[Gpredict-discussion] GPredict and SatNOGS rotor

[Sims, W. H. (MSFC-ES63) <her...@na...>]

Guys and Gals,

Two questions for the group.

First, is there a way within GPredict to determine if TWO ground stations can see the same satellite at the same time?  Along a work related question we (Marshall Space Flight Center, MSFC) are doing some experiments on the International Space Station (ISS) RF test-bed and due to licensing issues on the station we cannot downlink data while NOT over pre-determined ground stations (in our we are NOT one of those ground stations but Glenn Research Center, GRC, is).  What we want to do is determine when both MSFC and GRC can see ISS at the same time.  Is it possible with GPRedict?  I realize we can use something Like Satellite Tool Kit but that requires funding other NASA people so I am trying to save our project some money (since I’m already on it).

Second, I am using a SatNOGS rotor (AZ/EL) and was simulating tracking a satellite yesterday and noticed something that concerns me.  The satellite started on the horizon at say 10 degrees azimuth and during the pass went from 10 – 360 – 350 – 340 to finally close to 190 degrees.  The question I have is that once the projected azimuth hit 360 the SatnOGS rotor spun all the way around (went clockwise from 0.1 degrees to 180 to 359 degrees) instead of continuing in a counter-clockwise direction (this is, I believe, because I had the rotor controller set to 0-180-360).  I believe had I set the controller to -180-0-180 that it would have worked as expected.  The problem is, if I get a scenario of another satellite track that goes from 170 – 180 - -170 - -160, etc. and I was set up for the -180-0-180 it would do the same thing (i.e. go 170, 179.9 then swing all the way around counter-clockwise to -179 etc.).  Is that something that one “just has to live with” or should the rotor be capable of doing a full 720 degrees (2 * 360) too keep this from happening?  I realize that it would then wrap the coax around the system, but I just want to make sure that I am not missing something here.

Thanks,

Herb


Dr. Herb Sims
EV41
Bldg. 4600 / Room 4113
Control Systems Design & Analysis Branch
MSFC, AL 35812
256-961-3214
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