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."

Tis but a scratch

[Anonymous Coward]

I've had worse.

Re:Tis but a scratch

[metricmusic]

A scratch? Your wheel's off!

We thank thee Lord, that in thy merc-

C'mon ya pansy

[Anonymous Coward]

The NASA engineers always triumph!

Re:C'mon ya pansy

[Krakhan]

*Rushes in* No one expects the Spanish Inquisition!

Conversation I never Overheard

[Black Copter Control]

Martian1: It broke it's leg. I say we shoot it and put it out of it's misery.
Martian2: nah. It seems to have such a drive for life.

Re:Conversation I never Overheard

[Anonymous Coward]

Martian3: How come neither of you knows how to use apostrophes correctly?

/shoots martians 1 and 2

Re:Conversation I never Overheard

[bckrispi]

Oh, you make me verrry angry. Verrry angry indeeeeed!!

Late Breaking News:

[iced_773]

A sense of triumph swept our fair red world today when reports came in that the Grand Army of the Council had damaged one of the robotic invaders from the evil blue planet. K'Breel, speaker for the Council of Elders, made the following comment:

This was a great victory in our war with the evil blue planet. While we have only impaired the horrid machine's movement, we will continue to strike until it and its dreadful twin are pools of molten metal.

When a journalist suggested that the terrible monstrosity had merely worn out one of its locomotive rotators, K'Breel had the traitor's gelsac mutilated immediately.

Apologies to TripMaster Monkey.

Re:Tis but a scratch

[buswolley]

Lets all bow our heads for a moment.... for the loss of the sixth wheel.

Not so surprising

[Reverend528]

That's what happens when you only test the wheels for 9 days.

Re:Not so surprising

[slightlyspacey]

What do you expect? The rover has lasted *8* times longer than design. That's the equivalent of driving 400,00 miles on tires rated for 50,000 miles. It's a heck of an accomplishment and I can only applaud the terrific job the design engineers and builders did.

Re:Not so surprising

[Chowderbags]

It might even be the equivaltent of driving 400,000 miles on those tires too!

Re:Not so surprising

[slightlyspacey]

Hey, it's still within an order of magnitude of the right answer and I didn't confuse English with Metric measurments :)

Still a tossup - Rovers dead before Vista released

[SpaceLifeForm]

I still believe both rovers will be alive
when and if Vista is ever released.

Re:Still a tossup - Rovers dead before Vista relea

[therage96]

Aha, but will they still be functioning when Duke Nukem Forever gets released? I mean, 2514AD is a long ways away!

Re:Still a tossup - Rovers dead before Vista relea

[c_forq]

I don't know, I'm pretty sure Google^H^H^H^H^H^HSkyNet will attian self-awareness well before then. And I'm sure once the AI takes control of production it will be finished within a week.

Re:Still a tossup - Rovers dead before Vista relea

[GKThursday]

I don't think their hardware meet Vista's specs.

Re:Still a tossup - Rovers dead before Vista relea

[rspress]

The computer in each Mars Exploration Rover runs with a 32-bit Rad 6000 microprocessor, a radiation-hardened version of the PowerPC chip. This chip is used in IBM's heavy duty computers and is the same family of chip in the pre-intel Macs, Xbox 360, GameCube and the Cell version will run the PlayStation 3.

The chips are fairly cheap and have lightning fast floating point calculations via alti-vec. They are also very easy to program for.

NASA claimed they would only work for 90 days due to the high iron content of martian soil. In 90 days the solar cells were supposed to be covered with magnetized iron dust and the cells would not get enough sun to charge them. That never happened. Considering the cold, dusty, unsheilded environment they are in it is amazing they have lasted over two years.

Re:Still a tossup - Rovers dead before Vista relea

[yoprst]

If memory serves me well (and it often doesn't), Rad 6000 is something like $600000

Re:Still a tossup - Rovers dead before Vista relea

[Moridineas]

Uhm, this gets informative? The Rad6000 chip runs at 20mhz according to wikipedia and 25mhz according to other sources. The chip is based on EARLY power cpu designs (think early/mid 1990s), and most definitely does NOT include any sort of altivec technology.

No radiation hardened space suitable chips are "cheap." Expect to spend tens, if not hundreds of thousands of dollars per CPU.

