This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Satellite Constellations – Set 3”.
1. A satellite constellation is generally feasible for Earth-monitoring and works best for _____________
a) equatorial orbits
b) low-inclination orbits
c) low-inclination to high-inclination orbits
d) geostationary orbit
View Answer
Explanation: Earth-monitoring by a single satellite is usually convenient for equatorial orbits since the satellite revisits the region of interest frequently (this is because the area of Earth being monitored is situated at the equator itself, and the satellite always remains in the equatorial plane). Spacecraft in an inclined orbit see different locations as they traverse different latitudes due to the fact that the Earth itself spins underneath the revolving satellite. It takes several orbits in order to revisit the same place. A constellation that holds a number of adequately spaced satellites is able to overcome this issue to an acceptable level by crossing the target area more often than is possible with just one spacecraft.
2. The primary motivation for a satellite constellation is ___________________
a) continuous coverage
b) better resolution
c) redundancy
d) lower cost
View Answer
Explanation: Occasionally, there is a need to keep an eye on a particular region of Earth without interruption, perhaps for scientific purposes like weather monitoring, precipitation measurement, etc. This continuous coverage is not possible with a single satellite for the simple reason that the spacecraft remains above any given location on the surface for only a short duration (because the satellite is moving much faster than Earth’s rotation) and takes time to come back and monitor the same place. A constellation is able to resolve this issue by distributing the workload amongst many satellites in such a way that when one of them goes out of range of its target, the other one enters and maintains an unbroken link.
3. The ground track of a satellite on a map of Earth takes the shape of a __________ for equatorial orbits.
a) sine wave
b) line
c) helix
d) triangular wave
View Answer
Explanation: Since the satellite stays in the equatorial plane, its ground track on a map is just a straight line passing through 0 degrees latitude.
4. An LEO satellite is best suited for _______________
a) Earth-monitoring
b) communications
c) astronomical imagery
d) tracking and positioning
View Answer
Explanation: LEO satellites, due to their close proximity, have a better resolution and accuracy in Earth-observation techniques and largely used in such applications. Communications and tracking & positioning do not go well with near-Earth spacecraft due to their enormous velocities and frequent passages into and out of the coverage area of a ground-station. Astronomical imagery is possible with LEO satellites, but space-based telescopes have no significant advantages over observatories on Earth.
5. Which of the following is not a satellite constellation?
a) IRNSS
b) GPS
c) Iridium
d) Hubble
View Answer
Explanation: Hubble is one of the most successful Earth-orbiting telescopes, and was launched by NASA way back in 1990. IRNSS (India) and GPS (USA) are satellite constellations dedicated for tracking and positioning of ground-based entities. The Iridium constellation holds 66 satellites built exclusively for mobile communications.
6. Geostationary orbit can have an inclination between ___ and ___
a) -90˚ to +90˚
b) 0˚ to 90˚
c) -15˚ to +15˚
d) -90˚ to 0˚
View Answer
Explanation: The geostationary orbit is actually a near-equatorial orbit with an allowance of ±15˚. This gives rise to the observed shape of the so-called geostationary ‘ring’.
7. Any two satellites part of a constellation that revolve along the same orbit can never collide with each other.
a) True
b) False
View Answer
Explanation: Both spacecraft operate in the same orbit, are part of a constellation, and therefore must revolve in the same direction. As a result, there is absolutely no possibility of a collision due to the fact that they are in the exact same orbit and thus move with identical orbital speeds.
8. You are a satellite designer and given the job of coming up with an early cyclonic warning system for the Indian coastal region. Which among the following can fulfill this task?
a) A polar satellite
b) A satellite constellation
c) A low-inclination satellite
d) A geostationary satellite
View Answer
Explanation: Such an early warning system needs to monitor the coastal region in order to keep track of the onset of a cyclone so that it is possible to inform authorities of the potential danger and facilitate prior evacuation. A satellite constellation can satisfy the objective of continuous monitoring, while a single satellite spends most of its time out of range of the area to be scrutinized and therefore cannot be used.
9. Five satellites have been planned to form a constellation and must be put into the same circular orbit of radius 6450 kilometers. What is the on-orbit separation between each satellite (in kilometers)?
a) 7765.2
b) 6370
c) 1290
d) 8105.3
View Answer
Explanation: Circumference of the orbit = 2×π×r
Here, r = 6450 km. Therefore, circumference = 40526.545 kilometers.
The separation between each satellite is the circumference of the orbit divided by the number of satellites.
On-orbit separation = Circumference/(Number of satellites)
Number of satellites = 5. So the distance between each satellites is 40526.545/5 = 8105.3 kilometers
10. What is the main disadvantage of a satellite constellation?
a) Launch costs
b) Cost of manufacturing
c) Collisions
d) Tedious to keep track of each constituent satellite
View Answer
Explanation: The cost of manufacturing is very high for constellations. This is because designers need to build multiple satellites with the same scientific instruments rather than just one spacecraft.
All satellites can be made compact and accommodated as a single payload, so launch costs are not an issue. Analysts can plan out the constellation orbit(s) in such a way that a collision is next to impossible, so that isn’t a problem either. Keeping track of each satellite is accomplished quite easily with ground stations (the level of involvement is no higher than that for a single satellite).
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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