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GRAVITY- ASSIST ENGINE FOR SPACE PROPULSION

Presented by

Akhil Vijayan

Class No:06

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CONTENTS

1. Introduction

2. Gravity Assist

3. Tidal Locking

4. The Spinning Springbell

5. Computational Approach

6. Numerical Simulation

7. Escape from orbit

8. Springbell driven Trajectories from the earth

9. Conclusion

10. References

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1.INTRODUCTION

• A new type of engine for space travel is presented

• Inspired from the famous ‘Gravity Assist’ concept

• The aim of this new concept is to find more direct and easy

trajectories for space travel hence reducing propelling time of the space probe

• Indicates that there are ways to convert the rotational motion of a astronomical body to orbital motion

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2.GRAVITY ASSIST

• A three body problem involving gravitational interaction between Sun, spacecraft and a planetary body

• Used to accelerate/decelerate a spacecraft and redirect its path without the use of propellant

• Velocity of the space craft is changed by entering the gravitational well of the planetary body

• It also explains the ways to emulate the Tidal locking of the gravitating body to raise or lower the orbit of rotation

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Fig.1: Gravity Assist working

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3.Tidal locking

• Tidal locking makes one hemisphere of an astronomical body to always face the parent body around which it revolves.

• This occurs due to the induction of tidal forces on the revolving body by the gravity of the parent body

• These forces are called Tidal bulges

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4.The Spinning Springbell

• A Three-body problem is recreated by replacing two of the three gravitationally interacting body in the gravity assist concept with two large masses

• The springbell is onboard to the vehicle and hence an onboard gravity assist is proposed

• The orbital angular momentum of a spacecraft is changed by manipulating the spin of the springbell.

• This technique thus helps in changing the orbit of the spacecraft

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Fig.2: The spinning springbell

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5.Computational Approach

• The accelerations ä1 and ä2 of the two masses in the plane of rotation is

ä1= -GMâ1/a12+ K(L-a12) â12

ä2= -GMâ2/a22+ K(L-a12)â12

• The corresponding velocities in the next time step is

å1→ å1+ä1dt

å2→ å2+ä1dt

• and r1 & r2 defining the trajectory is calculated as follows

a1→a1+ a1dt+ 0.5ä1dt2

a2→a2+ a2dt+ 0.5ä2dt2

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6.Numerical Simulation

Fig.3: Trajectory of a springbell in orbit around a parent gravitating body without any velocity increment/decrement pairs and thus following normal elliptical trajectory.

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7.Escape from Orbit

Fig.4: Springbell trajectory for velocity decrement pairs in some spatial direction to lose part of its Orbital angular momentum and spiral towards the central gravitating body.

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Fig.5: Springbell trajectory for velocity increments in any spatial direction to gain orbital angular momentum and spiral out towards escape trajectory.

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8.Springbell driven escape trajectories from the earth

Fig.6: Simulation for spinning springbell in earth orbit with no increment/decrement dv Per time step, thus resulting only in a stable circular orbit.

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Fig.7: Simulation of springbell in earth orbit and a modest change of orbit.

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9.Conclusion• Propulsion based on the conservation of angular momentum is

more advantageous than that based on conservation of linear momentum

• Recreation of artificial tidal bulge system by manipulating the spin of the springbell can be used to raise/lower the orbit of the space craft

• The method of propulsion discussed here requires only internal energy and no emission of exhaust gases

• A powerful internal energy source such as a nuclear reactor can be used for the energy requirement of spinning the springbell

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10.References

1. Arne Bergstrom, Acta Astronautica99(2014)99–110, B&E Scientific Ltd, Seaford, United Kingdom, BN25 4PA(February 10, 2014). [1] [4] [5] [9]

2. M. Minovitch, An Alternative Method for Determination of Elliptic and Hyperbolic Trajectories, Jet Propulsion Laboratory Technical Memos TM-312-118 (July 11, 1961). [2] [6] [7]

3. M. Minovitch, A Method for Determining Interplanetary Free-fall Reconnaissance Trajectories, Jet Propulsion Laboratory Technical Memos TM-312-130 (August 23, 1961). [7] [8]