Understanding weightless flight
Understanding weightless flight involves grasping the principles of gravity and the effects of microgravity experienced by astronauts and in various simulated environments. Gravity, the mutual attraction between masses, is a key factor that influences weight, defined as the pull one feels from Earth’s gravity—approximately 9.8 meters per second. When in space, astronauts experience a sensation known as zero-G or microgravity, which occurs when they and their spacecraft are in free fall together around the Earth. This creates the illusion of weightlessness, as both the astronauts and their craft accelerate at the same rate toward Earth while following a curved orbit.
Various methods can recreate this sensation without leaving the Earth's atmosphere. For instance, NASA employs facilities such as the Neutral Buoyancy Simulator and the Zero Gravity Research Facility to simulate weightlessness for training and experimentation. Commercial companies have also started offering weightless flight experiences to the public, utilizing parabolic flight patterns to achieve brief moments of microgravity. Overall, understanding the physics behind weightless flight opens avenues for space exploration, scientific research, and thrilling recreational experiences.
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Understanding weightless flight
Summary: The forces to experience the sensation of weightlessness, or zero-G, can be calculated and achieved in a variety ways.
Gravity is the mutual attraction of two masses. Important aspects of the mathematics and the theory of gravity were described centuries ago by Galileo Galilei and Isaac Newton. Albert Einstein’s work was critical to the modern understanding of gravity and weightlessness. Mass is the measure of the amount of matter in an object. For living beings, weight can be thought of as the subjective experience of muscles resisting the pull of the much larger Earth on their smaller masses. On the Earth’s surface, gravitational acceleration is about 9.8 meters per second (one gravity or g). Other planets have different gravity. For example, an Earth person would feel about 2.5 times heavier on Jupiter. Infants learn to accommodate gravity’s pull when performing the activities of daily life until the force feels natural and largely unnoticed. However, sometimes people experience other forces acting on their bodies that counter the pull of gravity and change their perceptions of weight. For example, the quick start or stop of an elevator can make a person feel heavier or lighter. Roller coasters purposely induce similar effects for amusement. Parabolic drops, turns, and loops exert temporary linear or angular forces on a moving body, some of which act along a different directional vector than gravity and combine mathematically to alter the body’s perception of weight. Mathematicians, scientists, and engineers precisely calculate the net effect of gravity and other forces on objects for a wide range of applications, such as banked curves on racetracks and highways, the movement of subatomic particles, launching spacecraft to the moon, and of course, ever more thrilling amusement park rides.
Zero-G
The planet’s mass exerts a strong gravitational pull even on objects in space. This force is what keeps satellites in position. However, many people have seen video images of astronauts who are floating around as if they are weightless. This effect is known as zero-G or, more accurately, “microgravity” (about 1×10-6 g). Like roller coasters, this effect results from a combination of forces acting on the body. At any given instant in time, the astronauts are accelerating freely toward the Earth inside an object that is accelerating freely at the same rate. They can be visualized in that instant as falling on a straight line drawn from the spaceship to the Earth, perpendicular to a tangent line drawn at the ship’s current position in its curved orbit. However, the ship’s directional vector is constantly changing because of its curved orbit, so it perpetually “falls” in a new direction—around the Earth, instead of toward it. The spacecraft’s precisely calculated inertial trajectory effectively counters the astronauts’ constant “falling.” As a result, the astronauts do not move with respect to their immediate surroundings, so they look and feel as if they are floating weightlessly. A spacecraft lands by altering its curved orbit so that the gravity is no longer sufficiently opposed.
Free-fall or zero-G can be achieved in several ways without leaving Earth’s atmosphere. NASA’s Neutral Buoyancy Simulator uses the world’s largest indoor pool, containing over six million gallons of water, to simulate weightlessness without flying or falling, while their Zero Gravity Research Facility can achieve just over five seconds of free fall in a 467-foot long steel vacuum chamber, which is used to test microgravity effects on phenomena such as combustion and fluid physics. As part of a series of experiments in the 1960s, Air Force Captain Joseph Kittinger parachuted from a gondola at an altitude of almost 103,000 feet. He achieved a speed of over 600 miles per hour on his descent but he reported having no real subjective sensation of the incredible speeds. Standard aircraft can be used to create brief periods of weightlessness, about 30 seconds, by flying in a parabolic pattern or “Kepler curve,” named for Johannes Kepler. National Aeronautics and Space Administration (NASA) uses this method to train astronauts, and the weightless effects seen in the 1995 movie Apollo 13 were produced using parabolic flight. Several commercial companies also offer the experience to the general public. A privately funded experimental “spaceplane” called SpaceShipOne achieved suborbital flight in 2004. A revised commercial version called VSS Enterprise flew for the first time in 2010 and is taking reservations for future commercial flights that will launch passengers into suborbital space.
Bibliography
Clement, Giles, and Angeli Bukley. Artificial Gravity. New York: Springer, 2007.
Erickson, Lance. Space Flight: History, Technology, and Operations. Lanham, MA: Government Institutes, 2010.
Sparrow, Giles. Spaceflight: The Complete Story From Sputnik to Shuttle—and Beyond. New York: Dorling Kindersley Publishers, 2007.