This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Satellite Constellations – Set 2”.
1. Name the unique attribute of a sun-synchronous orbit.
a) Has the same period as that of the Sun’s rotation
b) Has the same period as that of Earth’s revolution around the Sun
c) Maintains a constant angle with respect to the Sun’s rays throughout a year
d) Lies in the ecliptic plane
View Answer
Explanation: A sun-synchronous orbit is an orbit which precesses in such a way that there is no change in the angle between the orbital plane and the Sun’s rays. So while its orientation with respect to our own planet varies, its angle with respect to the Sun-Earth line remains fixed.
2. Orbits that lie below geostationary orbit are also called _________________ and those above geostationary orbit are called _________________
a) prograde orbits, retrograde orbits
b) sub-synchronous orbits, super-synchronous orbits
c) low earth orbits, high earth orbits
d) intermediate orbits, graveyard orbits
View Answer
Explanation: The geostationary belt is generally referred to as a synchronous orbit due to the fact that satellites in such an orbit complete one revolution in the same time as that taken by Earth to rotate about its axis once. Orbits below this synchronous orbit are termed ‘sub-synchronous’, and those above are called ‘super-synchronous’.
3. An orbit with a greater altitude than that of geosynchronous orbits is called ____________
a) Geostationary orbit
b) Graveyard orbit
c) Super-synchronous orbit
d) medium earth orbit
View Answer
Explanation: Generally, a super-synchronous orbit is one that sits on top of a synchronous orbit (an orbit with a period equal to the period of rotation of the central body).
4. An object in a super-synchronous orbit will appear to move __________ as seen by an observer on the surface of the Earth.
a) prograde
b) East
c) outward
d) retrograde
View Answer
Explanation: Super-synchronous orbits are higher than a synchronous orbit and hence associated with a longer time period. The Earth rotates faster than a satellite in such an orbit, meaning that a ground-based tracker will see the satellite move ‘backward’, or in a retrograde sense.
5. A satellite at time t=0 is stationed above a particular location on Earth. After exactly one orbit, the satellite seems to above a different place.
a) True
b) False
View Answer
Explanation: Note that in this question, we are talking about the satellite’s location ‘above’ a point on Earth, not its position in the orbit. While the satellite is in the process of completing one orbit, our planet continues to spin about its own axis. By the time it has finished one revolution, the satellite sees a different location on the surface below it.
6. The number of orbits per day by a MEO satellite 20,200 kilometers above Earth is ___________ (assume Earth’s mass to be 5.972 × 1024 kg and radius as 6370 km)
a) 12 hours
b) 24 hours
c) 8 hours
d) 36 hours
View Answer
Explanation: We know that
T2 = \(\frac{4π^2}{GM} r^3\)
Here, r = (20,200 + 6370) x 103 m
i.e., r = 26,570,000 m
Substituting the values, we have T = 43102.76 seconds = 11.97 hours ~ 12 hours
7. Sun-synchronous orbits are usually ________________
a) equatorial
b) low-inclination
c) near-polar
d) synchronous
View Answer
Explanation: Sun-synchronous orbits usually have inclinations close to 90 degrees, categorizing them under near-polar orbits.
8. The eccentricity of a Molniya Orbit (apogee: 39,300 km; perigee: 538 km) is ______________
a) 0.9729
b) 0.3365
c) 0.737
d) 0.0973
View Answer
Explanation: Eccentricity is given by
e = \(\frac{r_a – r_p}{r_a + r_p}\)
Here, ra = 39,300 + Earth’s radius = 39300 + 6370 = 45670 km
rb = 39,300 + Earth’s radius = 538 + 6370 = 6908 km
Substituting the values, we have e = 0.737
9. What is the primary advantage of geostationary orbit?
a) Uninterrupted link
b) Better resolution for Earth-monitoring
c) Larger field of view
d) Easy to reach
View Answer
Explanation: The biggest merit of geostationary orbit is that the satellite appears fixed above a given location on Earth, allowing for uninterrupted communication with a ground-station in the satellite’s field of view. This is because the satellite revolves with the same angular velocity as that of Earth’s rotation, with no relative motion between a point on the surface and the satellite.
10. What is the speed with which a geostationary satellite moves (assuming it is at a height of 36,000 kilometers)?
a) 11 km/s
b) 8 km/s
c) 3 km/s
d) 9 km/s
View Answer
Explanation: Given, r = 36,000,000 + Earth’s radius = (36000 + 6370) x 103 m = 42370000 m.
Since geostationary orbit is circular and has a period of approximately 24 hours, we have
v = \(\frac{2πr}{T}\)
Here, T = 24 x 60 x 60 seconds = 86400 seconds
Substituting the values, we have v = 3081.23 m/s ≈ 3 kilometers per second.
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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