Providing a striking contrast to the semi-annual launches of the 1-meter balloon-borne telescope are the almost weekly flights of the Kuiper Airborne Observatory , 'KAO' for short. This observatory also has as its goal the ability to take infrared instruments high above the majority of the atmosphere. But whereas the balloon-borne telescope can survey large areas of the sky very rapidly, the KAO facility permits detailed observations of small regions of the sky. Both types of infrared observing are invaluable to studying the large-scale and small-scale structure of young star forming regions in the Milky Way. Unlike ballooning, astronomers using the KAO get to ride along with their equipment which means that if anything goes wrong, you can usually repair the problem without having to abort the whole mission. The KAO is also very similar to other observatories in that your research program is granted a fixed block of observing time during the year and, barring unusual circumstances, (e.g., weather, maintenance work, legal holidays), your flight is guaranteed to occur during that time. The telescope, together with its guidance and pointing systems, are among the best that a multi-million dollar annual engineering budget can provide. The only items that require preflight testing are the infrared detectors and their associated electronics. These items can be checked out exhaustively at the astronomer's lab back home, which shortens the preflight period to a day or two. Then, of course, you don't have to travel to a distant secluded town like Palestine, but instead fly to picturesque San Francisco and drive 45 minutes south on Highway 101 to Moffett Field near Mountain View. Since I was raised in Oakland, I have a greater enthusiasm for the Bay Area than, say, Eastern Texas.
I arrived in San Francisco in January of 1983 and joined Harley Thronson from the University of Wyoming, and Bob Lowenstein and Bill Glaccom from the University of Chicago , to observe and map eight infrared objects. Some of the objects were known, from studies at other wavelengths, to be ejecting plumes of gas out of regions where stars had just been born. We were hoping to learn more about how these plumes are produced and about their environment by mapping the hot dust in their vicinities. The infrared detector we were using had been developed by Paul Harvey at the University of Chicago and was capable of providing high resolution and sensitivity measurements at several far-infrared wavelengths; capabilities that were ideal for studying these objects.
I drove through the security gate at the Ames Research Center and followed a set of roads that led me through a maze of giant hangar buildings. These eerie buildings sprouted gigantic pipes, wind tunnel air outlets and other strange growths, but I had no time for sight-seeing. I was anxious to get to Building 248 where the C-141 Airborne Observatory lived, and see for myself what this famous astronomical facility looked like. It was, in fact, quite a bit larger than I had expected, about the size of a DC-8. The hangar was enormous and could have accommodated two of these aircraft. Unlike a passenger plane, though, there were no familiar rows of windows on the fuselage, just a giant hole up front near the crew compartment through which the telescope could peer into the depths of space. This opening was sealed while the C-141 was on the ground, to prevent dust from collecting on the telescope mirror.
I found my way into the plane and greeted Harley and Bob, who were bolting their equipment into a cabinet near the telescope. We talked about the schedule of events for the next few days and since I had never used this facility before, we agreed it would be a good idea for me to get familiar with how an observing program is scheduled. There wasn't much time left for this today, so we agreed to meet the next day and start afresh.
Thursday, January 7: The next morning, while Harley and Bob busied themselves with checking out the dewar, I worked upstairs in the computer room on a Tektronix terminal, learning how to use the programs needed to assemble an observing schedule. The basic idea is rather simple. Just as for the balloon program, you begin with a list of objects to study for a specific amount of time; you have to make sure the telescope is pointed in the right direction to see them. Translating this into an actual program for the KAO is quite another story, however. You see, the KAO telescope can only move up and down 30 or 40 degrees and left to right 10 degrees or so. To point from one object to another, the plane has to be moved from one flight path to another. Each path has to be accurately known beforehand so that the flight plan can be checked and submitted to the FAA. Also, it's a good idea to end up on a flight path that takes you back to Moffett Field within 8 hours from take-off or the fuel runs out!
I read all the handbooks carefully, and after experimenting with some trial runs I worked out what looked like a sound observing schedule. There would be 11 'legs' to the flight which would take us eastward over Nevada, Utah and Colorado and Kansas to observe W-3, S-209 and AFGL-490. We would turn around and fly west to pick-up NGC-2024, NCG-2264 and CIT-6. The total trip would take about 7 hours and we would have to be at cruising altitude by 5:55 PM. I talked this plan over with Harley and he thought it sounded OK. We gave it to Allan Meyer who was in charge of 'star tracking' just to get his feedback on it. Although there were no major problems, he was able to fine tune it by adjusting observing times or moving an object from one part of the schedule to another.
Friday, January 8 Today is flight day. We arrived early and at 9 AM the dewar was topped off with liquid helium and its liquid nitrogen reservoir was re-filled. We attended to a variety of last-minute details, not the least of which was buying 'Flight Food'. Flight Food is a euphamism for what other people might choose to call junk food. I collected money and food preferences from everyone and drove off-base to the nearest grocery store. An hour later, I returned with two large bags overflowing with sandwiches, potato chips, cookies, softdrinks and anything else I could think of that might taste good around midnight at 40,000 feet up.