That's not to say it's not a great chip for what it does, but come on...

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.

Re:Still a tossup - Rovers dead before Vista relea

[flyingsquid]

To be fair the rovers were lucky to land in areas with lots of whirl-winds to clean them. If it was not for the whirl-winds the rovers would probably be paper-weights by now.

Well, future rovers could carry around little Roombas to run around and vacuum off the top of their solar cells.

Re:I'll take the Offtopic hit for this

[DaveAtFraud]

<br> at the end of the line and post using HTML given the software used by slashdot. Some oher sites such as Groklaw use different software that attempts to maintain formatting in simple text posts. Use preview and see what works on different sites.

The extra credit question is: How did I get "<br>" to show up instead of being interpreted as HTML?

Cheers,
Dave

Re:I'll take the Offtopic hit for this

[jrockway]

> <ecode><br><//ecode>

No. You use &lt; and &gt; which means &lt;br&gt; converts to <br>.

Or you can use "extrans" mode, which is what I did for this post :)

At first read, I get dissapointed

[R2.0]

Then I remember a story Spider Robinson told about a cheap digital watch that died on him. He was pretty pissed off, but then he remembered that:

a) it was originall a Crackerjack prize or some other freebie.

b) it was 5 years into it's projected one year battery life.

At this point he gave it a solemn memorial service and kept it in a revered place (I think he may have buried it).

Whenever they finally die, I hope that they find an honored place in whatever museum the future Mars colonists decide to set up.

R2.0

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.

Re:At first read, I get dissapointed

[timeOday]

Another way to think about it, if you design a switch to last 1000 cycles with 99.99% probability, it will probably last 10 times that long with 99% probability. (I made up the numbers but you get the point.)

This is the same reason I prefer an 80,000 mile powertrain warranty over a 40,000 mile warranty when buying a car - not because any modern car is likely to last under 80,000 miles, but because I figure the one with the longer warranty is more likely to go 150,000+.

Re:At first read, I get dissapointed

[HoneyBunchesOfGoats]

Or, car manufacturers could decide that you'll assume "longer warranty == longer-lasting car," raise their warranty to 80,000 miles regardless of the fact that the car is crap, and bank on the fact that you'll want a new car within a couple years anyway.

Re:At first read, I get dissapointed

[loraksus]

This is the same reason I prefer an 80,000 mile powertrain warranty over a 40,000 mile warranty when buying a car - not because any modern car is likely to last under 80,000 miles

I worked for GM as CAC manager for a couple months, trust me, that assumption is not one that you want to make.
For other car companies, it may be advertising, for GM, it is something to strive for.

Re:At first read, I get dissapointed

[Jeff DeMaagd]

A lot of money is spent on probes. I think it would have been unreasonable to expect a 3-5 year life, these things seem to be the longest operating extra terrestrial land rover to have been made. Pathfinder was apparently noted for having an extremely low mission cost for a planetary probe.

I thought it was pretty plausible that they expected them to only last 90 days simply because of the dust problem, that it would cover the solar cells. For a while, it didn't even look like they would last a month due to the software and hardware issues.

Re:At first read, I get dissapointed

[edremy]

If you read Squyres' book, you'll see you're sort of correct. Yes, they designed them for more than 90 days- that was the *minimum* they were willing to accept. However, they fully expected both to be dead long before this, victims of dust buildup on the solar panels. They didn't expect the Martians to be cleaning them off so frequently.

Re:At first read, I get dissapointed

[Dominic_Mazzoni]

That's partially true, but another important aspect of it is that if they had planned on a five-year mission up-front, the budget would have been several times larger - and in fact the project might never have been funded at all. So they decided on a mission length long enough to get some interesting science done, but short enough to look cheap.

After 90 days, they went and asked for additional money. What's NASA going to do, stop running the rovers because they're over budget? Of course not. Unfortunately now they're eating into money that would have gone to other Mars missions. But it's still far more sensible to spend a dollar on the rovers already on Mars than on a future rover that may or may not make it to Mars.

Or like in Star Trek Enterprise...

[antdude]

... in one of the episodes (forgot which one -- probably Terra Prime with Peter Weller), there was a memorial scene of it on Mars.

