SPENT STAGE RETARDATION

INTRODUCTION

Stage separation is important in multistage vehicles to drop the burnt out stages from a moving vehicle to improve the performance.

Stage separation failure leads to Mission failure. To avoid this problem separation of burn out or spent

stage has to been done with out any failure. But in stage separation in space removed stage follows

ongoing vehicle with some velocity after the separation due to inertia

STAGING Generally in multi stage vehicles staging is classified in to

two types: Parallel staging. Tandem or serial staging.

In parallel staging both stages fire simultaneously at launch, but the first stage (booster) drops off in mid –flight when spent, while the second stage continues on.

 In serial or tandem staging schemes, the first stage is at the bottom and is usually the largest, the second stage and subsequent upper stages are above it, usually decreasing in size. In this one by one get fire after the spent of below stage

PARALLEL STAGING TANDOM STAGING

IMPORTANCE OF STAGE SEPARATION

A multi stage rocket uses two or more stages, each stage fires for a specified period of time and then drops off. This reduces the weight drastically and allows the rocket to reach higher altitudes with low fuel usage.

Multi stage rockets are more efficient than A single stage rocket engines in accelerating the rocket

STAGE SEPARATION

Stage separation program broadly effects on the success of any launch vehicle.

Separation of spent stages as early as possible is a standard practice adopted for improving the performance of multistage launch vehicle.

Stage separation in multi-stage launch vehicles is broadly classified in to 2 types:

I. Stage separation within the atmosphere.

II. Stage separation in space

STAGE SEPARATION

Two possible separation sequences are available for safe separation

Firing of the upper stage motor before the thrust of lower stage motor has decayed

The use of short duration solid propellant rockets to bridge the gap caused by the decay of lower stage thrust

STAGE SEPARATION

STAGE SEPARATION

Some functional requirements essential for separation system in long range missiles

Collision free separation of spent stages Minimum shock transmission to continuing stages Achieve separation in minimum time Mechanism Provides structural rigidity

SEPARATION ELEMENTS

Generally three elements are require to functioning of stage separation process

Actuator - to trigger the event. Release system - for physical separation Jettisoning system - to impart sufficient release

separation velocity to the system

ACTUATOR

actuator is a mechanical device for moving or controlling a mechanism or system.

It takes energy, usually transported by air, electric current, or liquid, and converts that into some kind of motion.

Generally two types of actuators are use in space applications

1. electric based 2. probased

RELASING SYSTEM

Release systems imparts the physical separation to two stages

Various mechanisms can be deployed for stage separation of a large multistage vehicle, and its choice depends on availability of space and requirement of mission.

These systems break the connection between spent stages and moving vehicle with suitable mechanism.

RELASING SYSTEM

Two types of release systems are available i.e.I. Pyrotechnic systems: In pyrotechnic systems Electro explosive devices

(EED) ignite by radio frequency or electric discharge then two stages are separated by releasing the link between them .

Ex: FLSC, explosive bolts, pyrotechnic nuts II. Mechanical systems: Mechanical systems are generally available along with

zip cords and springs these are helps in separation of two stages

Ex: ball and socket, pin pulleys etc

PYROTECHNIC SYSTEMS

EXPLOSIVE BOLTS

PYRO TECHNIC BOLTS1  Light blue First stage 2 Dark blue Second stage P Yellow Piston C Light Green Clamp and extension B Dark Green Pyro body F Grey Fixation wire X Red Pyro charge

PIN PULLEY

JETTISONING SYSTEM

Jettisoning systems are provide the required separation velocity to separating stages.

These systems helps in collision free separation between two stages

These can be active or passive. Passive systems being those which does not require additional systems for jettisoning the spent stages.

Energy required for jettisoning the systems are provided by employing following

Spring thrusters Pneumatic thrusters Rocket thrusters

SPRING THRUSTERS

SEPARATION WITH IN ATMOSPHERE

Generally first stage of launch vehicles are separated with in the atmosphere.

Due to the aero dynamic forces and gravity effect the separation with in the atmosphere don’t cause damage to ongoing vehicle

Spent stages with in the atmosphere easily separated by using suitable release and jettisoning system

STAGE SEPARATION IN SPACE

All stages except first stage are separated in space Stage separation Beyond the atmosphere effected by the

delay between the burnout of lower stage and light up of upper stage. it causes the problem due to absence of aerodynamic forces

Here separation of the two stages is not sufficient because empty shell of lower case follows the upper case

RETRO MOTORS

Retro motors also called as retro rockets and small rocket motors

These are produce the reverse thrust to retard the spent body

The arrangement of retro motors in motor case sweeps equal angles with respect to reference axis

The structural components are

Chamber shield

Propellant grain

Nozzle

RETROMOTOR COMBUSTION CHAMBER

RETROMOTORS

Chamber outer shield is made with HE15 aluminum alloy

Other aluminium alloy useful which are withstands chamber internal pressure forces

Inner surface of the chamber lined with olass-phenolic composite ablative material to with stand thermal protection of motors

RETROMOTORS

The propellant should be high energy type and keep minimum weight and at the same time mechanically strong to with stands pressure loads

The double base propellant has got excellent mechanical properties with very low smoke exhaust.

INGREDIENTS

Nitrocellulose (NC) -51.3 - Binder

Nitroglycerine (NG) -43.0 - Reactive plasticizer

Diethyl phthalate (DEP) -3.0 - Plasticizer

Ethyl centralite (EC) -1.0 - Stabilizer ,oxidant

Candelilla wax - <1 - Lubricant

RETROMOTORS

These motor exhaust nozzle canted(kept at an angle) for convenience of structural arrangement

Retromotor exhaust nozzles are cant angle such that thrust doesn't effect the vehicle

STAGE SEPARAION USING REROMOTOR

All the motors which are placed in the rocket case ignite at one time

These are produce the 06 to 10% of vehicle velocity in opposite direction

After the separation is made by the release system these are retard the spent body to decelerate the velocity of sent stage

RETARDATION OF SPENT STAGE USING RETRO MOTORS

RETROMOTOR DESIGN

Retro motors are designed based on the ongoing vehicle velocity at that stage separation

Material selection depend on the chamber internal pressure forces

Propellant grain and its structures restricted to some types depend on the requirements

CONCLUSION

Stage separation beyond the atmosphere is higher importance

Retarding the spent stage after the separation in space should be done for not disturbing the path of ongoing vehicle

Use of small rocket motors for retarding the spent stage is advantageous than use of spring thrusters

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