October 16, 2007: North Korea test fired another of its KN-02 ballistic missiles last Summer. This weapon is a modified SS-21 Russian system, originally introduced in 1976. Russia still maintains a force of 300 SS-21 launchers (a special truck design for carrying and launching one missile). Syria apparently 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 ( the 120 kilometers version) to foreign nations. 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, where they were moved to get out of range of North Koreas artillery. North Korea sells about a hundred missiles a year to customers like Iran, Syria and Yemen. These sales are a major source of hard currency.