Mars Rover Spirit Down a Wheel

riflemann writes "NASA is reporting that two years into its 90-day mission, Spirit has lost one wheel and is now running on five wheels, dragging the broken wheel. With this reduced mobiity, the rover still needs to make its way to a slope where it can catch enough sun over the Martian winter to keep it operating. 'Even though the rovers are well past their original design life, they still have plenty of capability to conduct outstanding science on Mars.', says project leader Dr. John Callas."

Comments

Cold

[MichaelSmith]

Its almost winter in the southern hemisphere of Mars. I wonder if there is a chance that a contact has contracted in the cold enough to break off power to this motor. Who knows? Spirit has been lucky before. Perhaps this wheel will start working again in the summer.

Failing that I am available to fix the broken motor, assuming that NASA can provide transportation :)

Re:At first read, I get dissapointed

[partymonkey]

Maybe it's just me, but I doubt they spent all that money on the rovers for just 90 days of operation. I'd be willing to bet that they designed them to last 3-5 years. Also, they were probably just setting expectations *really* low, so if the rovers failed early then they still looked good in the public eye.

Failed brushes?

[dougmc]

"It is not drawing any current at all," said JPL's Jacob Matijevic, rover engineering team chief. One possibility engineers are considering is that the motor's brushes, contacts that deliver power to the rotating part of the motor, have lost contact.

Brushless motors are generally 1) more efficient and 2) longer lasting (with no brushes to wear out) and 3) more expensive (especially when you include the ESC, electronic speed control) than otherwise similar brushed motors. (But when you send something into space, who cares about an extra $1000 on motors?) I'm rather surprised that they didn't go brushless in something like this. Brushless motors are also cleaner, as there's no brushes to wear down over time. This is critical in zero gravity environments like orbit (nobody wants brush-dust floating around) and wouldn't be so important on Mars, but even so ... I wonder why they used brushed motors. Even if they things weren't supposed to last very long, you'd think brushless motors would be more efficient, giving them some extra power to work with, for not much extra money.

(My experience with brushed and brushless motors comes from R/C planes, where a brushless motor is sometimes twice as powerful and 50% more efficient than a similarly sized brushed motor. Of course, a large part of this is that the brushed motor is dirt cheap, made cheaply in every way, and the brushless motors are of higher quality, but even so, even when comparing high quality stuff (and not cheap speed 400 can motors) the brushless are signifigantly better.)

Re:Failed brushes?

[Anonymous Coward]

Actually, having recently heard a talk with people from JPL I can tell you why. They went with brushed motors because it was what had been previously used and was, therefore, seen as a safe option. For future robotic missions they plan on using brushless motors.

Re:Failed brushes?

[v1]

Brushless motors are more complex, and require an array of active electronics inside them to produce the AC and modulating magnetic field they need to operate. Most brushless motors are lower torque than their brushed counterparts. (majority, I know there will be exceptions) Brushed motors are more mechanical in nature and suffer from the usual mechanical issues, but they are less prone to failure than brushless. Also, traveling through space and landing on a planet that may not have a protective magnetic field, active (transistor based) electronics must be carefully protected against emi that can disable or damage them.

I'm sure they went brushed for a variety of very good reasons. The technology of brushless was available when the rovers were designed, and I can't imagine NASA not seriously considering them.

Re:Failed brushes?

[dougmc]

Second of all the, Mars' rovers spent considerable time in transit to Mars with no outside protection at all.

As a general rule of thumb, ionizing radiation doesn't usually immediately destroy electronic components (at least those that we've hardened for space duty) when it hits it. The damage can accumulate over time, or it can cause a `glitch' changing a 0 to a 1 in a digital circuit (which can do nasty things like crash computers (which is taken care of by watchdog systems that initiate a reboot when needed)) but things don't generally just `stop working'.

This page gives some good information on exactly what the effects are and what can be done about them.

Third of all while there is some protection offered by Mars, it is still much worse than anything on Earth.

I was wrong when I assumed that Mars had a substantial magnetic field -- it does not. But even so, the atmosphere, even being only 1% as thick as ours, would provide considerable protection. The Martian surface probably gets far less ionizing radiation than a satellite in Earth orbit would, for example.

And don't forget that the Mars rovers are controlled by computers. Computers are far more vulnerable to ionizing radiation than other forms of electronics. And really, ESCs are pretty simple, being mostly just analog components. They should be relatively resistant to ionizing radiation -- far more so than the computer components that control them. So I don't think that's really a big issue -- just protect them half as well as you protect the computer parts, and you'll be just fine. And also don't forget that the Mars rovers already almost certainly have several ESCs ... it's not like using brushless motors would add ESCs where there were none before.

all alone in the cosmos

[JTW]

The rovers are interesting critters.. not unlike their older sibling Pioneer 10.

I guess we've given up on artificial intelligence, but I rather think what we altogether thought was a mind of information is actually a mind of situation and evolving spirit that simply exists in the moment. If that be true, even an Ant could have artificial intelligence.

Its interesting we drive these things into the ground, or until they run out of power, or we loose interest.

It may be lame, But I'd think it might be more interesting in the long run to upload a final survival program into these critters and turn them loose.. perhaps in the long run we'll come to those ideas and terms. Perhaps years from now when astronauts decide to land there they really will find martians!

Of course if we have a nuclear or biological melt down, then perhaps they will out live us.

There was a SciFi story long ago called NightFall.. it would make an interesting animated short or story to tell the story from the rovers perspective... and in the end they are given their freedom and continue to look up at the night to the twinkle in the sky where their makers live, and then.. they loose contact, perhaps they merely lost interest in their creations.. or perhaps the makers are no more, and they truly are all alone.. and as the cold surrounds and grips them they fold up their solar wings preparing for another martian winter and the rovers go to sleep.. perchance to dream.. of other worlds.

Even if it can't make it up the slope...

[artifex2004]

Why would the rover actually permanently die if it ran out of power?
Surely when the Martian winter comes to an end, and the area it's in is flooded with sunlight again, the solar cells could still work, the battery could recharge, and it could wake up?

Or did nobody think about a cold restart?

Re:It's not "dragging" the sixth wheel

[Tablizer]

yeah this is a year old, what the hell, you suck slashdot

Hold on, Tex. The older problem was that it drew too much current. It still worked and they used it for occasional tight maneuvering. Now it appears to be all-the-way gone. However, it went back to normal for a while before it completely failed. It is even possible the problems are not related.

The speculation was that lubricant was not spreading around enough, creating friction, and that the problem went away because lubricant finally dripped into the right place. A sudden failure does not really match that hypothesis as one would expect the friction (power current needed) to slowly drift upward again before the failure. At this point nobody really knows what happened.

Either way, the first problem was less severe and thought to have since gone away.

Re:Only lost 1 wheel? pfft

[Rob Carr]

Our vet got a call for a dog involved in an accident. When the vet got there, she found a dog that had lost most of the front right and rear left legs to a crush injury. The dog was running around and was hard to catch. They expected the vet to put the dog down, but she wound up cleaning up the amputations and infections. The dog was given to a family. Last I heard, dog and family were doing fine, although if the dog gets out of the house without a leash, it is still hard to catch.

Re:Still a tossup - Rovers dead before Vista relea

[rspress]

Yep you are correct. Sorry I was confusing the RS6000 brand of IBM chips with the RAD 6000.

I was also quoting NASA as for them being cheap. When the landers were on there way they said in interviews on TV that they were cheaper chips......looking at wiki it is hard to find many other RAD hardened chips.