So this is what you need if you just want to get a picture of the night sky. You don't have to buy an expensive DSLR camera to just getting started.

However, an action camera is not a DSLR, and it has a reason for the cheap price compared to a flagship DSLR camera. The lens is fixed, the sensor is small, the features are limited, parameters are not clear (deliberately, by the manufacture).

With all those efforts, I think that's the best of what I can get from this cheap (350 USD) action camera. However, with a proper DSLR camera, I don't mean the flagship one, but any decent one, I think that will be the worst you can get, and with the same effort (I spend a lot of time on calculating the NPF rule, testing the pre-processing software, and the camera itself), I'm sure you can get much better result, even with less effort.