51.3.6 Telemetry, tracking and command

Telemetry, tracking and command (TT&C) facilities are needed, in the launch phase and in normal operation of communication satel­lites, for a variety of purposes. Telemetry is used to monitor and evaluate the performance and behaviour of the satellite and to provide the ground control station with data for the diagnosis of fault conditions that may arise. Tracking facilities, used in conjunc­tion with the command system, enable the location, velocity and orbit of the satellite to be determined, enabling the orbit and the nominal location in orbit to be set up initially, then maintained throughout the satellite's operating life. Command facilities are required for the initiation of all the manoeuvres which cannot be automated for on board control and which are required of the satellite as a vehicle and as a complicated piece of communications equipment.

The signal channels between satellite and control earth stations required for these functions are carried by two radio subsystems. One subsystem operates at low microwave frequencies allocated to the space operations service, using low gain satellite antennas; this subsystem is used during the launch phase, when TT&C may be required, for example between the launch site and the satellite and the attitude of the satellite is not normal. The other subsystem operates in a narrow band within the frequency bands appropriate to the mission of the satellite and uses the mission satellite antennas, often of high gain; this subsystem is used during the normal oper­ation of the satellite.

Exercise 1: Terms to know

Perturbation	-помеха; нарушение; возмущение
Coincidence	-совпадение; совмещение
Phase coincidence	-совпадение фаз
Ellipticity	- эллиптичность; коэффициент эллиптичности
Oscillate	-колебаться; осциллировать
Thruster	-ракетный двигатель малой тяги; двигатель реактивной системы управления
Propellant(P.)	-ракетное топливо
Bifuel(double-base)P.	-двухосновное ракетное топливо
Solid P.	- твердое ракетное топливо
Triple-base P.	-трехосновное ракетное топливо
Simple-base (single-base); self-contained	-одноосновное ракетное топливо
Directive(directional) satellite antenna	-направленная спутниковая антенна
Spinning	-быстрое вращение
Axis (мн. Axes)	-ось; осевая линия
Pitch axis	-ось килевой качки
Pitch-roll axis	-степень подвижности по наклону-вращению
Roll axis	-ось бортовой качки
Yaw axis	-ось рыскания
Yaw pitch axis	-степень подвижности по наклону-качанию
Wheel	-круговое движение; вращение
Momentum	-количество движения; импульс
Gimbal	-универсальный (карданный) шарнир; кардан; шарнир Гука
Silicon solar cell	-кремниевый солнечный элемент
Hydrogen cell	-водородная ячейка(элемент)
Tracking	-слежение; следящая коррекция; следящий прием
Telemetry	-телеизмерения; телеметрия
Wire telemetry	-проводная телеметрия
Satellite telemetry	-спутниковая телеметрия
Real-time telemetry	-телеметрия в реальном(масштабе) времени

Exercise 2: Answer the following questions:

1. What can you tell about orbital perturbations and their correction ?

2. How do the gravitation fields of the Sun, the Moon, the Earth and the pressure of solar radiation and solar wind influence the location of a geostationary satellite ?

3. How does the ITU regulate orbital perturbations ?

4. Why are bi-propellant thruster systems and electrically powered ion engines coming into use ?

5. Why is stabilization of a communication satellite’s attitude relative to the Earth ?

6. What is the difference between spinning body stabilization and three axis body stabilization ?

7. Can you report in Russian the main information about electrical power supply in space ?

8. What purposes are telemetry, tracking and command facilities needed for ?

9. Why are the signal channels between satellite and control earth stations carried by two radio subsystems ?

Exercise 3: Give the Russian equivalents:

1. non-uniformity of the gravitation field of the Earth

2. to cause interference to or from another network

3. bi-propellant thruster systems

4. the gain of directive satellite antennas

5. spinning body stabilization

6. three axis body stabilization

7. antenna pointing accuracy of ±0.2°

8. to employ an internal momentum wheel

9. the pitch axis

10. the control about the yaw and roll axes

11. to increase the dimensions of deployable solar panels

12. to have body mounted arrays of solar cells

13. to evaluate the performance and behavior of the satellite

14. to provide the ground control station with data

15. to operate at low microwave frequencies

16. to be set up initially

17. to be maintained throughout the satellite’s operating life