Third World Missile and No-dong-A Warhead Dynamic Performance

© Charles P. Vick 2007 All Rights Reserved

March 22, 2007 - April 9, 2008

Disclaimer

The opinions and evaluations stated here in are only the authors and cannot be construed to reflect those of any Government agency, company, institute or association. It is based on public information, circumstantial evidence, informed speculation, declassified U.S. intelligence community documents, official Iranian and North Korean government documents and histories, oral histories, interviews and reverse engineering analysis. As with all data regarding the Iranian and North Korean strategic space and ballistic missile programs, this analysis is subject to revision--and represents a work in progress.

Iran’s 3 rd Generation New Warhead Re-entry Vehicle Design Introduced

Iran has introduced a third generation tri-conic re-entry vehicle (RV) design for the advanced Shahab-3 series that falls exactly between the cone shaped Shahab-3A design and the four-conic Shahab-3B, 3C, Sejjil design. The new tri-conic re-entry vehicle had been known about since it was paraded in Tehran , Iran earlier in 2010 on the Shahab-3. Its design variation introduces a longer double cone design with a very steep tapered cone short cylindrical like base design foreshortening the original cone design but matching the four-conic base flared skirt base diameter of 0.855 meters design from the missile adapter 1.35 meter cylindrical main Shahab-3 missile body diameter. It therefore has a larger volume for a potential conventional high energy weapon or a future nuclear device the design of which is believed to be in development in Iran which is better than the four-conic configuration.  It may also resemble the Shahab-4, No-dong-B, RV design

Third World Missile and No-dong-A Warhead Dynamic Performance

Recently it was suggested that the Third World missile programs warheads would be tumbling about their center of gravity during re-entry making then difficult to identify. This was because they were not being spun-up along their longitudinal axis prior to re-entry through the atmosphere. Also the shape of the re-entry vehicle can affect its accuracy and this is why we see round blunted cone shaped as well as Icononic shaped warhead designs both of which are design for high velocity re-entry. The cone shaped war heads do not perform as well as the Icononic shaped warhead design for hyper velocity IRBM and ICBM flight performance. More recently the Icononic nose cones have been replaced with more rounded nose design icononic designs for greater accuracy.

A warhead is much like a bullet fired from a rifle barrel. If the barrel is grooved to spin up the bullet along its longitudinal axis it tends to fly through the atmosphere to its target more smoothly and accurately. If the barrel is not build with this capability the bullet tumbles uncontrollably about its center of gravity through out its flight in the atmosphere to its target. This tumbling actually reduces the accuracy of the projectile.

However spin stabilization is not the panacea for re-entry warhead stability. For the most subtle reasons spin stabilization can go wrong in spite of it being the space industry standard approach to stability issues for satellite orbit insertion. Spin stabilization can in fact tumble badly out of control especially with as simple an issues as low level propellant tank sloshing and whip antenna vibrations to name but a few reasons. Even an active liquid fuel attitude controlled stability system for spin stabilization or none spin stabilization can be overwhelmed by fuel tank low level propellant sloshing. An active attitude control system without spin stabilization is in fact the best option for accurate re-entry vehicle control as long as the propellants are kept pressurized by bladders. Other options include small repeated solid motor chain link firings or a cold gas based system.

This kind of missile warhead tumbling was noted in the ballistic flights of Iraqi’s Scud-B, Scud-C/Al-Hussein, Scud-D/Al-Abbas ballistic missiles during the Gulf war. In this particular case all of the warheads remained attached to the Scud derived rocket bodies. The length of the Scud-B and C missile bodies and the failure to spin up either the missile with its warhead or separate the warhead after missile spin up made them extremely unstable and in accurate during re-entry to their target area’s.

