The greatest strategic threat to the United States is an attack by one or more ballistic missiles armed with nuclear or other weapons of mass destruction. Today, the United States remains completely vulnerable to this form of attack.
Missilethreat.com is dedicated to explaining this threat, and the urgent need for robust and layered missile defenses. Systems based on land, sea, air, and in space which are capable of intercepting a missile during any phase of its flight are necessary to provide for the common defense.
An intercontinental ballistic missile (ICBM) accelerates a warhead to velocities of approximately 7km/sec. By comparison, a space launch vehicle must accelerate a satellite to around 8km/sec. For a given payload, it would require more thrust to put an object into orbit than to deliver it over an intercontinental distance, but it is slightly easier to put a very small object into low earth orbit than it is to accelerate a larger payload to a slightly lower velocity. The weight of the Iranian satellite (some 27kg) is considerably less than that of a nuclear warhead or other weapon of mass destruction. Iran therefore likely has some improvements to make before demonstrating true ICBM capability. Nevertheless, this week's test represents a considerable achievement for Iran's missile program.