Curiosity rover stretches its arm for first time

Aug 21, 2012
NASA's Mars rover Curiosity extended its robotic arm on Aug. 20, 2012, for the first time on Mars and used its Navigation Camera (Navcam) to capture this view of the extended arm. Image credit: NASA/JPL-Caltech

(Phys.org) -- NASA's Mars rover Curiosity flexed its robotic arm today for the first time since before launch in November 2011.

The 7-foot-long (2.1-meter-long) arm a turret of tools including a camera, a drill, a , a scoop and mechanisms for sieving and portioning samples of powdered rock and soil.

"We have had to sit tight for the first two weeks since landing, while other parts of the rover were checked out, so to see the arm extended in these images is a huge moment for us," said Matt Robinson of NASA's Jet Propulsion Laboratory, lead engineer for Curiosity's testing and operations. "The arm is how we are going to get samples into the laboratory instruments and how we place other instruments onto surface targets."

Weeks of testing and calibrating are ahead before the arm delivers a first sample of to instruments inside the rover.  Monday's maneuver checked motors and joints by unstowing the arm for the first time, extending it forward using all five joints, then stowing it again in preparation for the rover's first drive.

"It worked just as we planned," said JPL's Louise Jandura, sample system chief engineer for Curiosity. "From telemetry and from the images received this morning, we can confirm that the arm went to the positions we commanded it to go to."

The turret has a mass of about 66 pounds (30 kilograms). Its diameter, including the tools mounted on it, is nearly 2 feet (60 centimeters).

"We'll start using our sampling system in the weeks ahead, and we're getting ready to try our first drive later this week," said Mars Science Laboratory Deputy Project Manager Richard Cook of JPL.

Curiosity landed on Mars two weeks ago to begin a two-year mission using 10 instruments to assess whether a carefully chosen study area inside Gale Crater has ever offered environmental conditions favorable for microbial life.

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User comments : 15

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JustChris
4.3 / 5 (6) Aug 21, 2012
Metric system please.
Egleton
2.8 / 5 (4) Aug 21, 2012
Nonsense. Lets go the whole hog and use the Russian Imperial system.
How many Poods in a Zlotky?
Flatline____
5 / 5 (1) Aug 21, 2012
Metric system please.

I was wondering, do they mean 66 pounds / 30 kilograms measured with earth gravity, or with martian gravity?

So, can I suggest adding Martian metric system? :P
Mayday
1.3 / 5 (4) Aug 21, 2012
Oh, yeah. Love the idea of a Martian metric system! Someone here has to bring it! It couldn't be any less intuitive than the Earthly metric system, could it? Well, I guess maybe it could, but doesn't the rigor of scientific logic demand its use? :-) I'll be the first to buy a Martian metric ruler. That would be awesome.
Doug_Huffman
not rated yet Aug 21, 2012
Why would y'all expect a vernacular description of local space-time to be intuitive? Even here in your native province, descriptions of S-T curvature (mass) and its effect (weight) are confused and conflated.
JustChris
not rated yet Aug 21, 2012
I don't see why anyone would need a Martian metric system.

To make things clearer in the future, we should all switch from using kg to define anything's weight and use Newtons instead. Then, when we see *grams in an article, we know for sure the author was talking about mass not weight.
GSwift7
3 / 5 (2) Aug 21, 2012
I was wondering, do they mean 66 pounds / 30 kilograms measured with earth gravity, or with martian gravity?


That's 66 Earth lbs. It's only about 1/3 of that on Mars. For that matter, the entire 2000 lb rover is only 1/3 of that on Mars.

When people eventually do go to Mars, that 1/3rd gravity will be nice, as well as having relatively no wind or other weather. It should be possible to build amazingly tall structures on Mars, if anyone ever wants to. Communication towers, for example, can be made much taller there. Conditions on Mars allow many structures you could never build here on Earth. On the other hand, gravity based processes like refining would suffer, and you would need to find a Martian version of cement.
danlgarmstrong
3.5 / 5 (2) Aug 21, 2012
"I was wondering, do they mean 66 pounds / 30 kilograms measured with earth gravity, or with martian gravity?"

