Comments on: SOFIA flies!

By: bueggel

bueggel — Fri, 01 Jun 2007 12:39:42 +0000

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

SP fan — Sun, 29 Apr 2007 18:14:57 +0000

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

OZ — Sun, 29 Apr 2007 13:06:55 +0000

Jack Hagerty wrote: “Iâ€™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

John — Sun, 29 Apr 2007 08:15:23 +0000

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

Murff — Sun, 29 Apr 2007 04:41:51 +0000

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

SP fan — Sun, 29 Apr 2007 03:16:43 +0000

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

Trebuchet — Sun, 29 Apr 2007 02:00:19 +0000

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!

By: Brian

Brian — Sat, 28 Apr 2007 13:50:53 +0000

How will this project compare in terms of discovery power to ESA’s Herschel?

By: Chris

Chris — Sat, 28 Apr 2007 08:37:16 +0000

Steve: the way FAA regulations are, if you want to take a class of students up the plane has to be registered as a passenger vehicle. This means that you can’t have a honking great hole in the back with a telescope poking through it. Kuiper got around this by being registered as a non-passenger vehicle, and the teachers were designated crew members.

Basically, SOFIA was registered as a passenger vehicle, then they found out they couldn’t take students up because of the hole in the fuselage.

By: Monkey

Monkey — Sat, 28 Apr 2007 03:33:22 +0000

the obvious question beckons:

How do teachers sign up?

Can a salivating canuck sci-guy go up? And, assuming that an earlier post was somewhat on the mark, would a special student group be awarded the privy of going up?

Or was the teacher-in-the-sky idea purely ideological?

By: SP fan

SP fan — Sat, 28 Apr 2007 03:00:33 +0000

Jack’s estimate on altitude is accurate. They didn’t go beyond 12K altitude. Gear was down most of flight though i heard it was exercised. The telescope is likely in that position because they had to beef up the structure to hold the 20-ton telescope. To to that, they put in a new pressurized bulkhead and reinforced the structure. Couldn’t do that where the wing or tail was located since those are helpful for flight How many engineers have to ride in the front end to get the CG right? Maybe they could fill it with schoolkids instead of engineers.

By: Cameron

Cameron — Sat, 28 Apr 2007 02:23:28 +0000

Blizno: They don’t appear to be at particularly high altitude. Judging by the hi-res image, and speaking as a student pilot, I’d say they are between 5,000 and 10,000 feet. They might have left the gear down for the whole flight, as I would for the first flight in years of a renovated airliner, or it might be preparing to land or have just taken off.

By: Murff

Murff — Sat, 28 Apr 2007 01:55:00 +0000

When I was at Travis AFB, I got to see the Kuiper C-141A. It was a nice tour, looked like they had some Commodore 64 technology in it!!

…then I had to change all 14 tires, thats when the novelty wore off.

By: Jack Hagerty

Jack Hagerty — Sat, 28 Apr 2007 01:30:44 +0000

This is great news! 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. The KAO (Kuiper) had the telescope right in front of the wings. They had to offset it a little since the C-141 is a high-wing airplane.

I got a tour of the KAO in the late ’80s when it was parked at NASA Ames between missions. I remember most vividly the description of a member of the science team talking about the flight up through the lower atmosphere on their way to operational altitude. The telescope in the KAO was in a sealed box since it opened to the outside (the viewport was just a big square hole in the side) and they wanted to keep the rest of the cabin pressurized (duh!). The telescope mount bearings stuck through the walls of the box, though, and as they rode through the turbulence on the way up, you could see them bouncing around quite violently. “But then I thought,” said the crewman, “it isn’t the 10,000 lb (5,000 Kg) telescope bouncing. It’s mounted on vibration isolators. It’s this 150,000 lb airplane that’s bouncing that fast!”

It was an amazing piece of hardware, and I’m sure Sophia will be even better.

- Jack

By: blizno

blizno — Sat, 28 Apr 2007 00:27:26 +0000

Why is the landing gear still down at that altitude?

By: Steve

Steve — Sat, 28 Apr 2007 00:01:15 +0000

“when they land, they go back to the classroom and tell their students how totally cool it is fly on a NASA jet with a honking big telescope”

I’d hate my teacher if they did that! Why can’t the class come along?!?