I'm not intimately familiar with the go-pro. I took a quick glance a the contents page and noticed there's an option for multiple exposures. To accomplish that you'll need something with which to track stars.
Generally that requires an expensive equatorial mount tripod for astronomy telescopes There is a cheaper way. Use your favorite search engine and find the well published free plans for a homemade stat tracking device called a "barn door tracker."
Most DSLR cameras have 3 ways to increase the light gathering properties which are:
1 - Shutter speed - you already set that to about the max for the desired subject.
2 - Aperture - open your aperture wider if possible until you get more light to the camera.
3 - ISO sensitivity - if you can - increase your ISO setting to allow the camera sensor to be more sensitive to the amount of available light. Increased ISO settings will cause "noise" on thefinal product.
Another few things you can experiment with are:
1 - Try shooting brighter objects before going after dim ones. It moght not feel like much of a challenge to shoot the moon, but watch how your camera settings react on the mood and change settings as needed to get a better picture.
2 - After shooting the moon shoot subjects which are less bright such as planets and bright constellations like the 7 sisters or orions belt.
3 - after learning how your camera reacts to the various settings you'll have a better idea how to set the camera when photographing dimmer objects.
4 - Experiment - Experiment - Experiment