Question

1. Discuss propulsion subsystem of a typical satellite station?                                        
2. A satellite uplink link has a RSL(receive signal level) of -100.57 dBW. The receiver has a 15 MHz bandwidth, and its noise figure is 6 dB. If the downlink also offers 30dB CNR. What is the total CNR of this single hop wireless link?                                                              
3. A VSAT antenna must have a gain of 40 dB at a frequency of 11.5 GHz. Assume the 3dB beam-widths Ө₁ = Ө₂ and use the approximate expression for the gain to calculate:
4. 1. The antenna diameter.                                                                                              
   2. The antenna beam width; and                                                                                  

Answer 1

Answer a:

Propulsion sub-system is nothing but the reaction control sub-system which is carried by the satellite in geostationary orbits for generating forces on it whenever required. It brings satellite to its target position in orbit for kept in that state and to maintain spin axis direction and  altitude control.

Generally propulsion sub-system consists of three units.

1) Low thrust (10.3 to 20 N) actuators, which is reaction control system

2) High thrust (400 to 50,000 N) motor (Apogee kick motor or Apogee boot motor), which initiates velocity increment for injecting the satellite into geostationary orbits from transfer orbit apogee.

3) Perigee kick motor, which generally used for velocity increment needs to inject the satellite into the transfer orbit.

Low Thrust Actuators are most important as they are responsible for maintaining the satellite in orbit with its exact altitude. They can be either chemical or electrical thrusters.