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Mars Rovers Have Incorrect Instruments Installed
Christopher Reimer writes "The New Scientist is reporting that the twin Mars rovers, Opportunity and Spirit, has instruments installed in the wrong rovers. From the article: '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.'"
It's not intentional. Building something exactly to spec is impossible. The sensors are not identical for this reason. Not really a problem when you do a proper calibration.
Of course, it becomes a problem when you use the wrong calibration curve for the sensor.
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To clarify the summary: it's not that the WRONG instruments were installed, but that the SAME instruments were installed but calibrated for the OPPOSITE rovers. So, the data have been slightly off in a predictable way. In the end, it's not too surprising nor is it devastating. The data is still valid and is being readjusted.
They're the same device on each machine, with the same function. The only problem has been that the data received has been interpreted with the wrong calibration adjustments. Swap the calibration adjustments and rerun the data, and it'll be correct.
It would have been far worse if, say, one had a spectroscope and the other had a *drill*, and they were swapped, and each rover couldn't use the other's tool. And in that kind of a switch, it would be really bad, because the two devices would be visually distinct. But the swapping of two devices that are 99.99% identical, on two rovers that are identical, is no big thing.
Compared to the fact that the rovers are still running long after they were expected to die, this is a tiny, tiny thing.
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The sensors are built and configured the same, and the raw data they collect is sent back to earth.
However, nothing is perfect, and each sensor has slight imperfections. Before they were sent up, each sensor was measured so that those imperfections could be accounted for. This calibration data is unique to each sensor. They used the calibration data for Spirit on the data from Opportunity, and vice versa. Luckily, since they still have the original(un-corrected, raw) data, it is easy to correct.
one word: Tolerances.
when you have 100 resistors at 0.5% tolerance, you are gonna have drift, and you will have to calibrate them to the right parts, you can make 100's of those cars of the same make and model, but none will be exactly the same, especially when you have sensitive equipment. (Think odometer)
>once lost a Mars spacecraft because engineers mixed up metric and imperial units.
I'm getting pretty tired of this sound (text?) bite the media throws out. It wasn't mixed up units; it was error accumulation from switching back and forth between the units.
Identical parts are not exact duplicates. Go to Radio Shack and buy some resistors, all marked for the same value. Take them home and measure their actual values with a multi-meter. You will find that the measured values are scattered over a range that is centered on the marked value of the resistors. That's why each resistor has a tolerance specification. For example, a resistor may be marked 47 ohms, plus or minus 5%. The value of the resistor is guaranteed to lie within that range. It isn't guaranteed to be 47 ohms. The same thing applies to capacitors, transistors, and other parts. Circuits built from these parts inherit some of the variability of their component parts.
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They don't need to upload the files to the rovers because they're getting raw data here on Earth. They simply need to switch the calibration data in the software.
This is not a major thing. Yes, all the data collected from these sensors will have to be re-analyzed, but that should be a simple thing.
Damn your Dumb! Read before posting dumb things. No two things are exactly the same even if designed as such. And yes you can get in two identical cars and one will perform different.
It's a calibration, the whole concept is no two things are the same. Any piece of instrumentation needs to be calibrated and that calibration is set for that device. No manufacturing can produce 2 identical things, just not possible since the two items could not share the same time and space in the universe together thus both are going to be slightly different.
Anytime you get a piece of gear, you get it setup, then you take some means of calibrating it and test it with something that has deemed to be as accurate as possible. Maybe some source such as a rock. But basically anything that will provide a common test basis for the device.
So say you are measuring temperatures on something in a lab. You set up a big system for collecting data off a bunch of thermocouples. Each one has it's own channel through it's own voltage modules and thermocouples and so forth. So you take a calibrator and have it feed a signal through the system to mimic a thermocouple. you get a calibration curve for a channel, then you go to the next channel with the same device and do the same for the next channel, this will be a different calibration. and then you work through them all. I have system set up with 16 channels at work and all use the same parts, but there is about 4 closely similar calibrations across the channels, but no two channels follow the same calibration.
NASA did the same, they built the devices, then calibrated them with the same rocks, and developed a calibration curve for each system, and that was to be kept with each rover, they swapped the instruments, so now they switch the calibrations and everything is fine.
This all goes back to simple accuracy and how close you can get things, but bottom line no two things are the same. Look at computers, you can have 100 computers, exactly the same built right in a row, with the exact same software and so forth. Turn them on and let the run under exact same conditions, some will have hardware failures, some will have software get wacky on them and so forth. It's just the way it works.
RTFA. NASA swapped the instruments inadvertently but since both the rovers and the detectors are manufactured identically the only consequence was that we were using the calibration data file from one instrument to analyze the data coming from the other. Swap the calibration files so they are coupled to the correct instruments again, reanalyze the raw data, and the problem is solved without having to privatize NASA.
How can i possibly advocate for a mars mission when they can't even get this shit right?
The Mars mission is stupid but not for the reason you give.
As a science teacher, I weep. For any instrument, it's important to perform calibration: to check the instrument against known samples, values, whatever, so that you can take the unique response of the instrument and convert it into a believable interpretation of the data. Every instrument has its own peculiarities, resulting from the (essentially unknowable) history of the construction of the instrument. Most of these features are entirely unimportant, if you know about them. So you run calibrations and figure out how to correct for the individual features.
NASA did its job here, in that the instruments were calibrated. Yay. Then they mixed up the instruments and installed package A into rover B, meaning the calibrations were in fact wrong. Luckily they keep all the raw data, so they can simply run it through the correct calibration filter now. Double yay.
But for all those saying "This is a small thing.": Wrong. They mixed up an entire package. Didn't it occur to anyone to actually, you know, label the two? Or to in fact make sure they weren't in the same lab at the same time? Or if that proved impossible, to keep track of which was which? Or to -- oh, I don't know -- check which package they were installing?
Excusing this as "just a minor thing" is akin to minimizng a case where you fall asleep while driving and are awakened by the rumble strips on the side of the road. Sure, you fell asleep. But you woke up and no one was hurt. No harm, no foul, right?
A minor screw up on its own, it still speaks volumes about NASA's continuing inability to cross all the t's and dot all the i's. And it's a pretty close relative to the error that cost us Mars Observer.
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"On September 27, 1999, the operations navigation team consulted with the spacecraft engineers to discuss navigation discrepancies regarding velocity change (V) modeling issues. On September 29, 1999, it was discovered that the small forces V's reported by the spacecraft engineers for use in orbit determination solutions was low by a factor of 4.45 (1 pound force=4.45 Newtons) because the impulse bit data contained in the AMD file was delivered in lb-sec instead of the specified and expected units of Newton-sec."
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