8 hours and 48 minutes for this !

[te51cle]

Just reading a seventies book about how things work and came across some information on the early digital cameras used on satellites and space probes. One of the early Mars probes, Mariner IV, had a camera on it that took pictures at 200x200 'picture point' (pixel) resolution, exposure time was 0.2 seconds then the analogue to digital conversion took 24 seconds with the result being recorded on magnetic tape in the probe running at a high speed of 13 inches per second. The A to D convertor could assign any one of 64 brightness values - that's just 6 bits - to each pixel. The tape was then played back at 0.01 inches per second for sending back to earth by a 10watt transmitter, a process that took 8 hours and 48 minutes for each image.

According to my maths that's a data rate of 7.576 bits per second (don't know what form of error detection/correction was used). So, if they were still using the same transmission technology today, an 8 megapixel 24 bit colour image would take about 293 days to send ! Makes you think just how good 56k dial-up is !

OK, time over.