All You Need To Know About The Mars Rover Landing
By on August 4th, 2012

The new Mars Rover, Curiosity, is poised to land on the Red Planet at 0524 GMT on 6th August. There have been no reported delays or corrections for tomorrow. The final path corrections were made today, and now Curiosity is out there on its own. From the time the Rover, called Mars Science Laboratory or MSL, enters the atmosphere to the time it touches down, the whole world will hold its breath. This is to so-called “seven minutes of terror”.

Curiosity!

In this article, I’ll give you everything you need to know about the landing – the time, the place and more. Buckle up!

Landing: The Time!

If everything goes smoothly, Curiosity should touch down at 0731 CET (Central European Time) or 0531 GMT. I will take you through these seven minutes before they happen in this article. The times (all in GMT) given below are all expected times as given by ESA and NASA:

Time: T–6 min, 41 sec; 05:24:34 AM

At an altitude of 125 km, the Curiosity payload sheds two 75-kg tungsten weights. This reduces the weight, but it still can’t fly. Perhaps Allen Chen, JPL’s operations for entry, was paraphrasing Douglas Adams when he said “We’re flying like a brick”. The spacecraft’s internal gyroscopes have to all coordinate to keep the spacecraft aimed at the Gale Crater. The target is barely 20 km across.

Time: T–5 min, 26 sec;

The Earthly package is in free-fall. The atmospheric drag increases the surface temperature to about 21000C. Carbon tiles, specially made to handle such high temperatures, protect the precious load inside. Curiosity is nestled safely inside this package.

Time: T–2 min, 28 sec; 05:28:46 AM

The parachute deploys! It’s nearly 16 meters in diameter! The hearts of all the NASA and ESA engineers are in their mouths. The parachutes are one of the parts most likely to fail, even though that failure possibility is quoted at 1%. This will be a real test for the parachutes, since they have only cushioned drops for much lighter payloads. The altitude from ground is 11km and the payload is still travelling faster than sound at an estimated 425 m/s.

Time: T–2 min, 4 sec; 05:29:07 AM

The heat shield separates! The payload starts sensing the ground approaching. The current altitude is just 8 km and the payload is now moving at 125 – 130 m/s, still too fast to make a proper landing. Crucially, three radar antennas switch on and this is how it knows how far the ground is. The data is useful for the craft to adjust its actions. For the first time, the craft has eyes and its guidance system can kick in.

Time: T– 53 sec; 05:30:40 AM

The back-shell separates. Finally, the world gets a glimpse of the new Rover! The back-shell flies off with the parachute! Curiosity drops down towards the surface, cushioned by the thrust of eight retrorockets. The altitude is less than 2 km from the surface and the craft is moving at a speed of 80 m/s.

Time: T–20 sec; 05:31:17 AM

The sky crane is deployed! This is a complete transformation from previous landings by NASA. So why this sudden transformation? Simple – Curiosity is just too heavy. This calls for a new arrangement – the wheel suspension system can be used as a landing gear. The main craft, Curiosity, then drops down as a thread unspools from the sky crane. The craft gently drops down at a nice pace of 0.75 m/s.

Time: T–0 sec; 05:31:37 AM

Touchdown!

Landing: The Place

The site of the touchdown is Gale Crater. The crater is 154 km wide, but the target area is just 20 km. The High Resolution Stereo Camera (HRSC) on the Mars Express spacecraft has just sent back a very interesting picture of the landing area. The image is a false colour image as shown below:

The Gale Crater

The image suggests the presence of water-based minerals, which might form the basis of life. The lower elevated areas are shown in purple and this forms the target landing area. But don’t miss out on the elevation right in the middle – it’s called Mount Sharp and rises to 5.5 km above the crater floor. Scientists want the rover to land closest to this mountain, as the geologic features there are “very interesting”. The rover will land in the depression, scour around for interesting geologic artifacts and then trudge towards the elevation.

The Eyes and Ears of Curiosity

Meanwhile, the Mars Express will be eyes and ears of the Mars Science Laboratory. The Mars Express Lander Communication (MELACOM) will be switched on at 0205 GMT on 6th August, long before the touchdown.

M-Ex starts recording

Radio signals transmitted by the Mars Rover will be recorded by the Mars Express starting from 05:09 to 05:37 GMT. (For CET times, just add two hours.) This is when the MELACOM receiver switches off and the Mars Express starts off from the dark area of Mars to point at Earth.

M-Ex starts transmitting

The Mars Express starts transmitting recorded signals back to Earth at 06:10 AM (GMT). The data will be transmitted for over 40 minutes with the transmitter shutting down at about 06:42 AM. The only thing left to do for ESA is to transfer the data to NASA.

The Final Words

We’ll be there with you when the massive Mars Rover, weighing in at 900 kg, touches down on the surface. The leaps made have not only been in terms of the technology packed in the machine, but also in the new ways devised to land a very heavy craft precisely on the surface of another planet. The unexpected hurdle came in the form of the black out for the “seven minutes of terror”, during which Curiosity will land, but NASA will be completely blind to it.

So what can go wrong? Charles Bolden, NASA administrator, has a very simple answer – “All sorts of things can go wrong”.

What about all the simulations of worst-case scenarios, rigorous testing of each part and lessons learnt from previous missions? Shouldn’t they be enough? Steven lee, mission’s control systems manager, working in JPL has the perfect closing line:

Probably the overall biggest risk is our lack of imagination.

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Author: Debjyoti Bardhan Google Profile for Debjyoti Bardhan
Is a science geek, currently pursuing some sort of a degree (called a PhD) in Physics at TIFR, Mumbai. An enthusiastic but useless amateur photographer, his most favourite activity is simply lazing around. He is interested in all things interesting and scientific.

Debjyoti Bardhan has written and can be contacted at debjyoti@techie-buzz.com.
 
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