EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
UNIT II
SPACE SEGMENT
Spacecraft Technology- Structure, Primary power, Attitude and Orbit control, Thermal control and
Propulsion, communication Payload and supporting subsystems, Telemetry, Tracking and
command-Transponders-The Antenna Subsystem
2.1 Spacecraft Technology
2.1.1 Structure
2.1.2 Primary power
2.1.3 Attitude and Orbit control
2.1.4 Thermal control and Propulsion
2.1.4.1 Thermal Subsystem
2.1.4.2 Propulsion Subsystem
2.1.5 Communication Payload and supporting subsystems
2.1.6 Telemetry, Tracking and command
2.1.7 Transponders
2.1.8 The Antenna Subsystem.
2.1 Spacecraft Technology
Introduction:-
➢ Satellite communication system can be classified into two segments,
(i) Ground segment
(ii) Space segment
➢ Space segment includes satellite, but it also need ground facilities to keep the satellite in operation such
as TT&C.
➢ Generally a separate ground station is employed for TT&C purpose.
➢ In space segments of satellite, it is classified as (i) pay load and (ii) bus.
➢ Pay load refers to service providing.
➢ Bus refers to provide the power, attitude control, orbital control, thermal control and command and
telemetry functions required to service the payload.
➢ Equipment which provides communication between satellite transmit and receive antenna is referred
as “Transponder”.
2.1.1 Structure
1. Explain in detail about the Structure of space craft.
Structure of space craft:-
➢ Structure of space craft must be designed to withstand variety of loads.
➢ There are varieties of disturbances such as vibrations aerodynamics loads, operating thrust centrifugal
stress thermal stress, particle radiation.
1
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
,EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Variety of materials are used such as
✓ Aluminum
✓ Magnesium
✓ Stainless steal
✓ Invar
✓ Titanium
✓ Graphite – reinforced phonemic
✓ Fiber glam epoxy
✓ Beryllium
Some Common Structures are,
Longeron Truss Thrust Tube
Figure: Typical Structures
➢ Typically percentage of total space craft man is less than 20%
➢ Mass percentage tends decrease. When the space craft is body stabilized.
➢ Mass percentage increase. When the space craft is spin stabilized.
➢ Empirical date based on many space craft shows.
2.1.2 Primary power
2. Explain in detail about the Primary power of space craft.
Primary Power:-
➢ Two possible sources of primary power for a satellite,
✓ Nuclear supply
✓ Solar supply
➢ Nuclear supplies can be divided into two categories.
➢ Small nuclear reactor heats a boiler with a working fluid such as Mercury and the vapor is used to drive
turbine alternator combinations, typically in a Bray ton cycle.
➢ Single Radio isotope thermoelectric generator (RTG) that heats lead telluride thermocouples to
generate electricity.
✓ More frequency used.
✓ For small power supplies.
Advantages:
➢ No need of batteries during eclipse.
Disadvantages:
➢ Require substantial shielding to protect the space craft electronics from radiation damage.
➢ Nuclear fuels.
2
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
,EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Curium 244 and plutonium ➢ Strontium 90
→ Easy to handle → Difficult to handle
→ Require little shielding → Dangerous
→ Expensive → Cheap and easily available
➢ Nowadays, almost all space craft uses solar cells.
Estimating Primary Power Needs:
➢ Consider a general case, the solar array mounted on either the flat panels of a three-axis stabilized
satellite (or) drum of a spin-stabilized satellite
➢ Estimate of total power requirement must consider the variety of transmit and receive powers,
housekeeping power and battery service during eclipse.
➢ In general, solar array are used to receive solar energy.
Figure: Block Diagram of Generalized Solar Primary Power System
➢ If n → no. of transmitters
Pt → RF transmitted power
i → efficiency of 4th transmitter type.
Then, total transmitted power,
n
Pi
Pt = ni
i =1 i
➢ Receive power primary be known separately and added to pt (or) taken as factor ‘a’ of transmitter
power
total transponder power PT = Pt + Pr
Where,
a 1.05 for larger satellite
a 1.10 for smaller satellite
3
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
, EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Housekeeping power, Ph = Pho + Pr
Where,
Pho → Constant Component
➢ During eclipse, eclipse heater power ‘ Phe ’ ie., also considered.
Ph = Pho + Pr + Phe
➢ Power provided by batteries during eclipse
ePT + Ph (e + h) PT + Pho + Phe
Pt = =
d d
Where,
e → eclipse factor
d → battery, discharging efficiency
Pete
➢ Total battery energy is, U = (watt hours)
d
Battery capacity (Ampere hours)
U Pete
C= =
Vd Vd d
where,
t e → maximum eclipse period ()1.2 hurs)
d → depth of discharge (0.8)
Vd → discharge voltage.
➢ If battery is to be charged in time t c with efficiency c , then charging power is,
dU Pete
PC = =
c tc c tc
total primary power that must be provided by the solar array is,
P = K ( PT + Ph + PC ) = K (a(1 + h) Pt + Pho + PC
where, K → design margin 1.05 1.1
➢ Electric power subsystem generally divided into two-half systems. played & Bus
Solar array requirements and size:-
➢ Solar array must be sized to provide the power required.
