RT-20P / SS-15 SCROOGE
The RT-20P was a two-stage missile which was unique in that it used dissimilar solid and liquid propellants in the first and second stages. The first stage used a solid propelled engine which featured four rotating nozzles to conduct flight control. The second stage was liquid propelled sustainer using asymmetrical dimethylhydrazine and nitrogen tetraoxide in a single chamber. The development of a mobile ground-based missile system equipped with an intercontinental ballistic missile (ICBM) began at the Yuzhnoye Design Bureau in Dnipropetrovsk in 1964. The first variant of the RT-20 ICBM (8K99) was a three-stage solid-propellant rocket. During the next stage of design work to reduce the launch weight of the rocket, it was decided to develop a two-stage RT-20P with a first stage equipped with a solid-propellant rocket engine and a second stage with a liquid rocket engine. This decision was made because the missile was placed on a mobile caterpillar self-propelled unit based on the T-10M tank (Object 821), which could not transport a missile weighing more than 30 tons.
The 8K99 missile was supposed to be used in two versions: with light and heavy head parts. The head parts are monoblock, thermonuclear. The "light" head had a body made in the form of a set of three truncated cones with spherical blunting. To reduce the aerodynamic drag on the "light" head part, a conical fairing was installed, which was discharged during the operation of the second stage engine when the rocket reached the depleted layers of the atmosphere.The head part was attached to the upper connecting frame of the instrument compartment with the help of three rupture bolts. The rocket stages used three reverse-thrust engines.
The instrument compartment in the case of using the "light" head part has the form of a truncated cone, the "heavy" head part is a cylindrical shape. The main part of the devices of the missile control system is located in the instrument compartment. The missile control system 8K99 is inertial, autonomous with gyro-devices on the air suspension (weight of SU-250kg) and a high-speed digital computer.
The connection of the on-board equipment with the launcher is carried out with the help of two terminal blocks, one of which is located on the side surface of the instrument compartment's other housing - on the container. Before the rocket leaves the container with the help of bursting bolts and repulsive springs, the block of container connectors is divided. After the rocket leaves the container, the rocket connector unit is likewise divided. The part of the block remaining on the rocket is closed with a lid. The instrument compartment is bolted to the upper end frame of the fuel compartment.
The fuel compartment is a tank divided by an intermediate bottom into two cavities: the upper one for the oxidant and the lower for the fuel. As an oxidizing agent, nitrogen tetraoxide is used as fuel - asymmetric dimethylhydrazine (NDMG). To the lower end frame of the fuel compartment, a liquid rocket engine 15D12 of the second stage is fixed by means of a rod frame. Control of the second stage in the angles of pitch and yaw is carried out by blowing turbogas into the supercritical part of the engine nozzle. For roll control, two pairs of tangentially installed control nozzles, also using turbogas, served.
The separation of the stages is "hot", i.e. the bursting bolts are triggered after the start of the propulsion system of the second stage. In the shell of the transition compartment, there are windows that ensure the escape of gases at the initial stage of the separation process. The collision of the casing of the transitional compartment with the engine of the second stage during separation is excluded by specially adopted structural measures.
The transition compartment is bolted to the solid-propellant first stage engine. At the front of the engine of the first stage, there is a powdered rocket engine of the final stage, launched after the fuel burns in the engine of the first stage and finishing its work after the rupture of the links between the rocket stages. The nozzle of the final stage engine goes into the cavity of the main engine.
To the lower end frame of the engine of the first stage is attached the tail section, which protects the engine nozzles and the steering drive from the effect of air flow and gas jets. The executive bodies of the control system of the first stage are four rotary nozzles of the solid fuel engine. Along the hulls of both stages of the rocket, the onboard cable network is laid from the outside and fixed by means of brackets, along the opposite side along the body of the second stage, the pipelines of the pneumohydraulic system are laid.
Mounting of the rocket to the support pins of the container is made with the help of eight rupture bolts, mounted on the lower end frame of the engine of the first stage. Radial movement of the missile and the container is impeded by four support rings.
The rocket is launched from a vertically arranged container. The starting container is thermostated. Before the launch, the azimuth aiming of the rocket is carried out, which consists in aligning the X axis of the gyrostabilized platform with the shooting plane. A coarse alignment of the X axis with the shooting plane (± 10°) is made by turning the launching unit, into exact alignment by turning the gyro-stabilized platform. The entry of the flight task in the SU is remote.
According to Russian sources, the RT-20P, had a launch weight of 30.2 tons and could either carry a payload of 545 kg delivering a single warhead with a yield of 550 Kt up to 11,000 km, or a payload of 1410 kg and a 1.5 Mt warhead up to 8,000 km. Western sources believed that the missile was capable of delivering a 1000-lb reentry vehicle to a range of 5,300 nm with a CEP of 1.0 to 1.5 nm.
A new command structure substantially increased the time the missile could be maintained in an operational mode. The missile had an inertial guidance system, and the development of new high-precision gyroscopic devices allowed for improved accuracy as well as improved capability for remote input of mission data. Approaching the target, the missile produced false targets and distorted its radar characteristics.
To move the container with a rocket weighing 38.8 tons, the chassis of a heavy tank T-10M (Kirov Works, Leningrad) was used. On a flat road the vehicle developed a speed of up to 40 km / h.
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