1. Characteristics of remote sensing
satellites

2. • Satellites generally vary in their architecture
• Usually remote sensing satellites are having two plateforms
• These are main plateform (MPL) and payload plateform (PPL)
• MPL is having power systems, telemetry, tracking and
command systems, attitude and orbit control sensors and
communication subsystems

4. • MPL is also known as module or satellite bus
• PPL is having the imaging sensors, star sensors
• Satellite housing: all the subsystems are mounted on it and it
provides the overall mechanical integrity to the satellite
• Power system: for every satellite the main source of power
comes from solar cells
• Solar cells convert light energy into electricity

5. • Solar cells are arranged and attached on a surface called solar
panel or solar arrays
• Panels are folded while launching
• To provide peak power requirements as well as during
satellite eclipse, batteries are used
• Batteries are recharged during the sunlit portion of the orbit
• Star sensors is a devise which measures the position of the
stars using the camera

6. Attitude and orbit control system
• A satellite must maintain a certain attitude (orientation) to
allow pointing the camera to the earth
• Factors such as magnetic field, earth’s non uniform
gravitational field, solar wind etc disturb the satellite orbit and
attitude that needs continuous adjustment
• Attitude control of a satellite is done by two methods
• Spin control and three axis control

7. • Spin control is used for geosynchronous meteorological
satellites
• Three axis control is mainly for remote sensing satellites
• Orbital changes are corrected by the propulsion system
carried in the satellite
• Propulsion systems are small rocket boosters that give a thrust
on the various faces of the satellite to bring it back into the
correct orbit and attitude

8. • Propulsion system is operated by giving
command from the ground

9. • The entire satellite including its antenna(s) spins
• Spinning can be achieved using rods with coils of wire around
them
• When current is passed through the rods, magnetic field is
generated around the wires
• When this rod's magnetic field interacts with Earth's magnetic
field, the rod begins to spin
• If we have rods in three opposing directions we can have our
satellite spin stably in all three axes (up, down, and out)
Spin control

10. Three axis control
• Three-axis stabilization is done by using electrically-
powered reaction wheels, also called as momentum wheels
• These wheels are mounted in three orthogonal axes on the
spacecraft
• To rotate the vehicle in one direction, we spin up the proper
wheel in the opposite direction.

11. Telemetry tracking and command
• Telemetry system collects data on the health of the
satellite and communicate it with the satellite control
station
• Command system receives and process the command
from the ground station
• Commands are sent from the ground such as to correct
the orbit or to turn on/off the remote sensing camera

12. Communication subsystems
• Responsible for maintaining communication links
between satellite and ground stations
• It is used to send the information about the satellite
health or to send a data recorded by the remote
sensor to ground