North Korea apparently fired a modified SS-21 missile towards Japan on May 1st. The SS-21 is a Russian system, introduced in 1976. Russia still maintains a force of 300 launchers (a special truck design for carrying and launching one missile). Syria was reported to have sold North Korea some SS-21 launchers and missiles in 1996, for the purpose of allowing North Korea to copy the design. Russia continues to refine the SS-21 design. The original model had a range of 70 kilometers, but the current one is said to go for 120 kilometers, or maybe as much as 185 kilometers (and still able to use the original launcher vehicle.) The original SS-21 weighed two tons and carried a half ton warhead. Russia still sells SS-21s to foreign nations, a version with a range of 120 kilometers. North Korea is believed to be building the 120 kilometer range version, which means they have mastered solid fuel rocket technology. This is not particularly difficult technology, but requires exacting manufacturing procedures. Solid fuel rocket motors are easier to handle, and have a shelf life of 10-15 years, if you make them right. The SS-21 also has a good guidance system, which puts the missile within about a hundred meters of the aiming point. It is believed that the North Koreans would use their SS-21s to hit the new American bases being built further south of the DMZ, to get U.S. forces out of range of North Koreas artillery.