Mariner 9

The Mariner Mars 1971 project was designed as a pair. Two identical orbiters, known before launch by letters rather than numbers, would split the work: Mariner H would fly Mission A and photograph about 70 percent of the surface at medium resolution, while Mariner I flew Mission B and watched selected places change over time. Mariner H left Cape Kennedy on 8 May 1971 local time (01:11 UTC on 9 May). The Centaur upper stage began oscillating after ignition, shut down early, and dropped the spacecraft into the Atlantic. Engineers traced the failure to a faulty diode on a circuit board. That left one spacecraft and 22 days to rebuild two missions into one. Mariner I lifted off on 30 May 1971 at 22:23:04 UTC on Atlas-Centaur AC-23 from Launch Complex 36B, six minutes into its window after a scrub the previous evening, and became Mariner 9 once it was safely away. It weighed 997.9 kg fully fuelled, of which 439.1 kg was propellant and pressurant, and carried 63.1 kg of instruments on a steerable scan platform: two television cameras, an infrared radiometer, an ultraviolet spectrometer and an infrared interferometer spectrometer, with the radio link doing double duty as an occultation and gravity experiment. A single midcourse correction on 5 June, a 5.1 second burn worth 6.7 m/s, was so accurate that the second correction, pencilled in for 26 October, was waived.

On 22 September 1971, with Mariner 9 still seven weeks out, ground-based astronomers watched a bright cloud spread across the Noachis region of Mars. Within three days it had covered a distance two thirds of the way around the planet, and by the first week of October most of Mars had vanished. The first pictures Mariner 9 sent back, on 8 November, showed a blank disk. One scientist joked that they must have gone to Venus by mistake, and the joke was not well received. Harold Masursky, who led the television team, said the storm shook everybody up because they could in effect see nothing. The elaborate mapping plan, which needed 20 days of orbital photography to build a control net before real work began, was simply dumped. The insertion burn went ahead regardless. The engine lit at 00:17:39 UTC on 14 November 1971, burned for 915.4 seconds, took 1,600.5 m/s off the spacecraft's speed and left it circling Mars every 12 hours and 34 minutes. Being in orbit rather than flying past is what saved the mission: an orbiter can wait out weather, and this one did, filling the time by photographing the moons. The Soviet Mars 2 and Mars 3 arrived on 27 November and 2 December and released landers that could not wait. The Mars 2 descent module entered too steeply and crashed. The Mars 3 lander reached the surface intact, the first soft landing on Mars, and fell silent about twenty seconds into its first picture. NASA's history of the period records that Soviet scientists blamed the storm; NPO Lavochkin's own anniversary account attributes the Mars 2 lander's loss to an entry angle far outside its limits.

Four dark spots showed through the murk, along with the south polar cap. Working from classical maps and Earth-based radar, the imaging team matched one of them to Nix Olympica, the Snows of Olympus, a bright patch telescopic observers had puzzled over for decades and which radar had already flagged as high ground. Computer enhancement of the 14 November frames found volcanic craters on the summits of all four mountains, and when they were rephotographed closer in, they strongly resembled terrestrial calderas. The other three were catalogued by position at first. North Spot, Middle Spot and South Spot became Ascraeus Mons, Pavonis Mons and Arsia Mons when the IAU approved Martian names in 1973, and Nix Olympica became Olympus Mons. On 17 November a bright streak appeared along the classical canal Coprates. As the dust settled through December and January it resolved into a rift system that NASA describes as more than 4,000 km long, up to 200 km wide and more than 7 km deep in places, with the USGS putting the deepest floors nearer 10 km below the plateau and merged troughs as much as 600 km across. It was named Valles Marineris in honour of the mission. Elsewhere the cameras found sinuous channels with tributaries, and Masursky told reporters that his team was hard put to find a mechanism other than water to cut them. Mars had been a dead cratered ball since Mariner 4 flew past in 1965. Mariner 9 replaced that planet with one that had volcanoes, fault zones, polar caps seen in detail for the first time and, most unsettling of all, dry riverbeds.

Mapping was patient, repetitive work. The orbit was tuned so that 35 revolutions equalled 17 Martian solar days, which meant the ground track repeated with the Sun in nearly the same place, and the second trim on 30 December 1971 raised periapsis to 1,650 km and set the period at 11 hours 59 minutes 28 seconds so periapsis would fall over Goldstone's 64 m antenna. Systematic mapping began on revolution 100, on 2 January 1972, at 32 pictures a revolution, with each longitude band taking 39 revolutions. The spacecraft aged as it worked. A travelling-wave-tube amplifier failed on revolution 48 and the backup took over. The wide-angle camera's filter wheel jammed on revolution 118 and stayed jammed, leaving only the 60 degree polarising filter, so the team substituted narrow-angle frames. A ground command error on revolution 31 drove the scan platform against its stops for about an hour while chasing Phobos. Mariner 9 nevertheless returned the first resolved pictures of both Martian moons, close enough to show that Phobos is a battered, irregular lump, and it refined their orbits enough for the cameras to find them reliably. NASA announced on 11 February 1972 that the mission had met all its objectives, and the standard 90-day mission closed the next day. The spacecraft then stood down from 2 April, while solar occultations shaded its panels and Goldstone was busy relaying Apollo 16, before beginning an extended mission on 4 June 1972.

The end came from the smallest tank aboard. Attitude control used cold nitrogen jets on the solar panel tips, and once that gas was gone the spacecraft could no longer hold its aim. On 27 October 1972 controllers at JPL sent the command that shut down the transmitters; last contact is logged at 22:32 UTC. Mariner 9 had spent 348 days in Mars orbit and returned 7,329 pictures and 54 billion bits of data. Those images became the first global map of Mars and the basis for choosing where Viking would land three years later. Its tracking data went into a time-delay test of general relativity by Irwin Shapiro and Robert Reasenberg, who could not yet separate Einstein's prediction from a scalar-tensor rival and quoted roughly 10 percent uncertainty on the gamma parameter. Its infrared spectrometer weighed the airborne dust and found it silicate rich, near 60 percent silica. Its ultraviolet and infrared instruments had meanwhile observed large parts of the planet alongside the cameras. The spacecraft itself was left in the orbit it had flown, and NSSDCA's entry says only that the orbit should not decay for at least 50 years. Predictions of a fiery arrival in 2020, and then 2022, have circulated for years, and nobody has announced that it happened. As of August 2026 the honest answer is that the first spacecraft to orbit another planet is most likely still going round, unpowered and silent, with no published observation either way.