SpaceX Satellites Visible from Earth Renew Curiosity over Orbiting Objects

Elon Musk’s SpaceX program is raising eyebrows with hundreds of satellites, Forbes reported. Its new endeavor, Starlink, has sent 360 satellites into orbit, which are visible from the Earth. Putting a satellite into orbit is both fascinating and complex.

According to Forbes, Starlink hopes to “beam the internet to Earth from space”—and the 360 satellites that Starlink has put into orbit are just the beginning. “SpaceX’s ultimate goal is to blanket the space around Earth in these satellites,” the article said. “They plan to operate 12,000 Starlink satellites in orbit, and potentially up to 42,000. Today only about 2,000 active satellites orbit Earth; SpaceX will increase this by six times, and possibly by 21 times.”

When scientists put a satellite into orbit, they have a lot to consider, from altitude to footprint.

Rocket Science for Beginners

Understanding orbital mechanics is literally rocket science, but it’s still possible to understand.

“There are five key concepts in orbital mechanics that we need to understand,” said Dr. Stephen Ressler, Professor Emeritus from the United States Military Academy at West Point. “One: A satellite’s orbit is elliptical, with the planet located at one focus of the ellipse. Two: On an elliptical orbit, the closest point to the planet is called the perigree, and the farthest is called the apogee.”

The third concept, Dr. Ressler explained, is that if a line were drawn from the planet to the satellite, the line should sweep out an equal area in an equal period of time anywhere in the orbit. This means the satellite moves faster when it’s closer to the planet and slower when it’s farther away.

“Four: Once a satellite is in orbit, the orbit’s characteristic shape and orbital period won’t change, unless the satellite is subjected to an applied force, such as thrust from a rocket engine or drag caused by interaction with the atmosphere,” Dr. Ressler said. “Five: As the two foci of an elliptical orbit get closer together, the shape of the orbit becomes progressively closer to a circle. Mathematically speaking, the ellipse becomes progressively less eccentric.

“Thus, a circular orbit is really just a special case of an elliptical orbit, one for which the two foci correspond.”

Low Earth Orbit

The Forbes article said that Starlink’s satellites orbit “between 340 and 550 kilometers,” or about 210 to 340 miles, above the Earth. Dr. Ressler said that a low Earth orbit (LEO) includes satellites ranging anywhere from 100 to 1,240 miles above Earth’s surface. Using so many at once is called a constellation. So why not go into higher altitudes like geostationary orbit (GEO) satellites, which take advantage of their very high altitudes to orbit the Earth exactly once a day?

“A constellation of LEO satellites […] are less expensive to launch, require less power for signal transmission, and are much less susceptible to the transmission delays associated with GEO satellites,” he said. “However, these systems require far more satellites to provide adequate coverage of the Earth’s surface. And because LEO satellites move at such high speeds, transmissions are constantly being handed off from one satellite to the next—in much the same way that cellular systems hand off calls from one cell to the next.”

One of the most common examples of LEO satellites we use every day is the Global Positioning System (GPS), which gives us constant feedback about our current location in order to provide accurate map information and driving instructions.

Dr. Stephen Ressler contributed to this article. Dr. Ressler is Professor Emeritus from the United States Military Academy at West Point. He earned a B.S. from West Point and an M.S. and a Ph.D. in Civil Engineering from Lehigh University, as well as a Master of Strategic Studies from the U.S. Army War College.

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