According to Aviation Week, this was a secret Magnum ELINT (ELectronic INTtelligence) gathering satellite headed for geosynchronous orbit, like those launched by STS-51-C and STS-38.
According to Aviation Week, STS 33 launched a secret, Magnum ELINT (ELectronic INTtelligence) gathering satellite into geo-synchronous orbit. An identical one was also launched by STS-51-C and STS-38.