Backstory
A century in the future, humans land on Venus and colonize it. Below the surface, thousands of miles of artificial tunnels are discovered. They are believed to have been built thousands of years ago by an alien species known as the Heechee, but little else is known about them until an explorer discovers a Heechee ship, intact and operational, in one of the tunnels.
Rather than report his findings, he climbs in and activate it. The ship launches and goes into "TAU Space," a faster-than-light travel method. It arrives at a huge space station carved out of an asteroid floating halfway between Venus and Mercury, which is full of thousands of similar ships, but otherwise empty. However, the explorer is unable to figure out how to return to Venus, and faced with a lack of supplies, figures out how to detonate the fuel cell of the ship he came in. The detonation kills him, but also attracts the attention of a NASA tracking station, who send an expedition to investigate.
The discovery of the station and its ships allow humanity to verge into deep space. Although they were unable to reverse engineer the Heechee technology, they can use the ships' stored destinations and the station becomes humanity's "Gateway" to outer space, hence the name. This almost leads to war among the superpowers of Earth over ownership, until a compromise is finally worked out. A co-operative called the Gateway Corporation is formed, with the superpowers each holding one quarter of company stock.
The alien ships that are found still function, but their built-in destinations are a mystery. Navigation is accomplished by using 5 digit codes with the ships' computers, but there is no way to tell what codes go where. Volunteers called prospectors come to Gateway to test the codes and pilot the ships to their destination, explore and report back what they find (as well as bring anything interesting back). A large majority of the prospectors return with little or nothing, a tenth never return, but the remaining 1.5% return with artifacts or knowledge that make them incredibly rich.
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