Re:At first read, I get dissapointed

[livewire98801]

Scotty: 8 weeks, sir

Kirk: Mr Scott I-

Scotty: But you don't have 8 weeks, so I'll do it for you in 2

Kirk: Mr Scott, have you always multiplied your repair estimates by a factor of four?

Scotty: Of course, Admiral, how else can I keep my reputation as a Miracle Worker?

Kirk: Your reputation is secure, Mr Scott.

If I recall, this dialoge was in ST:3, but I'm not sure of that.

Re:At first read, I get dissapointed

[AnotherBrian]

Specify Relics [wikipedia.org]

PHB Response

[Golias]

It's remarkable how much longer these guys have still been alive even after they already completed their originally planned goals. Here's one thing that NASA did right.

What are you talking about? Their projections were WRONG by an order of magnitude. They should all be fired for failing to predict the life-span of these rovers accurately.

Re:PHB Response

[SEWilco]

The cost of support operations for the rovers is way over budget.

Re:PHB Response

[Golias]

Now usually, when somebody tried to riff on somebody else's joke on Slashdot, it's not even a little bit funny.

But that was hilarious. Hats off. :)

It's not "dragging" the sixth wheel

[parc]

It's more accurate to say that the wheel is free-spinning. It isn't contributing to drive power, but it's not drawing any current, either. It can still steer, so it's not off at some odd angle.

Additionally, there's only been a couple days worth of data -- noone really knows why the motor stalled.

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

[cmacb]

Doesn't really LOOK like it's free spinning:

http://marsrovers.jpl.nasa.gov/gallery/all/2/f/781 /2F195698779EFFAQ15P1210L0M1.JPG [nasa.gov]

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

[Prof.Phreak]

Depends on the motor type; it may just lock when no power is applied to it.

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

[Saeed al-Sahaf]

http://origin.mars5.jpl.nasa.gov/gallery/all/2/f/7 82/2F195787507EFFAQ67P1209L0M1.JPG [nasa.gov] Yes, it looks like it's locked up. (have a look at the pic)

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

[petermgreen]

i'm not aware of any type of motor that simply locks up when no power is applied.
the most obvious is one with a worm gear drive (often seen inside low rpm gearmotors)

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

[AaronLawrence]

That wouldn't be the *motor* that's locking up then, would it?

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

[Firehed]

Doesn't look like there's a trail to indicate the other wheels are spinning correctly, either. I'd wager that neither one of us knows enough about martian spacecraft design to say for sure. Having said that, the long gouging of dirt inclines me to agree with you.

Re:Your sig: "annulment"

[Firehed]

If you want to win off-topic of the month award, at least be aware that I stole it from ZDNet so you can blame them (their inherent lack of commas tends to throw things off, but I'm lazy; get the hell over it). Give the same argument about UCE. Once it was recoined to spam (which is an acronym, by the way, self-/sales promotional advertising message), people started caring. If you like the idea of not being able to listen to your music, go on making pointless arguements. _|_

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

[Tablizer]

They stopped using the wheel about a year ago for a while because it was having problems as if the lubricant was wearing off, and it indeed did *not* free-spin when power was not sent to it. They simply dragged it around by running the rover backward. They found it easier to control the rover by dragging the bum wheel rather than by pushing it. They only used the wheel for close-up control when rocks were being targeted. Eventually it started working properly for a while, and now won't turn at all. It does not appear they have a "free spin" mode. Dragging is it.

I beleive they have a video about the last time the wheel was left dragging. They did some test-bed simulations of an Earthly rover copy. Page down to the "Driving Uphill Backwards" portion, about half-way down the page:

http://marsrovers.jpl.nasa.gov/gallery/video/spiri t01.html [nasa.gov]
     

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.
       

Only lost 1 wheel? pfft

[Anonymous Coward]

If a dog can walk on two legs you better hope this thing keeps going, otherwise it's pretty embarassing.

http://youtube.com/watch?v=OZqVvYkCe68 [youtube.com]

Re:Only lost 1 wheel? pfft

[wik]

... but engineers are still trying to get four legs [youtube.com] to not look like a hysterical, deranged beast.

Pfft, try just ONE leg...

[ChePibe]

This little guy [homestarrunner.com] seems to make it on his own just fine on one leg. Although, admittedly, he'll prob'bly never take him a wife.

