One of the most ambitious landings in planetary science came off with apparent near-perfection early this morning when NASA's Mars rover, Curiosity, was gently deposited on the red planet by cables from a hovering rocket-powered platform.
Flight controllers at NASA's Jet Propulsion Laboratory in Pasadena, California, broke into applause as data came through - from NASA's Mars Odyssey and the European Space Agency's Mars Express orbiters - indicating that Curiosity had been released safely. Minutes later a first image from one of the rover's onboard cameras confirmed that the craft had survived its nearly nine-month journey to Mars and "seven minutes of terror" descent through the Martian atmosphere, to reach its Gale Crater landing site.
The novel "sky crane" landing technique was devised to cope with Curiosity's great mass; at 3m (10ft) long, the rover is the size of a small car and about five times the size - and 10 times the mass - of NASA's 2003-launched Mars rovers Spirit and Opportunity. Parachutes and air bags would have been insufficient to protect the rover from impact with the surface, so entry, descent and landing was controlled by a normal heat shield-protected trip through Mars's upper atmosphere followed by parachute deployment and then the upper stage's eight rockets. With the rover dangling beneath on four cables, the rockets slowed the rate of descent to 0.75m/s (148ft/min) or less while searching for a suitable spot to deposit Curiosity and its payload of cameras, surface drill and chemical analysis laboratory.
As the rover touched the surface, the cables were released and the upper stage flew away to crash far from the landing site, ensuring that no debris fouled the rover.
Speaking after the touchdown and return of first pictures, NASA's Adam Steltzner, who led the team designing the entry, descent and landing mechanism, stressed that all data was preliminary but that early indications showed the system performed as planned, and that the targeted landing site was reached with great precision. Those early indications, he added, were gleaned from what data could be sifted through the jubilant chaos at JPL after touchdown, so it would take much more detailed analysis before the performance of the flight system could be described in detail.
Mars Odyssey flew over Curiosity at just about the time of touchdown and returned a first image showing the rover's shadow on the surface, and one of its six wheels. Another Odyssey flyover followed about 45 minutes later, returning another image of the horizon.
The first images were remarkably clear but showed that a great deal of dust had been kicked up by the rocket-slowed descent. As dust shields are removed from Curiosity's cameras, greater resolution images should be available.
Project scientist John Grotzinger, who leads the on-surface mission team at NASA, said that the next few weeks will be about making sure the rover is functioning properly, before it begins its exploration of what is hoped to be a geologically interesting Martian region. He said: "We want to make sure we're firing on all cylinders before we go blazing across the plain."
Curiosity will travel mere centimetres per second and operators will track its progress by using on-board cameras to study the wheel tracks in the sand, counting wheel revolutions by markers machined into the solid-aluminium "tyres". And, as deputy project manager Richard Cook observed, Curiosity's journey will be "like a family holiday where your family is 400 scientists who want to look at every rock".
Scientists have been training to operate the rover on a simulated Martian surface inside the Pasadena complex. As it is not possible to drive the rover like a radio-controlled car - even at light speed, radio waves take 20min to reach Mars - the rover must be given destination instructions and then take some decisions itself about how to proceed. Mars has no GPS system, but fortunately it is well-mapped owing to data returned over the past decade, by NASA's Odyssey and Reconnaissance orbiters, as well as ESA's Mars Express, which helped track the spacecraft's final approach.
Returning data from Curiosity depends on those three satellites in orbit around the planet.
As a NASA video illustrating the Curiosity landing technique highlights, our nearest neighbour has been a voracious consumer of spacecraft: "One a scale of one to 10, landing on Mars is a 20."
Indeed, ESA's Mars Express, launched in 2003, had a paired lander, Beagle 2, with which contact was lost after the two craft separated on approach to Mars.
NASA itself lost an orbiter and a lander mission en route to Mars in 1999. Those failures contributed to a decision to cancel a 2001 lander mission, though that mission's orbiter, Mars Odyssey, went ahead and is still operating. NASA's Spirit and Opportunity rovers reached Mars, though, in 2004 and are still operating.
However, NASA's role beyond the current Curiosity mission remains unclear. NASA had planned to provide the launch for a pair of ESA missions, in 2016 and 2018, to test a descent module and then follow with a sophisticated, deep-drilling rover. But the US Congress pulled the funding earlier this year, leaving ESA without transport for its ExoMars projects until the Russian space agency, Roscosmos, stepped in with launches and additional scientific payloads.
ESA insists the door remains wide open for NASA to rejoin ExoMars. But as one official in NASA's international liaison office confided to Flightglobal earlier this year: "We're not being very good partners on Mars these days."
Roscosmos will be keen to join ExoMars, as Soviet and Russian Mars missions have a long history of flops, most recently this year's failure of the Phobos Grunt sample return mission to get beyond Earth orbit.
Phobos Grunt could have been a historic milestone in planetary exploration, as sample return is probably the ultimate ambition for Mars study. Indeed, ESA stresses that much of the purpose behind ExoMars is to prepare for an international effort at sample return. NASA, meanwhile, has long said that the large-payload delivery capability now successfully demonstrated for Curiosity could be key to sending a large enough mission to Mars to be able to collect samples, package them and launch for a return journey.
Source: Flight International