As Curiosity Nears Mars, the Sky Crane is On Deck

Sky Crane in action: the descent module lowers the rover Curiosity in this artist's impression. Image credit: NASA

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 sent back this picture taken inside its aeroshell on May 7, 2012. Photo credit: JPL/NASA

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.

A family portrait of the 2016/2018 ExoMars spacecraft that never will be. Image credit: ESA

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.


  1. This is a classic example of the engineering miracles NASA can create. Every penny spent on this mission is money very well spent, and this is most certainly not the time to cut the NASA planetary science budget. Robotic and human exploration of the cosmos makes NASA, in the words of Dr. Neil deGrasse Tyson, “a force of nature” driving technological innovation and inspiring our young people as nothing else can. I’m counting down the days until Curiosity (so named by a young student) touches down on Mars and begins it’s mission to satisfy our curiosity about our planetary neighbor. Great article Amy!

  2. Interesting how we cannot find the few billions for this robotic research…Then again Mars is not quite the waste land that NASA has indicated…Maybe they really DON’T want to learn anything more complex then geological water traces….I have doubts about this landing system…Couldn’t we have sent 10 smaller rovers to mars for the price of this one?

    • Ten? Probably not. The MERs Spirit & Opportunity, after mission extensions, clocked in at around $1B ($800M before extensions, back when they thought the rovers would last about 3 months.. Heh)

      So the same money on smaller rovers might have gotten you five, but only if they were very similar. Spirit & Opportunity were identical, so building two was cheaper than building two robots with different sets of instrumentation. Curiousity also has some advantages in its size. More instruments means a wider range of experiments on the same area. It can also clear much more difficult terrain if the need arises.

      I’m all for lots of smaller exploration launches, but there is also a hazard in doing that; it gives Congress more targets for cancellation. For example, back when the New Millennium program was running, they intended to launch nearly a dozen small, fairly cheap spacecraft. Most got cancelled before having a chance to launch, but the ones that did launch were table to test all sorts of new technologies.

      • So were the rovers over engineered or did they not have the correct enviroment parameters??? Did they really not know about the Wind? Or the Warmth? Or the Water on mars??? If they had could they have….Would they have spent less on rovers that have lasted 9 years rather than 3 monts?

        • Tracy, a robot is a collection of subsystems, each of which has to work for the robot to function. So when they design something and say it ought to last 3 months, that is 3 months until one subsystem fails at a level of severity that disables the entire rover.

          And then take each subsystem and it is made of components, and you repeat the same analysis. Each of the components has to last 3 months, and redundancy is built in to protect against failures.

          But you don’t know to the minute how long anything lasts. So what you do is compute the probability per day or hour of a particular failure, smash all those probabilities together, and then say that the robot will last 3 months with, say, 95% probability.

          Engineers, though, are a cautious lot. So everyone makes worst (or at least bad) case assumptions when doing all this math. Bad weather, bad wind, bad landing, bad dust, and so on.

          If you don’t get things as bad as you feared, the robot lasts longer than 3 months.

          • So it would appear that putting a man or woman on mars will be easier than the $ Trillion + 1 or 2 that NASA, Boeing, And LockMart project?…Alot easier….

            I wonder if that is what Elon Musk sees…

  3. One clarification – this is not the “same basic aeroshell” since Viking. This is the biggest aeroshell ever built, which required new technology development. The larger design required new manufacturing processes, a new thermal protection material for the heat shield, new separation mechanisms, and new ballast ejection mechanisms to enable a controlled entry. So the aeroshell is another example of how this mission has advanced our technology.

  4. Why are we spending billions on this type exploration? All we ever get out of it is new technologies, experienced wicked smart engineers, technological spinoffs to launch new industries…

    We could be spending this on bailing out Wall Street Bankers and their financial engineers who develop.. well.. not sure what they develop other than WMED, Weapons of Mass Economic Destruction. Oh yeah Banks are now allowed to invest my depositers money into risky assets all backed by the now exposed FDIC. Exposed to abuse by these same bankers when Glass-Steagul was repealled.

    It’s sad to say but American engineering excellence is being starved to death by our ‘greed is good’ F.I.RE. economy and its darth vaders on Wall Street

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