There are a few other instances, I think, on other non-NASA aircraft where these kinds of things have been done before and they’ve been successfully done. One of the things we’re concerned about is, we’ve modeled extensively and we believe that we’ve got the problems solved, but of course we’re worried about acoustics in the cavity when you open the door and you’ve got the air-stream blowing by. We’re very interested in that airflow along the outside of the aircraft and what sorts of things happen as we get to the ramp at the door. So a lot of the early testing that’s done will be to characterize the telescope – how well it points and its stability – and how well we see out of the cavity.

NTB: What about pressurization throughout the rest of the aircraft?

Austin: The dome-shaped rear pressure bulkhead that airline passengers may be familiar with has been removed and replaced with a unique SOFIA design. The bulkhead – this flat, very thick bulkhead in which the telescope is mounted and pivots on this spherical bearing – that’s the pressure boundary between the cabin and the remainder of the telescope aft of that. That’s been extensively modeled.

NTB: I would think it affects the stress patterns in the rest of the airframe, too, right? Were any other major modifications made to accommodate this?

Austin: In terms of the actual specifics, certainly one of the challenges is the aircraft fuselage is certainly not a rigid structure. And now we’ve put this massive bulkhead in the aft part of the cabin, so we not only have the pressure differential across the bulkhead, but now we have a very stiff part of the aircraft that didn’t used to be there. So a lot of work was done to transfer those loads effectively into the rest of the airframe without having enormous stress concentrations. Again, that’s been modeled and instrumented quite a bit and those things, of course have been of the utmost interest, not only just basic aircraft controllability and how the aircraft is functionally compared to a normal 747SP, but structurally what’s going on in the airframe with this modification. That’s really been, and will continue to be, the focus of these early flight tests.

NTB: Aside from the telescope, which is the major part of the payload, what types of other instrumentation will the plane carry to support its mission?

Austin: Well, we’ve got the telescope, and we’ve got a large science instrument. I don’t recall now the maximum mass of the science instrument, but it’s maybe 500 – 1000 kg, or something like that. They’re fairly large and, of course, they carry cryogens. Associated with the instrument are the electronics to actually run the instrument and store the data, so along with the instrument comes a couple of racks of electronics.

In a sense, think of the aircraft as a ground-based telescope, as what goes on at the top of a mountain in the dome. Fundamentally the arrangement of the instrumentation and the electronics and systems onboard the aircraft doesn’t change. You’ve got the telescope there, that’s kind of maintained in a steady state, and then all we do is swap out the instrumentation. That’s pretty much all that we change. Of course, like any observatory we’re expecting to be operating in a continuous improvement program. We’re taking a lot of housekeeping data, as well as scientific data to really understand how well the observatory is operating, to make sure it’s operating efficiently. That will also give us some insight, between the scientific data and the housekeeping, or engineering, data. It’s one of the areas where, with some hardware and software improvements, we could improve the effectiveness and the performance of the observatory. That will be an ongoing activity.

NTB: That leads nicely into the final question. When do you expect SOFIA to begin collecting scientific data and what typical operational scenario do you envision for it over its career?

Austin: Presently, you’re probably aware that we’ve been going through flight tests, so we completed the functional flight checks for the aircraft from Waco to Dryden in the April-May timeframe. We’ve been conducting a series of what we call “closed door flight tests.” These are probing the aircraft performance envelope to understand how it’s performing and, again, look at the stresses and the controllability of the aircraft.