Tuesday, February 14, 2012

ARISSat-1 Keplerian Element Analysis - First Shot

Here are the preliminary results of my code that will ingest ARISSat-1 Keplerian Elements and output KML.  I generated a plot of the position of ARISSat-1 over the lifetime of its mission.  I accomplished this by examining the satellites position at one minute intervals in-between keplerian element epochs.  If you plot each position over every minute of the satellites lifetime, you end up with an image that looks like this.  Yes, that is quite a few lines!  Each colored line represents the trajectory defined by an individual Keplerian element (from its own epoch until the next Keplerian elements epoch).


Update:  I posted the image above and received many comments referring to how the orbits transit-over the south poll.  This would be incorrect for an orbit with an inclination of 51deg.  The reason the image above looks like this is because of where I have the eye-point set.  We are really looking over the top of the Earth, from far north of the equator.  The two images below will clarify what is taking place around the north and south polls.  Here is a shot of our South Poll.


And here is a clear shot of our North Poll.  Hopefully this clarifies the situation :-)


Now back to business.  The first Keplerian element results in the following trajectory over time.  Specifically, this is a plot from 2011/08/04 18:02:17 until 2011/08/05  05:05:17.  This is an image of the starting point.


This is an image of the ending point for the first Keplerian Element.  Notice where the line ends right over Nova Scotia, the satellite passed this point at approximately: 2011/08/05 : 05:05:17.


The next plot illustrates the first and second ARISSat-1 keplerian elements.  The blue line still represents Keplerian Element 1 and the green line represents Keplerian Element 2.  You can clearly see how the green line picks up from where the blue line leaves off.


Each of these plots is being rendered via Google Earth using a KML file that I am generating in my code.  Besides trajectory at any minute, I am also calculating when the satellite was and was not eclipsed.  Here you can see a brief view of when ARISSat-1 left eclipse for the first time.


What if we are interested in other eclipses?  With my generated KML, it is trivial to plot them.  Here is another shot that shows the first three times ARISSat-1 eclipsed.


I just made a couple of quick updates to my tool and this is what the data looks like now.  The left hand side of the image shows what the layer looks like within Google Earth.  The names are the satellite sequence numbers.  You will have multiple entries for each Kelperian sequence, depending on whether or not the satellite is eclipsed.  The color is black if eclipsed and orange if not eclipsed.  The descriptions contain the epoch for the starting point of the segment.



Let me know if you have any questions about these plots.  At this point in time, I have the following values being calculated and dumped to a table:  TIME, LAT, LON, ELEVATION, SEQUENCE#, ECLIPSED.  I post-process these values from the table into a KML file for visualization.

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