Comments on: SOFIA flies! http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/ I am an astronomer, writer, and skeptic. I likes reality the way it is, and I aims to keep it that way. My real name is Phil Plait, and I run the Bad Astronomy blog. Fri, 09 Jan 2009 03:58:09 +0000 http://wordpress.org/?v=2.3.1 By: bueggel http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35232 bueggel Fri, 01 Jun 2007 12:39:42 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35232 Landing gear: the gear was down the whole time during first flight, tested in a simulated landing and then left down again. The flight was performed at about 11.000 ft and very low speed, another reason for leaving the gear down, acting as a kind of brake. Telescope (TA): the mirror system is in the cavity, open to the environment (when the door is open), the bearing around which the TA will be moved for observation sits in the middle of the new bulkhead, and the science instrument (SI) will be mounted to the so called Nasmyth Tube extending into the cabin. The SI will move with the TA-motion, but could -in principle - be accessed by the experimenter. Visitors: there is some space foreseen for visitors in the nose of the aircraft, so there is a chance for teachers, students, other interested people to fly with SOFIA. However, there are still some years of flight testing ahead of us, so don't rush for tickets now, it's way too early. Landing gear: the gear was down the whole time during first flight, tested in a simulated landing and then left down again. The flight was performed at about 11.000 ft and very low speed, another reason for leaving the gear down, acting as a kind of brake.
Telescope (TA): the mirror system is in the cavity, open to the environment (when the door is open), the bearing around which the TA will be moved for observation sits in the middle of the new bulkhead, and the science instrument (SI) will be mounted to the so called Nasmyth Tube extending into the cabin. The SI will move with the TA-motion, but could -in principle - be accessed by the experimenter.
Visitors: there is some space foreseen for visitors in the nose of the aircraft, so there is a chance for teachers, students, other interested people to fly with SOFIA. However, there are still some years of flight testing ahead of us, so don’t rush for tickets now, it’s way too early.

]]> By: SP fan http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35231 SP fan Sun, 29 Apr 2007 18:14:57 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35231 The telescope cavity on SOFIA is segregated from the area where scientists and crew will be. No one will be able to get to it during flight. The bulkhead installed in front of the cavity has area at its center where the telescope instruments can be attached to the telescope from within the passenger area. No one will be in there during flight - if they are, it will get awfully chilly. A liquid nitrogen system will be cooling that cavity to 40-below zero to prevent fogging of the mirror when the door opens at altitude. And again on the gear, I heard it was at least exercised up and down during the flight. The telescope cavity on SOFIA is segregated from the area where scientists and crew will be. No one will be able to get to it during flight. The bulkhead installed in front of the cavity has area at its center where the telescope instruments can be attached to the telescope from within the passenger area. No one will be in there during flight - if they are, it will get awfully chilly. A liquid nitrogen system will be cooling that cavity to 40-below zero to prevent fogging of the mirror when the door opens at altitude.

And again on the gear, I heard it was at least exercised up and down during the flight.

]]> By: OZ http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35230 OZ Sun, 29 Apr 2007 13:06:55 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35230 Jack Hagerty wrote: "I’ll have to look into this to see what engineering rationale they used to put the telescope so far back in the fuselage. You always want to put the big load on an airplane right over the wings, if possible." Hi Jack, hi BA-Fans! What I learned during my diploma thesis which dealt with the aerodynamics of SOFIA was this: The first designs of SOFIA featured a bigger telescope in front of the wing, taking advantage of the wider fuselage diameter in the two-floor part of the 747 SP. But there were some lessons learned from the KAO: A thin boundary layer (which occurs in the forward section of the aircraft) corresponds with higher pressure fluctuations inside the telescope cavity. This will reduce the pointing stability of the telescope and the lifetime of the structural components. A thin boundary layer just before the forward edge of the cavity also produces a shear layer flow over the cavity which reduces the seeing of the telescope. As a boundary layer naturally grows downstream, those problems are reduced without any intervention. For the KAO a porous fence had to be applied in front of the cavity to control these unwanted effects. So I agree that putting a 20 t telescope in the back of an aircraft is not what you have in mind when your only concern is cargo and flight stability, these other reasons might have played a role in the engineers' decisions. Greetings from Stuttgart, Germany ... where the German SOFIA Institute is located. Jack Hagerty wrote: “I’ll have to look into this to see what engineering rationale they used to put the telescope so far back in the fuselage. You always want to put the big load on an airplane right over the wings, if possible.”

