SOFIA (Stratospheric Observatory for Infrared Astronomy) is a joint venture between NASA and the German space agency, DLR, involving the use of a modified Boeing 747SP aircraft as an airborne astronomical observatory. Edward Austin is the SOFIA Science and Mission Operation Project Manager.

NASA Tech Briefs: You are currently the science project manager for the SOFIA, which stands for Stratospheric Observatory for Infrared Astronomy.

Edward Austin: That's correct. About a year ago the SOFIA program was split. Originally there was a single program and all of the project and program work was done under just the program managers. Now the program manager is at Dryden and underneath that there are two projects that make up SOFIA during the completion of development and during its operational life. There's what we call the "platform project," which is the aircraft engineering and development and flight testing at Dryden, and then we have the science project – SOFIA being a science project – I manage the development of the science systems and science center, actually, development and maintenance of the science vision and implementation of that vision at Ames.

NTB: Exactly what does NASA hope to accomplish with the SOFIA project?

{ntbad}Austin: Well, a lot of what we get astronomically in terms of our observations, people are familiar with - visible light, images and what-not. The real product we're getting from the infrared part of the spectrum is that you can actually observe black holes and phenomenon through dark clouds. A lot of things that are obscured in the galaxy that we would want to see visibly, you can't see. So we can use infrared and we can penetrate all kinds of obscurations and we can look at black holes and star forming regions in the center of the galaxy and stuff. You can actually determine molecular composition of regions of stars and planet formation; in looking at what are called occulations, we can probe the sizes, atmospheres, and possible satellites of Kuiper Belt objects and newly discovered planet-like objects in the outer solar system.

The benefit that makes SOFIA very unique is a great deal of the infrared spectrum is actually blocked by water vapor in the earth's atmosphere. So the benefit of putting a telescope on an aircraft is that you can get above 99-percent or so of the water vapor in the atmosphere. If you're flying an infrared telescope around at 37,000 to 45,000 feet, there are a lot of things that you can now begin to observe that you cannot possibly observe on a ground-based telescope from the highest mountains. That's what's really kind of unique.

Obviously we've got the Spitzer space telescope, and there are other space- based observatories…

NTB: Like the Hubble and the proposed James Webb Space Telescope, which would be another infrared telescope?

Austin: Exactly! You've got Herschel [Space Observatory] and there are a bunch of space-based programs that, of course, don't deal with any water vapor at all, but again, the benefit of SOFIA is the kind of instrumentation we take off and land with every day. We can swap out state-of- the-art science instruments and state-of-the-art infrared detectors that are really geared for looking at particular kinds of phenomenon and hopefully obtaining specific kinds of science results. You can't do that so easily on a space-based platform. It's extremely expensive to go service Hubble.

So, we can switch-out instruments. We also have the capability to fly state-of- the-art instruments with lower technology readiness levels because they're not going up and orbiting the earth for years, making them expensive or impossible to replace. We can have an entire mix, so we kind of fill a gap between the ground-based systems, and we have some advantages over the space-based systems. It's actually a nice complement to the rest of the observatories that are either operating or in development.

NTB: Okay, those are the advantages. Obviously a Boeing 747 is a moving platform and anyone who has flown knows that even on a smooth flight there is a certain amount of vibration and turbulence. Won't that affect the images being collected by the telescope?

Austin: Actually, no. The telescope has a well-developed vibration isolation system and inertial stabilization system. [Thanks to its] predecessor, Kuiper, the US/German SOFIA team has actually gotten a lot of experience on telescopes and aircraft. Essentially what you'll see is the telescope appearing to move while you're in flight, but in fact the telescope will be very stable and I think our pointing accuracy will be within a couple of arc-seconds.

The telescope will be very stable when pointed at an object. The aircraft is essentially moving about the telescope, and we really think that, whether it's up to moderate turbulence, we think that we really won't have those kinds of problems.

NTB: You mentioned the Kuiper, which went into service in 1974 and was retired in 1995. How does the SOFIA compare to its predecessor?

Austin: Well, I, of course, wasn't involved in the Kuiper. That was something, I believe, on the order of a meter [in diameter] telescope. Our primary mirror is actually 2.7 meters, but we really use the 2.5 meter inner diameter of that mirror, so our telescope is a lot larger. SOFIA,with its larger telescope, offers much improved sensitivity and resolution than Kuiper. We've added improved accommodations and systems for EPO staff and visiting educators onboard. Like the Kuiper, we'll conduct deployments to the southern hemisphere – probably New Zealand – and we'll make short deployments throughout the world in order to access any target.