Re:Only lost 1 wheel? pfft

[archen]

Actually I used to have a dog with two legs. I named him cigarette. Ever day I'd take him out for a drag.

heh, sorry.. had to make the joke...

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.

exploration will continue

[MoFoYa]

I think its great that the mars rovers lasted as long as they have. when you consider the failed mars mission attempts, spirit and opportunity are huge successes that have long outlasted their expected lifespan. The new mars orbiter "MRO" is sure to provide more information about the surface of mars, and possible landing sites for even more capable landers in the future. my question to /.ers is this: should we be focusing so much on mars or should we be looking toward other possible outposts/life harboring worlds like europa. and the new horizons mission to pluto - a waste of time, or an exciting new learning opportunity? personally, i doubt life will be found on mars. and i'm doubtfull any significant life will be found anywhere in our solar system. but, we are natural explorers who will continue to explore, even with a bum wheel.

Re:exploration will continue

[Telvin_3d]

I think that we should explore anywhere and everywhere. We still know so little about anywhere in out solar system that any single mission is going to bring huge returns, regardless of where it goes. Frankly, if there was real investment in knowledge going on (or any real long term interest in science and research), there should be at least one mission heading to every piece of rock in the solar system large enough to be considered a moon. Part of that is that we would find out all sorts interesting things about them, and get sent back millions of desktop worthy pictures, but mostly because the biggest jumps in our technology have always come when we were trying to achieve things beyond what we had any right to expect. Many business and government leaders like to continentally forget that their products are built on the side benefits of major projects that came from areas like cold war weapons research or the space race (arguably two sides of the same coin, but that is something else), and there lies the real benefit of these missions.

Yeah, Spirit and Opportunity have let us learned a lot about Mars, but how much have we learned about remote robotics, operating machines under extreme conditions, and low maintenance designs? Personally, I think the later are the best reasons to be on Mars.

Yeah, Spirit and Oprotunity have let us learned a lot about Mars, but how much have we learned about romote robotics, operating machines under extreme conditions, and low matiance designs? Personaly, I think the later are the best reason to be on Mars.

Re:exploration will continue

[cashman73]

my question to /.ers is this: should we be focusing so much on mars or should we be looking toward other possible outposts/life harboring worlds like europa.

Didn't HAL (or Dave Bowman, or whomever the aliens were) tell us, "ALL THESE WORLDS ARE YOURS EXCEPT EUROPA. ATTEMPT NO LANDINGS THERE."?

Re:exploration will continue

[aussie_a]

For one, we need to know if there is life on Mars so as not to contaminate either or both planets.

Too late buddy. Most current scientific theories on such things say that nature has more then had plenty of opportunity (and the means) to send life one way, or even both ways. So it's quite possible one of our planets (if not both) were contiminated by the other.

Re:exploration will continue

[aussie_a]

We won't really know until we study Mars life in detail

Which many say won't be possible until we get to Mars.

Even if there is only a 1 in 1000 chance of a human-ending bug on coming back from Mars, that is still too high for comfort.

The existence of there being life at all on Mars is only theoretical, so much so that you won't get a statistic of any sort (well, of any reliability, I'm sure plenty of scientists have made claims, but I doubt they agree with each other within any realistic range), let alone the existence of a bug that can be transmitted to humans, let alone the existence of a bug that has the ability to wipe out mankind. The fact that there has to be two other criterias (both of which the possibility are currently unknown) before we can even get to a bug that will wipe out mankind, I'd say the possibility is fairly small. Much smaller then your 1 in 1000

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:Cold

[HermanAB]

Sure, they can provide transport - one way - and there is that little niggling problem with orbit insertion and parachute deployment that sometimes crop up... :)

Re:Cold

[Prof.Phreak]

Sure, they can provide transport - one way - and there is that little niggling problem with orbit insertion and parachute deployment that sometimes crop up... :)

In other words, they'll use a large trebuchet to get you there (or somewhere... either way, it will be fun!)

Re:Cold

[Petrushka]

--
Magnus frater spectate!

I don't think that sig means what you think it means. To illustrate: what it actually means is, "Big brother -- hey, you lot, take a look!" If you want it to mean what I think you want it to mean, try "magnus frater te spectat."

