OFJ Field Journal from Glenn Orton - 10/27/95

A GLIMMER OF HOPE, THEN THE BOTTOM DROPPING OUT

Keep in mind that for 17 years, I've been preparing for the chance to compare direct atmospheric data from the Galileo Probe with various remote sensing results (that is, images) from the Orbiter. The point is to learn about the relationship is between what we determine from external sensing of radiation and what's really there, as well as how the Probe entry site compares with other interesting regions.

Then the "tape anomaly" occurs. So maybe we don't have a tape and we don't get any Orbiter data.

Then the early tests show that we DO have a tape, we can read data.

The tests that took place later, backing up the tape 25 "windings" from the tape end to cover a spot where the tape might have been worn a little thinner, were also successful. So, we'll live with a little less tape, and the show goes on.

Not.

The Project decided that since the Probe data are so valuable, and since they won't trust their primary medium for recording them-- you guessed it, the tape recorder-- that they'll back everything up in the spacecraft's computer memory. That's fine with me, since I'm quite concerned with the value of the Probe data.

Now for the Catch-22... In order to do that, they make room in the memory by erasing all the commands for the scan platform and the various remote sensing instruments. So, NO Probe entry site observations - also no Io clasp observations (which REALLY has the "Io-philes" upset!).

Worse yet, they're not even sure how data from the SSI (the solid state imaging camera) is going to be played back. The tape recorder has to be running at relatively high speed to capture SSI data. However, the tape recorder tests were run at a low speed, no faster than what's required for the Probe "relay link" (when the Probe sends its data to the Orbiter; the Orbiter will later relay the data back to Earth). So, maybe there is an outside chance that the Ultraviolet Spectrometer (UVS) or the Photopolarimeter Radiometer (PPR), (two imaging instruments that don't need to have the tape recorder running at high speed) can get data, but there is no guarantee of anything else. These tests won't be made until after the safe arrival of the Probe.

So this week, I went to two "emergency" meetings to help determine how we'd use Galileo to conduct an atmospheric investigation without any tape recorder at all. Answer: it's still possible - about 20-30% of our tape-relayed data would be returned to Earth. However, we'd have to change the way we plan observations. Right now, if we want to observe a certain feature in Jupiter's atmosphere, we simply schedule a "window" of time to look at it. Under the new strategy, we'd first look at it when the "downlink" between Galileo and Earth was high (meaning that the spacecraft's transmission rate was as high as possible), then look at ground- based observations of Jupiter and pick out whatever interesting objects were available at that time. Not a big worry - there is an endless list of interesting things on the planet, but our ties with ground-based observers had better be extremely good!

All during this time, I was working with a visiting scientist from Queen Mary / Westfield College, University of London, preparing him for helping to model the atmosphere of Saturn (and other outer planets) in anticipation for the operation of the Long-Wavelength Spectrometer on the European Space Agency's Infrared Space Observatory (ISO) mission, due to be launched on November 10. So, while emergency meetings came and went, I had to see what I could teach him about my radiative transfer programs and, in general, about Saturn.

When it rains it pours...

The Probe Net Flux Radiometer, Dr. Larry Sromovsky, and his colleague, Dr. Andrew Collard, at the University of Wisconsin have been emailing me trying to get me (as a co-investigator on their experiment) to figure out, with them, why their programs and mine don't converge to similar answers. Finally, I think we did it, but they're now pushing that last 10-15%, narrowing down the answers to using a finer and finer vertical grid scale. This means more programming on my part, too.

I'm way way behind on getting similar, less well defined, work on creating model atmospheres for the Probe Nephelometer (cloud particle measurement) instrument, on which I'm also a co- investigator.

Even though it'll be daytime here in the western United States during the Probe mission, we might still be able to use some telescopes here to observe Jupiter during that time. I managed to make some contact with the person working at NASA Headquarters on Planetary Astronomy who is contacting Kitt Peak National Observatory and Sacramento Peak Observatory on using their solar telescopes during the Probe entry time to "characterize" Jupiter. I've also started working with the Infrared Telescope Facility (IRTF) staff in a very preliminary way, to determine how we might leave much of the mirror uncovered and use the solar cover only over a part which will be covered by the sun. Our original plan was to cover the whole thing, back when the Near Infrared Mapping Spectrometer (NIMS, another imaging instrument) was going to get images and spectra from the Orbiter, and just concentrate on thermal images at wavelengths longer than 4 microns where the cover can transmit very well. Now, with no NIMS observations, we're going to try for a little bit more.

I also got off a general message to the group of "jovi-philes" who are on the receiving end of the International Jupiter Watch / Atmospheres Team email list, after my outgoing email problems finally cleared up. (Nothing like using the mighty computing power of JPL's Cray Y/MP for email service!) This message told everyone of the problem and asked for help (the message can be obtained from an anonymous ftp site: 128.149.11.11 (lono.jpl.nasa.gov) in pub/ijw/ijwnotices as go951027.

Now I have to prepare for the observing run next week at the NASA IRTF.