Alien Games: Running the Death Gauntlet

Three hundred meters down a tunnel on an asteroid the miners nicknamed Kitty, a door to another world is found. The mining company sees unlimited riches to be made. Without telling the government, they outfit a powerful expedition and put their best man, Bob Orem, in charge. Bob's men step into Hell and the company refuses to pull them out: the fate of the human race rests on the shoulders of a mining supervisor whose education ended with junior college. It's a good thing asteroid miners are tough sons-of-guns.