Mars Curiosity rover success depends on 'crazy' landing


Project architect Adam Steltzner explains how the Mars Curiosity rover is expected to land on Mars (animation is courtesy of Nasa)

"The average person on the street thinks it's crazy. Even the team that's working [on] it - sometimes we think it's crazy."

Adam Steltzner is responsible for getting Nasa's $2.5bn Curiosity rover mission to the surface of the Red Planet on Monday 6 August.

This mobile Mars Science Laboratory (MSL) should bring about a revolution in our understanding of the geological history of the planet… provided it can land safely.

Steltzner and his team have devised a breathtaking approach to the problem that involves a rocket-powered crane.

"It's so ambitious, it's so audacious, it's so unconventional. It doesn't feel like there's a lot of shelter," he tells the BBC's Horizon programme.

"You can't say, 'Oh, I'm doing what they did before and, oh, it just didn't work out; I didn't get lucky'.

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"No, we're not doing what we did before. We're doing something completely novel, hanging it way out there. You feel exposed."

But although Steltzner admits to the odd moment of panic in the middle of the night, he and his team actually have high confidence they can pull this one off.

"Reasoned engineering thought," he says, will get them through the white-knuckle ride that is entry, descent and landing - or EDL.

This is how the drama will unfold.

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When the rover's wheels touch the ground... they must be moving no more than about 1m/s.”

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The 900kg rover will approach Mars enclosed in a protective capsule - the biggest capsule Nasa has ever used, bigger even than the Apollo Command Module.

It will arrive at the top of the atmosphere travelling 20,000km/h.

All that energy has got to be dumped. When the rover's wheels touch the ground six-to-eight minutes later, they must be moving no more than about 1m/s.

What scares the uninitiated most perhaps is the complexity of it all.

It starts with very precise navigation through space.

If the rover has any chance of reaching its equatorial target of Gale Crater, it must first hit an "entry keyhole" in the sky just a few kilometres across.

Curiosity - Mars Science Laboratory

MSL (Nasa)
  • Mission goal is to determine whether Mars has ever had the conditions to support life
  • Project costed at $2.5bn; will see initial surface operations lasting two Earth years
  • Onboard plutonium generators will deliver heat and electricity for at least 14 years
  • 75kg science payload more than 10 times as massive as those of earlier US Mars rovers
  • Equipped with tools to brush and drill into rocks, to scoop up, sort and sieve samples
  • Variety of analytical techniques to discern chemistry in rocks, soil and atmosphere
  • Will try to make first definitive identification of organic (carbon rich) compounds
  • Even carries a laser to zap rocks; beam will identify atomic elements in rocks

As the capsule thunders downwards, it ejects ballast blocks to move its centre of gravity and tilt its angle of attack.

This will give the vehicle lift. And with the aid of thrusters and some dead-reckoning, the entry capsule will fly a path through the upper atmosphere.

The underside of the capsule will get hot as it pushes up against the Martian air - the heat shield will experience temperatures above 2,000C.

More ballast blocks are then ejected to straighten the vehicle before, at 11km altitude and with the descent velocity now reduced to 1,400km/h, the capsule deploys a supersonic parachute.

This immense canopy will open instantaneously and must absorb an impulse of almost 30 tonnes.

Half a minute later, what is perhaps the most important event occurs - the separation of the heat shield.

Unless it comes off, Curiosity's descent radar cannot see the ground.

"The radar is fundamental," says Matt Wallace, the flight system manager on the project.

"You have to land softly or else you'll break the rover. To land softly, you have to know how high you are, obviously, from the ground. But more importantly you have to know how fast you are going - both vertically and horizontally.

Nasa's Matt Wallace: The radar system is very precise and doesn't get spoofed

"It's a pulsed-Doppler system and has the benefit of being extremely accurate in both velocimetry and altimetry, and it's very hard to fool."

The parachute will further slow the fall to about 450km/h, and it's at that point, at an altitude of about 1.5km, that we see the so-called "crazy" stuff.

A "sky crane" holding the rover drops away from the parachute, using thruster rockets to further slow its descent as it heads down towards the surface.

