Built-in Sequel
The shockwave is supposed to reach Earth in 51 years. By that time, Nick and Kayla's child will be 50 years old, and probably have enough experience that she will be put in command of the mission that deflects, dissipates, or otherwise tries to neutralize the shockwave so that Earth will be saved. A built-in sequel. And since so much time will have passed, they can save money by not hiring the same stars. They can do it any time they want... provided they have enough guts to make a sequel to this movie! But there is a core of fans -- soft-core, apparently -- that would see it, even if it goes straight to video.