This is an article from new scientist..... I find it amazing that this kind of mix up could occure in something so important and costly

"NASA's Mars rovers Opportunity and Spirit are identical twins - so alike that they even fooled NASA. Researchers have discovered that they sent the robots to Mars with an instrument meant for Opportunity inside Spirit and vice versa. While the bungle does not undermine the main scientific conclusions drawn from the data collected by the rovers, it is an embarrassing slip-up for a space agency that once lost a Mars spacecraft because engineers mixed up metric and imperial units.

The rovers made near-perfect touchdowns on the surface of Mars in January last year, and their mission has been considered an unqualified success. Spirit and Opportunity provided the first irrefutable evidence that there was once liquid water on the surface of the Red Planet and are still roaming long after their scheduled 90-day mission.

But something was worrying Ralf Gellert of the Max Planck Institute for Chemistry in Mainz, Germany. Gellert runs an instrument on the rovers called the alpha-particle X-ray spectrometer (APXS), which analyses the chemical composition of rocks. Opportunity had found higher concentrations of certain elements in the soil at its Meridiani Planum landing site than Spirit had at the Gusev Crater, but on a windswept Mars the concentrations should have evened out all over the planet.

Gellert published the data last year (Science, vol 306, p 1746). "No one really asked about the differences," he recalls. "I thought about it very, very heavily, but I couldn't come up with a solution."

“The bungle does not undermine the main scientific conclusions. This is a lucky case where the data makes more sense now”"Now the reason for this is obvious," Gellert told New Scientist. "We found proof that we unintentionally swapped both instruments." Spirit is carrying the spectrometer destined for Opportunity, while Opportunity is in possession of Spirit's.

Although their designs are identical, each instrument is unique because of quirks in the materials they are made from. So before the rovers were launched, each instrument was calibrated using known rock samples. The measurements from each rover are then processed using the calibration files, but because of the mix-up, researchers were using the wrong ones. As a result, small errors have crept into the APXS results, affecting measurements of sodium, magnesium and aluminium abundance.

Fortunately, now that the goof-up has been spotted, it is easily fixed by reanalysing the raw data with the right calibration. Corrected values for the first year's data will be available soon, says Steve Squyres, the chief scientist for the rovers. The corrections are very small because the instruments are so similar, he says. "None of our substantive scientific conclusions are affected." Gellert is relieved: "This turns out to be a lucky case where the data makes more sense now."

Squyres is "not embarrassed at all" about the slip-up with the rovers. "It was an easy mistake to make," he says. "It happened during some very busy and stressful times." He also says it is not fair to compare it to past mishaps (see Box) because the spacecraft suffered no damage. "There isn't going to be an investigation. We know when it happened," he says. "There was a point when both of them were sitting on the same bench, and that has to have been it."

From issue 2489 of New Scientist magazine, 05 March 2005, page 18

just one of those cheeky gremilins doing a swap of the calibrating data

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Thats kinda funnny...

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yah, and the amount of money that is invested in these projects... you'd think they would make sure something they were going to send millions of miles to gather data would have the *correct instrument to do so... but good thing in this case it didn't really matter since they were the exactly the same.

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“Squyres is ‘not embarrassed at all’ about the slip-up with the rovers.”

What a dumb thing to say. He should be embarrassed—mortified and humiliated is more like it.

I would have appreciated something more like, “We are very, very disturbed at this situation. While we can, and will, completely recover from this error, lapses of this nature can have the most dire consequences including losing the mission. This problem has shown the necessity to re-evaluate all of the mission critical functions in light of the potential for this type of issue. And we will proceed to close this barn door, and any others we can ferret out. Thank God, in this case, before the horse has fled. This has been a sobering lesson in humility.”

Don’t get me wrong. NASA does very marvelous things. Today, and yesterday, NASA is almost the whole story when it comes to space exploration. Consider:

Missions to Mercury: NASA 2. Rest of the world –0-.
Men on the Moon: NASA 14. Rest of the world –0-.
Rovers on Mars: NASA 3. Rest of the world –0-.
Missions to Jupiter: NASA 6. Rest of the world –0-.
Missions to Saturn: NASA 5. Rest of the world –0-.
Missions to Uranus: NASA 1. Rest of the world –0-.
Missions to Neptune: NASA 1. Rest of the world –0-.

But NASA's not perfect, and it needs to be close to perfect as is humanly possible. I think it's obvious that not being embarrassed by an awful goof is a poor start towards perfection--or even "pretty good."

Bob

Bobunf, you should know they're not going to admit something like that. Their resources are too small as it is, they are not going to risk getting any bad publicity because that could drop their public approval which means a smaller budget. Of course they would be embarrassed, but they aren't going to admit it, they simply tried to make the best of it.

There seems to be a bit of denial going on. The scariest bit of the whole quote is that they don't know how it happened, but they have made an assumption about when, where and how it occured, so therefore there won't be an investigation.

As a computer analyst, I can tell you that the bugs that you haven't analysed thoroughly, but you just assume you know how they must have happened; those are the ones that come back to bite you.

Yes Bob. I wunder if there's a blond at work there. We can all remember waiting for the news of that Mars lander. lbs of thrust vs kilo's of waight. . . Oops. Now we are told of a goof in the placment of the right parts on the wrong craft. Fortunatly its done little or no damage other than the embarasment of the puplication of this blunder. The fact that we are aware of this is good for us all. If only to remind us to err is human. whats wrong with these people,? Did they not have a diferent part # . Craft A and Craft B. part number A-256, or part B- 256. Why is it not that simple.? Shame on you and feel ashamed. This is rocket science. I expect more of you. :angry:

Well,I'd sure be embarassed!In light of the recent terrible loss of life within the Space Program I'd be looking for the nearest exit!

Many identical items are a safety necessity in order to supply the host of back-up systems,especially in a manned craft,and the latest SST crew must fly, reminded of yet another potential problem that's not potential,anymore.

I have great admiration for our scientists and astronauts and am certain they must have taken steps long ago to deal with "like kind" equipment.

But,it's rude to criticize without offering some possible solution,so please accept my humble, crude attempt at rocket science technology, and I ask that you don't laugh:simply machine a shallow detent onto the mounting surface,to be matched by one on the instrument,a certain distance from the centerline or other easily measured point.Each instrument's would be at a different distance so no two could fit anywhere but in it's own place.Sorta like the notch in a stick of SD RAM that insures one's not putting it in backwards.Simple,cheap and effective. h34r:

C'mon,I asked you not to laugh!The point is this was a problem that should never have occurred considering how easy a cheap,reliable fix could have solved it.