Hi Jack, hi BA-Fans!

What I learned during my diploma thesis which dealt with the aerodynamics of SOFIA was this: The first designs of SOFIA featured a bigger telescope in front of the wing, taking advantage of the wider fuselage diameter in the two-floor part of the 747 SP. But there were some lessons learned from the KAO: A thin boundary layer (which occurs in the forward section of the aircraft) corresponds with higher pressure fluctuations inside the telescope cavity. This will reduce the pointing stability of the telescope and the lifetime of the structural components. A thin boundary layer just before the forward edge of the cavity also produces a shear layer flow over the cavity which reduces the seeing of the telescope. As a boundary layer naturally grows downstream, those problems are reduced without any intervention. For the KAO a porous fence had to be applied in front of the cavity to control these unwanted effects.
So I agree that putting a 20 t telescope in the back of an aircraft is not what you have in mind when your only concern is cargo and flight stability, these other reasons might have played a role in the engineers’ decisions.

Greetings from Stuttgart, Germany … where the German SOFIA Institute is located.

]]> By: John http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35229 John Sun, 29 Apr 2007 08:15:23 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35229 blizno: First test flights - and frequently a number of flights thereafter - are always flown entirely with the gear down. Remember that the first flight of a new plane (or a significantly modified one!) is simply to get it in to the air and back down again, testing a few systems enroute. The last thing you want to worry about on such a flight is "does this landing gear work?". blizno: First test flights - and frequently a number of flights thereafter - are always flown entirely with the gear down. Remember that the first flight of a new plane (or a significantly modified one!) is simply to get it in to the air and back down again, testing a few systems enroute. The last thing you want to worry about on such a flight is “does this landing gear work?”.

]]> By: Murff http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35228 Murff Sun, 29 Apr 2007 04:41:51 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35228 It might be similar to the Kuiper set up. There's a hatch just aft of where the scope sits, so it is probably located in a box structure to separate it from the pressurized portion of the aircraft. The scientists would be able to walk on 3 sides of the scope, just like the Kuiper. On the Kuiper, you entered the aircraft just forward of the scope, and walked around it to where the workstations were, just aft of the scope. It might be similar to the Kuiper set up.

There’s a hatch just aft of where the scope sits, so it is probably located in a box structure to separate it from the pressurized portion of the aircraft. The scientists would be able to walk on 3 sides of the scope, just like the Kuiper.

On the Kuiper, you entered the aircraft just forward of the scope, and walked around it to where the workstations were, just aft of the scope.

]]> By: SP fan http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35227 SP fan Sun, 29 Apr 2007 03:16:43 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35227 The link below shows the bulkhead. It's not your father's Oldsmobile. http://www.sofia.usra.edu/Science/newsletter/2002/newsletter_2002_v6.html Teachers will be able to apply to fly via the education and public outreach office. Try the SOFIA homepage for more info. http://www.sofia.usra.edu/ Being Canadian may not get you on unless you bring the beer. The link below shows the bulkhead. It’s not your father’s Oldsmobile.
http://www.sofia.usra.edu/Science/newsletter/2002/newsletter_2002_v6.html

Teachers will be able to apply to fly via the education and public outreach office. Try the SOFIA homepage for more info. http://www.sofia.usra.edu/ Being Canadian may not get you on unless you bring the beer.

]]> By: Trebuchet http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35226 Trebuchet Sun, 29 Apr 2007 02:00:19 +0000 http://blogs.discovermagazine.com/badastronomy/2007/04/27/sofia-flies/#comment-35226 I'd love to see the bulkhead they put in to keep the forward fuselage pressurized. I know what the one on Boeing's Large Cargo Freighter looks like. I suspect this one is different, probably a relatively thin dome like the normal aft bulkhead but relocated forward. Perhaps that's just what they did. You'd probably want to remove the aft dome anyhow for CG reasons. (As the LCF did.) Too bad it's an SP, just about the ugliest airplane Boeing ever made. I know, it's all about the telescope but I can't help being an airplane guy! I’d love to see the bulkhead they put in to keep the forward fuselage pressurized. I know what the one on Boeing’s Large Cargo Freighter looks like. I suspect this one is different, probably a relatively thin dome like the normal aft bulkhead but relocated forward. Perhaps that’s just what they did. You’d probably want to remove the aft dome anyhow for CG reasons. (As the LCF did.)

Too bad it’s an SP, just about the ugliest airplane Boeing ever made. I know, it’s all about the telescope but I can’t help being an airplane guy!

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