Background: setting 1998 earth, with incompetent bureaucracy ruling the USA, has already scuttled NASA and decided to go with a space program under direct congressional control (!). The ship travels by exploding fusion devices behind it and travelling forward on the strength of the blast. Obviously it has a very strong shield on the back. Obviously it is not aerodynamic.
The ship's mission is to go to Alpha Centauri and gather data on whether or not the system is suitable for human habitation (earth is becoming uninhabitable because of pollution and mismanagement).
The characters all have hidden motives, as they are all agents of one or another secret society in the fragmented USA government. They have to depend on a navputer+, a navigational computer that is programmed to take care of all their needs. ;-)
The problem is that Djin wants to look at the world after 500 years, and to play off the humor of all these relics of ancient days wandering around in the brave new world of 2500 AD. Since the trip to AC will only take about 9 years of objective time, what to do?
I'm getting an evil idea...
The Navputer+ gets close enough to Alpha Centauri to check it out. Orders sent in the mean time by genius senator Orrin Hatch's subcommittee on efficient space exploration have downgraded the importance of human observation on this task. Quickly confirming that there is no suitable planet for life, the Navputer decides to continue on to Barnard's star before waking up the crew!
The crew awakens and starts working, then discovers that the starfield is all wrong and they're not in the solar system they expected, then they notice that huge gas giant in orbit. They discover a planet in the habitable zone, though calculations are difficult because of that huge companion planet. They also discover that they're short on fuel to get back. If they just head back they'll take about 100 years to make it the 9 ly (or so) back from Barnard's star. After much racking of brain they find a black hole passing by the solar system, just a little bit off the plane of the galaxy, and decide to use the black hole's gravity to give them a boost back towards Sol (it's going that general direction anyway).
Anyway, after much panicking and gnashing of teeth they go for it. Only complication is that the acceleration is going to be so strong that no human will be able to pilot through the black hole. They'll have to go into cryo and let the navputer (the one that didn't wake them up last time) do the steering, and don't have a big window for operations on the other end either, since food is running short.
And finally, the experiment backfires again, though the trip is made at near light-speed (about 9 years) unpredictable time "currents" around the black hole make them *go away* for 500 years.
Finally, the heroes awake in the solar system, speeding past Neptune at .9C. Can they slow down in time to stop at earth, or do they have to depend on earth to save them? They'll probably try to pull another deceleration manoeuvre, but this time the only available large body is the sun. Can it stop them without killing them (is the nuclear shield on the back large enough to shield them)?
At long last the heroes arrive on earth, only to find it is 500 years later, nobody knows them, and their ship is an interesting relic. Their knowledge of Barnard's star is dated. The only unique information they have is on the black hole and the time dilation they experienced. It might be worth big bucks, but how to use the information?