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Let's go to Mars

Mars Reconnaissance Orbiter becomes the eye and the relay

The sharpest camera ever sent to another planet resolves 30 centimetres per pixel from 300 km up, and the same spacecraft relays much of what the rovers below it send home.

A tall spacecraft in an industrial test bay, photographed from above. A large circular dish antenna, draped in a dark, wrinkled cover with a taped rim, caps the top. Below it the body is a dense mass of gold and silver foil insulation, trusses and instruments, one of them shrouded in a black bag with a red cover at its end, and a dark solar array panel, its cells visible as a fine grid, angles out to the right. Technicians in white coveralls, hoods and blue gloves work around the spacecraft, one of them reaching in from the right at the level of the dish, with a yellow step ladder at the front and blue steel columns and red railings behind.
Mars Reconnaissance Orbiter in environmental testing at Lockheed Martin Space Systems in Denver, early January 2005, fitted with five of its six primary science instruments, both solar arrays and its 3-metre high-gain antenna, here still under a protective cover. The technicians are installing test instrumentation to measure vibration and acceleration levels during acoustic testing. · Image: NASA/JPL/Lockheed Martin

On 10 March 2006 a 2,180-kilogram spacecraft, launched the previous August on an Atlas V, burned 1,641 seconds into a 400 by 35,000 km polar orbit with a 35-hour period. Six months of aerobraking, about 445 passes through the top of the atmosphere, drag in place of propellant, shrank that to 255 by 320 km: twelve laps a day, periapsis over the south pole, sun-synchronous, every image at three in the afternoon local time. Science began in November 2006, once the Sun cleared from between the two planets.

HiRISE is a 0.5-metre f/24 telescope aimed at the ground: from 300 km, 30 centimetres per pixel over a swath more than 6 km wide and up to 60 km long, sharper than anything flown to another planet. Five more instruments: CTX at 6 metres per pixel across 30 km for context; CRISM reading mineral spectra at about 18 metres per pixel for rocks that form only in water; SHARAD sounding a kilometre into the crust; MCS slicing the atmosphere every 5 km in altitude; MARCI mapping global weather daily.

Viking's ellipses ran more than a hundred kilometres long and had to be survivable throughout; Pathfinder aimed at an outflow channel mouth. With HiRISE the boulders are counted first: Curiosity's target at Gale was about 20 by 7 km, one stack of layered rock, and Perseverance dodged hazards at Jezero by matching its descent camera to a map built from orbital images.

MRO is also the relay: a 3-metre steerable dish pushes up to 6 megabits per second to Earth, an Electra UHF radio talks to the surface. Rovers cannot reach Earth directly at a useful rate, so they hand data to whatever orbiter is overhead; MRO owns the widest pipe at Mars. It photographed Phoenix under parachute in 2008, Beagle 2 half-opened in 2014, Schiaparelli's fresh impact scar the day after the crash, and, with its weather camera, the 2018 storm that ended Opportunity.

CRISM's cryocoolers failed and the spectrometer was retired in 2023. HiRISE took its 100,000th image on 7 October 2025: mesas and dunes in Syrtis Major, about 80 km from Jezero.