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A lander is a spacecraft which descends toward and comes to rest on the surface of an astronomical body. For bodies with atmospheres, the landing is called re-entry and the lander descends as a re-entry vehicle. In these cases landers may employ aerobraking and parachutes to slow down, often with small landing rockets which fire just before impact to bring the lander to rest relatively gently. The Mars Pathfinder mission also used inflatable airbags to cushion the lander's impact. (When a high velocity impact is planned, the spacecraft is called an impactor.^[1])

Contents 1 Comet and asteroid landers 2 Jupiter entry probe 3 Moon landers 3.1 Historic 3.2 Future 4 Titan lander 5 Venus landers 6 Mars landers 7 References

The Rosetta probe, launched 2 March 2004, is planned to put a lander on comet 67P/Churyumov-Gerasimenko in 2014; due to the extremely low gravity of such bodies, Rosetta's landing system includes a harpoon launcher intended to anchor a cable in the surface and pull it down.

A landing on a similarly small body, the asteroid 433 Eros, was performed by the satellite NEAR Shoemaker despite the fact that NEAR was not originally designed to be capable of landing.

The Hayabusa probe made several attempts to land on 25143 Itokawa with mixed success, including a failed attempt to deploy a rover.

The Galileo probe dropped a small reentry vehicle into the atmosphere of Jupiter, but as Jupiter is a gas giant with no well-defined surface it is debatable whether this was a "lander" per se.

A number of Moon probes, such as some members of the Soviet Luna program and the American Ranger program, were hard-impact landers which were not intended to continue providing useful data after their high-speed landings.

The Surveyor program was designed to determine where Apollo could land safely; thus these robotic missions required soft landers to sample the lunar soil and determine the thickness of the dust layer, which was unknown before Surveyor.

Each Apollo Lunar Module used a rocket descent engine for a soft landing of two astronauts on the Moon, on the six times this was carried out.

The Lunar Surface Access Module is the planned lander for Project Constellation, which NASA intends to use for Moon landings beginning around 2020.

The Huygens probe, carried to Saturn's moon Titan by the Cassini probe, was specifically designed to survive landing on land and on water. It was thoroughly drop-tested in Europe to make sure it could withstand impact and continue functioning for at least 3 minutes. However, due to the low speed impact, it continued providing data for more than two hours after it landed.

The Soviet Venera program included a number of Venus landers, some of which were crushed during descent much as Galileo's Jupiter "lander" and others of which successfully touched down. The Soviet Vega program also placed two balloons in the Venusian atmosphere.

Viking 1 and 2 were launched respectively in August and September 1975, each comprising an orbiter vehicle and a lander. Viking 1 landed in July 1976 and Viking 2 in September 1976. The Viking program ended in May 1983, after both orbiters landers had died.

Mars Pathfinder was launched in December 1996 and released the first rover on Mars, named Sojourner, in July 1997. It failed in September 1997, probably due to electronics failure caused by the cold temperatures.

Mars Exploration Rovers Spirit and Opportunity were launched in June and July (respectively) 2003. They reached the Martian surface in January 2004 using landers featuring airbags and parachutes to soften impact. As of May 2007, both rovers are still active, having survived more than three years when their design lifetime was three months.

1. ^ Technology: Impactor. NASA.