➢ Solar cells degrade due to radiation damage and seasonal variation, by an exponential factor of e − t ,
where, t → design life time
τ → 0.25
➢ Solar flux density ( G ) varies during the year, because of varying distance to the sun and varying
inclination as,
cos
G= = F
r2
where, → sun’s inclination
4
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
UNIT II
SPACE SEGMENT
Spacecraft Technology- Structure, Primary power, Attitude and Orbit control, Thermal control and
Propulsion, communication Payload and supporting subsystems, Telemetry, Tracking and
command-Transponders-The Antenna Subsystem
2.1 Spacecraft Technology
2.1.1 Structure
2.1.2 Primary power
2.1.3 Attitude and Orbit control
2.1.4 Thermal control and Propulsion
2.1.4.1 Thermal Subsystem
2.1.4.2 Propulsion Subsystem
2.1.5 Communication Payload and supporting subsystems
2.1.6 Telemetry, Tracking and command
2.1.7 Transponders
2.1.8 The Antenna Subsystem.
2.1 Spacecraft Technology
Introduction:-
➢ Satellite communication system can be classified into two segments,
(i) Ground segment
(ii) Space segment
➢ Space segment includes satellite, but it also need ground facilities to keep the satellite in operation such
as TT&C.
➢ Generally a separate ground station is employed for TT&C purpose.
➢ In space segments of satellite, it is classified as (i) pay load and (ii) bus.
➢ Pay load refers to service providing.
➢ Bus refers to provide the power, attitude control, orbital control, thermal control and command and
telemetry functions required to service the payload.
➢ Equipment which provides communication between satellite transmit and receive antenna is referred
as “Transponder”.
2.1.1 Structure
1. Explain in detail about the Structure of space craft.
Structure of space craft:-
➢ Structure of space craft must be designed to withstand variety of loads.
➢ There are varieties of disturbances such as vibrations aerodynamics loads, operating thrust centrifugal
stress thermal stress, particle radiation.
1
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
,EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Variety of materials are used such as
✓ Aluminum
✓ Magnesium
✓ Stainless steal
✓ Invar
✓ Titanium
✓ Graphite – reinforced phonemic
✓ Fiber glam epoxy
✓ Beryllium
Some Common Structures are,
Longeron Truss Thrust Tube
Figure: Typical Structures
➢ Typically percentage of total space craft man is less than 20%
➢ Mass percentage tends decrease. When the space craft is body stabilized.
➢ Mass percentage increase. When the space craft is spin stabilized.
➢ Empirical date based on many space craft shows.
2.1.2 Primary power
2. Explain in detail about the Primary power of space craft.
Primary Power:-
➢ Two possible sources of primary power for a satellite,
✓ Nuclear supply
✓ Solar supply
➢ Nuclear supplies can be divided into two categories.
➢ Small nuclear reactor heats a boiler with a working fluid such as Mercury and the vapor is used to drive
turbine alternator combinations, typically in a Bray ton cycle.
➢ Single Radio isotope thermoelectric generator (RTG) that heats lead telluride thermocouples to
generate electricity.
✓ More frequency used.
✓ For small power supplies.
Advantages:
➢ No need of batteries during eclipse.
Disadvantages:
➢ Require substantial shielding to protect the space craft electronics from radiation damage.
➢ Nuclear fuels.
2
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
,EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Curium 244 and plutonium ➢ Strontium 90
→ Easy to handle → Difficult to handle
→ Require little shielding → Dangerous
→ Expensive → Cheap and easily available
➢ Nowadays, almost all space craft uses solar cells.
Estimating Primary Power Needs:
➢ Consider a general case, the solar array mounted on either the flat panels of a three-axis stabilized
satellite (or) drum of a spin-stabilized satellite
➢ Estimate of total power requirement must consider the variety of transmit and receive powers,
housekeeping power and battery service during eclipse.
➢ In general, solar array are used to receive solar energy.
Figure: Block Diagram of Generalized Solar Primary Power System
➢ If n → no. of transmitters
Pt → RF transmitted power
i → efficiency of 4th transmitter type.
Then, total transmitted power,
n
Pi
Pt = ni
i =1 i
➢ Receive power primary be known separately and added to pt (or) taken as factor ‘a’ of transmitter
power
total transponder power PT = Pt + Pr
Where,
a 1.05 for larger satellite
a 1.10 for smaller satellite
3
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
, EC8094 SATELLITE COMMUNICATION UNIT II - SPACE SEGMENT
➢ Housekeeping power, Ph = Pho + Pr
Where,
Pho → Constant Component
➢ During eclipse, eclipse heater power ‘ Phe ’ ie., also considered.
Ph = Pho + Pr + Phe
➢ Power provided by batteries during eclipse
ePT + Ph (e + h) PT + Pho + Phe
Pt = =
d d
Where,
e → eclipse factor
d → battery, discharging efficiency
Pete
➢ Total battery energy is, U = (watt hours)
d
Battery capacity (Ampere hours)
U Pete
C= =
Vd Vd d
where,
t e → maximum eclipse period ()1.2 hurs)
d → depth of discharge (0.8)
Vd → discharge voltage.
➢ If battery is to be charged in time t c with efficiency c , then charging power is,
dU Pete
PC = =
c tc c tc
total primary power that must be provided by the solar array is,
P = K ( PT + Ph + PC ) = K (a(1 + h) Pt + Pho + PC
where, K → design margin 1.05 1.1
➢ Electric power subsystem generally divided into two-half systems. played & Bus
Solar array requirements and size:-
➢ Solar array must be sized to provide the power required.
➢ Solar cells degrade due to radiation damage and seasonal variation, by an exponential factor of e − t ,
where, t → design life time
τ → 0.25
➢ Solar flux density ( G ) varies during the year, because of varying distance to the sun and varying
inclination as,
cos
G= = F
r2
where, → sun’s inclination
4
Compiled by: Mr.S.Parthiban, M.Tech., Asst. Prof., Dept. of ECE, VRSCET.