Re:Cold

[Fulcrum of Evil]

Linky! [everything2.com]

Centurion: What's this, then? "ROMANES EUNT DOMUS"? "People called Romanes they go the house"?
Brian: It, it says "Romans go home".
Centurion: No it doesn't. What's Latin for "Roman"?
Brian: (hesitates)
Centurion: Come on, come on!
Brian: (uncertain) "ROMANUS".
Centurion: Goes like?
Brian: "-ANNUS"?
Centurion: Vocative plural of "-ANNUS" is?
Brian: "-ANI".
Centurion: (takes paintbrush from Brian and paints over) "RO-MA-NI".
"EUNT"? What is "EUNT"?
Brian: "Go".
Centurion: Conjugate the verb "to go"!
Brian: "IRE". "EO", "IS", "IT", "IMUS", "ITIS", "EUNT".
Centurion: So "EUNT" is ...?
Brian: Third person plural present indicative, "they go".
Centurion: But "Romans, go home!" is an order, so you must use the ...?
(lifts Brian by his hairs)
Brian: The ... imperative.
Centurion: Which is?
Brian: Ahm, oh, oh, "I", "I"!
Centurion: How many romans? (pulls harder)
Brian: Plural, plural! "ITE".
Centurion: (strikes over "EUNT" and paints "ITE" to the wall)
(satisfied) "I-TE".
"DOMUS"? Nominative? "Go home", this is motion towards, isn't it, boy?
Brian: (very anxious) Dative?
Centurion: (draws his sword and holds it to Brian's throat)
Brian: Ahh! No, ablative, ablative, sir. No, the, accusative, accusative,
ah, DOMUM, sir.
Centurion: Except that "DOMUS" takes the ...?
Brian: ... the locative, sir!
Centurion: Which is?
Brian: "DOMUM".
Centurion: (satisfied) "DOMUM" (strikes out "DOMUS" and writes "DOMUM") "-MUM".
Understand?
Brian: Yes sir.
Centurion: Now write it down a hundred times.
Brian: Yes sir, thank you sir, hail Caesar, sir.
Centurion: (salutes) Hail Caesar.
If it's not done by sunrise, I'll cut your balls off.
Brian: (very relieved) Oh thank you sir, thank you sir, hail Caesar and everything, sir!
The scene cuts to a very tired Brian finishing off one last iteration of ROMANI ITE DOMUM. The camera zooms out to show the castle covered entirely in ROMANI ITE DOMUM
Brian: Finished!
Roman Soldier: Right. Now don't do it again. (Wanders off)

Re:Cold

[Petrushka]

There's no difference.

They'd be happy to send you!

[xiphoris]

Just make sure to give them your weight in kilograms, not pounds!

Late breaking news?

[Theatetus]

TripMaster Monkey, where are you?...

2 years into a 90 day mission...

[HermanAB]

Hmmm, typical NASA project, 21 months late and far over budget. :)

Shoulda got the AAA Extended Service Plan

[slickwillie]

100 mile free towing too!

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?

[HoneyBunchesOfGoats]

I have a hunch that the brushed motors NASA used in the rovers are probably a little bit more expensive and higher-quality than what you're used to dealing with on miniature airplanes. There are most likely some design issues we don't know about that made them use a brushed motor.

Re:Failed brushes?

[iggymanz]

The rover uses maxon's motors, which also are used in artificial hearts, surgical tools, and underwater robots. those aren't your mother's DC motors 8D

Re:Failed brushes?

[dougmc]

The rover uses maxon's motors which also are used in artificial hearts, surgical tools, and underwater robots

Maxon [slashdot.org] makes lots of motors, both brushed and brushless. If you look at their web site, you'll notice that most of their new motors are brushless.

As for the list of applications you gave, I'm guessing that new designs of these products use mostly brushless motors now, if only for the reason that they last longer and the brushes aren't ground down to dust over time.

those aren't your mother's DC motors 8D

My mother doesn't need a Rascal yet. In any event, I doubt these motors are that different from what use use down here on Earth. Sure, they're probably built better, with better materials and such, but the general design and layout is probably very similar.

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?

[griffjon]

IN fact, most likely they went with brushed for exactly reasons you mention: ...require an array of active electronics

Hm -- what things don't work great without a lot of shielding in space?

I'm not saying it couldn't be done, I'm saying it might've been the right choice given size and electronics-reliability constraints.

