Slightly bigger than a 35mm film canister.
Rolf's Dad - Klaus Ludwig - worked at the Hartebeesthoek Radio Tracking Station for 9 years from the mid 1960's to early 1970's. During those 9 years, both Klaus and Madlen (Rolf's late Mom) were sent to the USA for a year, to work directly for NASA at their head office in Washington DC.
What is now the "Hartebeesthoek Radio Astronomy Observatory" was originally built in 1961 by NASA, the National Aeronautics and Space Administration of the USA, as a tracking station for its probes that were being sent to explore space beyond Earth's orbit. It was also known as the Deep Space Instrumentation Facility (DSIF). Another station of this type was also set up in Australia.
This location was chosen by NASA as earlier construction of the Deep Space facility had been done and the location was excellent for their requirements.
Acknowledgements: http://www.hartrao.ac.za/other/dss51/dss51.html