OFJ Field Journal from Charlie Sobeck - 10/10/95
THE PROBE IS PREPARED FOR ACTIONHaving finished up my vacation and caught up on my work for other projects, it's time to get back to working on the Galileo Probe.
The Probe was separated from the Orbiter spacecraft this past July. It has no propulsion and will have no communications until after it hits the atmosphere of Jupiter. So it is simply falling towards the planet, being carried there by its initial momentum and the ever increasing gravitational pull of the giant planet. Once it gets there, it will turn itself on and collect data from above the atmosphere. Then when it hits the atmosphere it will decelerate from 100,000 mph to only 200 mph in just 4 minutes, losing nearly 200 pounds of mass from its heatshield in the process. Only after it has slowed down will it jettison the heatshield, deploy its parachute and begin to transmit data.
Until then, we will not hear from it. And even then we will not be able to send commands to it. So there's nothing left to be done with the Probe itself. But there is still work! The equipment we use to hear the Probe, the Relay Radio Hardware (RRH), is still on the Orbiter and we need to be able to command it properly in order to get the Probe data back. The RRH includes an antenna that we use to receive the signal the Probe will be sending. The Probe will be much too far from Earth to catch the signal from here, so we will depend on the RRH to collect the Probe data, and then hand the data to the Orbiter to send it back to Earth. The first thing we had to do was to point the receiving antenna. We did this in August after a couple months of preparation to ensure that we knew how to command it properly and how to interpret the data it sent back to us. But we finally moved it to the proper location in 15 small steps, and all the preparation proved to be worthwhile when the antenna moved exactly as predicted! It's now perfectly pointed so that when the Orbiter gets to Jupiter and flies over the Probe (which will be descending through the atmosphere on its parachute), the receiving antenna will be pointed at the Probe.
So now we turn our attention to other matters. Our ground engineers have finished putting together the computer networks we will use to distribute the data to the scientists over the Internet. Now we have to be sure that we have written procedures to tell us how to do this. Having a written procedure means there is less chance of someone making an error and delaying the distribution of the data. There will be a lot of excitement when the data finally comes in and when you have a lot of excitement, there's also a lot of confusion. The written procedure will help cut down on the confusion and will also help if someone on the ground team gets sick and we need to have someone new take over. The first draft of the procedure has been written and we will all review it this week to see if it is clear and understandable. After that the final corrections will be made and we will each take turns practicing the procedure in case we have to be the one to do it for real in December!
Also, we have written a draft contingency plan which describes all the things we can think of that might go wrong, and what to do about each one. The contingency plan we wrote for the Probe release in July was quite complicated and took a long time to write because we had to worry about everything that might go wrong on the Probe. But with the Probe now safely on its way and beyond our reach, we only have to worry about the RRH, and there is very little that can go wrong with that hardware (or, at least very little that we can do anything about). So this time the plan will be relatively simple. We will review this plan this week also, and then update it for the final corrections.