July 4th is a special date in American history, and this year it will, for space exploration enthusiasts be doubly meaningful, as it will mark the point at which we have been examining and exploring Mars continuously for 20 years without a single break.
Of course, attempts to explore and understand Mars began much earlier than that. We first started launching missions to the Red Planet far back in the 1960s. The first successful mission – the United States’ Mariner 4 probe – shot past Mars in July 1965, returning just 22 fuzzy images as it did so, travelling too fast and without any fuel to achieve orbit. In 1969, and total overshadowed by the Apollo 11 mission to the Moon, Mariner 6 also flew by Mars in July, and was followed in August by its twin, Mariner 7, becoming the first dual mission to visit another world in the solar system.
The first American mission to orbit Mars was Mariner 9, which arrived in orbit in November 1971, the exact time Mars was wreathed in a series of globe-spanning dust storms. Fortunately, the space vehicle had a planned orbital life of around 18 months, and successfully waited out the storms before returning the most spectacular images of Mars yet seen – including the mighty Tharsis volcanoes and the great gash of the Vallis Marineris, named in honour of the probe.
Russia also finally successfully reach Mars orbit in 1971 with the dual Mars 2 and Mars 3 missions. The former arrived just days after Mariner 9, and the latter became the first mission to successfully deploy a lander to the surface of Mars – although the craft ceased transmitting just 15 seconds after a safe landing had been confirmed, probably due to the dust storms. Unlike Mariner 9, the Russian orbiters had a shorter operational lifespan, and both ceased operations before the dust had fully cleared, resulting in them being classified as “partially successful” missions.
Then, in 1976 came the twin Viking Missions, comprising two pairs of orbiter and lander vehicles. Even now it remains one of the most ambitious robotic missions ever undertaken. The Viking 1 orbiter and lander combination launched on August 20th, 1975 and arrived in Mars orbit on June 19th, 1976. Viking 2 departed Earth on September 9th, 1975 and arrived in Mars orbit on August 7th, 1976.
Viking Lander 1 had been scheduled to depart its orbiter and attempt a landing on Mars on July 4th, 1976 – the 200th anniversary of America’s independence. However, images of the landing site taken by the orbiter revealed it to be far rougher terrain than had been thought, so the landing was delayed while an alternative site was surveyed. The lander eventually touched-down on July 20th, 1976, marking the seventh anniversary of the first mission to land on the surface of the Moon. Viking lander 2 touched down half a world away on September 3rd, 1976.
Viking really was a landmark – and controversial – mission. Landmark, because they utterly changed our understand over Mars during years both orbiters and landers operated. Controversial because it is still argued to this day by some that two of the five life-seeking experiments carried by each of the landers did find evidence of Martian microbes living in the planet’s regolith, although it seems more likely that the positive results – in both cases, from the same two experiments – were the result of inorganic chemical reactions between mineral in the Martian soil samples and elements within the experiments.
After Viking the came a pause. While missions continued to be launched to Mars by the USA and Russia in the 1980s and early 1990s, none of them were successful. It was not until 1997 that the current trend of having vehicles continuously operating around and on Mars began – and which NASA has been celebrating, having been the stalwart of the 20-year effort of these 24/7 operations.
This run technically started in early November 1996, with the launch of NASA’s Mars Global Surveyor (MGS) mission. It was followed a month later by the NASA Pathfinder Mission. By a quirk of orbital mechanics, the Pathfinder Mission – designed to test the feasibility of placing a lander and small rover on Mars – arrived at Mars first, performing a successful aerobraking and landing on July 4th, 1996.
The Pathfinder lander arrived in Ares Vallis on Mars, an ancient flood plain in the northern hemisphere in an innovative way. A conventional aerodynamic heat shield protected the craft through initial entry into, and deceleration through, the upper reaches of Mars’ tenuous atmosphere. Having slowed from a velocity of several thousand kilometres an hour to just over 1300 km/h, allowing a supersonic parachute to be deployed. This slowed the vehicle’s descent to around 256 km/h and lowering the vehicle to just 355 metres above the surface of Mars, where several things happened.
Firstly, a tetrahedron cocoon of protective airbags was inflated all around the vehicle in less than a second. A set of rocket motors in the back shell beneath which the airbags and lander were suspended, then fired. These slowed the vehicle almost to a hover about 15-20 metres above the ground, at which point the tether connecting the cocooned lander was cut, and the lander fell to the ground, bouncing several times before coming to rest and the airbags were deflated and drawn back underneath the lander. The triangular lander was designed to right itself while unfolding its three solar power “petals”, however, this was not required as the lander came to a stop the right way up, allowing the petals to be deployed, and – after check-out tests – the little Sojourner rover was command to drive down off of the lander and onto the surface of Mars. The same system would later be used for the MER rover missions.
As a proof of concept mission, Pathfinder was not intended to be a long duration mission. Just 65 cm (25.6 in) long and 48 cm (19 in) wide, the 10.5 kg (23 lb) Sojourner rover had a top speed of 1 cm a second, so it could never roam far from its base station; in fact it never went further than about 12 metres (39 ft) from the base station, which acted as a communications relay as well as studying the Martian atmosphere and imaging Sojourner in action. Nevertheless, the mission exceeded expectations, lasting some 3 months, with the little rover examining 16 points of interest with its humble 0.3 megapixel cameras and its on-board spectrometer.
The Mars Global Surveyor vehicle arrived in orbit around Mars even while Pathfinder was operating on the surface. It was the precursor to NASA’s still-operational Mars Reconnaissance Orbiter (MRO), carrying out a global mapping mission that examined the entire planet, from the ionosphere down through the atmosphere to the surface, as well as acting as a communications relay for missions on the surface of Mars and performed monitoring relay activities for sister orbiters during aerobraking into their orbits around Mars.
