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How NASA plans to land a 2000 pound rover on Mars


July 5, 2012

An artist's impression of the Mars Science Laboratory moments before touching the Martian ...

An artist's impression of the Mars Science Laboratory moments before touching the Martian ground (Image: NASA/JPL-Caltech)

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A month from now, the Mars Science Laboratory (Curiosity) rover is set to touch down on the surface of the Red Planet and begin its mission to learn more about the possible existence of life - past or present. Curiosity will attempt to touch down using a complex and unusual landing sequence unlike any other used for previous Mars rovers ... here's how the plan will unfold.

The challenge

In the past, NASA's preferred modus operandi for landing Mars rovers has been to wrap them into a spheric "airbag" that breaks the fall and absorbs the impact with the terrain. This time around NASA is going for a much more complicated, multi-stage approach that seems to have come out of a science fiction movie.

Among the stages are a sophisticated rocket-guided entry system, a huge supersonic parachute that will be traveling almost parallel to the Martian surface, and a skycrane that will tether the rover directly onto the Martian surface while hovering just a few feet above. The entire process will be executed completely autonomously, managed not by human intervention, but by a computer algorithm made of some 500,000 lines of code. The success of this ambitious US$2.5 billion mission lays in the balance.

An artist's impression of the Mars Science Laboratory moments before touching the Martian ...

"Most people look at this system - particularly the skycrane at the end - and they say, 'What are you guys thinking, are you out of your mind?,'" says Pete Theisinger, project manager of the Mars Science Laboratory. "But the vehicle is too big and heavy for airbags."

Curiosity weighs 2,000 lbs (907 kg) - making it five times as heavy as the Spirit and Opportunity rovers launched in 2003 - and carries an impressive 180 lbs (82 kg) of science payload. Theisinger says that, for its size, this is the safest, simplest landing sequence that NASA could muster.

A comparison between the wheels of recent Mars rovers. From the left: Pathfinder, Mars Exp...

During the landing phase, the main challenge is that Mars's atmosphere is 100 times thinner than Earth's - thick enough that engineers need to worry about a heat shield, but not quite thick enough to slow the spacecraft fast enough to prevent it from crashing to the ground at high speed. Altitude on Mars ranges from minus 4 to plus 12 miles (minus 6 to plus 20 km) and the whole of the southern hemisphere has positive altitude. Until now, no attempt has been made to explore this region because engineers need the extra space to slow down the rovers.

This is going to be a very risky landing. Only 40 percent of missions to Mars have been successful, either because of engineering problems or because of the hostile Mars environment. But at the very least, should the landing falter, the data collected on it by the three current Mars orbiters - Mars Express, Odyssey and Mars Reconnaissance Orbiter - will help scientists learn from their mistakes and increase the probability of success in future missions.

The testing phase

The technology behind the landing is an interplay of hardware and software. On the software side, the computer algorithms that guide each part of the craft can be tested from Earth, simulations can be run, and new software updates can be installed - the final stable version was uploaded in the last few days of May.

Testing the hardware was not nearly as easy, since the right conditions can't be recreated on Earth. "One of the problems you have with entry and descent landing with any Martian vehicle is, how do you test it on Earth? We have the wrong atmosphere, the wrong gravity, and we would need to start at 13,000 mph (20.921 km/h) outside the atmosphere," says Theisinger.

Testing of the high-velocity, high-altitude portion of the landing using an F-18 jet (Imag...

NASA's answer was to construct a long series of compartmentalized tests, and to then stitch them together using computer simulations. The individual tests were quite elaborate, and the scientists often had to go to great lengths to simulate the conditions they would be facing on Mars.

To test the radars that will help direct the thrusters toward the landing site, the devices were flown on a helicopter over a desert landscape (representative of the Martian terrain). To characterize the high-velocity, high altitude portion of the landing sequence, the equipment was put on a F-18 accelerating toward the ground (each dive only gathered about six seconds worth of data).

Landing on Mars, with style

In the context of Mars exploration, the landing ellipse describes the area inside of which a rover has a 99 percent chance of landing. Previous Mars landers (Spirit, Opportunity, Pathfinder and Phoenix) have operated with a ballistic landing system that meant a very elongated landing ellipse: Pathfinder, for instance had a 185 by 9 miles (300 by 15 km) ellipse, and the limited mobility of the rovers meant that scientist have had very little control over exactly which terrain the rovers would find themselves in.

The landing ellipse for Curiosity, inside of Gale Crater, which lies close to the Mars's e...

By contrast, Curiosity will use guided entry, including thrusters during the supersonic phase of the mission, to achieve a much smaller landing ellipse of only 4 by 12 miles (6 by 18 km). This allows scientists to select landing sites that would have otherwise been inaccessible, with the potential of a much greater scientific payoff.

Built to operate for at least two Earth years, Curiosity will be the first mission in which the rover will be able to venture outside its own landing ellipse.

The landing sequence will start at 13,200 miles (21,243 km) above the planetary surface, and will last only seven minutes. At the date of the scheduled landing, Earth and Mars will be separated by 14 light-minutes. The process will therefore be performed completely autonomously by the spacecraft, and it will be a grueling few minutes at NASA and around the world before news on the result, whether good or bad, reaches Earth.

