In Hunnicutt's book "Abrams" on p28 it says:
... it was directed that contracts be awarded to firms with recognised research and engineering staffs for the development of an X-weapon to perform the role of the medium tank. .. to be available for production 1958 (later 1961)
Ordnance Technical Committee minutes item 34753 24th April 1953 assigned the name ASTRON to identify the project.
Contractors were to be responsible for studying the X-weapon as a complete unit without restrictions being placed on any of the components. Seventeen proposals and bids were received from industry in response.
The following 10 pages in "Abrams" describe some of them. Some look fairly conventional. Others far from it.
It doesn't say what ASTRON stood for, if anything.
Official report pubd by OTAC, Center Line, Michegan, 1955