At just 20m above the ground, the sky crane hovers and lowers the rover down to the surface on three nylon cords.

Once the wheels make contact, the cords are cut, and the crane flies away to crash at a safe distance. Steltzner and his crew can breathe again.

All of this is automated; it's all pre-programmed. Earth and Mars are so far apart (250 million km) that communications links endure a 14-minute delay. Mission Control cannot intervene as if this were some online computer game.

My favourite number in this drama concerns the quantity of pyrotechnic devices.

These initiate key events, such as the severing of the nylon bridles or the opening of the chute housing.

All must blow - and in sequence - to ensure success. The number is 76.

Step by step: How the Curiosity rover will land on Mars

Aeroshell separates from cruise stage As the rover, tucked inside its protective capsule, heads to Mars, it dumps the disc-shaped cruise stage that has shepherded it from Earth.
Thrusters fired from MSL entry capsule The capsule hits the top of the atmosphere at 20,000km/h. It ejects ballast blocks and fires thrusters to control the trajectory of the descent.
Heat shield Most of the entry vehicle's energy is dissipated in the plunge through the atmosphere. The front shield heats up to more than 2,000C
Parachute deployment The parachute deploys when the capsule is about 11km above the ground but still moving at supersonic speed.
Parachute deployed above rover A key event is the dropping of the heat shield. This permits imaging and radar instruments to monitor the approaching surface.
Final moments before touchdown At about 1.5km above the ground and still moving at 80m/s, the rover and its sky crane drop away from the parachute and capsule backshell
Rover finally touches down Rockets on the sky crane slow the descent to 1m/s. Nylon cords spool the rover to the surface. Untethered, the crane flies to a safe distance and crashes.
Rover on the surface The rover is equipped with a nuclear battery and should have ample power to keep rolling across the Martian surface for many years.

But if all of this does sound a bit crazy, there is purpose.

We've grasped most of all there is to know about the simple geological history of Mars.

To deepen our understanding necessitates taking more sophisticated instrumentation to harder-to-reach places.

That means a bigger rover and a more robust landing system that can put down on the proverbial sixpence.

Consider all the surface missions Nasa has sent to the Red Planet, from the Vikings in the 1970s to the Phoenix probe in 2008.

Sanjeev Gupta: Gale crater rock layers could record 'ancient environments on Mars'

Each has had a more accurate landing system than its predecessor, but only with Curiosity's EDL technology could you confidently attempt to get inside Gale Crater, one of the deepest holes on Mars.

"Scientists want to go to somewhere rough because that's where the rocks are exposed. The engineers in the past wanted to go somewhere flat where their machines would be preserved," explains Prof Sanjeev Gupta, a Imperial College London-UK researcher on the Curiosity science team.

"But we've now moved on to the next stage. Issues of life and habitability are really locked in the rock record, and to see those rocks you need to go to canyons and mountains - to get the chronology, to see the relationships and understand past climate changes.

"You won't get that on flat plains."

Landing  ellipses
  • Engineers define an ellipse in which they can confidently land
  • Viking's ellipse was 300km across - wider than Gale Crater itself
  • Even Phoenix (100km by 20km) could not confidently fit in Gale
  • Curiosity's landing system allows it to target the crater floor

Curiosity is due to land on Mars at about 06:30 BST (05:30 GMT) on Monday 6 August.

Horizon: Mission to Mars is on BBC Two at 21:00 BST on Monday 30 July

Jonathan Amos Article written by Jonathan Amos Jonathan Amos Science correspondent

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  • rate this

    Comment number 47.

    To the naysayers saying the money could be spent on better things. $2.5 billion dollars doesn't go very far these days. The US spend twice as much on mobile ring tones every year. Think about that next time you see a starving African kid on TV. What benefit will a mobile ring tone have - compared to the offshoot technologies and advancement in knowledge that projects like this can bring.

  • rate this

    Comment number 46.

    BREAKING NEWS: Mars Curiosity rover achieves Martian landfall in carpark of newly built Starbucks.

  • rate this

    Comment number 45.

