Mars landing

A Mars landing is a landing of a spacecraft on the surface of Mars. Of multiple attempted Mars landings by robotic, uncrewed spacecraft, ten have had successful soft landings. There have also been studies for a possible human mission to Mars including a landing, but none has been attempted.
As of 2023, the Soviet Union, United States, and China have conducted Mars landings successfully. Soviet Mars 3, which landed in 1971, was the first successful Mars landing, though the spacecraft failed after 110 seconds on the surface. All other Soviet Mars landing attempts failed. Viking 1 and Viking 2 were first successful NASA landers, launched in 1975. NASA's Mars Pathfinder, launched in 1996, successfully delivered the first Mars rover, Sojourner. In 2021, first Chinese lander and rover, Tianwen 1, successfully landed on Mars. The British Beagle 2 landed in 2003, but because of loss of contact and mission failure its landing would only be confirmed in 2015.

Methods of descent and landing

As of 2021, all methods of landing on Mars have used an aeroshell and parachute sequence for Mars atmospheric entry and descent, but after the parachute is detached, there are three options. A stationary lander can drop from the parachute back shell and ride retrorockets all the way down, but a rover cannot be burdened with rockets that serve no purpose after touchdown.
One method for lighter rovers is to enclose the rover in a tetrahedral structure which in turn is enclosed in airbags. After the aeroshell drops off, the tetrahedron is lowered clear of the parachute back shell on a tether so that the airbags can inflate. Retrorockets on the back shell can slow descent. When it nears the ground, the tetrahedron is released to drop to the ground, using the airbags as shock absorbers. When it has come to rest, the tetrahedron opens to expose the rover.
If a rover is too heavy to use airbags, the retrorockets can be mounted on a sky crane. The sky crane drops from the parachute back shell and, as it nears the ground, the rover is lowered on a tether. When the rover touches ground, it cuts the tether so that the sky crane will crash well away from the rover. Both Curiosity and Perseverance used sky crane for landing.

Descent of heavier payloads

For landers that are even heavier than the Curiosity rover, engineers are developing a combination rigid-inflatable Low-Density Supersonic Decelerator that could be 8 meters in diameter. It would have to be accompanied by a proportionately larger parachute.

Landing challenges

robotic spacecraft, and possibly some day humans, on Mars is a technological challenge. For a favorable landing, the lander module has to address these issues:

Thinness of Mars's atmosphere
Measurement of distance to surface
Inadequate technology for ballistic aerocapture
Inadequate technology for retropropulsive powered descent
Inadequate mission designs
Shorter time to perform entry, descent and landing

In 2018, NASA successfully landed the InSight lander on the surface of Mars, re-using Viking-era technology. But this technology cannot afford the ability to land large number of cargoes, habitats, ascent vehicles and humans in case of crewed Mars missions in near future. In order to improve and accomplish this intent, there is need to upgrade technologies and launch vehicles. Some of the criteria for a lander performing a successful soft-landing using current technology are as follows:

Feature	Criterion
Mass	Less than
Ballistic coefficient	Less than
Diameter of aeroshell	Less than
Geometry of aeroshell	70° spherical cone shell
Diameter of parachute	Less than
Descent	Supersonic retropropulsive powered descent
Entry	Orbital entry

Communicating with Earth

Beginning with the Viking program, all landers on the surface of Mars have used orbiting spacecraft as communications satellites for relaying their data to Earth. The landers use UHF transmitters to send their data to the orbiters, which then relay the data to Earth using either X band or Ka band frequencies. These higher frequencies, along with more powerful transmitters and larger parabolic reflectors, permit the orbiters to send the data much faster than the landers could manage transmitting directly to Earth, which conserves valuable time on the receiving antennas.

List of Mars landings

In the 1970s, several USSR probes unsuccessfully tried to land on Mars. Mars 3 landed successfully in 1971 but failed soon afterwards. But the American Viking landers made it to the surface and provided several years of images and data. However, the next successful Mars landing was not until 1997, when Mars Pathfinder landed. In the 21st century there have been several successful landings, but there have also been many crashes.

