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Газета Nezavisimaya Gazeta Интернет-версия

03.12.1999 00:00:00

Iskander-E"s guidance system is a combination of inertial with radar area guidance


The Iskander-E missile system, developed at the Kolomna Engineering Design Bureau, became the main sensation of the MAX-99 aerospace constructors fair in Zhukovsky. Possible revenue from export sales (the letter "E" stands for "export") certainly matters for Russia"s cash-strapped defense industry. But what is even more important is that the development of the missile system allows to close the gap that appeared in the Russian defense and, perhaps, build in the future a new ideology of relations with NATO.
What makes Iskander-E particularly attractive both its manufacturers and potential buyers is its full compliance with some very serious restrictions imposed by the control regime over the proliferation of missile technologies. According to them, countries with missile technologies do not have the right to export missiles with a range of more than 300 kilometers. Iskander-E"s range is 280 kilometers. The control regime says that the weight of pay load should not exceed 500 kilograms. Iskander-E carries 480 kilograms.

And, unlike Scuds, the new system uses solid fuel, which makes it much harder to increase its firing range.
Solid propellants are easier to make, safer to store, lighter in weight (because they did not require on-board pumps), and more reliable than their liquid predecessors. Here the oxidizer and propellant are mixed into a canister and kept loaded aboard the missile, so that reaction times were reduced to seconds. However, solid fuels were not without their complications.

First, while it was possible with liquid fuels to adjust in flight the amount of thrust provided by the engine, rocket engines using solid fuel cannot not be throttled. Also, some early solid fuels had uneven ignition, producing surges or abrupt velocity changes that could disrupt or severely confound guidance systems.
Iskander-E can be used to deliver cluster-bomb-type (with 54 elements) and landmine-type warheads. It allows to hit small and large-size enemy targets, airfields and air defense systems.
The missile system includes a missile, a self-propelled launcher, mobile means of technological support, and a training complex.

The one-stage missile has an engine with one nozzle and is guided by aerodynamically-balanced elevators. According to our sources, Iskander-E may be as difficult to shoot down as Topol-Ms.
Most importantly, Iskander"s launcher, unlike Tochkas and Okas, may carry two instead of one missile, with one-minute interval between the two launches. The launcher was developed by Titan, a design bureau in Volgograd.

The use of non-nuclear warheads and hence the importance of greater accuracy warranted the development of a new guidance system.

Iskander"s self-homing device, designed at the Central Research Institute of Automatics and Hydraulics and shown by tests to equal in terms of precision the Tomahawk target seekers, can also be installed on ballistic and cruise missiles of several classes and types (including intercontinental).
This, military analysts say, may be a major breakthrough for Russian designers. The United States and the former Soviet Union traditionally followed different paths in exploiting missile technology. Soviet cruise missiles, for instance, were designed mostly for tactical antiship use rather than for threatening strategic land targets (as was the U.S. emphasis).

Throughout the ballistic missile arms race, the United States tended to streamline its weapons, seeking greater accuracy and lower explosive power, or yield.

Meanwhile, the Soviet Union, perhaps to make up for its difficulties in solving guidance problems, concentrated on larger missiles and higher yields. Most U.S. systems carried warheads of less than one megaton, with the largest being the nine-megaton Titan II, in service from 1963 through 1987.
The Soviet warheads often exceeded five megatons, with the largest being a 20- to 25-megaton warhead deployed on the SS-7 Saddler from 1961 to 1980 and a 25-megaton warhead on the SS-9 Scarp, deployed from 1967 to 1982.

Iskander"s guidance system is a combination of inertial with radar area guidance.
Most ballistic missiles use inertial guidance to arrive at the vicinity of their targets. This technology, based on Newtonian physics, involves measuring disturbances to the missile in three axes. The device used to measure these disturbances is usually composed of three gyroscopically stabilized accelerometers mounted at right angles to one another. By calculating the acceleration imparted by external forces (including the rocket engine's thrust), and by comparing these forces to the launch position, the guidance system can determine the missile's position, velocity, and heading.

Then the guidance computer, predicting the gravitational forces that will act on the reentry vehicle, can calculate the velocity and heading required to reach a predetermined point on the ground. Given these calculations, the guidance system can issue a command to the missile thrust system during boost phase to place the payload at a specific point in space, on a specific heading, and at a specific velocity-at which point thrust is shut off and a purely ballistic flight path begins.

Ballistic missile guidance is complicated by two factors. First, during the latter stages of the powered boost phase, the atmosphere is so thin that aerodynamic flight controls such as fins cannot work and the only corrections that can be made to the flight path must come from the rocket engines themselves.
But, because the engines only provide a force vector roughly parallel to the missile's fuselage, they cannot be used to provide major course corrections; making major corrections would create large gravitational forces perpendicular to the fuselage that could destroy the missile.
Nevertheless, small corrections can be made by slightly gimballing the main engines so that they swivel, by placing deflective surfaces called vanes within the rocket exhaust, or, in some instances, by fitting small rocket engines known as thrust-vector motors or thrusters. This technique of introducing small corrections into a missile's flight path by slightly altering the force vector of its engines is known as thrust-vector control.

A second complication occurs during reentry to the atmosphere, when the unpowered RV is subject to relatively unpredictable forces such as wind. Guidance systems have had to be designed to accommodate these difficulties.

Even after a missile's guidance has been updated with stellar or satellite references, disturbances in final descent can throw a warhead off course. Also, given the advances in ballistic missile defenses that were achieved even after the ABM treaty was signed, RVs remained vulnerable.
Two technologies offer possible means of overcoming these difficulties. Maneuvering warheads, or MaRVs (first integrated into the U.S. Pershing II IRBMs deployed in Europe from 1984) contain a radar area guidance (Radag) system that compares the terrain toward which it descends with information stored in a self-contained computer.

The Radag system then issues commands to control fins that adjusted the glide of the warhead. Such terminal-phase corrections gave the Pershing II, with a range of 1,100 miles, a CEP of 150 feet. The improved accuracy allowed the missile to carry a low-yield 15-kiloton warhead.
MaRVs would present ABM systems with a shifting, rather than ballistic, path, making interception quite difficult. Another technology, precision-guided warheads, or PGRVs, would actively seek a target, then, using flight controls, actually "fly out" reentry errors. This could yield such accuracy that nuclear warheads could be replaced by conventional explosives.

Most military experts agree that Iskander-E is superior to both the Russian-made SS-1 Scuds and the U.S.-made ATACMS. Scuds have ranges of up to 185 miles (300 kilometers), but their technology is 30-40 years old.

The ATACMS have a range of 115 kilometers which after upgrading can be increased to 190 kilometers (or 300 kilometers, according to some reports). But a longer range results in a dramatic decrease in throw weight-down to 160 kg from the initial 570 kg.


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