Apollo Lunar Module
The Apollo Lunar Module, originally designated the Lunar Excursion Module, 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 space, and remains the only crewed vehicle to land anywhere beyond Earth.
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, 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.
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 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.
Operational profile
At launch, the Lunar Module sat directly beneath the command and service module with legs folded, inside the Spacecraft-to-LM adapter attached to the S-IVB third stage of the Saturn V rocket. There it remained through Earth parking orbit and the trans-lunar injection rocket burn to send the craft toward the Moon.Soon after TLI, the SLA opened; the CSM performed a maneuver whereby it 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 Lunar Module pilot entered the LM to power up temporarily and test all systems except propulsion. The Lunar Module pilot performed the role of an engineering officer, 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 about systems status and navigational information. After the command module pilot visually inspected the landing gear, the LM was withdrawn to a safe distance, then rotated until the descent engine was pointed forward into the direction of travel. A 30-second descent orbit insertion burn was performed to reduce speed and drop the LM's perilune to within about of the surface, about uprange of the landing site.
File:Earth, Moon and Lunar Module, AS11-44-6643 c.jpg|thumb|, the Lunar Module ascent stage of Apollo 11, in orbit above the Moon. Earth is visible in the distance. Photograph by Michael Collins aboard the.
As the craft approached perilune, the descent engine was started again to begin powered descent. 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 braking, the LM descended to about, then, in the final approach phase, down to about. 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.
Astronauts flew Apollo spacecraft manually only during the lunar approach. The final landing phase began about uprange of the targeted landing site. At this point, manual control was enabled for the commander, who had enough propellant to hover for up to two minutes 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, one or more of three probes extending from footpads on the legs of the lander touched the surface, activating the contact indicator light which signaled the commander to shut off the descent engine, allowing the LM to settle onto the surface. On touchdown, the probes would be bent as much as 180 degrees, or even break off. The original design used the probes on all four legs, but starting with the first landing, the one at the ladder was removed out of concern that the bent probe after landing might puncture an astronaut's suit as he descended or stepped off the ladder.
The original extravehicular activity plan, up through at least 1966, was for only one astronaut to leave the LM while the other remained inside "to maintain communications". Communications were eventually deemed to be reliable enough to allow both crew members to walk on the surface, leaving the spacecraft to be only remotely attended by Mission Control.
Beginning with Apollo 14, extra LM propellant was made available for the powered descent and landing, by using the CSM engine to achieve the perilune. After the spacecraft undocked, the CSM raised and circularized its orbit for the remainder of the mission.
When ready to leave the Moon, the LM's ascent engine fired, leaving the descent stage on the Moon's surface. After a few course correction burns, the LM rendezvoused with the CSM and docked to transfer the crew and rock samples. Having completed its job, the ascent stage was separated. The Apollo 10 ascent stage engine was fired until its fuel was used up, sending it past the Moon into a heliocentric orbit. The Apollo 11 ascent stage was left in lunar orbit to eventually crash; all subsequent ascent stages were intentionally steered into the Moon to obtain readings from seismometers placed on the surface.
History
The Lunar Module was designed after NASA chose to reach the Moon via Lunar Orbit Rendezvous instead of the direct ascent or Earth Orbit Rendezvous 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 and construction location
In July 1962, eleven firms were invited to submit proposals for the LEM. Nine companies responded in September, answering 20 questions posed by the NASA RFP in a 60-page limited technical proposal. Grumman was awarded the contract officially on November 7, 1962. 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, Hamilton Standard, Marquardt and Rocketdyne.The Primary Guidance, Navigation and Control System was developed by the MIT Instrumentation Laboratory; the Apollo Guidance Computer was manufactured by Raytheon. A backup navigation tool, the Abort Guidance System, was developed by TRW. The landing gear was manufactured by Héroux.
Design phase
The Apollo Lunar Module was chiefly designed by Grumman aerospace engineer Thomas J. Kelly. The first LEM design looked like a smaller version of the Apollo command and service module 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. Egress while wearing bulky extra-vehicular activity spacesuits was eased by a simpler forward hatch.
The configuration was frozen in 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 in July 1963, and by January 1965 the Rocketdyne contract was cancelled.
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.
The initial design had three landing legs, the lightest possible configuration. But as any particular leg would have to carry the weight of the vehicle if it landed at a significant angle, this was also the least stable configuration 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.
In June 1966, the name was changed to Lunar Module, eliminating the word excursion. 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. Despite the name change, the astronauts and other NASA and Grumman personnel continued to pronounce the abbreviation as instead of the letters "L-M".