Thanks guys; I just downloaded the data sheet for the Aptina MT9M034 ccd chip which I understand is the one used by ZWO for the ASI120MM camera.
The chip dimensions are 3.54mm x 2.69mm and if I had known this before the ISS passage, I probably would not have attempted to arm wrestle a 2160mm focal length telescope with the hope that a few photons may serendipitously land on the chip!
Cheers
Dennis