The first ever digital camera, built in 1975 by Eastman Kodak engineer Steve Sasson. It weighed 8 pounds (~3.6kg) and recorded 100x100 pixel photos to a cassette tape.
It's worth noting this is the first commercially available digital camera. The digital camera aboard Landsat 1 (launched 1972) was developed in 1969, predating this by 6 years.
The Return-Beam Vidicon (RBV) sensor utilised vidicon tube instruments containing an electron gun that read images from a photoconductive faceplate similar to television cameras. The data stream received from the satellite was analog-to-digital preprocessed to correct for radiometric and geometric errors.
So... if I understand it correctly, it was an analog camera which signal was at the end converted to digital. But please correct me if I'm wrong!
If I understand correctly, that means it has a 6 pixel-row resolution that it uses to scan a 2D area.
Finally, I realized I was using a wrong idea of "digital camera". There is no true "digital sensor", all sensors are analog and always need a postprocess to convert to digital... right?
As always, it's impossible to provide a non-ambiguous definition. Is a 6-pixel row res instrument on a satelite a "digital camera"? ... kind of :)