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There seems to be a disagreement between two figures you have of the focal plane. Which is right?
Posted by Elena Scire on 21 November 2008 11:22 AM
Yes, there is a pair of figures, and both figures actually appear in the Spitzer Observer's Manual (SOM) (in addition to several other places) - one is Figure 2.1, and the other is Figure 4.5. These figures have caused a lot of hair-pulling and screaming all over the project for many, many years. The root of the confusion is that one (Fig 2.1) is the science apertures projected onto the sky, e.g. looking out of the telescope, and the other (Fig 4.5) is looking down the telescope. There is an inversion between these projections because Spitzer is a Cassegrain telescope. And, thus, the Sun appears to "flip sides."

These figures caused enough grief that there is an internal report that starts with photos of the spacecraft as it's being assembled and works through all of the possible combinations for another 20 pages. Both figures in the SOM are correct!