# Astronautics Questions and Answers – Earth Orbit Perturbations – Set 2

This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Earth Orbit Perturbations – Set 2”.

1. Orbital perturbations are generally classified as ___________ and _____________ perturbations.
a) secular, periodic
b) short-term, long-term
c) solar, lunar
d) internal, external

Explanation: At the most general level, perturbations can be grouped as secular or periodic. Secular perturbations are those whose effects continuously build up over time, while periodic perturbations repeat over regular intervals.

2. The effects of secular perturbations are _________
a) periodic in nature
b) insignificant over a long span of time
c) significant over a short span of time
d) significant over long periods

Explanation: Secular perturbations describe the long-lasting disturbances that act continuously and create negligible deviations at any instant that build up over time to cause significant errors in the orbit of a body.

3. Bringing back a satellite to its original trajectory through occasional corrective maneuvers is called _______________
a) propulsive burn
b) station-keeping
c) correction burn
d) telemetry

Explanation: Keeping the satellite in its original planned orbit by regularly correcting for any observed deviations in its actual trajectory is called station-keeping.

4. Orbital perturbations cause changes in the ______________
a) orbital elements
b) orbital energy
c) satellite’s lifespan
d) satellite’s efficiency

Explanation: Perturbations affect the orbital elements and force the satellite into a slightly different orbit after a long period of time. This causes a change in some orbit parameters. The orbital energy is a constant value and does not vary even in the presence of perturbing effects.

5. A radial disturbance to a satellite is an external force that acts _______________
a) perpendicular to the orbital plane
b) tangential to the orbit
c) along the line joining the central body and the satellite
d) obliquely

Explanation: The line-of-action of a radial disturbance is always aligned with the line joining the satellite and the central body. In case of circular orbits, this radial force acts along the orbit’s radius vector.

6. A transverse perturbation tends to change the _________________
a) orbital plane
b) eccentricity
c) size of the orbit
d) orbital energy

Explanation: A transverse perturbation acts perpendicular to the orbital plane. Such an out-of-plane disturbance is orthogonal to the motion of the object and hence does not have any tangential or radial component, thus changing only the orbital inclination (and therefore the orbital plane) in such a way that the other elements (eccentricity, size of the orbit, etc.) remain the same.

7. The result of a prograde burn by a satellite is to _____________
a) add potential energy at the expense of kinetic energy
b) add kinetic energy at the expense of potential energy
c) change the orbital plane
d) change the orbital inclination

Explanation: A prograde burn exerts a force tangential to and along the motion of the satellite. This causes an increase in orbital altitude, which is associated with an increase in potential energy and a decrease in kinetic energy in such a way that their sum (total energy) stays constant.

8. An increase in kinetic energy is achieved by exerting a force ___________ the satellite.
a) along the direction of motion of
b) against the direction of motion of
c) perpendicular to the motion of
d) transverse to the motion of

Explanation: A retrograde burn decreases the orbital height of the satellite at the point where it acts, thereby increasing velocity (and thus kinetic energy).

9. Orbital perturbing effects require that the satellite _______________
a) carry more fuel
c) be decommissioned sooner
d) change its mission objective frequently

Explanation: Perturbations make the satellite stray away from its orbit. The common methodology employed in order to prevent any large errors in the planned trajectory is to regularly execute propulsive burns using on-board thrusters for bringing back the satellite into its original orbit. As discussed earlier, this is also known as station-keeping.

10. Earth-orbit perturbation effects originate only from natural sources external to the satellite being perturbed.
a) True
b) False

Explanation: Perturbations on satellites come only from a natural origin and cannot be caused by the satellite itself, unless spacecraft themselves deliberately run their on-board propulsion units in order to intentionally deviate from the planed orbit.

Sanfoundry Global Education & Learning Series – Astronautics.

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