# Avionics Questions and Answers – Satellite Orbits

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This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Satellite Orbits”.

1. What happens if a satellite is launched vertically and released at its design altitude?
a) Continue to orbit the earth
b) Fall back
c) Overshoots the altitude and moves at a constant speed
d) Stays where it was released

Explanation: If a satellite were launched vertically from the earth and then released, it would fall back to earth because of gravity. For the satellite to go into orbit around the earth, it must have some forward motion. For that reason, when the satellite is launched, it is given both vertical and forward motion.

2. The satellite is accelerating as it orbits the earth.
a) True
b) False

Explanation: Although the speed of the satellite is constant its direction keeps on changing as the orbit is circular or elliptical. The rate of change of velocity vector is acceleration and hence its direction changes, the satellite is under acceleration.

3. Why does the orbit take the shape of an ellipse or circle?
a) Position can be easily determined
b) Consume less fuel
c) Most efficient geometry
d) Better coverage on earth

Explanation: A satellite rotates about the earth in either a circular or an elliptical path. Circles and ellipses are geometric figures that can be accurately described mathematically. Because the orbit is either circular or elliptical, it is possible to calculate the position of a satellite at any given time.

4. The direction of orbit in the same direction of earth rotation is called ______
c) Perigee
d) Apogee

Explanation: The direction of satellite rotation may be either in the same direction as the earth’s rotation or against the direction of earth’s rotation. In the former case, the orbit is said to be posigrade, and in the latter case, retrograde. Most orbits are posigrade.

5. When is the speed of the satellite maximum in an elliptical orbit?
c) Perigee
d) Apogee

Explanation: In an elliptical orbit, the speed changes depending upon the height of the satellite above the earth. Naturally, the speed of the satellite is greater when it is close to the earth than when it is far away. The closest point is called the perigee.
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6. Satellites closer to the earth travel at lower speeds than satellites that are far away from earth.
a) True
b) False

Explanation: Satellites that are near earth have to move at higher speeds to sustain their orbit since the gravitational pull is much higher. Since the effect of gravity is less at higher altitudes, satellites that far away require less speeds.

7. The time period taken by the satellite to complete one orbit is called ________
a) Lapsed time
b) Time period
c) Sidereal period
d) Unit frequency

Explanation: The period is the time it takes for a satellite to complete one orbit. It is also called the sidereal period. A sidereal orbit uses some external fixed or apparently motionless object such as the sun or star for reference in determining a sidereal period.

8. The period of time that elapses between the successive passes of the satellite over a given meridian of earth longitude is called as _____________
a) synodic period
b) Lapsed time
c) Time period
d) Sidereal period

Explanation: Another method of expressing the time for one orbit is the revolution or synodic period. One revolution (1 r) is the period of time that elapses between the successive passes of the satellite over a given meridian of earth longitude. Naturally, the synodic and sidereal periods differ from each other because of the earth’s rotation.

9. What is the angle of inclination for a satellite following an equatorial orbit?
a) 0°
b) 180°
c) 45°
d) 90°

Explanation: Another definition of inclination is the angle between the equatorial plane and the satellite orbital plane as the satellite enters the northern hemisphere. When the angle of inclination is 0°, the satellite is directly above the equator. Orbits with 0° inclination are generally called equatorial orbits.

10. The angle between the line from the earth station’s antenna to the satellite and the line between the earth station’s antenna and the earth’s horizon is called as ___________
a) Angle of inclination
b) Angle of elevation
c) Apogee angle
d) LOS angle

Explanation: The angle of elevation of a satellite is the angle that appears between the line from the earth station’s antenna to the satellite and the line between the earth station’s antenna and the earth’s horizon. If the angle of elevation is too small, the signals between the earth station and the satellite have to pass through much more of the earth’s atmosphere. Because of the very low powers used and the high absorption of the earth’s atmosphere.

11. To use a satellite for communication relay or repeater purposes what type of orbit will be the best?
a) Circular orbit
b) Elliptical orbit
c) Geosynchronous orbit
d) Triangular orbit

Explanation: The best solution is to launch a synchronous or geostationary satellite. In a geosynchronous earth orbit. Since the satellite remains apparently fixed, no special earth station tracking antennas are required. The antenna is simply pointed at the satellite and remains in a fixed position. With this arrangement, continuous communication is possible.

12. What percentage of the earth can communication satellites see?
a) 20
b) 50
c) 70
d) 40

Explanation: Most communication satellites in use today are of the geosynchronous variety. Approximately 40 percent of the earth’s surface can be “seen” or accessed from such a satellite. Users inside that area can use the satellite for communication.

13. What is the point on the surface of the earth that is directly below the satellite called?
a) Satellite point
b) Subsatellite point
c) Supersatellite point

Explanation: The satellite location is specified by a point on the surface of the earth directly below the satellite. This point is known as the subsatellite point (SSP). The subsatellite point is then located by using conventional latitude and longitude designations.

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