    This plan just seems very complicated, since there are no second chances, but I suppose they can't use the bouncing ball technology for a future manned landing so have to figure something else out. Let's hope it works and this rover is as successful as Spirit and Opportunity.

  • rate this

    Comment number 44.

    There will be many detractors saying "What are we getting from the billions spent on Space?" That's like the famous "What have the Romans ever done for us?" please add to the list of computer chips, satnav, non-stick frying pans, satellites which can detect plant disease from space, (even sky tv).

  • rate this

    Comment number 43.

    Amazing stuff! NASA does more for the USA's international reputation than anything else. Even if this audacious approach does not land the rover in one piece, the value of the research and development to other, unrelated possible applications is incalculable. I shall be wearing my old Beagle 2 t-shirt on 6th August!

  • rate this

    Comment number 42.

    @38. Chris "Dogmatic, religious ways of thinking will only end up taking mankind back to the medieval torture chambers."

    What a ridiculous comment. The majority of dogmatic, religious people are more than happy for this to happen. There's absolutely no conflict of interest in any way.

    Hopefully everything goes according to plan for the NASA team.

  • rate this

    Comment number 41.

    #36. Chris
    I agree with you 100%. Good on NASA, another small step...

    I expect it will be covered on the Internet, but for those of us with very flaky broadband, I am hoping there will also be proper coverage on a TV channel as soon as they get the first new images.

  • rate this

    Comment number 40.

    As Napoleon said when an officer was recommended for promotion "I know he's brilliant, but is he lucky?" We know the NASA scientists are pretty clever, but with so many things that could go wrong, the smallest one of which could mean disaster, here's hoping Lady Luck favours them as well.

  • rate this

    Comment number 39.

    This is exciting. I can not wait to get some new images of mars. Who is ready for Mars One? [Unsuitable/Broken URL removed by Moderator]

  • rate this

    Comment number 38.

    Creative, rational thinking can take mankind to the stars. Dogmatic, religious ways of thinking will only end up taking mankind back to the medieval torture chambers.

  • rate this

    Comment number 37.

    Let us hope Mar's reputation for eating science probes relents for the day. The bones of many (particularly Russian) spacecraft lie buried in the sand there. This is a very challenging project and I for one wish it Good Luck!

  • rate this

    Comment number 36.

    Next monday morning will the the closest my atheist self gets to a religious experience. I can't even being to describe how misguided I feel the naysayers are. This is THE most important, THE most impressive boundary being pushed by mankind today. Nasa are the one-shot kings: this whole system has never been integration tested... how could it be? And yet, they will make this work. Go NASA!!!

  • rate this

    Comment number 35.

    27. mrcynict4

    Agree entirely, better to spend money on this than McOlympics with it's sugary drinks and empty seats. This is some heavyweight [in all senses] science and, when we finally wreck here, we may need to terraform somewhere new...

  • Comment number 34.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this

    Comment number 33.

    I hate to tell you this, but you're not allowed to park there.

  • rate this

    Comment number 32.

    Sounds a really elegant approach... looking forwards to seeing it succeed.

    Go NASA!!

  • rate this

    Comment number 31.

    Good stuff; I’m looking forward to the sequel.

  • rate this

    Comment number 30.

    The whole of the Nasa budget amounts to 0.5% of 1 cent of every tax dollar. Half a penny! 1/200 of a dollar! If all you moaners think that if only you had that extra .5% of a penny everything will be ok? You have some other problems you need to address first.

    Why are we spending money up there and not down here? We are spending it down here. We spend over approximately 200x more down here.

  • rate this

    Comment number 29.

    "Next time pictures of starving Africans flash up on our TV"... come on! It's precisely because, sometimes, you just want to cry in frustration at the state of the world that i love stories like this. Look at the wonder of it! 9 billion pounds to watch some genetic freak run faster than another genetic freak? There's your waste.

  • rate this

    Comment number 28.

    This is proper science that will benefit mankind in ways the naysayers don't seem willing or able to try and imagine. Just like the great work being done here:
    I look forward to the BBC spending some money producing a balanced and informed item on that.


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