NASA’s next Mars rover, Curiosity, is less than 90 days from landing on the red planet. It’s the most challenging part of the mission: getting the SUV-sized vehicle to touchdown gently and safely inside Gale Crater next to a mountain 85 million miles from home with a 20 minute time communications delay. Luckily, the most intricate, complicated, and possibly coolest landing system is ready for the job.
It’s tough to land on Mars. The planet’s thin atmosphere means there’s less natural breaking power from atmospheric drag. And the atmosphere doesn’t stretch very high; from entry to landing a spacecraft has about six minutes to move through its entire entry, descent, and landing (EDL) sequence or it will smash into the surface. Add the communications delay that makes real-time intervention by engineers impossible and it’s no wonder Mars is a virtual robot graveyard. Two-thirds of all spacecraft designed to land on the planet crashed, fell silent, or were lost.
NASA has had spectacular success on Mars; only the Mars Polar Landing stands out as the one big failure in the agency’s Martian history. For Curiosity’s landing, scientists and engineers from NASA and JPL took everything they’ve learned from previous landings to create a remarkable system called the Sky Crane. This was absolutely necessary. The parachutes, retrorockets, and landing bags that have delivered all previous payloads to the surface can’t handle Curiosity’s size and weight.
Curiosity is currently en route to Mars nestled inside the aeroshell that will protect it from the friction and heat of atmospheric entry. This is the same basic aeroshell NASA has been using since it sent the Viking landers to Mars in 1976. Once the rover has passed through this first phase, at about four miles above the surface, the heat shield on the base of the aeroshell will fall away and a mammoth 65-foot parachute will deploy from the backshell. It’s the largest ever sent to the red planet, and it will slow Curiosity from 1,000 miles per hour to the much calmer 187 miles per hour. Conveniently, it’s also the size of NASA’s largest high altitude parachute test it undertook in the 1960s when gearing up for Viking.
Then the real fun begins. The heat shield will fall away, exposing the rover’s underside and ground sensing radar. A half mile above the surface, explosive bolts will fire to jettison the parachute and backshell, triggering ignition of small rockets on the underside of a descent module. These rockets will slow Curiosity’s descent. When the radar registers an altitude of 115 feet from the surface, the descent module will release the rover on a 65-foot tether. Still using its retrorockets, the descent module will lower Curiosity until its wheels are on the Martian surface. Another set of explosive bolts will fire to release the rover, the descent module will fly away and crash leaving Curiosity unhampered to begin its mission.
If the Sky Crane fails in August, it’s hard to say what the consequences will be beyond the obvious loss of a spectacular and expensive mission – its current price tag is in the realm of $2.5 billion. Curiosity’s capabilities outstrip anything that’s gone before it and the mission will certainly return a wealth of knowledge about our cosmic neighbour. Its arsenal of instruments is designed to test the landing environment for potential habitable environments for past or present life using cameras, an alpha-particle and x-ray spectrometer, and the capacity for in situ chemical, mineralogical, and radiation analysis. One of its really interesting targets is layers in the nearby mountain that hold evidence of a wet environment on ancient Mars.
But one of the most interesting aspects of the mission was its role in the bigger picture of Martian exploration. Last year, the Committee on the Planetary Science and the National Research Council released a decadal survey – a plan for the next ten years of planetary exploration. Mars emerged as the big winner with one mission every other year between 2013 and 2022 that would culminate in a sample returned from the red planet. Now that goal has been cancelled, a casualty of NASA’s newly diminished budget that is expected to stay low for the foreseeable future. When NASA pulled out of the joint ExoMars mission with the European Space Agency, it in effect cancelled missions that were going to find, store, and recover small samples of Martian soil. Even the plan for a revised 2018 rover mission under the new constraints is looking unlikely as NASA faces the realities of its new budget.
Even without its role to play in support of the sample return dream, Curiosity’s mission is one to watch. The JPL team behind the Sky Crane is ready and gearing up for landing, the day that Pete Theisinger, Mars Science Laboratory project manager at NASA’s Jet Propulsion Laboratory described as stimulating. “Our engineering and science teams continue their preparations for that big day and the surface operations to follow,” he said.
If all of the Sky Crane’s pieces work – particularly the explosive bolts and ground sensing radar – it will be an incredible landing and a great start to possibly the last Mars mission for a while. Of course, JPL designs its systems to work. We shouldn’t really expect anything but a smooth landing for Curiosity in August.