Launching a satelliteTo place a satellite in stable orbit, two
parameters need to be coupled together:The velocity vectorThe
orbital heightIts really very difficult to achieve the correct
velocity vector, along with the correct height, in the correct
direction to achieve the desired orbit.Example: GEO satellite
requires a height of about 35,786.03Km above the surface of the
earth with zero inclination and velocity of 3074.7 m/s.
The further the out from the earth the orbit is, the greater the
energy required from launch vehicle to reach that orbit.The largest
fraction of energy expended by rocket is used to accelerate from
rest until it is about 20 miles (32Km).For the efficient usage of
fuel, excess mass is shed from the spacecraft as it moves upward on
launch.
The earth spins towards east, which provides a rotational
velocity of 0.4651 Km/s.As a result, an easterly launch vehicle has
a velocity increment of 0.4651 Km/s by rotation of earth. For a
satellite in circular equatorial orbit requires velocity of 7.4
Km/s and thus the rocket launched need a velocity of 6.93 Km/s.
A satellite launched into an orbit from a latitude of degrees
will enter in an orbit with inclination of degrees to equator.
Launch VehiclesThere are two types of launch vehicles:expendable
rockets, which are destroyed while completing their mission, and
the Space Shuttle, which is reusable.Launch Vehicle selection
factors:Price/costReliabilityPerformanceSafetyAvailability
Expendable rockets for communication satellites have three
stages. The first stage contains several hundred thousand pounds of
liquid fuel, plus a number of solid fuel rocket boosters that
produce a tremendous display of flame--and ear splitting noise--as
the rocket lifts off the pad. It raises the satellite to an
elevation of about 50 miles. The second stage raises the satellite
to 100 miles, andThe third stage places it into the transfer orbit.
After the satellite is placed in its transfer orbit, the rockets
mission is complete, and its remnants fall to earth.
Placing the satellite in Geostationary orbitGTO and AKM
Geosynchronous transfer orbit Apogee Kick motor
GTO with slow orbit raising
Spacecraft thrusters used to raise the orbit slowly from GTO to
GEO.The satellite has two power level of thrusters:One for orbit
raising (more powerful)One for on orbit maneuver (low
thrust)Gradually increase in the perigee height.The burns are
typically 60 to 80 min long on successive orbit and up to six
orbits can be used.
