The British rocket Black Arrow was in fact already cancelled, when the Prospero satellite as a last effort was launched on 28 October 1971 at Woomera, South Australia.
The small satellite carried several experiments.
Beside larger solar cells for power supply, it carried smaller
experimental solar cells.
Prospero is still in orbit although it's tape recorders stopped working in 1973. It not expected to decay until about 2070, almost 100 years after its launch.
Books and other sources:
Brian Harvey, Europe's Spaceprogramme to Ariane and beyond
Douglas Millard, The Black Arrow rocket
H. J. H. Sketch, The Prospero Satellite
My own photos from Science Museum, London