Hello Gary. You might recall that I purchased an Argo Navis from you this summer so that I could control my AN/SServoCat system from my PC using an ASCOM driver. There have been a lot of adventures along the way but I have now put a camera on my dob and am trying to get the system working. One of the issues that has arisen in my efforts involves the tracking rate of the system after a go-to.

If I understand the manuals correctly, the AN/SC system almost always uses the sidereal tracking rate after a go-to. As far as I can tell, the only exception to this is the SmartTrack(TM) feature -- which will use the "proper" tracking rate for solar system objects if the user has the latest AN and SC firmwares (which I do). The AN manual says that SmartTrack(TM) is available if you dial up a solar system object from within MODE CATALOG, MODE IDENTIFY or MODE TOUR and then keep the scope pointed within 2.5 degrees of the object.

My question is whether SmartTrack(TM) will engage if MODE CATALOG is set to "From Planetarium" and a planetarium app on the PC (e.g., Stellarium) is used to initiate a go-to to a solar system object (say Jupiter, which is very prominent right now)? If the answer is yes, then would a properly coded ASCOM driver be able to access SmartTrack(TM) to set the correct tracking rate? If the answer is no, then is there any other way an ASCOM driver can override the sidereal tracking rate?

Thanks for your continuing support Gary. I think I am almost there.

Paul Abel

Hi Paul,

Thanks for the question.

Strictly speaking, Argo Navis doesn't use a sidereal rate when SETUP REFRACTION is switched to ON. Since refraction raises the apparent position of an object as a function of elevation above the horizon, the tracking rates continually and dynamically change accordingly.

To use SETUP REFRACTION, ensure your time is set correctly and that your approximate location is set in SETUP LOCATION. Switch SETUP REFRACTION to ON.

The best way to understand what tracking rate is is use at any one time is as follows.

If the object comes from one of the internal Argo Navis catalogs and it is a solar system object, Argo Navis will provide the tracking rates inherent to that object.
SmartTrack(TM) in that instance kicks in and provides tracking rates inherent to the target object when you are within 5° radius of a satellite or 2.5° radius of any other type of solar system object.

The tracking rates for any non-solar system object are sky position based rather than object based per se.

What that means is that the tracking rates are calculated according to where the scope is pointing in an RA/Dec sense at any one instant, again making small corrections for refraction.
So if you were to point at a star, then internally Argo Navis fetches the stars RA/Dec position and uses those coordinates to compute the tracking rates. As you move a little away from that position, likewise the tracking rates, being the first differential of pointing with respect time, will change by tiny, tiny amounts accordingly. In other words, the tracking rates in this instance are following the sky rather than following the object. Since star and deep space objects have essentially fixed RA/Dec's with respect time (over the time scales we are dealing with here), the tracking rates for them will be correct.

With this in mind, when one uses the FROM PLANETARIUM feature, what gets transmitted from the planetarium program is just a raw RA/Dec position rather than any information about the target. Since Argo Navis cannot determine whether the FROM PLANETARIUM position happens to be a solar system object or not, it always applies inherent position based tracking rates. This is due to the fact that ASCOM has no support to convey target information, it only conveys target RA/Dec coordinates.

It is not possible to override the tracking rates using ASCOM. What's more, from its very design inception, ASCOM made what I thought was a poor choice in tracking rate support. What it should have done is simply support the ability to set or retrieve arbitrary tracking rates for both axis in terms of radians/second. Instead, the designers chose to support the notion of four rates which they designated sidereal, lunar, solar (for the Sun) and King (which refers to tracking rate corrections to attempt to correct for refraction that were published by Edward Skinner King in 1931 - archaic today).

So even if we wanted to support tracking of say Jupiter from a planetarium at its inherent rate, to the best of my knowledge ASCOM unfortunately does not support it.

Gary, the technical support you provide to your customers is among the best I have experienced! Thank you so much for your complete and thorough response, which I am sure will help other users as well as myself. I have turned refraction on for my AN because I have inputted accurate time and location data. And now I know that if I want to view a solar system object I have to go-to that object from the AN and not the PC.

I hope to be able to share with you some first photos very soon.

Be well and clear skies.

Paul