Page 255 - Satellite Communications, Fourth Edition

The Space Segment 235

TABLE 7.1 NOAA-15 Characteristics
Main body 4.2 m (13.75 ft) long, 1.88 m (6.2 ft) diameter
Solar array 2.73 m (8.96 ft) by 6.14 m (20.16 ft)
Weight at liftoff 2231.7 kg (4920 lb) including 756.7 kg of expendable fuel
Launch vehicle Lockheed Martin Titan II
Orbital information Type: Sun synchronous
Altitude: 833 km
Period: 101.2 minutes
Inclination: 98.70°

SOURCE: Data obtained from http://140.90.207.25:8080/EBB/ml/genlsatl.html.

7.12 Problems and Exercises
7.1. Describe the TT&C facilities of a satellite communications system. Are
these facilities part of the space segment or part of the ground segment of the
system?
7.2. Explain why some satellites employ cylindrical solar arrays, whereas
others employ solar-sail arrays for the production of primary power. State the
typical power output to be expected from each type. Why is it necessary for
satellites to carry batteries in addition to solar-cell arrays?
7.3. Explain what is meant by satellite attitude, and briefly describe two forms
of attitude control.
7.4. Define and explain the terms roll, pitch,and yaw.

7.5. Explain what is meant by the term despun antenna, and briefly describe
one way in which the despinning is achieved.

7.6. Briefly describe the three-axis method of satellite stabilization.

7.7. Describe the east-west and north-south station-keeping maneuvers
required in satellite station keeping. What are the angular tolerances in station
keeping that must be achieved?

7.8. Referring to Fig. 7.10 and the accompanying text in Sec. 7.4, determine
the minimum 3-dB beamwidth that will accommodate the tolerances in
satellite position without the need for tracking.

7.9. Explain what is meant by thermal control and why this is necessary in a
satellite.

7.10. Explain why an omnidirectional antenna must be used aboard a satellite
for telemetry and command during the launch phase. How is the satellite
powered during this phase?