Hi Sevan,
Great to hear you have been doing satellite tracking with your Argo Navis for a while now. It's a lot of fun and it really gets the heart rate rising. It's really cool to do in that period at dawn when you have setup but it is not quite dark enough yet to observe deep sky objects.
Appreciate you wanting to retain alignment but we invalidate for a couple of good reasons, one of which is to ensure your ability to find stuff will remain as accurate as possible.
Whenever user objects are loaded via the SETUP LOADCAT menu, whether they be satellites, asteroids, comets or user defined objects, the alignment is intentionally and purposely invalidated.
In the case of objects such as user defined objects, we want to ensure that if they had been used as alignment objects or TPAS sampled data themselves that if they suddenly are then erased the "wheel's don't fall off" so to speak. In programming parlance, we would refer to it as avoiding a "null pointer reference". The very object that say the alignment was referring to vanishes.
The second and more important reason however is related to the fact that the FLASH memory in which the user objects reside is physically the same FLASH memory in which the program and data including the operating system reside. When Argo Navis boots the OS internally keeps track of time to very small fractions of a second. So for example, say you aligned on a star 100.0 seconds after the system starts and a second star at 132.562 seconds after the system started, a relative difference of 32.562 seconds during the alignment process. Since the Earth is rotating and with it the apparent position of the stars, the alignment process if also taking time into account including those sub-second timings when the star is centered.
The type of FLASH memory Argo Navis uses is known as NAND FLASH and it is exceedingly fast to read from. Much faster than the type of FLASH say used on a USB stick or SIM card. However, FLASH memory writes times for all types of FLASH is slow. When Argo Navis writes to FLASH memory it effectively suspends all other background processing activity because the same memory it operates from is in a busy state whilst the FLASH device commits the write. It thus looses track of internal time, not by much, but depending on how much is written to the FLASH.
Since Argo Navis needs to suspend operation it looses its tracking of sub-second relative time. Hence we purposely invalidate the alignment.
The time of day clock - the RTC - however maintains time during FLASH writes so it does not need to be re-synchronized.
The alignment invalidation can be inconvenient but it is there for a good reason.
As you will be aware and is detailed in the Argo Navis User Manual, it is highly recommended to update the TLE's just before an observing run.
Satellites in low Earth orbit in particular, such as the ISS have orbits that decay and change very quickly from day to day and split second timing is everything.
The Argo Navis clock scaling feature also helps with precision timing.
Enjoy those passes!
Best Regards
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Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place
Mount Kuring-Gai NSW 2080
Australia
Phone +61-2-9457-9049
sales@...
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https://www.wildcard-innovations.com.au
