Stephen Robinett’s 1976 Stargate is a standalone SF novel set in the same universe as his short piece “Jenson’s Folly.” It was originally serialized in Analog under Robinett’s pen-name Tak Hallus. It is one of three SF novels Robinett wrote.
Downsized engineer Robert Collins needs a job. Co-worker Bernie Mitchel, also downsized, has found a senior engineering spot at Merriweather Enterprize [sic], but cannot accept it due to a heart condition. He cedes the opportunity to Robert.
The job turns out to involve cutting edge technology, corporate espionage, murder, and quite possibly the destruction of the entire Solar System.