Joshua Pollack over at armscontolwonk posted about a recent Iranian test of its Qiam-1 missile. His post and the comments raised a number of interesting questions about the missile. Since I couldn’t post figures in a comment there, I’m posting here some ideas about what may be going on and what some of the claims by Iranian Defense Minister Ahmad Vahidi and others may mean. I suspect some of the claims are bluster, but some are not.
-This is the first Iranian missile without fins. Fins on a missile are not useful on descent, but are used to aerodynamically stabilize the missile during boost. If you have a good enough guidance system that can sense changes in the motion of the missile and feed back corrections quickly enough, you can actively stabilize the missile and don’t need fins. The reason you would like to get rid of fins is that they add mass and aerodynamic drag to the missile, which slows it down and reduces its range (for a given payload), as General Seyed Mehdi Farahi noted.
-Vahidi’s statement that getting rid of the fins increases “agility” is right in this sense: A missile is controlled by varying the direction of the thrust, which causes the missile to rotate. If there are fins on the missile, that creates aerodynamic resistance to moving the rear of the missile sideways, and therefore slows the reaction of the missile and makes the maneuvering more sluggish. (This is the same reason that highly agile fighter planes are made aerodynamically unstable, since that reduces aerodynamic resistance to their maneuvering.)
-The improved guidance system may rely on ground controls rather than relying on an internal guidance system in the missile. For example, ground radars can track the flight of the missile and a ground station can radio guidance maneuvers to the missile. This could increase the accuracy of the missile during boost phase and allow the active control needed to remove the fins, although it might not be necessary for that. This kind of guidance can be done for short-range missiles since the boost phase remains within the range of the radar, and this is what was done on a number of early, short-range missiles. A clue that this may be done here are the tabs sticking out from the front section of the Qiam-1:
which are reminiscent of the guidance antennas on China’s DF-2A, which can be seen in this picture that I took at a museum in Beijing:
-If this is what Vahidi means by the “smart navigation system” then the decreased “possibility of it being targeted by other projectiles” may refer to the likelihood of the missile being targeted during boost, not during reentry. Having fins on the missile provides corner-reflectors that can give a large radar return, making the missile easier to see by a defense radar. So removing the fins would also have the advantage of making it somewhat more stealthy during boost.
-Vahidi’s statement that a “smart targeting system” would reduce launch time may simply refer to having better computer systems to calculate faster the burnout trajectory needed to hit a target, and coupling it to a GPS system that knows the launcher’s location. In the past, it was a problem for mobile missiles to know accurately where they were launching from, unless they went to a pre-surveyed site.
-One reason fins wouldn’t help on reentry is that, as we saw with Iraqi Al Husayn missiles during the Gulf War, the aerodynamic forces on a reentering missile with a range of about 500-km or longer are large enough to tear the empty missile body off the warhead. This process, as well as any rough flanges that may remain on the back of the warhead, can cause the warhead to corkscrew or tumble, which greatly reduces its accuracy. That’s why you expect missiles of this range to have separating warheads.
-The greater accuracy Vahidi talks about may be a combination of better guidance during boost and a separating warhead that is not tumbling or wildly corkscrewing. While this may be an improvement over its past missiles, I expect the inaccuracy of this missile would still be large.
-Unlike speculation in Josh’s post, I think it’s extremely unlikely that Iran has developed a maneuvering reentry vehicle, which is technically difficult if the goal is higher accuracy. It’s one thing to get an RV to maneuver—intentionally or not—during reentry to avoid defenses, but that usually comes at a big cost in accuracy. It is another thing altogether to develop the capability for a maneuvering RV (1) to know where it is so it can maneuver back to the target and (2) for it to have a system on board that allows it to actively do those maneuvers in a controlled way.
Support from UCS members make work like this possible. Will you join us? Help UCS advance independent science for a healthy environment and a safer world.