OFJ Field Journal from Steven Collins - 11/20/95

MY WEEK FOR AACS

I have a computer program that I wrote that draws "Sphere plots." They are kind of like drawing pictures on the surface of a computerized globe. This turns out to be a very good way to look at geometry problems for spacecraft because you can think of the globe as the sky and plot some stars and planets on it, and then mark where the spacecraft is pointed and the camera is looking.

I used a program called SKYBALL a lot this week. On the 7th of December we are going to use a small antenna (called the Relay Radio Antenna, or RRA for short) to pick up the science data from our probe as it enters Jupiter's atmosphere. To make it all work, this antenna has to be pointed at exactly the spot where the probe is. I was asked to make one last quadruple check of the commands that the spacecraft will use to point the antenna, so I used my Sphere Plot program to make a picture of where the Earth and Sun and Jupiter will be on Dec. 7 and then plotted where the spacecraft's spin axis was pointed and where the commands will point the antenna. Everything checked out fine.

I also used SKYBALL to see where one of the science instruments was pointed to help the scientists understand their data better. I build lots of little programs to plot or compute things, so knowing how to work with and program computers is very important for my job. My little programs are like a set of *tools* and I have a "toolbox" of my favorites that I use and work to improve all the time.

I went to a meeting to figure out how to use our not-quite-healthy tape recorder to play back the data we record from the probe. The meeting was long and there was lots of heated debate over the way to get the job done. In the end the project manager put off the decision till later and give the anomaly team (the group of people working on the problem) a little more time to work. It's pretty common for "decision" meetings to end this way.

I'm helping the tape recorder anomaly team by finding, plotting and looking at lots of telemetry from the tape recorder (I'll write about how I ended up doing this in another message).

I wrote a little program to look through a whole bunch of tape recorder telemetry (the signal that we receive from the spacecraft) and pull out just the data when the recorder was playing or recording at its lowest speed. Some folks are working on some new software for the spacecraft that will automatically check to see if the tape recorder is slipping or acting funny. If it is, the new software will respond by stopping the recorder. The people working need to know how much power the tape recorder uses at different places on the tape and how much it changes I also found some data on the pressure inside the recorder's sealed case. It turns out that the pressure also serves as a sensitive measure of the *temperature* of the recorder. This is a good example of how we sometimes have to use things (and data) in ways that were not originally intended.

Well, that's all the stuff I can think of at the moment. I'll write again soon...