Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
Module 2
Satellite Subsystems and Earth Station
POWER SUPPLY SUBSYSTEM
The power supply subsystem generates, stores, controls and distributes electrical power to other
subsystems on board the satellite platform.
The electrical power needs of a satellite depend upon the intended mission of the spacecraft and
the payloads that it carries along with it in order to carry out the mission objectives. The power
requirement can vary from a few hundreds of watts to tens of kilowatts.
Types of Power System
Solar Energy Driven Power Systems
Solar energy will mean the photon energy of the solar radiation unless otherwise specified. The
major components of a solar power system are the solar panels (of which the solar cell is the
basic element), rechargeable batteries, battery chargers with inbuilt controllers, regulators and
inverters to generate various d.c and a.c voltages required by various subsystems.
Figure 4.13 shows the basic block schematic arrangement of a regulated bus power supply
system.
Major components like the solar panels and the batteries are briefly described in the following
paragraphs. During the sunlight condition, the voltage of the solar generator and also the bus is
maintained at a constant amplitude with the voltage regulator connected across the solar
generator.
The battery is decoupled from the bus during this time by means of a battery discharge
regulator (BDR) and is also charged using the battery charge regulator (BCR) as shown in the
figure. During the eclipse periods, the battery provides power to the bus and the voltage is
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 1
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
maintained constant by means of the BDR.
a. Solar Panels The solar panel is a series and parallel connection of a large number of solar
cells. Figure 4.14 (a) shows this series–parallel arrangement of solar cells and Figure 4.14
(b) shows the image of a solar panel.
The voltage output and the current delivering capability of an individual solar cell are very
small for it to be of any use as an electrical power input to any satellite subsystem.
The series–parallel arrangement is employed to get the desired output voltage with the
required power delivery capability.
A large surface area is therefore needed in order to produce the required amount of power.
The need for large solar panels must, however, be balanced against the need for the entire
satellite to be as small and light weight as possible.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 2
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
The three-axis body stabilized satellites use flat solar panels (Figure 4.15) whereas spin
stabilized satellites use cylindrical solar panels (Figure 4.16). Both types have their own
advantages and disadvantages. In the case of three-axis stabilized satellites, the flat solar
panels can be rotated to intercept maximum solar energy to produce maximum electric
power.
b. Principle of Operation of a Solar Cell
The operational principle of the basic solar cell is based on the photovoltaic effect. According
to the photovoltaic effect, there is generation of an open circuit voltage across a P–N junction
when it is exposed to light, which is the solar radiation in the case of a solar cell.
This open circuit voltage leads to flow of electric current through a load resistance connected
across it, as shown in Figure 4.17.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 3
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
It is evident from the figure that the impinging photon energy leads to the generation of
electron–hole pairs. The electron–hole pairs either recombine and vanish or start to drift in the
opposite directions, with electrons moving towards the N-layer and holes moving towards the
P-layer.
This accumulation of positive and negative charge carriers constitutes the open circuit voltage.
As mentioned before, this voltage can cause a current to flow through an external load. When
the junction is shorted, the result is a short circuit current whose magnitude is proportional to
the incident light intensity.
Figure 4.18 shows the current–voltage and power–voltage characteristics of a solar cell. It is
evident from the figure that the solar cell generates its maximum power at a certain voltage.
The power–voltage curve has a point of maximum power, called the maximum power point
(MPP). The cell voltage and the corresponding current at the maximum power point are less
than the open circuit voltage and the short circuit current respectively.
Solar efficiency is the ratio of the maximum electrical solar cell power to the radiant power
incident on the solar cell area. The efficiency figure for some crystalline solar cells is in excess
of 20 %. The most commonly used semiconductor material for making solar cells is silicon.
Both crystalline and amorphous silicon are used for the purpose. Another promising material
for making solar cells is gallium arsenide. Gallium arsenide solar cells, when perfected, will be
lightweight and more efficient.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 4
Module 2
Satellite Subsystems and Earth Station
POWER SUPPLY SUBSYSTEM
The power supply subsystem generates, stores, controls and distributes electrical power to other
subsystems on board the satellite platform.
