OFJ Field Journal from Ed Hirst - 11/29/95
CONFIGURING THE DEEP SPACE NETWORKLast night it hit me... SMACK... right in the face... eight days, EIGHT DAYS!
You see, on the west side of JPL, right near the main entrance, there is a mall and in that mall there is a billboard-sized sign. The sign currently contains trajectory information for Galileo and Ulysses*, showing the solar system (out to Jupiter), so people can see the locations of the spacecraft. As Jupiter Orbit Insertion (JOI) day got closer, the public affairs people added an "Orbit Insertion" countdown to the Galileo section and went from weekly updates (every Monday) to what looks like daily updates. Last night, as I walked out to my car, I glanced over at that sign. It is not like I was looking for something new or different. I had seen that sign hundreds of times, but this time it hit me... EIGHT days to ARRIVAL!
About a week ago, the January 1996 issue of Astronomy magazine showed up in my mailbox (Isn't it weird how when you subscribe to a magazine you get your issues one to two months before it hits the newsstands? I've already received my February issues of my surfing and bodyboarding mags, but..). Galileo got the cover. I recall thinking "cool, the cover," and proceeded to read the article.
It was a good article, but that was the end of it. No big deal. But then it was prior to the Thanksgiving holidays, so maybe that had something to do with it. I guess there was too much going on between then and Arrival Day, but now... eight days, wow. I've only been waiting for this for two years, but for some people, the wait has been a couple of decades.
I also saw a fawn grazing on the grass just a few steps from that sign. JPL sits at the base of some mountains, and when there isn't enough food or water, the deer will come down onto the Lab for a little snack. I had heard about this, but had only seen one once before. It was pretty cool. Maybe it was some kind of symbol. Maybe Galileo is like that fawn, which looked like it was out on its own for the first time, and we're also about to cross one of the big steps in our....
Nah, I don't think so. Galileo has a team of close to 300 people looking out for its well being, so that can't be it.
So, what have I been doing since my last journal entry? Well, a little bit of this, a little bit of that. That is the nature of being in the Mission Planning and Outreach Coordination Office.
For the mission planning part of my job, I spent the last few weeks applying what we had recently learned about telecom performance (basically, how well we can "hear" the spacecraft) to the Arrival Day time period. Just a few days ago, we issued the final decisions on how we'll be configuring the Deep Space Network and telecom from the end December 5th through the beginning of the 9th of December. The configuration for Arrival Day itself is of particular importance.
On Arrival Day, Galileo will perform some of the most important activities for the mission: Io Torus science data collection, the Probe entry and relay of its data, and the JOI. We had a very complicated set of requirements to juggle: we have to maintain the best real-time visibility into spacecraft operations (that is, get as strong a radio signal as possible), send real-time commands to the spacecraft at specific times, and get navigation data so that we can see how the JOI burn went (this information is needed so that the nav team can start the design of "cleanup" maneuvers, specifically the first Orbit Trim Maneuver which is only about a day and a half after orbit insertion). If you recall my previous journal, two-way antenna setups are needed for sending commands to the spacecraft and for getting navigation data, while one-way setups provide the best real-time visibility ("best" as in giving higher radio signal strength for locking onto Galileo's signal). There is even a special one-way setup called "ultracone" which provides even better real-time visibility (this configuration is only available at the Canberra antenna, see below). Well, what did we end up with?
Fortunately, two of the three antennas that we are using on Arrival Day have overlapping "view periods" (view periods are the times when a particular antenna can point at Galileo and receive its signal). The 70-meter diameter antennas that we use are in Madrid, Spain; Canberra, Australia; and Goldstone, California. The view periods of the antennas at Goldstone and Canberra overlap for 4 hours. The layout of activities to antennas goes kind of like this: Io Torus Science and preparation for Relay occurs over Goldstone only, Relay occurs over the Goldstone / Canberra overlap and JOI occurs over Canberra only. The best real-time visibility possible is required (or highly desired) during this whole period. Commanding is required all the way from just after the Io Torus science collection through just prior to the end of JOI and then stops for awhile and, depending on the how the spacecraft is doing, could start back up a few hours after JOI. Navigation data, again depending on how the spacecraft is doing, is required for a couple of hours, starting a few of hours after JOI. Juggle away!
