The SDI Defense is the only protection from the Nuclear Missile. With a 70% hit rate, you are sure to be protected. The SDI works as a satellite in low orbit, tracking missiles from space. Any unknown object or a potential Nuclear missile can be taken down with a massive laser shot, disabling the Nuke completely. Although being the only weapon against the Nuke, the SDI is not totally effective. For example, if there are 4 Nukes incoming, the SDI can protect you 100%. However, if there are 10 or more Nukes incoming, then at least one of them is going to hit you.