Satellite technology

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Brianna Potter
10 years ago
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1 Satellite technology

2 Overview What is a satellite? The key elements of orbital position Satellite manufacturers and design The components of a satellite: payload and bus Digital versus analogue How do we control a satellite? The life of a satellite The way to geostationary orbit Your questions 2

design The components of a satellite: payload and bus Digital versus

3 What is a satellite? Natural or artificial object that revolves around a larger astronomical object, usually a planet. The Moon is the most obvious example. Moon Space Station Hubble 3

4 What are artificial satellites used for? Telecommunications Weather forecasting Scientific missions Earth Observation Military purposes 4

5 How do satellites fly? The higher the release speed the further the ball will fly with sufficient speed, the ball will continue to orbit around the Earth, with no need for additional propellant! 5

6 What are the possible orbits? A satellite always moves in a fixed plane, the orbital plane. The orbital plane always passes through the center of the Earth The speed and the orbital period of a satellite vary according to their distance from the Earth s surface: Space Station: altitude ~350 km km/hour, 1 period is 92 minutes ASTRA spacecraft: altitude ~36000 km km/hour, 1 period is 24 hours The Moon: altitude ~ km 3600 km/hour, 1 period is ~28 days 6

according to their distance from the Earth s surface: Space Station: altitude ~350 km 27700 km/hour, 1 period is 92

7 Why is geostationary orbit so attractive? The geostationary orbital period of the satellite is equal to the Earth s rotation period, so your TV dish at home can be fixed! 7

8 How are the orbital positions defined? ASTRA at orbital position 19.2 East 8 East longitudes 19.2 E Greenwich West longitudes

9 Access to orbital positions and frequencies Frequency allocations are agreed at the ITU a United Nations agency periodic meetings of the World Radio Council agree amendments to the allocations Frequencies are classified in a number of ways Planned FSS BSS Unplanned FSS 9

the World Radio Council agree amendments to the allocations

10 Frequency allocation Planned Frequencies allocated to given countries At specific orbital positions co-ordinated Unplanned Available on first-come, first-served basis must be co-ordinated Application for use must be made through state agency (e.g. FCC, UKRA, Luxembourg Govt.) Position must be brought into use within a specified time period 10

must be co-ordinated Application for use must be made through

11 Security of access After being brought into use, an operator has a high degree of security automatic renewal after first 15 year period, under ITU rules Interruption of existing business is considered unlikely 11

renewal after first 15 year period, under ITU rules

12 Cost of access Cost of access varies according to jurisdiction annual management fee (US, Gibraltar) franchise fee (Luxembourg) related to profitability Typically relatively modest 12

13 How to maintain the orbital position? Periodic stationkeeping manoeuvres are needed because natural forces are continuously perturbing the satellite position The Sun and Moon affect the orbit The earth s equator is not a perfect circle! 13

natural forces are continuously perturbing the satellite

14 What is Satellite Co-location? Co-location allows ASTRA to maintain several satellites in the same box 150 Km Km It is interesting because only one dish is needed to receive TV channels from all satellites backup capacity is directly available it allows an efficient utilization of the geostationary ring The ASTRA satellites at 19.2 East seen from Betzdorf 14

1 150 Km It is interesting because only one dish is needed to receive TV channels from all

15 How to perform station-keeping manœuvres? The Propulsion Subsystem Thrusters push the satellite according to commands sent from the control center Enough propellant for ~15 years 15

16 Who manufactures the SES satellites? It s not SES! SES closely follows the design and manufacturing! 16

17 What does a communication satellite look like? (1/2) 2 basic designs Spinner satellite 3-axis satellite Simple More channels Light More power Inexpensive Longer lifetime Quick to build More coverage 17

18 What does a communication satellite look like? (2/2) 2.8 m 26 m 7 m 2.2 m 750 kg (in orbit) 2300 kg (in orbit) 18

19 Payload and Bus The Payload is the reason why the satellite is there, and how we make money! includes the components to achieve the core satellite objective The Bus includes all the functions needed to support the payload: 1. Attitude control 2. Orbit control 3. Power management 4. Thermal control 19

includes the components to achieve the core satellite objective The Bus

20 Payload (1/2) The Payload performs reception, amplification and retransmission of a signal from the ground TWTA TWTA RECEIVER TWTA TWTA D/C TWTA TWTA 20

21 Payload (2/2) The Amplifiers have a high degree of flexibility and redundancy The shape and pointing of the Antenna define the footprint 21

22 Digital vs Analogue The Payload can carry analogue or digital transmission Digital transmission offers more capacity per transponder by means of compression Analogue to Digital Conversion

23 Keeping the right attitude The Attitude Control Ensures continuous spacecraft pointing accuracy Is very sensitive: 1 degree depointing = 600 km of footprint change! Is autonomous 23

24 Providing the electricity Electrical Power is needed to amplify and transmit the signals down to Earth provided by wings continuously tracking the sun and covered with solar cells or by batteries during the eclipses (March/September) 24

25 Controlling the temperatures The Thermal Subsystem keeps all the equipment within qualification limits fights the huge temperature gradient is made of active (heaters) and passive (blankets/radiators) devices 25

26 The life of a satellite Definition Definition of of requirements requirements Evaluation Evaluation Negotiation Negotiation End of life 5 ~3 months Commercial Commercial life life of of satellite satellite Years Manufacturing (~2.5 years) S/C S/C Hand-over Hand-over to to SES SES LEOP & IOT (~2months) OSD OSD Transfer Orbits D Bus IOT Payload IOT Drift to o.p. 6-8 days 1 day 5-7 days days 15 days S/C controlled from manufacturer S/C controlled from manufacturer S/C controlled from SES S/C controlled from SES 26

27 The way to geostationary orbit (1/2) The launcher must be powerful because the heavier the satellite can be more payload and fuel can be loaded! 27

28 The way to geostationary orbit (2/2) The launcher will just do a part of the job 28

29 What happens after a nominal end of life? After ~15 years the satellite approaches end of propellant Station-keeping control is not possible anymore The remaining fuel is used to push the satellite into a graveyard orbit, before complete switch off Graveyard orbit is ~ 300 km ABOVE geostationary orbit 29

30 Thank you for your attention! Do you have any questions? 30

Satellite Communication Systems. mgr inż. Krzysztof Włostowski Instytut Telekomunikacji PW [email protected]

Satellite Communication Systems mgr inż. Krzysztof Włostowski Instytut Telekomunikacji PW [email protected] Satellite Communication Satellite Communication combines the missile and microwave technologies