MSL meaning in Space Science ?

In military terminology, a missile, also known as a guided missile or guided rocket, is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles have five system components: targeting, guidance system, flight system, engine and warhead. Missiles come in types adapted for different purposes: surface-to-surface and air-to-surface missiles (ballistic, cruise, anti-ship, anti-tank, etc.), surface-to-air missiles (and anti-ballistic), air-to-air missiles, and anti-satellite weapons.

Airborne explosive devices without propulsion are referred to as shells if fired by an artillery piece and bombs if dropped by an aircraft. Unguided jet-propelled missiles are usually described as rocket artillery.

Historically, the word missile referred to any projectile that is thrown, shot or propelled towards a target; this usage is still recognized today.