Figure 2-2. Apollo Lunar Module. The designers of the Apollo lunar module (LM) could ignore the requirements for aerodynamic streamlining demanded by vehicles that flew in or returned through earth's atmosphere. This ungainly looking vehicle operated only in space. The two-stage spacecraft, carried to the vicinity of the moon docked to the Apollo command module, was designed to land two Apollo astronauts on the moon's surface. From lunar orbit, where it was released by the Apollo command and service module (CSM), the LM's descent and ascent stages functioned as one spacecraft. During their time on the surface, the crew lived in the LM's ascent stage. When it was time to return to the waiting CSM, the descent stage provided a launch platform for the ascent half of the lunar module.

It took more than two years to design the LM, with its makers, led by Grumman Aircraft Engineering Corporation, fighting weight gain long after a configuration was approved The most troublesome, critical, and heavy of the LM's components were its 18 engines-descent propulsion (43 900 newtons),- ascent propulsion (15 500 newtons), and 16 small attitude control engines clustered in quads around the ascent stage. Propellant for these engines accounted for more than 70 percent of the spacecraft's total' weight of 1500 kilograms.

The ascent stage was basically cylindrical 0.29-meter diameter, 3.75-meter height), but with angular faces. its aluminum skin was encased by a Mylar thermal-micrometeorite shield, The cruciform structure of the descent stage supported the descent engine and its 4 fuel tanks. Four legs (maximum diameter 9.45 meters), the struts of which were filled with crushable aluminum honeycomb ,for absorbing the shock of landing, were capped by footpads. The descent stage (3.23 meters high) was also constructed of aluminum alloy. A ladder attached to one of the legs gave the crew access to the surface. A docking tunnel (0. 81-meter diameter) was provided for crew transfer between the command module and the LM ascent stage. After the surface operations were completed and the crew returned via the ascent stage to the CSM, the LM was jettisoned. A LM was included on a manned Apollo mission for the first time in March 1969 (Apollo 9). For more information on spacecraft systems, see volume 2, table 2-55.

Source: JSC, "Apollo Program Summary Report," JSC-09423, Apr. 1975, p. 4-58.

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