David C. Wright, a senior scientist at the Union of Concerned Scientists, a private group in Cambridge, Mass., estimated that the rocket, if eventually successful, might lead to a ballistic missile that could throw a warhead of 2,200 pounds a distance of some 3,700 miles, far enough to hit parts of Alaska.He added that if the warhead’s weight could be cut in half, down to 1,100 pounds, the rocket would be able to hurl the weapon much farther, about 5,600 miles. That, in theory, would bring the West Coast of the continental United States within its range.