The commanding requirements forced us to set up Goldstone in two-way mode. Fortunately, the Goldstone view period was long enough and the timing on the commands was such that we were able to schedule the transmission of all the required commands over the Goldstone antenna, even those for just after JOI (you see, it takes the commands about 52 minutes to get to the spacecraft, so even though JOI does not occur over Goldstone, we can still send commands from Goldstone because they'll get to the spacecraft right around when JOI will be near completion). The two-way configuration for Goldstone did hurt our visibility for Io Science collection and preparation for Relay, but doing all of the commanding over Goldstone allowed us to set up the Canberra antenna using the "ultracone," which will provide the best visibility possible for Relay and JOI.
But, what about the commanding and navigation needs *after* JOI? If Canberra is in ultracone mode, we can't meet those requirements, can we? Yes, yes we can: antenna configurations can be changed in the middle of a "track" ("track" is just another name for a view period, except it is called a track once it gets allocated to Galileo by the antenna time planners - officially called Resource Allocation Team via the Resource Allocation Process - get it, RATs that RAP - I know, it's bad). The key is that these requirements are dependent on how the spacecraft is doing. The idea is the following: after JOI, once we are convinced that the spacecraft is in good health, we will change the setup of the Canberra antenna from ultracone to 2-way. That allows us to collect navigation data and send commands. After those requirements are met, we will switch the antenna back to one-way mode (but not back to ultracone because switching in and out of ultracone causes a 30 minute gap in our data and we already have had one of these gaps to be able to get into 2-way mode) to once again boost the signal strength as high as possible. Pretty fancy, huh? Well, it took *many* hours of work from *many* people to convince ourselves that this was the right thing to do. The good thing about it is that it is flexible and it meets all our requirements. And that is what mission planning is all about.
So that was a little bit of this, what about a little bit of that? My other tasks have been in the outreach section of the office (I don't know why I am calling it a section since our office has only 3 people in it). In order to get ready for Arrival Day, there is a lot of information that has to be transformed and compiled into summaries and non-detailed descriptions of the events that will be occurring... around here we tend to call it "putting something in human-readable form." So, I am producing a time-ordered listing for Arrival Day that will list orbiter, probe and antenna events starting from the 7th of December at 1 o'clock in the morning (Pacific Standard Time) through the 8th of December at 8 o'clock in the morning. The listing will be used by many different people, but mainly by the Public Information Office as a guide to what important events are occurring during the day. One other product I am currently working on is a Post-JOI Sequence of Events. This is a chart that shows the events that take place in the week after JOI. Most importantly, it shows when the first Orbit Trim Maneuver and the first Probe Symbol return are scheduled. I understand that these charts will be used at Arrival Day press conferences.
Well, that is enough about work. I am really looking forward to tomorrow. My sister and a cousin are coming into town. We plan to go to Disneyland on Sunday and up to San Francisco to visit some other cousins the weekend of the 9th. They will be staying in LA with me until the 13th of December which is when my holiday vacation starts. We will be going out to Thailand for 3 weeks. I have brother who works for an oil company out there and he wasn't going to be able to make it home for the holidays (for the second straight year). We decided that we would go out and visit him and his family instead. It should be a blast.
As far as my sporting activities, WE WIN, WE WIN, we finally won a basketball game. It has been a hard season, we lost most of our games in the final minutes, but yesterday we managed to keep it together for the whole game. The tournament play is scheduled for the weekend of the 9th, but I will not be able to play due to my trip to San Francisco. I'll find out how we do when I get back. Volleyball and Softball seasons are over. I am looking forward to when they start up again in January. As far as surfing, we finally have been getting some good swells. They are winter swells out of the west. I guess the south just didn't want to produce anything this past summer. Last weekend I went out at Zuma Beach in Malibu. It was Saturday and I had missed the bulk of the swell that hit the coast on Thanksgiving day, but the waves were still tasty. Water: 61-63 degrees F, chilly, full suit for sure. I caught this really good "right" (that's a wave that peels to the right). Had to paddle hard for it, but once I caught it I was in surf heaven. It had good size and was peeling nicely and was pretty long. No surf in Thailand, or so my brother says. Maybe we will take some trips to the surrounding islands. Some of the best surf in the world is in that part of the globe.
* The Ulysses Mission is the first spacecraft to explore interplanetary space at high solar latitudes. Ulysses is a joint endeavor of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) of the USA.