This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Satellite Constellations”.
1. The maximum latitude an Earth-bound satellite’s ground track can reach is limited by the orbit’s ______________
a) height
b) inclination
c) eccentricity
d) semi-major axis
View Answer
Explanation:
A line of latitude represents a great circle that wraps around our planet and runs parallel to the equator. Latitudes slice the Earth horizontally and are used to specify the angular distance of objects from the equatorial palne. Your own latitude can be determined by connecting the Earth’s center with your position on the ground and measuring the angle between this connector and the equatorial plane.
A ground track is an imaginary line or curve on the surface of the Earth traced out by a satellite’s projection (i.e., the line segment joining the satellite and the point on Earth’s surface directly below it). The line joining the center of Earth and the satellite can be split into two segments: the satellite’s projection and the projection’s latitude (which is nothing but the satellite’s latitude). So when the satellite reaches the highest (or lowest) point of its orbit, its latitude at that instant is maximum and equal to the orbital inclination.
2. A retrograde orbit must have an inclination _______________
a) between 0 and 90 degrees
b) greater than 270 degrees
c) lesser than 45 degrees
d) between 90 and 270 degrees
View Answer
Explanation: A retrograde orbit implies that an object in such an orbit revolves in a direction opposite to that of Earth’s rotation. This is possible with inclinations that lie between 90 and 270 degrees. On the contrary, objects in a prograde orbit circle the Earth along the same direction as that of our planet’s rotation. Prograde orbits fall between 0 and 90 degree inclinations as well as between 270 and 360 degrees.
3. Low Earth Orbit lies between ______________
a) an inclination of 0 and 90 degrees
b) an altitude of 20000 and 36000 kilometers
c) an altitude of 300 and 2000 kilometers
d) an inclination of 90 and 180 degrees.
View Answer
Explanation: Low Earth Orbit, abbreviated as LEO, starts from a height of 300 kilometers and extends up till 2000 kilometers above Earth’s surface, irrespective of the inclination.
4. Spacecraft orbiting close (within a height of 20,000 km) to Earth _____________
a) move faster than Earth’s rotation
b) lag behind Earth’s rotation
c) have a larger view of Earth
d) are on par with Earth’s rotation
View Answer
Explanation: Satellites very close to Earth revolve with high orbital velocities (on the order of 8 km/s, or 28,800 km/hr). Earth’s rotation is fastest at the equator, which drifts at a modest speed of just 1670 km/h (slower than the much more rapid near-Earth spacecraft).
5. A satellite very close to Earth will appear to move _______________ as seen by an observer on the ground.
a) retrograde
b) prograde
c) inward
d) outward
View Answer
Explanation: Since nearby spacecraft race ahead of Earth’s rotation, an observer on the ground will see the satellite move in an easterly sense (or West to East). This apparent motion still occurs in the same direction as that of Earth’s rotation, and is therefore considered prograde.
6. HEO stands for ___________
a) Highly Elongated Orbit
b) Highly Elliptical Orbit
c) Highly Eccentric Orbit
d) High Earth Orbit
View Answer
Explanation: HEO is an abbreviation for Highly Elliptical Orbit (HEO). HEO is usually misinterpreted as ‘High Earth Orbit’, but in the actual case no such orbit is officially designated as such. Molniya Orbit is an example of HEO.
7. Specifying the argument of perigee and inclination of an inclined elliptical orbit is not sufficient to fix the orbital plane for a ____________
a) polar orbit
b) low-inclination LEO
c) geostationary orbit
d) Molniya orbit
View Answer
Explanation: For a non-equatorial non-polar elliptical orbit, specifying the argument of perigee as well as inclination is enough to freeze the orbit in a single plane. Such a defining brings down the right ascension of the orbit to just two possible values (one for prograde motion and the other for retrograde motion), each one separated by 180 degrees. For a polar orbit, however, specifying the inclination (90 degrees by default) and an argument of perigee of 90 degrees (the case where the perigee sits right above the North Pole) does not fix the orbital plane. The orbit can still rotate about its major axis without changing both values.
8. A satellite’s ground track will cover the entire globe for _______________
a) equatorial orbits
b) geostationary orbits
c) low-inclination orbits
d) polar orbits
View Answer
Explanation: The highest latitude reached by the satellite’s ground track depends on the inclination of its orbit. A polar orbit is able to access the northernmost as well as southernmost parts of our planet. At the same time, Earth rotates beneath the orbiter. So a full coverage is possible with this type of orbit.
9. Geosynchronous orbit and geostationary orbit are two interchangeable terms for the exact same orbit.
a) True
b) False
View Answer
Explanation: A geosynchronous orbit is an orbit with a period equal to 24 hours (the same as that of Earth’s rotational period), whether the orbit is circular, inclined, elliptical, or polar. A geostationary orbit refers to an equatorial as well as circular geosynchronous orbit.
10. The angle made by an Earth-centered orbit’s plane and the Sun-Earth line continuously varies throughout the course of a year.
a) True
b) False
View Answer
Explanation: The Sun-Earth line is just the line joining the centers of the two celestial bodies. Any normal orbit around Earth has a fixed orientation with respect to our planet, but as the Earth revolves around the Sun, the angle made by the orbit with the Sun’s rays (and therefore the Sun-Earth line) changes.
Sanfoundry Global Education & Learning Series – Astronautics.
To practice all areas of Astronautics, here is complete set of Multiple Choice Questions and Answers.
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