Mechanical/Electrical Engineering Councel For Prototype

I need the expertise of experienced mechanical/electrical engineer/s to give basic advice on how a product could work. Said product will be an adaptation of already existing exploratory core sampling orientation tools. These tools attach to an inner tube which is then lowered into a barrel, drilling is commenced, when drilling is completed the tool logs the bottom of the hole, the inner tube is brought up, we then access the tools log via a phone which tells us where to mark the core sample. The tool needs to be a closed system to be kept dry so it would need to use its battery carefully and efficiency. Approximate size is 80mm long 50mm in diameter. With thread on one end and a shaft able to fit through the inside.