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Preparing for the (Un)Expectedby Greg Wilson
June 17, 1997
For the last couple of months we've been busy simulating our activities on the surface of Mars as we expect they'll occur on July 4. These simulations are called Operational Readiness Tests, or ORTs. We are also preparing for other scenarios such as what happens if the battery goes out or what happens if we only have a low-gain antenna mission like on Galileo? Each one of these scenarios requires different sequences, which are operations we write and upload to the computer on the spacecraft. This is all done at the Jet Propulsion Laboratory in the "sandbox" where we'll run for five days, working out all of our operational kinks and looking for mistakes in our sequences.
We just completed ORT 7, our nominal mission, which assumes that we land correctly and all our systems are functional. If we have a nominal mission it's going to be really spectacular--the images, the data, the rover operations...
The spacecraft will land at roughly 10 a.m. PST on July 4. We will get a few pings from the spacecraft as it goes through its air-bag retraction and opening. We're expecting to receive only 50% of the pings just based upon them not appearing or not getting them at the tracking stations correctly. But we will get the first low-gain antenna downlink at roughly 2 p.m., PST, with the first high-gain downlink at 4 p.m. From roughly 5:30-6:00 p.m., PST we will have our second press conference of the day, but our first with images. We'll have the first press conference at 3 p.m. where we will have a lot of the deceleration profiles as Pathfinder enters the atmosphere.
One of the toughest things for everyone on the team is the conversion between Pacific Standard Time to Universal Time to SCLK (spacecraft clock time). We also have SCET (spacecraft event time) and Mars Local Solar Time. So depending upon how you want to plan your activity in terms of time, you need to understand how all of those are interconnected. On July 4, 10 PST is roughly 3 a.m. Mars Local Time.
The other thing we need to work through is our own time schedules. You see, if the spacecraft lands at 10 a.m., we'll need to be at work by about 9 a.m. But our operations and our downlink continue until 11 p.m. that night. And then there'll be data analysis taking place through the next morning. Then at 8 a.m. that morning we'll need to have our sequences ready to go to the spacecraft for the following day. So basically, operations will be running 24 hours a day!!! The hard part is we have to get some sleep, but we'll want to be up all 24 hours!!! Each one of those tasks--downlink, analysis, planning for the next day--we'll want to be involved in! I think I can do a couple of days straight before I fall a part.
The engineers will be working 12-hours shifts, but they may cut that down because experience at JPL has shown that if something goes wrong and a person has to spend 14-16 hours solving a problem, they're going to mentally collapse. The managing of our time is one of the harder things to do and that's why we do these ORTs and we actually run them like they are official landings in terms of working through the night.
We've completed the last ORT, which we lovingly refer to as "the landed mission" or ORT 8. So now I'm going on vacation, as are a lot of other Mars folks. But whatever weaknesses were revealed last week in terms of--did you have your programs up and running to analyze the data correctly; do you have all the pretty pictures you want for the press conferences--we'll spend the next couple of weeks cleaning up our act and trying to fix some of the anomolies that we encountered this time and hopefully no new ones spring up during the mission.
So, it's pretty much business as usual right now. The engineers will be doing a Trajectory Correction Maneuver either this week or next. Come July 1, operations begin in full swing: they'll be tracking the spacecraft two-way, 24 hours a day and really refining the landing parabola.