Agni IIP (syn. Agni IIAT)
The Agni-IIP (AT) is the result of a CIP (Continuous Improvement Program) with Agni-II. Different reports indicate India developing a more advanced technology (AT) version of Agni-II putting into use, state-of-the-art technologies to significantly improve the Agni-II performance as well as to adapt it to the newer and lighter nuclear payload. The new propulsion system could greatly increase the missile's range to 4000 km (1500 kg payload) and potentially to ICBM range for lighter payload.
The Agni-IIP is likely to incorporate the following changes:
A larger diameter booster stage made of stronger 250-Marging steel, improving fuel loading and fuel mass-fraction.
Lightweight carbon composite motor casing for the second stage, instead of steel casing, improving its mass-fraction.
Lighter RV, with all carbon composite re-entry heat-shield, multi directional carbon re-entry nose tip and control surfaces.
First Stage: A new 1.3 meter diameter booster case made of 250-Maraging steel with improved chamber pressure and fuel mass-fraction. Approximately 11 meter long and 20 tonne mass
Second Stage: Lightweight filament wound carbon composite motor casing for Stage-II with improved fuel mass-fraction.
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Engine Terminology
Propellants: The Oxidiser and Fuel (listed in that order) used by the rocket engine. For solid fuel motors only the word 'Solid' is shown. For nuclear or electric motors, the fluid used by the motor to form the exhaust is shown. For air-breathing motors, 'Air' is indicated as the oxidiser.
Thrust(vac - kgf): The thrust the motor generates in a vacuum, expressed in the terms of 'kilograms-thrust (kgf)'. This is not a term officially recognised by the scientifically proper establishment but was used by the Russians in their rocket engineering (the Americans used pounds thrust).
Thrust(sl - kgf):
The thrust the motor would develop at sea level in terms of 'kilograms-thrust'. This may be zero for motors designed for upper-stage operation in a vacuum (see Expansion Ratio, below).
Thrust(vac - kN):
For purists, the thrust of the motor in vacuum in officially-correct kiloNewtons (= (Thrust-kgf) * g / 1000) where g = acceleration of gravity on Earth at sea level = 9.80665 m/sec^2.
Thrust(sl - kN): For purists, the thrust of the motor at sea level in kiloNewtons.
Isp-sec:
The specific impulse of the motor in vacuum. The higher the number, the more efficient the motor. The units here are seconds - because specific impulse represents the kilograms-thrust the motor generates per kilogram of fuel per second of operation (kgf/(kg/sec)) = sec). Important relationships are : effective vacuum exhaust velocity of the motor = Isp * g (this is also the specific impulse in kN thrust terms); fuel consumption of the motor = (Thrust in vacuum) / Isp.
Isp (sea level)-sec: The specific impulse of the motor at sea level. This is the same fraction of the vacuum specific impulse as the sea level thrust is to vacuum thrust. It can be zero (see Expansion Ratio, below)
Burn time:
The total operating time of the motor. For solid motors, this is the more-or-less unstoppable period of thrust until all of the propellant is consumed. For liquid motors, this is the rated thrust duration of the motor for a single operation. This is greater than the thrust time of the motor in actually use on a particular stage. The total tested or rated operating time of a liquid motor between overhauls (if it is reusable) is typically many times the total rated operating time per each use.
Mass Engine:
For liquid motors, the mass of the engine dry (without propellant in the lines).
Diameter: For liquid motors, the maximum envelope diameter of the motor. This is usually the same as the diameter of the nozzle exit, but in some cases may be more than that due to pumps, pipes, or structural attach points. For solid motors, the diameter of the main motor body.
Length: For liquid motors, the length of the motor and the pumps, pipes, etc. usually mounted above the thrust chamber. For solid motors, the total length of the motor.
Pc-bar: For liquid motors, the pressure of the combustion chamber in bar or atmospheres sea level pressure. The proper definition for the chamber pressure is the throat stagnation pressure (total pressure in the critical cross section). A small loss exists between the injector end of the chamber and the throat. American engineers usually give the throat stagnation pressure, Russians usually gives the injector end pressure. This is usually not stated explicitly and thus may be unknown. For solid motors, the pressure in the motor casing during operation.
Expansion Ratio: The ratio between the area of the combustion chamber exit and the area of the nozzle exit. A large area ratio improves the performance of a motor in a vacuum since the exhaust is expanded further, thus converting potential energy into kinetic energy. However, at sea level a high area ratio can result in flow separation, which can drastically reduce or eliminate the net thrust of the motor.
Oxidizer to Fuel Ratio: The ratio between the mass of oxidiser burned per mass of fuel burned (liquid motors only).
Thrust to Weight Ratio: The ratio between the vacuum thrust of the motor and the mass of the motor (liquid motors only).
Coefficient of Thrust vacuum: A measure of the flow expansion of the motor in vacuum.
Coefficient of Thrust sea level: A measure of the flow expansion of the motor at sea level.