NTB: Was the Kuiper an infrared system?

Austin: Yes. But both the telescope and the instrumentation were certainly old technology. One of the other fabulous things about SOFIA, frankly, is that entire aspect of educating the public, showcasing the very interesting and actually important scientific aspects of NASA's mission. I mean, that's why we do what we do.

SOFIA has accommodations to bring not only the science team, which includes people that are part of the program, but guest observers as well, people who propose and are awarded observing time on the observatory. We've also got a significant component that's really focused on educating the educators themselves in the K-12 range, so we'll eventually be bringing on educators, having them look over the shoulders and participate, if you will, as kind of an observer, but going through the training, flying on some of the missions and getting the chance to look over the investigators' shoulders. They'll look at the data, see how astronomy is done, and actually get an education from the science team about why we're looking at particular objects, what kind of information we're getting, and what those results mean in terms of understanding star formation and things.

NTB: Can journalists get their names on that list?

Austin: That's a good question. I actually don't know, but it sounds like a good idea.

NTB: I think so. Sign me up. The SOFIA project is kind of unique in that it's a joint venture between NASA and the German Aerospace Group (DLR). How's that partnership working out? Who's responsible for doing what?

Austin: It's an 80-20 partnership. In the broadest sense, the Germans – DLR is the German space agency – they actually funded the development of the telescope that is now in the aircraft. They designed and built that. And I think, although I wasn't on the program at the time when the telescope was delivered, but I believe it was installed in the aircraft around 2004, and there have been quite a few ground tests and the first 'activation' flight to begin to exercise the TA control system.

So that's their telescope, and integrating it into the aircraft was done by the US. The telescope was their major contribution as far as the hardware on SOFIA goes. They're also developing science instruments as well, so out of the nine instruments currently under development for the first generation, two of those are German instruments. There's a German instrument called GREAT (German Receiver for Astronomy at Terahetz Frequencies), and another one called FIFI (Field Imaging Far-Infrared Line Spectrometer). FIFI is being developed at the Max-Planck-Institut near Munich, at a place called Garching, and GREAT is at another Max-Planck-Institut in Bonn.

So, a couple of the science instruments, essentially 20-percent of the science opportunity, is funded by the Germans. They're also providing staff long-term as part of the twenty-or-so years of observatory operations. We have a German contractor organization through the Deutsche SOFIA Institut – DSI – in Stuttgart. They're providing a portion of the staff to assist in engineering maintenance and operation of the telescope. Their work is kind of matrixed into the US observatory organization, whose key element is science instruments, labs and science support, data archiving, and support to the investigator community. They're also contributing in other areas as well, such as instrumentation for flight test. That's a real big part of the collaboration.

The 80-percent on the US side includes the aircraft and the modification work to get the telescope in the airplane; build the bulkhead, door and the drive system; and the fairly complicated mission communication control system. So the interior of the aircraft aft of the flight deck on the first floor is….all of the passenger seats have been removed to get consoles in there for operating the telescope and the door, and operating the science instruments, and taking data and whatnot.

NASA is funding seven science instruments. We're building up a staff to actually operate the observatory and provide the same kinds of services you would get from a Hubble Space Telescope organization or the Spitzer Science Center. On the US side, in addition to the aircraft, the ground facilities are furnished by the US and outfitted generally by the US, as are the science instruments laboratories, the optics labs, and then a significant staff to actually operate the observatory, essentially in any mode, like a ground-based observatory in some ways and in some ways like a space-based observatory.

People who want to do research can go into our data archives and we offer, as do other observatories, proposal tools….you know, how do you become a researcher on SOFIA, what kind of objects do you want to look at and why, etc.? The US side does the scientific peer review and selections for the observing proposals for US telescope time, as well as the German side peer reviews and selection of proposals against German telescope time. Every four years or so we do new calls for science instrumentation, and then we fund the US science instruments and technology programs.

NTB: One of the major modifications made to the 747 was the cutting of a large 16-foot hole in the aft fuselage to accommodate the telescope and the installation of a special door that will open and close in flight. Has this ever been tried before?

Austin: On the Kuiper there was actually a similar concept, and again, not being familiar specifically with the Kuiper design, but yes, there was. On the Lear jet, I don't know. The Lear jet was a very small telescope, maybe 0.3 meters or something. I don't recall. So it has been done before with a telescope with an open cavity and a door. Certainly this is much larger than has ever been done before. This is huge by comparison.

