The Precipice by Ben Bova
Once, Dan Randolph was one of the richest men on Earth. Now the planet is spiralling into environmental disaster, with floods and earthquakes destroying the lives of millions. Randolph knows the energy and natural resources of space can save Earth's economy, but the price may be the loss of the only thing he has left - the company he founded, Astro Manufacturing. Martin Humphries, fabulously wealthy heir of the Humphries Trust, also knows that space-based industry is the way of the future. But unlike Randolph he does not care if Earth perishes in the process. And he knows that the perfect bait to ensnare Dan Randolph and take control of Astro is his revolutionary new fusion rocket propulsion system. As Randolph - accompanied by two beautiful women who are also brilliant astronauts - flies out to the Asteroid Belt aboard a fusion-propelled spacecraft , Humphries makes his move. The future of mankind lies in Randolph's hands.