ESRO 1A and 1B
ESRO 1 turned out to be such a successful mission for its time that ESRO decided to launch the spare spacecraft and instruments as a new mission (into a different orbit and a more dangerous environment), thus the naming ESRO 1A for the original spacecraft and ESRO 1B for the subsequent one. Please note the size of the spacecraft!

The pictures below were contributed by Mr P. J. Caseley (ESTeC Project Engineer): I worked with him on ESRO 1A and 1B, ESRO 4, for a small amount on Giotto and ISO. We are still in communication (since ~1966).

ESRO 1A at ESTeC

ESRO 1A in solar simulation at ESTeC

ESRO 1A on a trolley at ESTeC

People at ESTeC (including Tom Patrick, Peter Sheather and Tom Bowling)

People at ESTeC (including Peter Sheather, Tom Patrick and Tom Bowling)

ESRO 1B at Contraves, Zurich