Also, as a rebuttal to the "90 days was an intentional understatement", I'd put forward that it was probably an understatement, and that the 2-year mark is probably beyond design spec. What we're seeing here is a project where everything's gone Very Well. We all know that those are rare gems, so give NASA some share of the glory.

(...they at least got their measurement units right this time....)

Re:Failed brushes?

[fbg111]

Also, as a rebuttal to the "90 days was an intentional understatement", I'd put forward that it was probably an understatement, and that the 2-year mark is probably beyond design spec. What we're seeing here is a project where everything's gone Very Well. We all know that those are rare gems, so give NASA some share of the glory.

You're right, I attended a presentation by Steven Squyres, Mars Rover PI. During the QA I asked exactly this question and he pretty much said the same thing. Their goal was 90 days, but they overengineered the rovers to counter the uncertainty such a complex mission would entail. They wanted to guarantee 90 days, which they did. They also got really lucky - just as Rover was about to go offline due to dust buildup on its solar array, it crested the ridge of a crater and a gust of wind blew all the dust off, significantly extending its longetivity. Given Mar's thin atmosphere, they got really lucky to be in the right place at the right time for such an event.

Re:Failed brushes?

[dougmc]

Brushless motors are more complex

Actually, they're simpler, since there's no brushes. Generally the permanent magnets are on the shaft that rotates, and the electromagnets are on the part that doesn't, with three wires coming out (and possibly five more for a sensored model, but the sensorless models are more popular now.) Ignoring the older sensored models, the brushless motors are signifigantly simpler than brushed motors.

and require an array of active electronics inside them to produce the AC and modulating magnetic field they need to operate.

Actually, the electronics are generally outside the motor, in an ESC (electronic speed control), but I'll admit that it doesn't matter where they are. Brushed motors use an ESC as well to control the speed, so you've got some electronic parts either way. You're right that a brushless ESC is more complex than a brushed ESC, but the difference isn't really that signifigant.

Most brushless motors are lower torque than their brushed counterparts. (majority, I know there will be exceptions)

Torque is a function of motor design. It really has little to do with brushed or brushless, and you can certainly make high torque brushless motors if desired. If you need a motor with more torque but the same power (and less speed, since power = torque * speed) you either design an appropriate motor, or adjust your gear ratio so the amount of torque your motor does provide is appropriate for your use.

Brushed motors are more mechanical in nature and suffer from the usual mechanical issues, but they are less prone to failure than brushless.

And I disagree completely. Brushes wear out. (So do bearings and bushings, so it's a race to see which one wears out first, but in my experience, it's usually the brushes.) And for anything where you control the speed of the motor, you'll have an ESC (electronic bits) that can fail, but as a general rule of thumb, electronic bits are more reliable than mechanical bits.

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.

Even the brushed motors will have ESCs on devices like the Mars Rovers (since the alternatives suck for a robot) and so either way you'll have active electronics to deal with. Also, the Mars rovers aren't operating in space -- the atmosphere (thin as it is) and magnetic field of Mars do provide considerable protection (compared to a satellite or something that is in space) against things like ionizing radiation.

This stuff isn't rocket science. Even things like scooters [rascalscooters.com], Segways [segway.com] and electric cars use similar technology.

The technology of brushless was available when the rovers were designed, and I can't imagine NASA not seriously considering them.

I'm guessing that the AC who posted in this thread was right on -- that NASA used brushed motors because they've used them in the past and they worked fine then, so they'll work fine now -- when you're spending billions of dollars on things that can't be repaired in the field, you tend to stick with what's tried and true rather than what's 15% more efficient but not quite so well tested. I suspect that future rovers will have brushless motors, however.

Re:Failed brushes?

[Fulcrum of Evil]

as a general rule of thumb, electronic bits are more reliable than mechanical bits.

Does your general rule include high radiation environments? Mars has an atmosphere, but not much of one.

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 [aero.org] 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.

Re:Failed brushes?

[Tablizer]

While NASA is very proud to have exceeded expectations with the Rovers, I think this is mostly because their expectations of solar powered vehicles were so abominably low. Perhaps they will take things more seriously from now on.

