boacvc10
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NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Mon Jan 07, 2019 1:19 pm

I came across an article about SOFIA, "Stratospheric Observatory for Infrared Astronomy" a modified Boeing 747 operated by NASA/DLR. I have a question about the rear panel that has to be raised for operation. I see from the pictures in mid-flight the door follows the curvature of the upper fuselage and is placed on the OUTSIDE of the fuselage. Correct?

https://www.dailymail.co.uk/news/articl ... tdown.html

Are there any writeups on the reason they chose a sliding door that would be on the outside (creating drag) rather than inside (like many aircraft sliding doors)?

Also, can anyone shed light on why the telescope aperture is located at the back of the aircraft (more yaw) rather than place the telescope aperture in the middle which would have the least amount of moment around the center of gravity? Perhaps there is a structural/engineering reason ?

regards

BOACVC10
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zanl188
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Re: NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Mon Jan 07, 2019 2:06 pm

If memory serves.... floor was removed in the aft section to accommodate the telescope. This would be difficult if telescope was located over the wing. New pressure bulkhead was installed forward of the telescope. Any floor space needed for consoles, scientists, or other equipment would be difficult to locate if telescope was in center section.



As for the door, I can only speculate... I know that non turbulent airflow across the opening was needed for good “seeing”. It also appears that door opens quite a bit further than the typical cargo door. I presume this allows the telescope to point near zenith. Check out how far the door tracks extend down the starboard side.



This is the forward side of new pressure bulkhead.
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Tugger
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Re: NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Mon Jan 07, 2019 2:43 pm

While it is easy to google SOFIA and see why, here are the basics:
You are opening a big hole in the aircraft that will impact the airflow no matter where you put it. So first and most important, as is the case for any aircraft, you want clean undisturbed airflow over the wings.
Second all the crew, science support and tech, and needed hardware are forward of the wing for balance and ease of access.
Third the external door is integrated, the exterior of the airframe is built out, to smooth the airflow over the door and minimize disruption when closed and reduce impact during take-off and landing.

Tugg
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zanl188
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Re: NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Mon Jan 07, 2019 2:51 pm

Tugger wrote:
While it is easy to google SOFIA and see why


Concur. Check out the NASA NTRS server. Lots of SOFIA papers there. That led me to a paper that was promising but needed $18 to download...
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zanl188
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Re: NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Mon Jan 07, 2019 3:06 pm

This report on the heavy maintenance visit in 2014 notes that there are actually 2 doors over the telescope cavity.

https://www.dglr.de/publikationen/2015/370363.pdf
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Max Q
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Re: NASA/DLR SOFIA - Stratospheric Observatory for Infrared Astronomy, a modified Boeing 747,

Wed Jan 09, 2019 12:38 pm

Sofia trivia, the telescope lens cannot be exposed to direct sunlight or it will be irreparably damaged


Missions are operated at night and planned to return well before sunrise just in case the external door covering the telescope cannot be closed


In that case the aircraft would be placed back in the hangar before any damage could occur
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