Soon afterwards, we had a flight status meeting with Jim McClenahan and the rest of the KAO staff. The results of the morning weather forecast presented no problems and the C-141 was cleared for take-off. By 2:00 PM, the aircraft was rolled out of the hangar onto the tarmac, and the flight technicians prepared the jet. The dewar, containing the infrared detectors cooled to a few degrees above absolute zero, was carried inside, attached to the telescope and the vacuum pump hoses were installed.
About 20 minutes before take-off, we boarded the C-141, took our assigned seats and strapped ourselves in. The oxygen mask I had been issued was plugged into the orifice next to my armrest. While I waited I couldn't help but notice the rather bleak interior, gunmetal grey with plenty of room for cargo. The bare semi-circular ribs of the fuselage could be seen here and there where access pannels had been removed to reveal hydraulic line shut-off valves or junction boxes. No stewardess told us how to use seatbelts or tried to make life comfortable for us. Being the rookie on the flight, I was invited to sit up front with pilots Paul Saabo and Glen Stinnett. We saw and heard very little from them during the flight since they followed some prearranged protocol and spoke, via radio, only to Jim who acted as the flight operations director. Jim's morale-boosting jokes and witticisms came in very handy during the tense, exhausting times that were to follow.
Take-off at 5:05 PM was smooth and uneventful and by 5:53 we were at cruising altitude, setting-up to acquire our first target, W- 3. Harley selected the filter he wanted to map this object through, then Allan identified the star field around W-3 from its image on the TV screen. He found our offsetting star and after several attempts, was able to get the Digital Offset Guider , `DOG' for short, to lock onto it and step the short distance to where W-3 ought to be. It sounds simple, but, in fact, was a frustrating process. Each time we would lock on, the plane would hit an air pocket and jump. The DOG couldn't keep up with the rapid motion and would lose lock. Finally, at 6:33 PM we held lock long enough to offset to W-3 and obtain a single measurement of its brightness at a wavelength of 60 micrometers. This success was short lived because 2 minutes later we had to move to the next scheduled source, Elias 1-12, and start all over! The latter was a disappointment for different reasons. Although we had no trouble locking onto it, during the alloted 30 minutes we saw no sign of its infrared emission no matter what filter we tried. In spite of this disappointment, during the next few hours, we succeeded in mapping AFGL-490, S-209 but also got a second try at W-3 which obliged us this time.
During the second half of the flight our success continued as we succeeded in obtaining good measurements of M-42, NGC-2024 and NGC-2264. Then, at 11:45 our program was abruptly terminated. Fog was rolling onto Moffett Field which could prevent our returning to base. Hightailing it to Moffett, we ultimately lost our race against Mother Nature and at 1:30 AM were forced to land at the Norton Air Force Base 400 miles away in San Bernardino. The fog did not lift at Moffett until mid-afternoon the next day.
We got a second chance at completing our observations on Monday, January 11, following a similar routine as on Friday. But this observing run was also interrupted, not by Mother Nature, but by human error.
6:00 PM. Object: W3-OH
"Let's peak up on channel one again." "OK. Here's the update." "Let's do channel 2. " " YOU HAVE TEN MORE MINUTES." "This should be the channel 2 boresight...oh oh, I'm lost." "Hit clear and reset; take me back to the center position." "OK, here we are. We see a lot in the first channel." "How much more time?" "SEVEN MINUTES." "There it is...are you sure we got a good rotation? Usually we measure twice to see if we get the same stage angle." "OK, there...let's do some more nods."
7:12 PM. Object: S 209
"I'm going to change filters. We're at filter 2, by the way. We're going to want to make a map here." "OK. Just call out the flux readings and I'll plot them in the notebook as we go along. Remember to let me know your offset directions each time." "Let's go to the peak and do a point-by-point map." "There's a jet fighter exercise occuring at the end of this leg. Be advised we may have to abort at any time!" "OK." "OK, looks like heavy traffic." "But we're not in a restricted area!" "They say otherwise. They approved our flight path and now they're reneging." "Oh shit!" "We've been talking to them for the last five minutes but they seem unconvinced. We're making a course change because we're being chased out now. "How much of this leg will we be able to salvage?" "I'm hoping for half of it. "
10:30 PM. Object: NGC-2175
"Doesn't it make sense to look at the known far-infrared source first just to make sure the system is working OK?" "You're probably right. In fact, I'm sure you are." "Not much happening at the secondary CO peak. Must be a cold source." "How are we doing?" "About 3 sigma and that's not a real 3 sigma either - we're just looking at noise. " "How's our track doing?" "Not too bad. Here's a hard copy. " "Looks like we're headed toward another airforce base. Are you going to tell them about our problem? " "That was a very serious screw-up back there!" "Most of the noise we're seeing is detector noise, not sky noise." "I take it there's no signal?" "Nope, nothing at all." "I don't think that for an object like this an upper limit is worth much. The northern peak would have been more interesting. "
In spite of the many ups and downs during this second flight, we were able to get useful maps of W-3 and NGC-2264. Combined with our data for NGC-2024 and M-42, this KAO expedition viewed four intriguing infrared maps of those objects to take home and ponder.