Their budget was for 90 working days. That is how the contracts stipulated payment. Further, the solar panels have been cleaned repeatedly by dust devils. Experience with the 2 Viking landers showed that dust builds up pretty quickly on probes and they understandably factored this into the design. The dust devil cleansing was a lucky accident. They had no certain landing areas picked out when the rovers were being designed, so they could not expect to rely on landing in whirl-windy areas, even if such could be identified from orbit. (It appears there are more dust devils near the equator than where the Vikings landed. However, there are probably also regional variations, based on the "criss-cross" patterns seen from orbit and created by dust devils.)

In fact, it has been a while since Spirit has been cleaned by one, and that is one reason they have to rush to sun-facing slope. Future crafts that land in non-whirl-wind areas of Mars may face an early demise if they rely on solar (unless they bring their own cleaning systems).

I believe Spirit had about 2 whirl-wind "cleaning sessions". Next year when the winds pick up it may have 4 or zero. It is the luck of the cards that determine it, and so far only during the summer. Thus, Spirit may have a sluggish spring.

In short, I see no reason to bash Nasa's general approach. Sure, it would be nice to have a fat budget to include bells and whistles for extended missions, but the budget is the budget. Plus, they had a fairly short ramp-up time between approval and build. They had to use a lot of existing Sojourner technology almost as-is to reach the deadline.
         

Re:Failed brushes?

[Rakishi]

None of the design team expected the solar systems to work well or last long.

Dust buildup was supposed to render them useless after a while; luckily it seems some wind solved that problem for them.

The Rovers both carry a massive weight of non-rechargeable batteries (alkaline cells, or something) and very little of rechargeable cells. Unable to even discard the spent battery cells. The rovers have been carrying the spent cells ever since they ran flat, doing horrible things to the power to weight ratio and other such bad stuff.

Asfaik both rovers use Lithium-Ion batteries, well specially designed ones. Older rovers used non-rechargeable batteries, most likely to avoid potential failures.

Also, an efficient asynchronous electric motor design would have been about 30% the weight (or 70% more power, pick one) and running at greater than 90% efficiency. And I'm not talking untested prototypes, either. Motors of this design and build have been run in Solar Car races for the best part of a decade.

There is a difference between running something on earth with a checkup right before it's use, and sending something into space for over a year and having it then run (With no tune up) on an alien world. For example on Earth the radiation isn't high enough to fry normal electronic circuits. Not to mention that your nice solar car doesn't get to deal with temperatures that make Antarctica look pleasant.

Same thing with your rechargeable batteries, they may work great when they're brand new and in an ideal environment but given a few years and they may be worthless.

Efficiency was not on their mind because having it work was more important.

I'm still amazed....

[zappepcs]

This robot was supposed to last about 9 months... I think it has gone waaayyyy past the rated mileage for that wheel. The fact that it is free-wheeling and not a major hinderance is just a testament to how well it was actually designed. This 3x life-span thing is incredible if you take into account all of the challenges that the designers faced. I dabble in hobby robotics, and I can attest to the fact that designing a robot that does as well as it has done for as long as it has done, is a major accomplishment. Think about the warranty that you get on a new automobile... if it performed past its expected lifetime of usefulness to the tune of 300 percent, people would be driving vintage cars all over the place.... it is an amazing robot and planetary exploration vehicle!

Re:I'm still amazed....

[zappepcs]

Those are very good points, but I think that most of the reason for the unexpected longevity of the mars rovers is that they expected dust from dust storms to critically hamper the solar panel operation. What was a surprise is that the wind quite effectively kept the solar panels clear of dust, giving a much longer lifetime. I don't think that the engineers expected to have to worry about the motors lasting 36 months or more since it was not expected. Mars has quite extreme temperature swings, so the engineering is probably worth what it cost to build the rovers. Mother nature is something that just can't always be anticipated, unless, of course, you anticipate problems due to mother nature. In that case, any positive turn of fate leaves you in the position of underestimating vehicle longevity.

The temperatures, radiation, dust, vibration... these are very harsh environmental variables. It is just amazing that they are still running. I'm sure that NASA is still as amazed as we are, and pleased to be continuing the scientific research at what amounts to a budget bonanza.

You are most probably right in thinking that what was learned this time around will be incorporated in the next planetary exploration vehicles, and a longer lifetime expectation will be part of that. In line with that, recent NASA un-manned missions have been incredibly successful. I look forward to more solar system exploration, and also to commercial exploration based on NASA work.

