Abstract Space flight is the ultimate form of travel which takes humans from the confines of the earth, and space exploration is an important means of expanding the frontiers of science. However, there are many prevalent misconceptions regarding space flight, which are probably derived from the popular science fiction. One of them is the issue of weightlessness. Astronauts are supposed to become weightless as soon as they get into the space. This is far from being true. Our weight is the reaction we feel from the ground as we stand, sit, or lie on it, or from any platform which has a zero vertical acceleration relative to the ground. By Newton’s third law of motion (see Chap. 1), if any object (such as yourself) exerts a force on any other object (like a platform), the second object also applies an equal and opposite force (called the reaction) on the first object. The magnitude of the force applied is equal to your own mass times the acceleration relative to the platform, according to the second law of motion (Chap. 1). If the platform itself does not have any vertical acceleration, the reaction experienced by you from the platform is equal to your mass times the acceleration due to gravity, which is your weight. Now, suppose you are in an elevator which is accelerating upward relative to the ground (see Fig. 6.1). The net acceleration experienced by you from the platform is now greater than that due to gravity, and it seems as if your weight has increased because the platform exerts a larger reaction on you. If a tragedy were to happen in which the elevator’s cable snaps, then both you and the elevator would be falling down with the same acceleration due to gravity (this situation is called a free fall), therefore your relative acceleration due to the platform would be zero. Since now you will not feel any reaction from the platform, it would seem as if your weight has become zero. In fact, your weight is still the same as it was before you got into the elevator. Similarly, an astronaut only feels a zero reaction from the spacecraft, whereas both the astronaut and the spacecraft are falling freely with the same acceleration due to gravity. The same weightless sensation is produced in an airplane which is making a vertical turn in a downward direction with a rate such that the lift acting on the aircraft is exactly zero, and the centripetal acceleration is provided only by the gravity. Such a zero-lift (or ballistic) flight is used to train astronauts for space missions.
Space Flight
Basic Flight Mechanics ; 99-121
2016-01-01
23 pages
Article/Chapter (Book)
Electronic Resource
English
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