A Mars aircraft is a vehicle for flying in the atmosphere of Mars. So far, only lander entry, descent, and landing systems have operated in the Martian atmosphere. Aircraft may provide in situ measurements of the atmosphere of Mars, as well as additional observations over extended areas. A long-term goal is to develop piloted Mars aircraft.
Compared to Earth, the air is thinner at the surface (with pressure less than 1% of Earth's at sea level) but the gravity is lower (less than 40%). Mars air, consisting mostly of CO
2 gas, is over 50% denser than Earth air adjusted to equal pressure.
Before the start of Mars exploration with spacecraft, the density of Mars' atmosphere was suspected to be higher than was later measured to be, leading engineers to think that winged flight would be much easier than it actually is. In his "Mars Project" ("Das Marsprojekt") concept, Wernher von Braun proposed winged vehicles for landing human missions on Mars.
The first detailed Mars lander contracted by NASA was to Ford/Philco Aeronutronic in the early 1960s, which was for a lifting body design for the lander; this is when some of best estimates for the Mars atmosphere were significantly denser than revealed by the Mariner IV measurements in July 1965. The lander had a tub-shaped lifting body with winglets, and was one of the first detailed designs for Mars lander although it would not be able to fly in the revised figures for the Mars atmospheric conditions. The Aeronutronic Mars lifting-body lander design was based on Mars atmosphere of mostly nitrogen about 10% of Earth.
July 1965 marked a shift away from lifting body and winged glider style Mars landers to ballistic entry gumdrop style landers.
In the 1970s the Mini-Sniffer aircraft were made in several versions so it could also operate in an all-CO
2 environment. The Mini-Sniffer could run without oxygen by using hydrazine, and the design was considered for sampling the atmosphere of Mars. The airplane had a large propeller to be effective in the thin air and many flights of various configurations were made between 1975 and 1982.
A winged rover design was proposed in the 1970s, to cover more area than the stationary Viking landers. There was a proposal by NASA in the 1990s for a Mars airplane to fly on Mars by the anniversary of the Wright Brothers's first flight, in the "Faster, Better, Cheaper" era. The ARES Mars airplane proposal was selected as a Mars Scout Program candidate, but not selected for flight.
In 2015, a Mars aircraft was considered as an option in the re-boot of the Japanese MELOS mission. One early design proposed a wing-span of 1.2m, a mass of 2.1 kg, and with the following mission profile: During the landing phase of the surface element of MELOS, the aircraft would be released at an altitude of 5 km then fly 4 minutes, covering 25 horizontal km.
Prototype Mars planes have flown at close to 30 km (98,000 ft) altitude on Earth (in roughly half of the average air pressure at Mars surface), and tested expandable wings that cure in ultraviolet light. For flight in Mars' atmosphere, the Reynolds number would be very low compared to flight in Earth's atmosphere. Valles Marineris was targeted for an unmanned aircraft flight and by Mars' gliders.
Gliders could carry more scientific instrumentation, but cover less area. Hydrazine has been proposed as a fuel for Mars aircraft. At one point, NASA was developing plans for a wok-sized airplane "micromission", which would piggyback on a separate Mars bound payload. Mach 1 on Mars can be about 240 m/s (790 ft/s) while it is about 332 m/s (1,090 ft/s) on Earth.
Proposed Mars airplane concepts include:
Balloons may provide an alternative to parachutes, allowing for a soft landing. A balloon could allow a lander to take off and land at a new site. Two types of balloon technology are super-pressure and Montgolfiere. The super-pressure balloons try to contain the pressure caused by heating to maintain altitude.
The Montgolfiere would use heated Martian air to create lift. An example of concept for Mars balloon was the Mars Geoscience Aerobot. Some work has been done to develop extremely thin, flexible solar cells that could allow a balloon's skin itself to generate power from the Sun.
In 2002, a paper was published suggesting autonomous robotic helicopters for Mars exploration, possible for the Mars Scout Program. A number of advantages of a viable rotorcraft design were noted, including the ability to pass over difficult Mars terrain yet still visit multiple sites in situ. The short hop made by Lunar Surveyor 6 in 1967 was noted as example of hopping to visit another site.
A small scout drone, launching from a Mars rover has been in development in the late 2010s, including US$23 million for a helicopter demonstration in 2018. The program for the Mars Helicopter Ingenuity possibly for the Perseverance rover would have a high resolution, downward-looking camera for navigation, landing, and science surveying of the terrain, and a communication system to relay data back to the rover.
The Mars Express High Resolution Stereo Camera and the Mars Reconnaissance Orbiter's HiRISE camera can both provide virtual Mars flyovers by draping surface pictures over 3D terrain models.