Now that we know how to build robots to explore Mars, we can build them to explore other planets, and that ion engine thing is a Trekie's dream. The expectation bar is rising, and that is a good thing. The X-prize and similar efforts are creating huge scientific 'wealth' for all to use. Its all very cool.

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.

The Truth...

[Tatarize]

They made Spirit and Opportunity do some battlebot stuff. And well, Spirit is a puss.

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

[deong]

It's not that simple. The rovers are full of fairly sophisticated sensor packages, most of which can't handle the extremely low temperatures on the Martian surface. They need the batteries to basically, well, run the heater.

The principle investigator for the missions has written a book, "Roving Mars", that really is worth the read.

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

[ScottMaxwell]

It's not that simple. The rovers are full of fairly sophisticated sensor packages, most of which can't handle the extremely low temperatures on the Martian surface. They need the batteries to basically, well, run the heater.

Bingo. Indeed, it's even worse than that: if you can't run the heaters, all of the electronics undergo more extreme thermal cycling. This causes components to contract, flex, break, etc. Several critical components -- e.g., the CPU -- have no redundancy; if one of those goes, the whole rover goes.

This failure is the most dangerous thing to happen to Spirit since the flash anomaly on sol 18, when we effectively lost contact entirely for several days. Frustratingly, we're within sight of a safe haven -- only about a football field away -- but we might not be able to get there. Some people on the team think that if we have to drag a wheel, we can't climb the slopes we need to climb to make it to safety. I would just hate for Spirit to go this way; it would be like dying of thirst within sight of water, and she deserves better. (On the other hand, one thing I've learned is this: never bet against the rovers.)

The principal investigator for the missions has written a book, "Roving Mars", that really is worth the read.

Agreed! And since Steve's such a great guy, I'll linkify [barnesandnoble.com] that. :-)

Also looks like it's coming out in paperback [barnesandnoble.com] soon.

good point

[artifex2004]

I figured it had to be something obvious I was missing :)
And the book is on my buy list, now, since you're like the 4th person to tell me it's good.
Thanks.

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

[WoTG]

It's probably much more useful to use the rover for a few minutes a day than to let it sit idle for several months. After a long break, who knows what will break, stick, or die. The rover is well past it's best before date already, anything to reduce the stress on the machine is probably a good idea.

Pit Stop

[SuperKendall]

Hopefully at the next Pit Stop the guys that are wiping down the solar panels will also jack it up and change out the wheel.

Ten seconds! Go!

I am saddened...

[rice_burners_suck]

...to hear that the rover has lost a wheel,
though pain it does not feel.

Now it limps along the Martian soil,
alone in a great vastness of red sand and rocks.
I hope it reaches the top of the slope,
else alas for naught will it toil.
For in that vast desert there's no telephone box.
Nor much chance for hope.

Like the injured lone explorer,
Oh! What a horror!

it will suffer its demise,
Alone on that alien world,
Its nearest neighbor far away,
as no one hears its cries.
The wrath of Mars is unfurled,
And there alone will it lay.

Re:I am saddened...

[bloodstar]

For in that vast desert there's no telephone box.

Well, The Doctor could whip on over in his TARDIS and make a quick rover^w house call!

Tire tracks, not water

[tilde_e]

It is so interesting that we leave tire tracks on other planets. They may be that the first signs of life we find, or that other beings find.

Imagine the tension if we found ourselves face-to-face with a foreign martian rover!

Re:Tire tracks, not water

[Dr. Eggman]

Not quite. Martian weather is quite likly to blow away the tracks before anything found them.

You can get your Martian weather forecast here: http://astro.sci.uop.edu/~harlow/weather/mars.html [uop.edu]

One Wheel Dragging?

[Derling Whirvish]

One wheel dragging huh? Must be that the Mars rovers are manufactured by the same company that make the shopping carts for Walmart.

Overtime?

[DeadboltX]

"NASA is reporting that two years into its 90-day mission"

Talk about overtime, you think the rover gets time and a half now?

Re:Great...

[Anonymous Coward]

Dumbass. 5 != 3

Re:Great...

[Anonymous Coward]

My tricycle had training wheels.

Re:Martian AAA

[Saeed al-Sahaf]

Let's just hope it's not the same thing that happened to Spirit Rover [siliconsatan.com]...