Then Sevan Aydin added :
That's a fabulous scope for ISS tracking.? My 15" UC has about the same eyepiece height, and it works out great for ISS (don't forget about CSS).? You will absolutely have a hole around zenith depending on how fast your motors can slew.? If you can disengage your az drive quickly, move it yourself for the really high passes in az, while keeping the alt drive engaged.? It will still wonk out the AN because of its autlock, but it is the fastest way to reacquire after culmination.
"The pointing precision is not optimal and objects are classically not in the fov. 1 or 2¡ã away."
This is your problem!!!? Everything else is fine, except for the lack of a telrad (at least none that I can see).
The real issue is that that there simply aren't enough stars out to do a full TPAS run when the ISS is illuminated.? For some very, very stupid reason, whenever you update TLEs on ArgoNavis, it completely junks your alignment.? The "reason" for this is that Gary at AN wanted to ensure that whenever the catalogs update, the objects the user used to align are all still there.? Rather than checking which objects the user actually aligned on, AN just junks the whole alignment to "be safe".? The logic of "no one aligns on a satellite" made no difference, and this "feature" will not be fixed any time soon according to Gary at AN.? You absolutely need the very latest TLEs every time you observe LEO sats, so this "feature" is nothing other than a hindrance.? The only TPAS variables that will survive are those that are consistent from one session to the next.? Unfortunately, the most important ones such as collimation error do not.? If Gary at AN reads this, please remove this awful bug that junks the alignment when updating TLEs.
What that means in practice is that you need to get good pointing with standard alignment using only the few stars that are available during dusk.? For dawn passes, you have time for a TPAS (assuming you calibrated AN's crystal as spelled out in the AN manual).
"I will also use it to adjuct backflow."
Backlash during movement isn't a problem.? At best you are slowing down the speed of tracking, while still tracking in the same general direction.? It's only around culmination where alt changes direction.? Even around culmination, az is still going in the same direction.
It's during alignment that backlash is a problem.? My 15" UC has about 5 arcminutes worth of the virtual mirror box swinging on the trunnion whenever I switch directions in alt.? It grows to about 8-10 minutes very low down.? It's, again, only during switching directions in alt that I have this issue.? To take care of this during alignment, I do an eyepiece eyeball two star align just to get general tracking correct for different parts of the sky, trying to choose stars along the path the ISS will take.? Then I redo those stars with the clutches engaged, and with tracking on, using a reticle eyepiece.? I make absolutely sure to clear that mechanical backlash in alt when doing the final centering, starting from one or two eyepiece fields away, and ALWAYS doing that final approach in the alt direction of tracking.
Refine this procedure until your gotos are within about 15 arcminutes using only two star align.? Try to fix any non-perpendicularities in your mount as much as you can (TPAS will help you measure them).? Leveling the mount helps a lot to avoid lateral shift in your mirror throwing off the "center" alignment position with different alt/az locations.
Lack of a telrad
I don't see a telrad, but that doesn't mean it's not there.? As good as you try to get the alignment, it's still going to be off.? What important that hitting the ISS the first time you press the goto button is the updated rates it sends as it moves across the sky.? When tracking the ISS autotrack is always ON on AN, so wherever you're pointing is treated as correct when you are within five degrees of the computed position.? It helps a lot to park at some low alt before the pass begins in the general az of where it will be.? When AN is on ISS, it is tracking at those rates whenever it's above the horizon, but if it's below horizon, it will only track at the rate in az.? Once it gets above the horizon, it will start tracking in alt, so I lower it myself using "jog" (I'm already close), then get it in the Telrad.? I'm within five degrees, so AN has a lock on it.
Typically, my setup can handle a 6 Ethos at 300x, but then the seeing isn't good enough.? Whenever I used the 8 Ethos for about 230x, I end up saying "I should have used the six".? It is what it is!? With regular maintenance, such as cleaning the trunnions, I can reliably get passes up to about 65-70 degrees with tracking on, and only using the low speed guide button to adjust to recenter.? Above that, and I have to use the higher speed guide to adjust, and that works up until about 75 degrees or so until the motors just can't keep up.
The help me make updating TLEs, as well as calibrating AN's crystal easier, I wrote that into?.? It's a lot easier to update TLEs (and Asteroid/Comet elements) using buttons rather copying and pasting into text files, then using Argonaut.
Having done it once, you know that it is worth every ounce of effort!!!? Don't forget about CSS either.? It was fun to watch it growing, and it still is.? Depending on your latitude, Hubble may also get high enough to show detail, but it flares like crazy, so use two polarizers to adjust the brightness.? One fixed one on the coma corrector, or the like, and the second on the eyepiece.? Rotating the eyepiece crosses the polarizers and dims on the fly.? Envistat is also a big piece of junk whose apparitions last for weeks at a time.? When the Boeing X-37 was in LEO about two years ago, it barely showed extent with my 15".? It's in high orbit now, and its TLEs are often outdated, so that may take some searching around.? I tried to do the Artemis test run, but the TLEs only started once it was in lunar trajectory.? By the time it came around to me, it was already much too small.? The stuff before that could be done, if only NASA would actually update its space vector positions like it said it would.? You would have to make your own "osculating" TLEs with those data.
Beautiful scope with a great eyepiece height for LEO tracking.? Have lots of fun.
