Long ago, and asteroid was on a collision course with Earth. When collided, it wiped out all of the dinosaurs. Those who remain were killed off by the following Impact Winter. That was millions of years ago, when the world was young and fruitful. Though, with the extinction of the dinosaurs, came early mammals, eventually: Mankind.
Present time: Another asteroid is on a collision course with Earth, this time to wipe out all of mankind. One astronomer, notices it with his computer (while he was reading a newspaper that includes the rumoured USO), calls the CSA (Canadian Space Agency) about it. He describes it as a smooth, potato shaped one, with craters on it, with the might equivalent of the Tsar Bomba, the most powerful bomb ever built. While it won't completely destroy Earth, it will, of course, wipe out all life on it. He requests a visit to headquarters right away.
As he arrives, he passes on his information to the people within, saying that this may require an international effort to stop the asteroid from impact. Blowing it up from within won't work, given it'll split in half and hit Earth anyway. They can't capture the asteroid because how big it is-and even if they have to build a net of the asteroid's size, it would still take considerable amount of time. They can launch missiles at it because it's the same result as nuking it from within, if not worse. Then, the astronomer came up with an idea. Recalling his childhood hobby of baseball and the current development of spacecraft being built in orbit-as well as electric propulsion for spacecraft, he proposed the idea of strapping the asteroid with rocket engines to push it back into space.
And how to deliver the rocket engines to the asteroid is to build a spacecraft in orbit carrying the engines, crewed by a select few, able, smart and careful enough to pull off.
He calls the asteroid Godstone and This will be called Operation Baseball. Because...
"If god is the pitcher, we're the batter and Earth is the Umpire. One strike, We're out. Hit the ball (in this case fire the engines on the asteroid) Home run! It's that simple! But this scenario, not quite."
It doesn't matter when it'll hit the earth, what does is how long can the spacecraft be built in orbit to deliver the engines. So after months of painstakingly designing, launching and constructing the spacecraft which will be crimsoned as the ISC (International Spacecraft) Assegai! The crew also spend during that training, coordinating and planning out the mission through simulations. From piloting the Assegai to diving underwater to simulated a zero gravity environment wearing spacesuits, the crew do their best to be prepared for their mission.
And as the ship is complete and crew launched from Cape Canaveral Space Station where their rocket is ready for blast. The crew consist of one Canadian, a few Americans, one African, one French, one British, one Indian, one Chinese and one Japanese as they strap themselves in and blast off into orbit where the Assegai awaits. The capsule soon arrives at the behemoth of the ship (one engine in the back to give it acceleration, the one in the front to slow down, the bridge deep inside the ship, the cargo bay that stores the small engines to be delivered and radiator panels that absorb heat and delivered to the ships key subsystems to keep it and it's crew alive), with the astronomer look at Godstone via his telescope, seeing the intimidating asteroid with worry and hope. Soon, Assegai ignites it's engine approaching the asteroid. It then fires it's front engine to slow down. Synced with Godstone, the astronauts put on their spacesuits and go into the cargo bay to get the engines. The bay depressurizes then opens the doors.
With the doors fully opened, time against them and the engines held by the astronauts, the battle begins...
The Astronauts jump out of the ship, using grapplers to reach down to Godstone's surface at key points. One on top, one beneath, one on both sides each and one onto where asteroid is heading. There can be no mistakes, nor loss of the engines, if one is lost or the astronaut gone then the mission is blown. Through care and coordination, the astronauts eventually placed the engines on Godstone before heading back to the ship to ignite the ion engines. In case of an emergency, they can fire the rear engine to help push the asteroid away, then use the front engine to get themselves back to Earth. The Ion engines ignite, followed by Assegai's rear engine to give it a boost. As soon as the people all over the world see Godstone going away, they cheer with joy and relief, as does the astronomer, his theory proved correct and tosses his newspaper up in the air.
Now, all the astronauts can do is detach the asteroid and use it's front engine to return to Earth. They use the last of their fuel to slow themselves down and make a synchronized orbit around Earth and request another rocket launch to bring them back. The second rocket, which is next to the launched delivery rocket, launches into space to pick up the astronauts. And just before they enter the capsule to make their splashdown, they set the Assegai to make a slight course down to Earth-using the planet's gravity to pull the Assegai down, it will rip it apart and it's debris scattered around the world for the people to see.
And the astronauts cheer in triumph, having saved Earth and deserved a hero's welcome home celebration, the Canadian astronomer couldn't be anymore relieved and happy.