Sunday, September 27, 2015

New Picture Roll 9/26

The satellite has indicated it has another 30 pictures taken since yesterday.  Now to begin the process of analyzing sizes to see which ones might be interesting.  I scripted commands to read out the sizes of some of the files and got some responses but they are stuck in the buffer of my serial port reading software.  I was able to interpret the filecount command responses using an ascii chart which indicated that there are 60 (HEX) files stored.  The bird records 3 files for each snap. a picture, a GPS reading, and an IMU observation.  So that means there are 30 (decimal) pictures awaiting download.  Now I need enough downloaded data to flush the serial buffer which appears to randomly hang up and contains the size of several pictures, which I use to prioritize downloads of.  Many files are black or "flares" (pictures of the sun) and I want the pictures that contain the most detail.  So the biggest files, which have the most pieces to successfully download, are the ones of interest.  I want to try to take you through the process as I attempt to gather this roll so you can appreciate the amount of effort it takes to even get one of the pictures you see on this blog, which might be as simple as a picture of clouds and ocean.  Need to set up tomorrow's script to get some sizeable downloaded data so the buffer flushes and I can get the transcript of tonight's file size inquiries.  Then I can start decoding file sizes and figuring which pictures to start gathering.  Let's see how it goes.

To get this to happen, one program on one computer steers the antennas to match the pass track so we're pointing the antennas at the bird as it goes by.  This computer needs precise clock and latest NORAD data to be right.   Another program is used on this computer (with current NORAD data and the accurate clock) to tune the downlink (receive) radio to keep the frequency accurate as the satellite passes.  The 9600 baud packet radio protocol in use requires an error of less than 5 KHz, ideally less than 2.5 KHz to decode reliably with weak signal, which fades and returns as the satellite spins during the preciously short pass.   Another PC decodes the received audio (if recovered error free) and forwards it to a serial program that filters packets to only be from our satellite (another satellite running 9600 packet shares our frequency and has a very close orbit).  It stores the result in a log that I can then use the HEX of to convert to ASCII and DECIMAL to make sense of the data.  This is all fun and everything, but doing it in realtime so I can make mission communication and command decisions during a pass is an "all faculty" consuming task.  Unfortunately, I really have no one else who understands any of this, so I am on my own to make the best of this situation.

But all of this is an awesome problem to have.  The miracle of recovering this mission data and pictures, to have empirical proof that the Earth is actually round (not that I had doubt), the understanding I now have of planetary and orbital mechanics, and the number of people I have been able to influence and increase their interest in space over cocktail discussions.  Priceless!  By the way if you are feeling a little awkward at a social gathering, try starting a conversation with "Did you hear about the satellite I helped build?  Did you see the pictures it took?"  You will distance yourself farther from them, but the looks on their faces as they try to process the concept is priceless!

I'll keep you posted as we progress.

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