From what I remember from high school, pounds are a measure of force, while kilograms are a measure of mass. Therefore if the turret weighed 66 pounds on Earth, it would weigh ~22 pounds on Mars, but it would still possess 30 kilograms of mass.
The Singularity
1.3 / 5 (3) Aug 21, 2012
Like they did'nt calibrate all of the moving parts before it was sent to Mars??. The more we hear the more amatuerish it begins to sound. Like there was some last minute rush where they shoved the rover into its shell & said 'ah heck we can do all that important stuff when we get there.'
I "DONT BELIEVE IT" because A: they are proffesionals & B: they had 8 years to prepare. Whats really going on here?
GSwift7
5 / 5 (6) Aug 21, 2012
Like they did'nt calibrate all of the moving parts before it was sent to Mars??. The more we hear the more amatuerish it begins to sound.


lol. You can't calibrate a scientific instrument here on Earth, then launch it to Mars, and just assume that it stayed calibrated. Have you ever noticed that the pump where you buy gas is calibrated on a regular schedule? Police radar speed guns are re-calibrated, in the bakery where I work, scales, flow meters, thermometers, etc are all re-calibrated monthly. A competitive target shooter will re-calibrate his sights before every match.

Of course they calibrated everything before they launced it, but you have to check everything before you use it. That's how a professional scientist works. You don't just assume everything is working fine. You check it.
Kafpauzo
5 / 5 (2) Aug 21, 2012
Here's one example of calibration that is very easy to understand:

As mentioned above, the arm carries instruments that weigh 30 kilograms, 66 pounds. In the higher gravity on Earth the weight makes the arm sag more, in the lesser gravity of Mars it sags less.

Exactly how much does it differ? This is influenced both by the very exact weight and very exact placement of all the additional stuff (wires, details of joints, arm material thickness, everything along the arm) and also the very exact stiffness and flexibility of the arm's structural material, which is influenced by the exact thickness along the arm, the exact characteristics of every joint and every joint motor, and so on.

To simulate and calculate the exact characteristics would take a supercomputer quite a while. Even then, how do you know that you haven't missed something? A waste of effort for an uncertain result.

The obvious solution is to find the real, reliable answer, simply by checking on-site on Mars.
Telekinetic
1 / 5 (3) Aug 21, 2012
Those grousing about minutiae like measurements and calibration are missing the point. This is state-of-the-art tech that doesn't involve the killing or maiming of any living being. It's the most impressive display of know-how I've seen in a long time. A rolling lab that delivers detailed info from this incredible distance and hostile conditions is more than noteworthy, it's ingenious.
hagger
1 / 5 (1) Aug 22, 2012
Telekinetic bang on mate..it's the most incredible thing we have done out there in a long time..and the way it was put down on the surface was unreal..like the good ole sikorsky sky crane...so much could have gone wrong..and so many peoples reputations as well as NASA's were on the line...it's a rush...
Argiod
1 / 5 (1) Aug 22, 2012
Like they did'nt calibrate all of the moving parts before it was sent to Mars??. The more we hear the more amatuerish it begins to sound. Like there was some last minute rush where they shoved the rover into its shell & said 'ah heck we can do all that important stuff when we get there.'
I "DONT BELIEVE IT" because A: they are proffesionals & B: they had 8 years to prepare. Whats really going on here?


You cannot calibrate an instrument on Earth and assume it will stay calibrated on Mars. One always calibrates in the environment the device will be used in. The lift off to put it in orbit will affect calibration, as will orbital insertion and landing. Then you have to deal with the difference in atmospheric density, air pressure; which will also affect calibration. If you think it's all so easy, I invite you to go apply for a job at NASA or JPL. I'm sure they'll appreciate your expert opinion.
antialias_physorg
5 / 5 (1) Aug 22, 2012
To simulate and calculate the exact characteristics would take a supercomputer quite a while.

What you describe is forward calibration which isn't used much in high precision robotics. It is very easy to calculate even with very low level processors (a rasberry pi could do it dozens of times a second), but it's also very error prone.

The problem is that each joint has different slack, and this slack is dependent on position, orientation (and sometimes even speed of the motion and motion history). So what you usually do for calibration is to calibrate an object on the tip of the manipulator relative to your camera and adjust the motion control continually on the fly to give you accurate motion to a target position.

Calibration after a bumpy ride and temperature differentials is a must in any case.