Requirements:
Survive a low altitude ditching into the sea regardless of attitude (even if it flips over in waves.)
Must float (in salt water)
Must run ArduCopter (of course)
Must have one available serial port and I2C (for payload)
Maximum 50cm long/wide (smaller is better)
My payload will be only 100g - the quad can be quite small.
No camera(s) are required, but acceptable if it has.