Today this is not the case with North Korean, Iranian derived warhead technology. North Korea successfully demonstrated payload spin up with the satellite launch attempt of the Taep’o-dong-1 booster. The Taep’o-dong-1 solid propellant third stage both demonstrated a near full duration burn and the spin up of the stage and satellite along its longitudinal axis before it ruptured at orbital insertion de-orbiting the satellite. Whether the spin stabilization was overwhelmed in the last seconds of the burn before rupture is uncertain from the available evidence but it very well could have played a part in the satellites de-orbiting results.

Today this is not the case with North Korean derived warhead technology. North Korea successfully demonstrated payload spin up with its Taep'o-dong-1, solid motor third stage and satellite during that satellite launch attempt. This can plainly be seen in the publicly available North Korean videos released to the press on the Paeutusan-1 launch. Both the solid motor stage and the attached satellite are seen in the video rotating along the centerline longitudinal axis of the two elements. When you think about it technically applying basic Junior high school physics it had to be that way to perform its mission. The only way the stage and satellite combination could be stabilized was to spin them up along the centerline longitudinally axis in order to properly position the third stage solid motor for the orbital insertion burn which is confirmed by the video. While the combination payload rotates about its center of gravity that solid motor has to be precisely positioned and fired in order to place itself in Earth orbit. If it is positioned left or right or up or down from that centerline firing position the payload will be de-orbit by the burn. The Taep’o-dong-1 solid propellant third stage both demonstrated a near full duration burn and the spin up of the stage and satellite along its longitudinal axis. However, the third stage solid motor ruptured, de-orbiting the satellite, almost immediately after achieving orbital velocity. For further information see the North Korean Taep’o-dong-1/NKSL-1 web site.

Placing a satellite into orbit with spin stabilization is somewhat different from a re-entry warhead regime and how best to operate it. Spin stabilization of the North Korean and Iranian re-entry warheads designs may have been tested but an active stabilization regime is preferred over such a procedure. Iran has clearly introduced this kind of active re-entry vehicle control system for their Icononic shaped warhead design seen on the Shahab-3B and 3C/Ghadr missile systems and probably retro fitted it into their cone shaped Shahab-3A warhead cone designs.

It can therefore be assumed correctly that besides North Korea’s, No-dong-A both Pakistan’s Ghauri-II and Iran’s Shahab-3, 3A , 3B & 3C all benefit from this spin-up technology learned with the introduction of an active attitude control system using the cone shaped re-entry vehicle. The Shahab-3/Ghauri-II both apparently initially utilized spin up the single booster stage and warhead combination starting at about 110 seconds into the powered flight of 115 seconds. At this point after 115 seconds of powered flight the warhead is then separated from the booster stage to fly on to its target in a re-entry that remain stable to it target. The Shahab-3B with its active thrusters attitude control, Icononic shaped re-entry vehicle burns for about 112 seconds prior to the spun up re-entry vehicle separation but it is now believed that the spin-up procedure has been abandoned by Iran and North Korea for newer systems. With the addition of GPS targeting the warhead accuracy is greatly enhanced on the order of the suggested accuracy. There are still many in the analytical community that still question this suggested accuracy of 190 meters over a range of 1,350-1,500 km perhaps correctly. There can be no doubt that this spin-up technology did initially improve the accuracy of these warheads over the previously demonstrated poor capability but it has now been superseded by on board active attitude control and guidance packaging. Since the warheads are not tumbling it in fact enhances the interceptor sensor signature identification capability verses that of a tumbling warheads signature.

Equally revealing is the fact that this is the area where the Iranian Shahab-3 has repeatedly failed in flight test. If the steering vanes are not equally positioned correctly or are defective in any way the missile and warhead combination would tumble about its center of gravity out of control destroying the missile. The resulting tumbling warhead whether attached to the remaining missile body or not would in all probability be destroyed during its re-entry. It is known that Iran has and continues to suffer from a steering vane’s quality control problem for it Shahab-3, 3A ballistic missile until after 2002 that the Germans during WW-II solved and that the United States and former Soviet Union were able to easily resolve without using specialized coating. That quality control issue has clearly been addressed and resolved by Iran since 2003.