LLM meaning in Space Science ?

The Apollo Lunar Module, or simply Lunar Module (LM ), 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.

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 complete 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. Still, 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 $21.3 billion in 2016 dollars, adjusting from a nominal total of $2.2 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 launched were test flights in low Earth orbit—the first without a crew, the second with one. Another was used by Apollo 10 for a dress rehearsal flight in low lunar orbit, without landing. One lunar module functioned as a lifeboat for the crew of Apollo 13, providing life support and propulsion when their CSM was disabled by an oxygen tank explosion en route to the Moon, forcing the crew to abandon plans for a lunar landing.

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 burned up 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 complete, following emergency maneuvers.