This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Real Orbits – Third-Body Forces”.
1. Third body perturbations are caused due to ______________
a) the non-spherical Earth
b) non-spherical external bodies
c) gravity from Earth
d) gravity from external bodies
View Answer
Explanation: Third body perturbations are caused by the gravitational attraction of extra-Earth influences (like the Moon, Sun, and planets) and has nothing to do with their shapes.
2. Third body perturbations are greater for higher orbits.
a) True
b) False
View Answer
Explanation: The higher a satellite revolves away from Earth, the closer it is to external influences (like our moon, Venus, Mars, or the Sun) and hence is affected more strongly than when it revolves at lower altitudes. Its trajectory is then governed not only by the dominant planet Earth, but also to a small extent by these objects.
3. Choose the correct statement from the following list:
a) Third body perturbations are more for LEO satellites.
b) Third body perturbations are lesser for GEO satellites.
c) Third body perturbations are equal for both LEO and GEO satellites.
d) Third body perturbations are more for GEO satellites.
View Answer
Explanation: Geostationary Earth Orbit (GEO), being the higher orbit, is associated with stronger disturbances from external celestial objects (like the Moon, Sun, and planets).
4. The closest planet to Earth is _____________
a) Mars
b) Venus
c) Mercury
d) Moon
View Answer
Explanation: Venus is the third planet from the Sun and revolves closer to Earth than Mars. The Moon is not a planet and so cannot be taken into consideration.
5. The two major influences that constantly affect satellites in a high-altitude orbit around Earth are
a) Venus and the Moon
b) The Sun and the Moon
c) Venus and the Sun
d) The Moon and Mars
View Answer
Explanation: Satellites in a high altitude orbit experience constant gravitational tugs from two objects: the Moon and the Sun. Our moon lies closest to Earth and is massive enough to cause noticeable variations in a satellite’s trajectory. The sun, being much farther away, is the largest and most massive object in our solar system and is the primary body that governs the motions of all the planets. Satellites in a high geocentric (Earth-centered) orbit can never escape the influence of our mighty star. Remember that in the question, the word ‘constant’ is mentioned. The gravity from the planets disturbs satellites only at times when they come close to Earth (which happens just for a relatively brief length of time).
6. Perturbations from the Sun are greater than those from the Moon.
a) True
b) False
View Answer
Explanation: This is false because even though the Sun is much more massive than the Moon, it is also extremely far away. The Moon is much less massive than the Sun, but is also extremely nearby compared to the Sun. The net result is that third body perturbations on a satellite are usually dominated by the Moon.
7. Perturbations from third body forces are only periodic in nature.
a) True
b) False
View Answer
Explanation: Gravitational effects from third body influences cause both secular as well as periodic changes in the orbital elements.
8. The primary disadvantage of a high altitude orbit is that _______________
a) it is easier to reach
b) the perturbations from external celestial bodies are greater
c) the perturbations from the non-spherical Earth are greater
d) the perturbations due to non-spherical celestial bodies are greater
View Answer
Explanation: Satellites in a higher orbit are more strongly perturbed by external bodies than lower orbits due to their close proximity to these extra-Earth celestial objects.
9. When talking about ‘third body perturbations’, which among the following does not fall under the designation of ‘third bodies’?
a) The Moon
b) The Sun
c) Asteroids
d) Planets
View Answer
Explanation: Third body perturbations are only caused by massive planetary or moon-like objects that are large enough to exert a strong gravitational pull. Asteroids cannot be grouped under such a category.
10. How many times farther away from Earth is the Sun compared to the Moon?
a) 400 times
b) 800 times
c) 4000 times
d) 8000 times
View Answer
Explanation: The Sun lies approximately 400 times farther away from Earth than the Moon. The Sun’s distance from our planet is approximately 150 million kilometers, while the Moon is around 380,000 kilometers away from Earth.
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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