OFJ Field Journal from Glenn Orton - 11/30/95
THE FINAL PUSH: ON TO JUPITER!Less than one week from Arrival Day, and there is a massive effort to use as many telescopes around the world to obtain as many observations of Jupiter as possible, the better to see what the Probe is heading into. I've made preparations in the preceding days for people observing at the Swedish Solar Telescope at La Palma in the Calary Islands, and Mt. Wilson here in California. Others observers are or will be at Pic-du-Midi, a French telescope in the Pynenees which is obtaining some really great images; Yerkes Observatory near Chicago; a gifted amateur astronomer in south Florida; the McMath Solar Telescope at Kitt Peak - just outside Tucson; and my primary work at the NASA Infrared Telescope Facility. Part of our group will also try to observe from an old solar telescope at Mt. Wilson, the Snow Horizontal Solar Telescope.
All of the observing makes home life rather hectic. Two nights ago, my wife came in at 8:30, arriving from an observing run at Kitt Peak. I left for Mauna Kea, Hawaii, the following morning. On the plane from Los Angeles to Honolulu I made the best preparation that I could for my observations. But what occupied most of my time was writing out Christmas cards (early!).
I arrived to fairly cloudy skies. The weather map shows a relatively clear area to the west of the Hawaiian Islands - let's just hope that's where the weather is coming from. I also find that I totally forgot to pack both of my long- sleeve shirts. Two quick email notes to my wife and to a close colleague who will join me up on the mountain in a few days, asking for at least one shirt. One thing that I'd REALLY also like is a tube of Chapstick. I'm really needing it up here. I also forgot jogging shorts, but I'll have to live without them. Up here, there are no convenience stores.
I *hate* first nights on the mountain at 14,000 feet elevation, with only 60% of sea-level oxygen: you get headaches and sinus aches where the air trapped inside is bursting to get out. Plus, part of our imaging system (MIRAC -- Middle Infrared Array Camera, sensitive to Jupiter's heat (thermal) output) warmed up; it's supposed to be kept VERY cold - just a few degrees above absolute zero. To get it cold again, we have to pump the air out of a space between the very cold detector and the outside. We'll end up losing 1-2 hours of observing time before the detector is cold enough to use again.
1995 December 1
Shooting images through local cumulus clouds, I tried to work with the sensitive near-infrared camera. When we got near Jupiter, we weren't able to see anything. We tried playing with the electronics that control the image coming from the camera, trying to reduce the ferocious background "noise" caused by the thin layer of polypropylene (what potato chip bag liners are made of) which has been placed over the primary mirror to protect it from damage by sunlight.
MIRAC finally cooled down and we put it in place on the telescope. Some patches of blue sky are showing up! The Probe Entry site will rise about 3 hours from now, and I'm still very nervous about just how successful this is going to be! Or is it just that it's really cold up here?
Not much luck. We took some observations of the inside of the telescope dome (for later use in telling us about the sensitivity of different parts of the camera's detector), but clouds got in the way of Jupiter. :( On the other hand, if the weather holds up tomorrow, we should be able to observe many hours on the Probe Entry site rising before the great cumulus monster climbs up the mountain again... I hope! It depends on the direction of the wind and that's quite variable.
Of course, we're not the only observers hard at work. Two (very serious) amateur astronomers working in south Florida, have started their own attempt to image Jupiter before the Probe entry, in what they call their "Jupiter Imaging Marathon".
To my family I write: Linda, Gregg and Sarah,
I'm very nervous about succeeding in getting observations of Jupiter for helping to determine where the Galileo Probe went into the atmosphere. I've been waiting for this time for 17 years, since I first started working on Galileo.
I hope CC [our cat] got her stitches out without a problem. I'm sure
you'll do well on Sunday (don't forget Sunday school in the morning).
Pray for me here - I do miss you all. ...and I'm going to miss sleep soon
if I don't go to bed.
Everyone is having a hard time observing. Humidity is rising, with the threat of having to close the dome. Only 15% of the light gets through to the camera because of the polypropylene, so we have to "add" a lot of images together in order to get anything worth looking at. We are getting consistent clobbering by clouds by 1 PM. And it looked SOOOO very dry in the morning!
I'd consider the data we got today OK only in a pinch. Mostly we were testing and creating automatic programs for the instrument.
Tomorrow, we'll start our day even earlier, so that we can get more observing done. It takes a little longer to set up than usual, because we can't fill the cooling containers (with liquid nitrogen and liquid helium) until we've put on the plypropylene screen (which is taking less time than I had feared). Even so, one hour of setup time goes by until we get any real observing begun.
My other fear is that we and our long days are pushing Bill, the telescope operator. We seem to have good "bi-modal" observing: we're getting good data in the early morning and the late afternoon! Can we tell him to take a long siesta in the mid-day?
Today's email home to the family:
YAY YAY YAY YAY YAY :) :) :) :) :) :) :) :)
Sunday, Dec. 3
To my colleagues at JPL, I wrote:
Got a series of observations with PES [Probe entry site] rotating off very early in the day, starting with 4.8 and 8.57 microns [two wavelengths sensitive to clouds]. By the time we got to 7 microns, it was off. We tested and found that we could get a little better signal at 7.95 microns than our old standard at 7.85 microns, moving out of a real extinction feature in the polypropylene. At 8.00 microns we were getting better signal still, but not nearly so distinct limb brightening. At this point, I'd say to coadd everything that got created there: even with "improved" signal we were unable to see where waves exist.
Monday, December 4
Maybe there are some other reasons why the images aren't as good as last year's. The Sun's position, perhaps -- there's sunlight shining down onto the screen right over the hole in the telescope that leads to the instruments. That wasn't the case last year. Could that explain it? I lost sleep over the subject, trying to figure out what we were doing differently!
We awaken to a perfectly cloudless sky! The Probe entry site will be right in the center of the planet by 11 AM, so I hope clouds don't climb up over the top of the mountain again today!
The good news continues. Bill Hoffmann, the person who built the camera, suggested that we re-align the instrument. This is usually a long and tedious exercise, but Bill recommended a shortcut. That improved the signal by a good 40%. Although all this kept John Spencer, the telescope operator here a good two hours over his usual time, he used a lots of tricks to find Jupiter and peak up on its sensitivity at last!
Also at Bill's recommendation, we check that there is no new adhesive tape on the part of the solar safety screen right in front of the hole leading to the instruments. Tape might be glowing more than the screen and adding to the background that we're trying to get rid of. We can't see any tape, however.
Today's data look good. We've been transferring the data to JPL over the Internet, and our colleagues at JPL have been working on them. Along with a quick technical outline of what we've done today, instructions on some computer processing on some of the images, I summarize today's work: " Today we skirted disaster, made some improvements and hit paydirt obliquely."