DESIGN OF SUN-SYNCHRONOUS AND GEOSYNCHRONOUS ORBIT

Submitted by-MD SHAHID IQNAL ANSARIRoll No. MT/RS/10008/15

INTRODUCTION

What is an Orbit?

An orbit is a regular, repeating path that one object in space takes around another one. An object in an orbit is called a satellite. A satellite can be natural, like Earth or the moon. Many planets have moons that orbit them.

DEFINITION OF SYNCHRONOUS ORBIT

A synchronous orbit is an orbit where the orbital period equals the rotation rate of the orbited body.That is, an orbiting body (usually a satellite) has a period equal to the average rotational period of the body being orbited (usually a planet), and in the same direction of rotation as that body. So, the synchronous orbit is where the satellite has a period equal to the average rotational period of the planet.

ORBIT TYPES

Synchronous types are : Sun-synchronous orbit : An orbit which combines altitude

and inclination(angle between reference place and orbital plane) in such a way that the satellite passes over any given point of the earth surface at the same local solar time.It orbits at 700-800km altitude over the Earth surface and always same orientation

Geostationary orbit : An orbit around the Earth with an orbital period matching the Earth’s sidereal rotation period . It lies in the equatorial plane around earth. A satellite in such an orbit is at an altitude of approximately 35,786 km .

SUN SYNCHRONOUS ORBIT

Rate is equal to average rate of Earth’s rotation around the sun

Position of Sun relative to orbital plane remains relatively constant

Sun Synchronous orbits can be achieved around other central bodies

Usually near 90º inclinations

Sun-Synchronous:The satellite is always in the same relative position between the Earth and Sun.

Equatorial-Crossing Time:The local apparent solar time when the satellite crosses the equator.

Example: Terra has an equatorial crossing time of 10:30 am, and is called an “AM” or morning satellite.

Ascending Orbit:The satellite is moving South to North when that portion of the orbit track crosses the equator.

Descending Orbit:The satellite is moving North to South when that portion of

the orbit track crosses the equator.

Period:A typical polar, Sun-

synchronous LEO satellite takes about 90 minutes to

completely circle the Earth. This gives it about 16 orbits

per day.

Low Earth Orbit:Orbiting at an altitude

of 600-1,000 km.

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A geosynchronous orbit is an orbit around the Earth with an orbital period of one sidereal day, intentionally matching the Earth's sidereal rotation period approximately 23 hours 56 minutes and 4.9 seconds. The synchronization of rotation and orbital period means that, for an observer on the surface of the Earth, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day.

GEO-SYNCHRONOUS ORBIT

ORBIT DESIGN PROCESS

Step 1: Establish Orbit Types Earth referenced orbits

GEO, LEO Space referenced orbits

Lagrange points, planetary Transfer orbit

GTO, Interplanetary Parking orbit

Temporary orbit for satellite operational checks, EOL

OUTLINE

Orbit Design Orbit Selection Orbit Design Process ΔV Budget Launch

Earth Coverage Constellation Design

Basic Formation Stationkeeping Collision Avoidance

ORBIT DESIGN PROCESS

Establish Orbit-Related Mission Requirements

Altitude Resolution Lower altitude is better Swath width Higher altitude is better

Inclination Ground station coverage

Lifetime Survivability (ambient environment)

Must be able to survive the entire orbital profile (e.g. transit through Van Allen Radiation Belts)

EARTH COVERAGE

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