What does LEM mean in NASA

Lunar Entry Mode (LEM) is an abbreviation that is used to describe the mode in which spacecraft can enter the orbit of a planet or moon. This mode is designed specifically to protect both the spacecraft and its passengers from potentially hazardous conditions.

The length of time required for Lunar Entry Mode depends on factors such as the size and mass of the craft, any atmospheric composition present, and how far away from the desired destination it began its journey from. Generally speaking, however, spacecraft may spend up to several hours under Lunar Entry Mode before beginning their approach towards a target planet or moon.

Generally speaking, it requires several steps for a successful entry into Lunar Entry Mode. Specifically, these steps include decelerating from orbital speed down to subsonic speed; lowering navigation accuracy; selecting predetermined guidance data points; executing navigational maneuvers; and optimizing fuel usage via onboard thrusters while accounting for gravity effects and other external forces.

Besides being referred to as "Lunar Entry Mode," this process may also be referred to as "suborbital reentry," "terminal area energy management," or simply "entry."

Yes! Many companies are devoting energy towards automating many of the steps involved in making an accurate entrance into Lunar Entry mode easier via machine learning algorithms and better sensors/instrumentation technology. Automation has already begun proving its utility on missions such as SpaceX's Crew Dragon capsule demonstration flight which utilized automated systems throughout much of its mission protocols including lunar re-entry control algorithm tests using artificial intelligence technology.