Question

If an orbiting artificial satellite were to slow down, what would happen?

Asked by: Christopher Alec Maquiling

Answer

Artificial satellites slow down all the time, and uniformly, they are no longer able to resist the pull of gravity and fall back to Earth. Satellites like the Space Shuttle do it intentionally and can control their descent. The Mir space station was a controlled crash in the South Pacific, and countless other satellites have been accidentally lost.

The most common cause of what is known as orbital decay is the atmosphere. As you can imagine, there is no solid "border" to the atmosphere. Gravity holds most of it near the Earth, but out near the border of space there are very few particles, but certainly enough to slow down a satellite that ventures too close to the Earth. Satellites carry fuel to help maintain their orbits, but when that fuel runs out... sooner or later they will fall back to the ground. Hopefully it can be in a controlled manner. If you have any more questions, feel free to ask us, or hit up NASA.

Answered by: Frank DiBonaventuro, B.S., Physics grad, The Citadel, Air Force officer



It would fall to the planet's surface. Here's why:

Imagine a car driving around in a perfect circle. This is a centripetal acceleration described by

a = v^2 / r

where v is the velocity of the car and r is the distance of its revolution. This equation of acceleration also applies to the motion of the satellite as it moves around the planet. (Here we are not considering the planet's rotational motion.) Now if we want to consider centripetal force, we multiply the centripetal acceleration by the mass of the satellite; this gives:

F = m a

Next consider that the weight of the artificial satellite is given by the equation:

W = m g

Now g is the acceleration due to gravity. In the physics classroom its value is usually given at sea level, but in reality g is a variable: closer to the center of mass it is strong, farther away it is weak.

For the artificial satellite to orbit the planet without falling in, F and W must be equal. So then:

F = W
m a = m g
a = g
v^2 / r = g

Now if the satellite slows down, v decreases in value so that:

v^2 / r < g

This means that the acceleration due to gravity is greater than the centripetal acceleration. Gravity wins the fight and pulls the satellite to the planet's surface.

Answered by: Frederick Herrmann, B.A.

Search

Loading






Science Quote

'You cannot hope to build a better world without improving the individuals. To that end each of us must work for his own improvement, and at the same time share a general responsibility for all humanity, our particular duty being to aid those to whom we think we can be most useful.'

Marie Curie
(1867-1934)
Science Sidebar | Science Education Articles
Cool Summer Science Projects

Why not make science a part of your family’s summer? Perhaps you can set aside one day a week for outdoor projects—maybe Mad Scientist Monday or Scientific Saturday? Here are a few ideas to help get you started. Continue reading ...

10 Ways to Keep Your Kids Interested In Science

Young children are natural scientists: they ask questions, pick up sticks and bugs outside, and are curious about the world around them. But as they get a bit older, many kids gradually lose their interest in science. They might see it as just another task at school, something that doesn't apply to their lives. Of course nothing could be further from the truth, so here are ten ways you can remind your kids that science is everywhere. Most of these are fun for adults, too! Continue reading ...

Top Selling

Here are our physics & astronomy bestsellers:
Magnetic Levitator - Classic
3D Magnetic Field Tube
Revolving Multi-Color Fiberoptic Light
KonusScience 5 Way Microscope Kit
Periscope
Tin Can Robot 4M Kit
Mini Plasma Ball
Solar Radiometer
Wood Grain Newtons Cradle
12 inch Galileo Thermometer

Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department