"As small as possible" is pretty meaningless. What is the maximum size (in real measurements like inches or mm) that your device must be?It doesn't really sound like an Arduino project. You need lots of storage and very low power consumption and neither of those are what Arduinos are really good at. Steve
One way to do it would be to get an Arduino equivalent that has an SD card holder on it. The SD card would have ample capacity to store your position data.Hook it up to a GPS module, figure out how much battery capacity you would need for 72 hours and get an appropriate battery holder.The positional accuracy you're looking for is a little more than conventional GPS can manage unaided, but I notice that some vendors (e.g. Adafruit) sell modules that claim that they get less than 3m error.
About 100x100x20 mm would be the max, I could get away with....- A2035-H-V412 GPS module
These coordinates would have to be very accurate +/- 2-3 meters at most.
Take those coordinates and write them onto a tiny hard drive
If the battery happened to empty, it is crucial that the data meassured and writen on the hard drive remains uncorrupted.
because I need to make a small battery powered device