Upon further rabbit hole on this I found they actually fly between 39kft and 45kft and around 500mi/hr (434knots). Which made me take a look at the above pics and the ones on the SOFIA site to look at this idea of a bulkhead. I now believe what we are seeing in the picture above is in fact that bulkhead and the stuff we see are cameras and instruments attached to the 100" scope and likely feed through optics of some type, then to the scientists in the pressurized cabin at their stations.

Here is a quote from the Sofia video page:

"Inside NASA's SOFIA Airborne Astronomical Observatory
As the world's largest flying observatory, NASA's Stratospheric Observatory for Infrared Astronomy, or SOFIA, is a unique space-science asset. SOFIA incorporates a 19-ton German-built telescope with an effective diameter of 2.5 meters in a highly modified Boeing 747SP aircraft that flies astronomical science missions at altitudes between 39,000 and 45,000 feet, above 99 percent of the infrared-blocking water vapor in the atmosphere. Capable of conducting observations in visible through far-infrared spectra from any part of the globe, SOFIA provides access to a spectral region not currently accessible by ground or space telescopes. A joint program of NASA and the German Aerospace Center DLR, the SOFIA observatory is based at NASA's Science and Aircraft Integration Facility in Palmdale, Calif., a satellite facility of the NASA Armstrong Flight Research Center. NASA's Ames Research Center manages the science and mission operations in cooperation with the Universities Space Research Association and the Deutsches SOFIA Institut. SOFIA's Airborne Astronomy Ambassadors program provides educators hands-on experience as they work with scientists during missions on the flying observatory."

Here is the YT video...11:25 and worth the watch to answer some of these questions and more.



I see the value of it now much better as well as its uses.