|During the recent testing the Shahab-3B proved several significant differences over the basic production variant, with the most important changes being done on its guidance system and the warhead, but few small also on the missile body.
The most significant change is a new re-entry vehicle, with terminal guidance system and a new steering method, completely different from the normal re-entry vehicle with spin stabilization of the Shahab-3A.
The new re-entry vehicle has now place for a rocket-nozzle control system so that no spin stabilization is needed anymore - at least not during all of the flight after the boost phase. Nevertheless, this new nozzle-control system enables the Shahab-3B guidance and steering in all phases of the flight, so that course corrections can be done at any time.
The missile could change its trajectory several times during re-entry and even terminal phase, effectively preventing pre-calculated intercept points of radar systems - which is a method nearly all ABM systems using these days. As a high-speed ballistic missile and pre-mission fuelling capability, the Shahab-3 has an extremely short launch/impact time ratio. This means that the INS/gyroscope guidance would also remain relatively accurate until impact (important, given the fact that the gyrosopes tend to become inaccurate the longer the flight lasts). With that guidance system, the Shahab-3B could archive an accuracy of around 30-50m CEP or even less. The Iranians have already proved of developing even more precise systems, then their Fateh-110 missiles have an electro-optical terminal guidance system: Shahab-3B is not known of having anything similar, but should be fully dependent on INS and ? likely ? GPS.
This new improved accuracy was apparently the reason why the warhead weight has been significantly decreased - to suggested 500kg. This, namely, is sufficient for pin-point target attack capability. Another reason for the 500kg warhead would be the improved range, which is reported to be meanwhile between 1.700 and 2.500km.