>>11780777After watching this video, I got to thinking about the WMAP engineering itself... How stable is the WMAP hardware over time? Given the tiny temperature variations measured, the overall WMAP electronic system stability should be a significant design constraint. BTW, the measured CMB temperatures show up as variations in measured RF (radio frequency) amplitudes at specific frequencies (the bands referenced in the video).
Here is a very interesting WMAP Observatory Thermal Design and and On-Orbit Thermal Performance document from the NASA Technical Report Server at
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030093646.pdf There's a lot of stuff only and RF Electrical Engineer or Physicist can appreciate in it, but the statement I find most interesting is:
>The mission was designed to keep pixel to pixel variance due to the systematic effects of the instrument to 5% of the random noise. The total systematic error was therefore specified as <5 micro-K rms per sky map pixel, which translates to a key thermal stability requirement for selected microwave components of <0.5 milli-K rms per spin period. Another thing I find interesting about the design is that it utilizes passive cooling. Control of the temperature of high accuracy RF components is essential for consistent results. Variations in the RF component temperatures will result in variations in readings, especially when looking for stuff in the noise regions.
All-in-all, I would expect variations in the CMB map over short periods of time let alone longer multi-year periods, and likely the overall system measurement variations (inherent system noise) swamps out the desired CMB data.
