Which of these orbital transfers is the most energy efficient?

Correct Answer : Option (A) :   Energy change

Explanation : There are four types of single impulse maneuver-Adjustment of perigee and apogee height, simple rotation of the line of apsides, simple plane change and combined change of apsis altitude with plane orientation. There is no change in energy involved by applying single impulse.

Correct Answer : Option (D) :   Rocket fires long bursts for long time for the required delta-v

Explanation : When the thrust applied by the rocket is done over a longer period to obtain the required delta-v, it is known as the non-impulsive maneuver. Unlike impulsive maneuver it does not involve applying impulse over a short period.

Correct Answer : Option (C) :   Cranking maneuver

Explanation : Each impulsive maneuver results in a velocity change of the spacecraft. This velocity change yield both magnitude and direction change of the velocity vector. When Δv represents a change in direction it is referred as a cranking maneuver.