AJ, Bear and the Russian are the only survivors from the second shuttle. They climb into the armored "Armadillo" vehicle, shoot through the shuttle wall, and drive off into the sunset aimlessly - not sure where to go, and not wanting to help the cause by drilling.
Back on the ground they have regained contact with Harry and Colonel's Sharp's shuttle. The drilling isn't going so well and they have just managed a little over 50ft of their 800ft target. The decision is made by the President to remotely detonate the nuclear bomb. Sharp wants the team back inside the shuttle to take off immediately and pulls a gun on Harry.
Harry somehow convinces Sharp to let him continue digging, even though it's not working out, and with the help of Truman to stop the uplink they turn off the timer. The other bomb in the second shuttle still explodes ruining everyone's day! No wait, everyone has forgotten about that one. We're ok.
Rockhound soon suffers from space dementia and is useless. The big guy in Harry's Armadillo hits a gas fissue and is blown out into space.
At this moment AJ appears on the horizon, and the team can start digging again.
Without much time to spare, AJ uses his "skills" (which is basically to tell the team to keep digging, even when it seems they should stop), and although they are drilling through impenetrable iron plates they reach the 800ft depth in super slick time and many hours faster than the best computers known to man could estimate through softer rocks with undamaged machinery and more men. Who needs Bill Gates when you have Harry and AJ.
They drop in the bomb - but suddenly realise that someone must stay behind to detonate it. They all volunteer. They draw straws and AJ is picked. Harry escorts him out the shuttle - then tears out his oxygen, throws him back inside, and tells him to take care of his daughter. It's a good job AJ doesn't suffocate.
The team fly out. Harry gets blown around a little, and with a second to spare detonates the asteroid. His life flashes before his eyes.
People all over the world, but mainly in India and hillbilly backwater US towns, see the explosion and start to celebrate. The asteroid splits in half and passes hundreds of miles either side of earth - probably taking out Venus. Also seems the NASA computer had that one wrong too - they could have managed another minute or two inside easily.
The shuttle lands. The survivors open the doors to find that the world is being ran by darn dirty apes!! No one saw that coming.
No wait, the survivors are heroes. Rockhound is back to reality and finds his stripper. Colonel Sharp shakes Grace's hand as she is the daughter of the "bravest man he has ever known". Grace is happy to see AJ and forgotten already about her old man.
In the credits we see the wedding of AJ and Grace, shot with a state-of-the-art 1960s video camera.