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.

We're now conducting one or two what we call "telescope activation flights." The doors are closed but now we're going to release the brakes on the telescope and uncage it so the telescope will be floating and we'll go through some flight tests to actually understand how well the telescope vibration isolation system and inertial stabilization system works. Again, with the door closed you're not looking at anything.

After that the aircraft will land at Palmdale, at what is the SOFIA operations center, and we'll remove the upper rigid door, we'll remove all the door systems, and we'll be doing major telescope maintenance. We'll actually remove the primary mirror so that we can aluminize the mirror in preparation for doing science.

We have a basic aircraft with a telescope that flies. But now these systems we've been talking about, the rest of the observatory systems, over the next five years we will be completing the development and installing these scientific systems onboard the aircraft such as the mission communication control system to control the telescope and the door that would be the aperture – the upper rigid door and the flexible lower door – and all that kind of stuff. All of those systems will gradually be put into the airplane over the next few years.

Then, in 2009, even though many of these systems won't be complete, we're going to initiate science flight operations. The plan is to bring on two science instruments, one US and one German, and we're going to conduct a period called "early science." What that means is that even though the observatory doesn't have most of its eventual capability, we want to make sure at the absolute earliest opportunity that the aircraft is safe to operate with the door open and that tracking objects with the telescope is actually safe to do.

We actually want to start doing some astronomy, so we've got this early science program that consists of what we call "short science." Each of these two instruments will be put on the telescope and we'll do a number of flights to check out the telescope and the instrument and then go get some images, maybe go look at star-forming regions in Orion, or something like that. Or, depending on the time of year, maybe look at Sagittarius. So we're going to get some images; we'll get some spectra.

The two instruments are, right now, for the US instrument, FORCAST (Faint Object InfraRed Camera for the SOFIA Telescope), which is an infrared camera, and GREAT, which is a heterodyne spectrometer. We'll just do a very short science program and that will give us some understanding of how well the observatory is working. We'll go get some images and really show people why SOFIA is going to be a fabulous observatory.

Then, after a period of maybe a few months, while we're continuing to install some hardware and software and enhance the capability of the observatory, from this most basic mode we're going to go into what we call a "basic science period," and that's a fairly significant observing program with one instrument and we're actually going to be soliciting proposals to involve people – astronomers – who are outside of the SOFIA program itself, who aren't developing instruments. We want to engage the external scientific community to see how they would suggest using one of these two SOFIA instruments, FORCAST and GREAT.

Then we'd actually conduct a fairly good program, something meaningful on the order of maybe 50 to 100 observing hours, so actually flying probably 60 or so total hours, or maybe up to 120 hours, but we want to get about 50 to 100 hours of something that's of real significant scientific value. We don't know exactly what that's going to be. We certainly have targets given the time of year and the performance that we expect to get out of the telescope.

We need to stay within the vicinity of the Dryden and Edwards Air Force Base area, Again, this is very early in the flight test and operation of the observatory, so we're making sure that this is done with the utmost safety. We're not quite sure what the observatory ops will be, but, for example, we're not flying over the ocean or things like that. That's in 2009. I think we're starting to see some excitement return here in the external science community, so we're heavily engaged in making sure we can pull off doing science in 2009.

After that we're going to increase frequency. In the early years there's not a whole lot of science done. Starting in 2009 we'll actually have the capability to start doing science, longer duration flights, greater frequency. So we'll get into this mode where the aircraft comes down after flying this basic science, we integrate some additional capability into the observatory, we fly a little science, we improve the capabilities of the observatory by adding on things that have always been in the program but aren't finished yet. We'll get those in, we'll do some flight tests, we'll go fly some more science, we'll do some more astronomy, we'll land, and we'll do some more capability development.

We'll go through that process and as time goes on, essentially, we'll arrive at what we call "full operational capability" – FOC – in late 2013 or early 2014. At that time all of the capability that we would have expected of the observatory is complete. We're ready to really conduct normal operations and really leverage off our lessons learned over the previous years, operate efficiently, and the ultimate goal is to essentially obtain about a thousand hours of meaningful astronomy annually. I believe the Kuiper, at its peak, operated something on the order of about 400 hours per year. Fairly early on in the SOFIA program – I don't actually know the calendar year – but before we get to FOC, even though we're not operating at maximum efficiency, we're still learning things about the observatory, we're still doing system development, and we will actually be flying more observing flights than Kuiper ever did.