Following up on @TomSpiker's answer, Lunar Prospector carried an IR lunar limb sensor made by Ithaco. It's described in the Lunar Prospector Mission Handbook as (page 4-15)
4.2.5.3 Earth/Moon Sensor (EMS)
The Lunar Prospector Earth/Moon Sensor (EMS) is manufactured by Ithaco Space Systems. The EMS (P/N P108SA12), which consists of optical elements, infrared filters, a detector/sensing element, and associated electronics, provides electrical signals representing the 30 to 100 micron radiometric profile of objects (earth, moon and sun) as the sensor optics/detector scans across them. The scanning motion is provided by the angular rotation of the Lunar Prospector spacecraft. The analog output signal, representing the radiometric profile, goes to the C&DH electronics where threshold detection defines the leading and trailing edge of the scanned body. The leading and trailing edge threshold transitions are time-tagged and telemetered to the ground for further processing to (a) determine the angle between the LP spin axis and the nadir vector to the scanned body and, in conjunction with data from the sun sensor, (b) determine the dihedral angle between the sun and the scanned body.
There's also information about power, size, launch configuration, etc in that document.
Via $\lambda_\rm{peak}$ (microns) = $2900/T$ (K), the "30 to 100 micron" IR wavelength band correspond (as peak emission) to temperatures down to about 100 to 30K, well below lunar surface temperature even at dawn.
Incidentally, if you want to see the computations needed to convert the sensor data into attitude information, there's a description starting on about page 34 of the Lunar Prospector Ground System Software manual.