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1RE ENTRY OF SPACE VEHICLE

1. INTRODUCTION

The successful exploration of space requires a system that will

reliably transport payload such as personnel and instrumental etc. into space

and return them back to earth without subjecting them an uncomfortable or

hazardous environment. In other words, the spacecraft and its payloads

have to be recovered safely into the Earth. We have seen the re-entry

capsules and winged space vehicles approach the earth followed by safe landing.

However, this could be accomplished only after considerable research in high

speed aerodynamics and after manyparametric studies to select the optimum

design concept.

Re-entry systems were among the first technologies developed in

1960s for military photo-reconnaissance, life science and manned space flights.

By 1970s, it led to the development of new refurbish able space shuttles. Today

space technology has developed to space planes which intend to go and come

back regularly from earth to space stations. USAs HERMS and Japans

HOPE is designed to land at conventional airports. Few significant advances

in current proposed re-entry capsules are ballistic designs to reduce development

and refurbishable cost, to simplify Operations.

For entering into atmospheric and non-atmospheric planet the

problem involves is reducing the spacecrafts speed . For an atmospheric

planet the problem involves essentially deceleration, aerodynamic heating,

control of time & location of landing. For non-atmospheric planets, theproblem involves only deceleration and control of time & location of landing.

The vehicle selected to accomplish a re-entry mission incorporates a thick

wing , subsonic ( Mach < 1 ) airfoil modified to meet hypersonic

DEPARTMENT OF MECHANICAL ENGINEERING


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(Mach>> 1 ) thermodynamic requirements. The flight mechanics of this vehicle are unique in

that rolling manoeuvres are employed during descent such that dynamic loading and

aerodynamic heating are held to a minimum.

Therefore re-entry technology requires studies in the following areas:

1. Deceleration

2. Aerodynamic heating & air loads

3. Vehicle stability

4. Thermal Protection Systems (TPS)

5. Guidance and Landing.



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CONTENTS

1. ABSTRACT

.2. INTRODUCTION

3. RE ENTRY MISSION PROFILE, CONSTRAINTS, AND VEHICLEREQUIREMENTS

4. ENTRY CORRIDOR

5. GAS DYNAMICS AND DECELERATION

6. AERODYNAMICS HEATING

7. MATERIAL SELECTION IN DESIGN

8. THERMAL PROTECTION SYSTEM (TPS)

9. VEHICLE GUIDANCE AND LANDING

10. CONCLUSION

11. REFERENCE



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1. ABSTRACT

In recent years, industry has produced high-temperature fiber and whiskers. The author examined

the atmospheric reentry of the USAs Space Shuttles and proposed the use of high temperature

tolerant parachute for atmospheric air braking. Though it is not large, a light parachute decreases

Shuttle speed from 8 km/s to 1 km/s and Shuttle heat flow by 3-4 times. The parachute surface is

opened with backside so that it can emit the heat radiation efficiently to Earth-atmosphere. The

temperature of parachute is about 1000-1300o C. The carbon fiber is able to keep its

functionality up to a temperature of 1500-2000o C. There is no conceivable problem to

manufacture the parachute from carbon fiber. The proposed new method of braking may be

applied to the old Space Shuttles as well as to newer spacecraft designs.

Re-entry capsules promises to intensify international competition in launch services,

microgravity research and space technology development. These systems will also confer an

important strategic advantage in the conduct of materials and in life science research.

The objective of this paper is to provide a modest degree of understanding of the complex inter-

relation which exist between performance requirements mission constraints , vehicle design and

trajectory selection of typical re-entry mission. A brief presentation of the flight regimes, the

structural loading and heating environment experienced by booth no lifting and lifting re-entry

vehicle is given.



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2. RE ENTRY MISSION PROFILE, CONSTRAINTS AND VEHICLE

REQUIREMENTS

The safe recovery of the spacecraft and its payloads is made possible by the

re-entry mission. According to the different constraints the mission profile can be divided into

three distinct flight segments:-

1. Deorbit and Descent to sensible atmosphere at an altitude of nearly 120kms.

2. Re-entry and hypersonic glide fight.

3. Transition flight phase, final approach and landing.

The unguided first flight segment (Keplarian trajectory) initiated by

a rocket reboots maneuver at a specific orbital point determines the flight

condition at re-entry. The second flight segment covers the atmospheric glide

at an altitude of 120 km to 30 km during which the re-entry vehicles high initial kinetic energy

is dissipated by atmospheric breaking. The third flight segment does the final approach and

landing. All these phases are shown in Fig.1.

The various forces acting on the re-entry vehicle are:-

1. Gravitational force acting towards the centre of the planet.

2. Gas dynamic force opposite to the direction of motion of the vehicle.

3. Centrifugal and gas dynamic lift force acting normal to the direction of

motion of the vehicle.

Along the re-entry flight several mission constraints much be

Imposed arising from the structural limit, crew comfort and control limits.



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These limits require the flight State of the vehicle to the

constrained such that the:-

1. Load factor n


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Cd= drag coefficient

Depending on the specified mission requirements the second or third property is chosen as

design drivers.

2.Parts of a space vehicle

3.ENTRY CORRIDOR



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An entry corridor is a range of entry conditions within which an entry

is possible. The undershoot boundary and overshoot boundary forms the upper and the lower

limits of the entry corridor. Terrestrial flights are tolerant of guidance error accompanying a

landing approach. An undershoot may cause destruction of vehicle during entry and an

overshoot may result in a homeless exit to space.

Figure shows the explanation of entry corridor and possible path for vehicle with lift to Venus,

Mars, and Titan.

If the guidance error results in an excessive undershoot as shown by the two dashed

trajectories, the vehicle will enter the atmosphere at an excessively steep angle, thereby

experiencing too much deceleration. If the guidance error results in an excessive overshoot as

shown by the two outer dashed trajectories, the vehicle will not slow down considerably in order

to complete entry in a single pass. Hence the shaded portions representing excessively overshoot

and undershoot are excluded as not representing the intended entry maneuver.

Although overshoot at hyperbolic velocity > (2gRo)1/2 may result in a homeless exit to

space, overshoot at the outer corridor at parabolic speed = (2gRo)1/2or at an elliptical speed

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