of the Apollo Spacecraft Program Office, this was because NASA was afraid that the word "excursion" might lend a frivolous note to Apollo.[9] After the name change from "LEM" to "LM", the pronunciation of the abbreviation did not change, as the habit became ingrained among engineers, the astronauts, and the media to universally pronounce "LM" as "lem" which is easier than saying the letters individually.
Astronaut training[edit]
Lunar Landing Research Vehicle (NASA)
To allow astronauts to learn lunar landing techniques, NASA contracted Bell Aerosystems in 1964 to build the Lunar Landing Research Vehicle (LLRV), otherwise known as "The Flying Bedstead," which used a gimbal-mounted vertical jet engine to counter 5/6 of its weight to simulate the Moon's gravity, in addition to its own hydrogen peroxide thrusters to simulate the LM's descent engine and attitude control. Successful testing of two LLRV prototypes at the Dryden Flight Research Center led in 1966 to three production Lunar Landing Training Vehicles (LLTV) which along with the LLRV's were used to train the astronauts at the Houston Manned Spacecraft Center. This aircraft proved fairly dangerous to fly, as three of the five were destroyed in crashes. It was equipped with a rocket-powered ejection seat, so in each case the pilot survived, including the first man to walk on the Moon, Neil Armstrong.[10]
Development flights[edit]
LM-1 was built to make the first unmanned flight for propulsion systems testing, launched into low Earth orbit atop a Saturn IB. This was originally planned for April 1967, to be followed by the first manned flight later that year. But the LM's development problems had been underestimated, and LM-1's flight was delayed until January 22, 1968, as Apollo 5. At that time, LM-2 was held in reserve in case the LM-1 flight failed, which did not happen.
LM-3 now became the first manned LM, again to be flown in low Earth orbit to test all the systems, and practice separation, rendezvous, and docking. planned for Apollo 8 in December 1968. But again, last-minute problems delayed its flight until Apollo 9 on March 3, 1969. A second, higher Earth orbit manned practice flight had been planned to follow LM-3, but this was canceled to keep the program timeline on track.
Apollo 10 launched on May 18, 1969, using LM-4 for a "dress rehearsal" for the lunar landing, practicing all phases of the mission except powered descent initiation through takeoff. The LM descended to 47,400 feet (14.4 km) above the lunar surface, then jettisoned the descent stage and used its ascent engine to return to the CSM.[11]
Production flights[edit]
The Apollo 11 Lunar Module Eagle in lunar orbit
The first manned lunar landing occurred on July 20, 1969 with the Apollo 11 LM Eagle. Four days later, the Apollo 11 crew in the Command Module "Columbia" splashed down in the Pacific Ocean, completing President John F. Kennedy's goal of "landing a man on the Moon and returning him safely to the Earth."
This was followed by precision landings on Apollo 12 (Intrepid) and Apollo 14 (Antares).
In April 1970, the Apollo 13 Lunar Module Aquarius played an unexpected role in saving the lives of the three astronauts after an oxygen tank in the Service Module ruptured, disabling the CSM. Aquarius served as a "lifeboat" for the astronauts during their return to Earth. Its descent stage engine was used to replace the crippled CSM Service Propulsion System engine, and its batteries supplied power for the trip home and recharged the Command Module's batteries critical for re-entry. The astronauts splashed down safely on April 17, 1970. The LM's systems, designed to support two astronauts for 45 hours (including twice depressurization and repressurization causing loss of oxygen supply), actually stretched to support three astronauts for 90 hours (without depressurization and repressurization and loss of oxygen supply).
Hover times were maximized on the last four landing missions by using the Service Module engine to perform the initial Descent Orbit Insertion burn 22 hours before the LM separated from the CSM, a practice begun on Apollo 14. This meant that the complete spacecraft, including the CSM, orbited the Moon with a 9.1-nautical-mile (16.9 km) perilune, enabling the LM to begin its powered descent from that altitude with a full load of descent stage fuel, leaving more reserve fuel for the final approach. The CSM would then raise its perilune back to the normal 60 nautical miles (110 km).[12]
Extended J Class Missions[edit]
Decreased clearance led to buckling of the extended descent engine nozzle on the landing of Apollo 15
The Extended Lunar Modules (ELM) used on the final three "J-class missions", Apollo 15, 16 and 17, were significantly upgraded to allow for greater landing payload