Until the arrival of MRO in 2006 – the two missions overlapped slightly, and might have run in parallel – MGS had the most powerful imagining system ever sent to Mars. In fact, such was the success of the MGS cameras, an even high-resolution system was made a core element of MRO, which uses many similar elements to MGS. The mission returned some of the clearest evidence for the effects of water action on the surface of Mars, and the primary mission of 1 year 9 months was twice extended (by a year and then a further 11 months), before the mission switched to its Relay Mode, supporting other Mars missions – a role it performed for close to four further years.
MGS might well have continued operating into the 2010s have it not been for an error while attempting to reorient a solar panel on November 2nd, 2006, resulting in the loss of communications. Despite several attempts to re-acquire and correctly orient the vehicle between then and the end of 2006, MGS we declared lost. Nevertheless, the wealth of information it provided is huge, and sits alongside that of MRO’s ongoing work.
Further missions to Mars followed between 1997 and 2001 all of which failed in one way or another, except for NASA’s Mars Odyssey mission. Today, Odyssey holds the record for the longest continuing mission in Mars orbit – 16 years, 2 months and 24 days at the time of writing. Designed to detect evidence of past or present water and ice on Mars, as well as study the planet’s geology and radiation environment, Odyssey frequently sits in the shadow of the more glamorous MRO and rover missions, and is responsible for mapping the distribution of water in the surface of Mars, working in concert with the Phoenix Lander mission.
As well as acting as a communication relay, Odyssey has also surveyed the landing sites for NASA’s MER roves, the Phoenix Lander and the Mars Science Laboratory. Despite several faults and a couple of failures aboard the craft, it is hoped that it will be able to continue its mission well into the 2020s.
2003 marked the start of the time when things really got busy around and on Mars. It was in this year that Europe launched it Mars Express vehicle, and NASA launched its two Mars Exploration Rovers, Spirit and Opportunity.
Mars Express arrived in Mars orbit on Christmas Day, 2005. The mission had already captured hearts and minds across Europe and around the world, not so much because of the orbiter vehicle, but because of its additional payload – the British-built Beagle 2 lander. If Mars Express was ambitious for a first time planetary mission be the European Space Agency, Beagle 2 was downright cheeky.
Never really a part of the original mission, the opportunity to add a lander came along quite late. As a “bolt on mission” it was outside of normal European Space Agency funding channels, so those trying to build the lander had to rely on other means for funding – and initially, the UK government was only minimally interested. Nevertheless, in typical British boffin fashion, and blessed with a gift for showmanship, the late Professor Colin Pillinger led the UK’s efforts to finance and build the lander, even in the face of changing requirements from ESA.
Beagle 2 had also been due to land on Mars on Christmas Day 2005 – and I was actually there, in the UK’s “mini mission control” on the day, along with dozens of others, as Colin and his team nervously waited for confirmation that the clam-like lander was safely on Mars and calling home. The signal never came. It was not until 2014 – and sadly after Colin had passed away – that it was finally confirmed Beagle 2 had safely landed on Mars, but had suffered a mechanical failure which prevented a solar panel from deploying and allowing it to establish contact with any of the vehicles orbiting Mars.
Nevertheless, Mars Express has gone on to be one of the most successful Mars missions, easily equalling that of NASA’s MRO, carrying out high-resolution imaging and mineralogical mapping of the surface, radar sounding of the subsurface structure down to the permafrost, precise determination of the atmospheric circulation and composition, and study of the interaction of the atmosphere with the interplanetary medium.
As noted, the Mars Reconnaissance Orbiter mission arrived in orbit in 2006. In just over a decade of operations, it has utterly revolutionised our view of Mars, and has been responsible for some of the most remarkable images yet captured around the Red Planet. It was the HiRISE camera on MRO which in 2014, confirmed Beagle 2’s presence on Mars, and also for images like the one below.
As I’ve written about NASA’s MER rovers elsewhere in this blog, I’ll move on to NASA’s Phoenix mission of 2008, which landed near the north polar cap of Mars on a mission to search for environments suitable for microbial life on Mars, and to research the history of water there. The static lander was successful in locating shallow subsurface water ice – in fact the blast from the vehicle’s landing thrusters may have blown away surface dust and material to reveal ice under the lander. Given the high latitude in which the lander touched down, the vehicle’s solar panels received less and less sunlight as the Martian winter progressed, until in November 2008, a critical threshold was crossed and the lander went into a power-conserving safe mode. Even so, it wasn’t until 2010 that the mission was officially drawn to a close, just in case the lander managed to revive itself under summer time sunlight.
Today, Mars is home to eight operational missions: MER Opportunity, Mars Odyssey, MRO, Mars Express, MSL Curiosity, India’s Mars Orbiter Mission, NASA’s MAVEN orbiter, and Europe’s Trace Gas Orbiter. In 2018 these should be joined by NASA’s InSight lander, and in 2020 by MASA’s Curiosity-like Mars 2020 rover and Europe’s ExoMars rover, all of which mark our continuing drive to understand the most Earth-like of the other worlds in our solar system, and also prepare the way for human missions to Mars.
More than that, however, they demonstrate the creative ingenuity of humankind as we seek to slake our thirst for knowledge about the worlds around us and the cosmos in which we reside.
To mark the 20th anniversary of their own continuous missions to Mars, NASA released a special video in June, highlighting everything from Pathfinder’s arrival in 1997 through to Curiosity, before looking to the future.