Mars probe program

The first probe intended to be a Mars impact lander was the Soviet Mars 1962B, unsuccessfully launched in 1962.
In 1970 the Soviet Union began the design of Mars 4NM and Mars 5NM missions with super-heavy uncrewed Martian spacecraft. First was Marsokhod, with a planned date of early 1973, and second was the Mars sample return mission planned for 1975. Both spacecraft were intended to be launched on the N1 rocket, but this rocket never flew successfully and the Mars 4NM and Mars 5NM projects were cancelled.
In 1971 the Soviet Union sent probes Mars 2 and Mars 3, each carrying a lander, as part of the Mars probe program M-71. The Mars 2 lander failed to land and impacted Mars. The Mars 3 lander became the first probe to successfully soft-land on Mars, but its data-gathering had less success. The lander began transmitting to the Mars 3 orbiter 90 seconds after landing, but after 14.5 seconds, transmission ceased for unknown reasons. The cause of the failure may have been related to the extremely powerful Martian dust storm taking place at the time. These space probes each contained a Mars rover, PrOP-M, although they were never deployed.
In 1973, the Soviet Union sent two more landers to Mars, Mars 6 and Mars 7. The Mars 6 lander transmitted data during descent but failed upon impact. The Mars 7 probe separated prematurely from the carrying vehicle due to a problem in the operation of one of the onboard systems and missed the planet by.
The double-launching Mars 5M sample return mission was planned for 1979, but was cancelled due to complexity and technical problems.

Viking program

In 1976 two American Viking probes entered orbit about Mars and each released a lander module that made a successful soft landing on the planet's surface. They subsequently had the first successful transmission of large volumes of data, including the first color pictures and extensive scientific information. Measured temperatures at the landing sites ranged from, with a variation over a given day of. Seasonal dust storms, pressure changes, and movement of atmospheric gases between the polar caps were observed. A biology experiment produced possible evidence of life, but it was not corroborated by other on-board experiments.
While searching for a suitable landing spot for Viking 2s lander, the Viking 1 orbiter photographed the landform that constitutes the so-called "Face on Mars" on 25 July 1976.
The Viking program was a descendant of the cancelled Voyager program, whose name was later reused for a pair of outer solar system probes.

''Mars Pathfinder''

's Mars Pathfinder spacecraft, with assistance from the Mars Global Surveyor orbiter, landed on 4 July 1997. Its landing site was an ancient flood plain in Mars's northern hemisphere called Ares Vallis, which is among the rockiest parts of Mars. It carried a tiny remote-controlled rover called Sojourner, the first successful Mars rover, that traveled a few meters around the landing site, exploring the conditions and sampling rocks around it. Newspapers around the world carried images of the lander dispatching the rover to explore the surface of Mars in a way never achieved before.
Until the final data transmission on 27 September 1997, Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that in the past Mars has been warm and wet, with liquid water and a thicker atmosphere. The mission website was the most heavily trafficked up to that time.

Spate of failures

Spacecraft	Evaluation	Had or was Lander
Phobos 1
Phobos 2
Mars Observer
Mars 96
Mars Pathfinder
Mars Global Surveyor
Mars Climate Orbiter
Mars Polar Lander
Deep Space 2
Nozomi

Mars 96, an orbiter launched on 16 November 1996 by Russia, failed when the planned second burn of the Block D-2 fourth stage did not occur. Following the success of Global Surveyor and Pathfinder, another spate of failures occurred in 1998 and 1999, with the Japanese Nozomi orbiter and NASA's Mars Climate Orbiter, Mars Polar Lander, and Deep Space 2 penetrators all suffering various terminal errors. Mars Climate Orbiter is infamous for Lockheed Martin engineers mixing up the usage of U.S. customary units with metric units, causing the orbiter to burn up while entering Mars's atmosphere. Out of 5–6 NASA missions in the 1990s, only 2 worked: Mars Pathfinder and Mars Global Surveyor, making Mars Pathfinder and its rover the only successful Mars landing in the 1990s.