Guiding on a Geostationary Satellite

[Richard Scott]

Will PHD2 guide on an object such as a geostationary satellite with the mount (Losmandy Gemini) in terrestrial mode (non-moving)?

Thanks,

Rick

[Brian Valente]

Rick

satellites are typically far too fast for guiding. You would use something like SkyTrack

https://www.heavenscape.com/

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Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Richard Scott]

Geostationary satellites barely move but I am looking at SkyTrack.

Thanks,

Rick

[Brian Valente]

If you're doing geostationary and they are 'barely moving' why not just use sidereal. Regular guiding would handle any small differences

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[Richard Scott]

Hi Brian,

The satelliite is not moving east/west but has a very small movement north/south over about a 4 hour period. If the mount was moving at a sidereal rate, the telescope would move west and leave the satellite behind. I would like to use PHD2 to track the slow movement because I'm focusing a transmitted signal from the satellite onto a fiber optic cable. The field of view on the sky from the point of view of the fiber is only 1.8 arcsec, not much different than a single pixel of a camera.

Rick

[Bruce Waddington]

Hi Rick.  I think there are two questions we don't know the answer to:

1.  Will your mount - whatever it is - process pulse-guide commands when the mount isn't tracking.  The answer may be different depending on whether you are using an ST-4 guide cable or are communicating via a mount driver.

2.  Will the geostationary satellite be recognizable as a suitable guide star based on its shape, size, and brightness

If the answers to both questions are 'yes', it might work, PHD2 doesn't insist that the mount be tracking at the sidereal rate. I think only a bit of testing will provide answers.  

Good luck,

Bruce

[Brian Valente]

Rick

I poked around a bit, and I still think SkyTrack is your best bet. Basically there is no sidereal movement (or tracking) so i'm not sure how PHD would even react to this. 

However, SkyTrack can be used and they even have a video demonstrating geostationary satellite tracking and imaging

https://www.youtube.com/watch?v=ooCTO9sARIA

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[Richard Scott]

Thanks Bruce. Those are two good questions. I did research on the mount and it turns out it will not process pulse commands when not tracking, so that kills the possibility. As for the second question, yes, the satellite will look like a star since I will be guiding on it's transmitter laser using a SWIR camera to drive the guiding software. I was hoping to use PHD2 but it's looks like totally custom software will be needed and a couple of project team members are currently working on that. This just means that they have more work to do. They we hoping to pipe the output of their software to PHD2 for the interface to the telescope mount. Such is life! Thank you for your time.

Thanks again,

Rick

[Johan Piek]

Just a random thought. What will happen if you tell the mount you are in the opposite hemisphere to where you actually are? South instead of north or vice versa. 

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[Dale Ghent]

An encoder mount with RA and Declination tracking rates set to values derived by the satellite's orbital TLE should be able to handle this, I would think. The tracking rates would need to be updated at regular intervals to account for the satellite's anelemmic motion, which is what I /think/ you're trying to compensate for?

As for pulse guide commands to mounts, your team is should get familiar with the ASCOM semantics around mount axes motion. Pulse guiding does indeed require the mount to be actively tracking but, as I mention above, most (but not all!) mounts allow the tracking rate for each axis to be modified, so custom tracking rates - including ones that approach zero movement - is possible.

/dale

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