OFJ Field Journal from Duane Bindschadler - 10/26/95
NEW PHASE 3 SOFTWARE WITHOUT ANY TAPE RECORDERIt's 7:15 in the morning, and I'm sitting in the JPL cafeteria having some breakfast and trying to write this log entry. As you might well imagine, things here have happening very quickly over the past week while the Galileo Project tries to grapple with the serious problem that appeared in the spacecraft tape recorder just 2 weeks ago today. In that time, the project has tested the tape recorder, made a preliminary diagnosis, and set in motion a plan to allow us to fulfill our mission at Jupiter without using the recorder, should that become necessary.
I've been spending a great deal of time in meetings during the past week. The purpose of these meetings is to create what is called a "point design" for "Phase 3." This may sound a bit mysterious, but what it means is that the scientists, engineers, and managers on Galileo are trying to define exactly how we can redesign Galileo's software (that's the "point design" part) to return data without a tape recorder (a no-tape-recorder mission would use the "Phase 3 point design."). Of course, we can't alter the mechanical part of the spacecraft -- Jupiter is a little too far for a mechanic to make a service call! But it is possible to rewrite the software that runs Galileo's computer. This has already been done once before ("Phase 2"), after Galileo's high-gain antenna failed to open.
For me, these meetings are often as much a learning experience as they are an opportunity to contribute to fixing the spacecraft. My primary contribution is to keep track of what is going on in these meetings and to keep Carol (my Team Chief, Carol Polanskey) informed. So it sometimes feels like I'm back in school, taking notes and listening as carefully as I can.
Besides all those meetings, I'm also trying to help with the building of a "strawman" sequence. For each of Galileo's ten orbits around Jupiter, the science coordinators build a sequence of commands to the spacecraft that tell it which instruments to use, and when to use them. This would be relatively easy to do, except that there are eleven instruments onboard Galileo. Each instrument may or may not interact with any other instrument. Each instrument requires a certain amount and type of power from the spacecraft. Each requires particular kinds of processing of their data by the onboard computer. Most of the remote sensing instruments use the scan platform -- what if one of those instruments wants to take a picture of Io at the same time that two of the other remote sensing instruments want to look at Ganymede?
The answer, of course, is that we have to work out all the conflicts and then put all the individual instrument plans together to integrate the sequence.
Getting back to the "strawman" sequence, the idea is that we try to put together an example of a Phase 3 command sequence for an orbit -- one that doesn't rely on the tape recorder to store data. Even though we don't know all the details of what the Phase 3 software will or won't do, we can still use the basic ideas and principles that go into a no-tape-recorder mission to build a model of a Phase 3 sequence.
It usually takes a couple of months to build an orbital sequence -- we started on Friday of last week and have to be finished by this Friday. Because we are using one of the sequences that was already done (the first orbit, called "G1" because it includes a close encounter with Ganymede) as a starting point, we'll get the job done. But time is of the essence.
Yesterday, Carol came into my office and asked me to take the orbital sequence command file, pull out only the commands to SSI (the Solid State Imaging subsystem, Galileo's primary camera), run those commands through one of our software programs that simulates the Galileo spacecraft's instruments, computers, and data flow, and find out how much data these commands were sending back and whether or not the SSI alone was monopolizing the data link to Earth. Without a tape recorder, Galileo must send all of its data back to Earth immediately. But without the high-gain antenna, it can only do so slowly.
"And can you have that for the folks working down in the SIWR* (pronounced "sewer") before your meeting at 1:00?" No problem, it was only noon. What I didn't know was that (1) the file containing the sequence of commands for G1-Phase 3 was very large, (2) there were a lot of individual SSI observations in the sequence (I lost count at about 70), and (3) there were other people running the spacecraft modeling program that I needed and so the computers were a little bit slower than normal. So it was only after a very busy hour and 15 minutes that I could show the members of several instrument teams that although the SSI images would demand a significant part of our resources, there was also room for sending other kinds of data to the ground.
One of the things that the past 35 years of space exploration has taught us is that there is a strong synergy in making complimentary observations with different instruments. What that means is if we take two different kinds of data for the same object or phenomena, we don't learn twice as much as we would have with only one kind of data. Instead, we learn three or four or five times as much.
Everything we are discovering about Phase 3 and the sequences we can build seems to show that even if we can never use the tape recorder again, we will still be able to return a set of data that will revolutionize the way that scientists think about Jupiter, its satellite, and its magnetosphere. That means that in a few years, many of the textbooks that we all use today will need to be updated and corrected because of what Galileo will teach us. And we will know a little bit more about the universe around us, and about how to face the inevitable challenges that it will present us with.
Online from Jupiter, this is Duane Bindschadler.
* SIWR is the Sequence Integration Work Room. It includes a large-screen display that can display whatever is shown on a computer workstation's display, and allows us to see the effects of changes we make to sequences as soon as we make them.