The electrical power needs of a satellite depend upon the intended mission of the spacecraft and
the payloads that it carries along with it in order to carry out the mission objectives. The power
requirement can vary from a few hundreds of watts to tens of kilowatts.
Types of Power System
Solar Energy Driven Power Systems
Solar energy will mean the photon energy of the solar radiation unless otherwise specified. The
major components of a solar power system are the solar panels (of which the solar cell is the
basic element), rechargeable batteries, battery chargers with inbuilt controllers, regulators and
inverters to generate various d.c and a.c voltages required by various subsystems.
Figure 4.13 shows the basic block schematic arrangement of a regulated bus power supply
system.
Major components like the solar panels and the batteries are briefly described in the following
paragraphs. During the sunlight condition, the voltage of the solar generator and also the bus is
maintained at a constant amplitude with the voltage regulator connected across the solar
generator.
The battery is decoupled from the bus during this time by means of a battery discharge
regulator (BDR) and is also charged using the battery charge regulator (BCR) as shown in the
figure. During the eclipse periods, the battery provides power to the bus and the voltage is
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 1
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
maintained constant by means of the BDR.
a. Solar Panels The solar panel is a series and parallel connection of a large number of solar
cells. Figure 4.14 (a) shows this series–parallel arrangement of solar cells and Figure 4.14
(b) shows the image of a solar panel.
The voltage output and the current delivering capability of an individual solar cell are very
small for it to be of any use as an electrical power input to any satellite subsystem.
The series–parallel arrangement is employed to get the desired output voltage with the
required power delivery capability.
A large surface area is therefore needed in order to produce the required amount of power.
The need for large solar panels must, however, be balanced against the need for the entire
satellite to be as small and light weight as possible.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 2
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
The three-axis body stabilized satellites use flat solar panels (Figure 4.15) whereas spin
stabilized satellites use cylindrical solar panels (Figure 4.16). Both types have their own
advantages and disadvantages. In the case of three-axis stabilized satellites, the flat solar
panels can be rotated to intercept maximum solar energy to produce maximum electric
power.
b. Principle of Operation of a Solar Cell
The operational principle of the basic solar cell is based on the photovoltaic effect. According
to the photovoltaic effect, there is generation of an open circuit voltage across a P–N junction
when it is exposed to light, which is the solar radiation in the case of a solar cell.
This open circuit voltage leads to flow of electric current through a load resistance connected
across it, as shown in Figure 4.17.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 3
, Regulation – 2022 Scheme SATELLITE AND OPTICAL COMMUNICATION – BEC515D
It is evident from the figure that the impinging photon energy leads to the generation of
electron–hole pairs. The electron–hole pairs either recombine and vanish or start to drift in the
opposite directions, with electrons moving towards the N-layer and holes moving towards the
P-layer.
This accumulation of positive and negative charge carriers constitutes the open circuit voltage.
As mentioned before, this voltage can cause a current to flow through an external load. When
the junction is shorted, the result is a short circuit current whose magnitude is proportional to
the incident light intensity.
Figure 4.18 shows the current–voltage and power–voltage characteristics of a solar cell. It is
evident from the figure that the solar cell generates its maximum power at a certain voltage.
The power–voltage curve has a point of maximum power, called the maximum power point
(MPP). The cell voltage and the corresponding current at the maximum power point are less
than the open circuit voltage and the short circuit current respectively.
Solar efficiency is the ratio of the maximum electrical solar cell power to the radiant power
incident on the solar cell area. The efficiency figure for some crystalline solar cells is in excess
of 20 %. The most commonly used semiconductor material for making solar cells is silicon.
Both crystalline and amorphous silicon are used for the purpose. Another promising material
for making solar cells is gallium arsenide. Gallium arsenide solar cells, when perfected, will be
lightweight and more efficient.
Prepared by: Prof. Martin Joel Rathnam & Prof. Mohanthi K Department of ECE, SSCE, Anekal, Bengaluru. Page | 4
