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It looks like a 90mm Maksutov, similar to the Meade ETX90.
I bought a cheap500mm camera "mirror lens" a few years ago for terrestrial, it was f8. Terrestrial was OK, a bit slow, but lotsof coma on night skies.
For $400, you could pick up a used ETX90, I'd investigate that as the optics would be far better.
I'd also check some of the Andrews 80mm refractors, on a simple az-el tripod for a start, which would be a lot faster.
If you have room at home, investigate 6" and 8" newt OTA's, fast and long FL too.
And as the final piece of advice all the 'experts' will give, the mount is the most important item for satisfying astro work. Perhaps invest in that and keep using your present zoom for a while. Lots of great widefield photo opportunities with it during the winter months from the Milky way being overhead.
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