Impactor (spacecraft)

A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. By contrast with an impact probe, which makes a hard landing and is damaged or destroyed so ceases to function after reaching the surface, a lander makes a soft landing after which the probe remains functional.

For bodies with atmospheres, the landing occurs after atmospheric entry. In these cases, landers may employ parachutes to slow down and to maintain a low terminal velocity. Sometimes small landing rockets are fired just before impact to reduce the impact velocity. Landing may be accomplished by controlled descent and setdown on landing gear, with the possible addition of a post-landing attachment mechanism for celestial bodies with low gravity. Some missions (for example, Luna 9 and Mars Pathfinder) used inflatable airbags to cushion the lander's impact rather than a more traditional landing gear.

When a high velocity impact is planned not for just achieving the surface but for study of consequences of impact, the spacecraft is called an impactor.

Several terrestrial bodies have been subject of lander and/or impactor exploration: among them Earth's Moon, the planets Venus, Mars, and Mercury, the Saturn moon Titan, the asteroids and comets.

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