Ten minutes before hitting the atmosphere, the "cruise stage" of the craft will separate and the final preparations for entry begin. Hitting the atmosphere at 13,000 mph, the spacecraft will start to slow down while using thrusters, guided by radars and data from the Mars orbiters, to help steer toward the landing target.

The parachute stage (Image: NASA/JPL-Caltech)

A supersonic parachute will be deployed to slow the craft down to the speed of sound and enable the rover to descend on an angle almost parallel to the Martian ground, gaining more time to slow the craft down. Meanwhile, the heat shield will separate to clear the view for MARDI, the rover's camera system, which will hopefully provide us with a spectacular, hi-def video of the descent at eight frames per second.

At an altitude of about a mile and speeds of 200 mph (320 km/h), the craft will then fire up its six landing engines, bringing the rover down very gently to only a few yards of altitude. The rover will then deploy its wheels and - this is the fancy part - a skycrane will slowly start lowering the vehicle to the ground.

After detecting touchdown, the skycrane will remove its tethers and fly away to a controlled crash far from the landing site, leaving the rover on the surface of Mars. Or, at least, that is the plan.

The NASA video below illustrates the different phases of the landing.

Source: NASA

About the Author
Dario Borghino Dario studied software engineering at the Polytechnic University of Turin. When he isn't writing for Gizmag he is usually traveling the world on a whim, working on an AI-guided automated trading system, or chasing his dream to become the next European thumbwrestling champion.   All articles by Dario Borghino

What could possibly be so valuable about Mars to warrant such an expense?

6th July, 2012 @ 05:35 pm PDT

Instead of crashing the skycrane, why not put a camera, microphone and a wind speed and direction instrument on it and attempt to have it do a controlled landing?

It'd be stationary but it'd be a useful scientific instrument package instead of a single use device.

Gregg Eshelman
7th July, 2012 @ 01:04 am PDT

The discovery of life on another planet? Sounds valuable enough to me. The Expense? About $357 Million a year over 7 years. Or about.....$1.19 for every citizen in the USA per year.

7th July, 2012 @ 01:34 am PDT

A very big mylar bag, inflated prior to reaching Mars, would allow visual tracking from earth and would act as an extremely big parachute, enough to "stick" to the Martian atmosphere and ease descent. Inflating other bags inside the big bag(s) would assure easy touch down.

NASA's Rube Goldberg wasteful system derives from an imbecile's exploration paradigm. You don't decide what to look for from Earth. You go to Mars and look everywhere. That means multiple, cheap, inflatable rovers all over the planet. Hopefully, exploiting some native power source (e.g. the Martian wind).

Facebook User
7th July, 2012 @ 04:46 pm PDT

"The landing sequence will start at 13,200 miles (21,000 km) above the planetary surface, and will last only seven minutes... Hitting the atmosphere at 13,000 mph..."

How is it going to land in 7 minutes from over 13,000 miles altitude if it is traveling at 13,000 miles per hour?

Dave Fuller
7th July, 2012 @ 11:43 pm PDT

You don't consider the possibility of finding alien life on another planet worth the effort???

8th July, 2012 @ 03:42 pm PDT

Name any form of life that can exist without the basics which support life. Now name any place in space that has all of the provisions to sustain life. It is sometimes called the circle of life. It just does not exist. When attempts are made to find this imaginary life - it reminds me of a dog chasing his tail.

9th July, 2012 @ 09:37 pm PDT

everyone misses the point... IF we find ANY life on mars at all, in any form, in any way, etc. then mars if OFF LIMITS for the whole human race forever! we simply can not risk any kind of alien organisms/pathogens to be brought back to earth...

10th July, 2012 @ 12:04 am PDT

Then Timothy, wouldn't it be cheaper to just leave it alone now? What is there to gain by confirming there are no Martians?

10th July, 2012 @ 06:42 am PDT

I want to see this because it looks freaking AWESOME! Although it has a very high "what could possibly go wrong?" factor, I think it is a super worthwhile project.

Alan Belardinelli
12th July, 2012 @ 04:50 am PDT


The landing sequence starts 13 k miles out doesn't mean the atmosphere is out that far. Earth’s atmosphere only extends about 60 miles from the surface

13th July, 2012 @ 04:31 pm PDT

Everything seems logical with the exception of everything. The location is wrong given new areas that leach water seasonally, its tragic to simply crash the sky crane - what a waste, as it could work as a back-up station and relay-up link, and has anyone thought of the tethered balloon for long range visuals and communications. Why are we still only on the ground? Is it not time for the mobile mars copter?

Dr. VonsterMonster
13th July, 2012 @ 06:31 pm PDT

I think there's a special on this on this History channel in a week or two.

19th July, 2012 @ 06:20 pm PDT

The sky-crane style landing was to try to eliminate dust getting into the instrumentation from the thrust of the lander. Ingenious. The cost of this mission is less then the cost of 1 x B2 bomber, and a lot less destructive. If the US spent more on this and less on war, we'd all be better off.

Congratulations to the team at JPL who bought this to us.

Bernie Glynn
6th August, 2012 @ 08:16 pm PDT
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