Sometimes the chain of measurement traceability—the unbroken series of links between a calibrated instrument and the official NIST standard—can get pretty long. But 250 million kilometers is remarkable, even for the National Institute of Standards and Technology (NIST).

That’s the current distance between the Curiosity rover on Mars and the temperature labs in Gaithersburg, Maryland, where the calibration process began for several small but critically important temperature sensors that monitor the rover’s power generator.

“They’re all handmade and hand-customized,” says Chris Albert of Sensing Devices Inc. in Lancaster, Pennsylvania, who designed the sensors to NASA contractor Teledyne Energy Systems specifications. “Each one has to be calibrated, and each one has to have NIST traceability.”

Figure 1: Physical Measurement Laboratory (PML) physicist Michal Chojnacky (right) demonstrates the method used to calibrate platinum resistance thermometers. At left is sensor designer Chris Albert.

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