Why is NEOWISE used for galactic observation?
After WISE ran out of cryogens to cool its detectors it was re-purposed to look for asteroids.  This was possible because the detectors for 3.4 microns and  4.6 microns could work at higher temperatures than the other detectors and passive cooling gets the spacecraft to 74 K.  It had already finished an all sky survey so there were no new deep space targets for it to study and, with only two detectors, the science would not be as significant, but it has been great as a detector of moving objects like asteroids since, for this, just one band-pass is enough.