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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.'"
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.
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)
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.
Mea navis aericumbens anguillis abundat
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.