"How to Write a Pathfinder Sequence"

David Mittman - June 23, 1997
Mission Planner, Pathfinder
Jet Propulsion Laboratory, Pasadena, California

    Monday, June 23, 1997

3:15 AM -- Argh. Isn't Monday bad enough without getting up at three o'clock in the morning? I showered in the dark so as not to wake up the kids, got dressed and went off to work. (By shaving the previous night I figure that I got about 10 extra minutes of sleep!)

Today I am a flight controller instead of a mission planner (see my previous journal entry). And while it's early morning here at the Jet Propulsion Laboratory in Pasadena, California, it's mid-morning in Madrid, Spain, where Deep Space Station 65 is located. Lucky Spaniards...eating lunch while I attempt to drink my first cup of coffee of the day.

And what a day! Today's activities are likely to be worth getting up early for! Today we collect together all the work we've been doing over the last several months and send it all to the Mars Pathfinder flight computer. All the flight engineers have been developing "sequences" -- collection of commands executed in order by the spacecraft -- in preparation for landing. Our sequences have been tested using a test spacecraft located in our lab and during the many Operational Readiness Tests (ORTs) we've had over the last few months. These sequences have gone through many reviews and revisions (some sequences have been changed as many as 20 times as we've learned more about how to operate Mars Pathfinder).

If you were a flight engineer, this is what you would see if you were writing a Mars Pathfinder sequence:

1997-186T10:02:51 IMP_CCD_HEATER("OFF")
1997-186T10:03:21 STORE_IMP()
1997-186T10:08:35 IMP_CAMERA_POWER("OFF")

There, you've just turned off the Mars Pathfinder camera for the night. Thanks! Of course, the Mars Pathfinder flight computer can't read English, so we have computer programs translate these sequences of commands into something like this:

C5A0 A572 0870 0000 A5C0 77A0 7003 A5C0 AB7A 7801 0000

Once the sequences are in a form that the Mars Pathfinder flight computer can understand, they need to be stored onboard in the spacecraft's memory. To get them to the spacecraft, we transmit them through space from Earth to the spacecraft. That's my job today, transmitting almost 300 different sequences to the spacecraft using the Deep Space Network's 34-meter antenna in Madrid, Spain. Traveling at the speed of light, each sequence takes 9 minutes and 40 seconds to arrive at the spacecraft. If you'd like to see where I work, take a look. I'm located just out of the picture off the bottom of the image. I'll let you know how it goes. I'm on duty until 2:30 PM today...

2:30 PM -- I'm about to go home for the day after a day of sending sequences to the spacecraft. A communications equipment failure here at JPL left us without spacecraft data for about 40 minutes but overall the sequence loading went well. Hopefully, technical glitches won't create these lengthy data outages on Landing Day!

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