Lost in Space: Satellites and Space Junk in Earth’s Orbit

December 29, 2015

6-minute read

What are satellites? How do we use them? And why are there so many of them hanging out in Earth’s orbit? Ask Science answers these and many other questions about satellites.

130 EE Satellites and Space Junk

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Hi, I’m Dr. Sabrina Stierwalt, the Ask Science, here with Quick and Dirty Tips to help you make sense of science.

This coming week is a holiday here in the United States in which we celebrate the life and accomplishments of Dr. Martin Luther King, Jr, a civil rights activist who played an important role in ending segregation.

In his commencement address at Oberlin College in 1965, MLK said:

“Through our scientific and technological genius, we’ve made of this world a neighborhood. And now through our moral and ethical commitment we must make of it a brotherhood. We must all learn to live together as brothers—or we will all perish together as fools.”

In honor of this message, let’s talk about what helps to make this world “a neighborhood” – something we rely on when driving to a new place, when watching news from all over the world, and even when predicting the weather. I’m talking about satellites, of course!

How far from Earth are they and what happens to them when they stop working? How much other space junk is actually out there and what is it doing?

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What Is a Satellite?

A satellite by definition is anything in orbit around a planet. The Moon is the Earth’s only natural satellite at about 240,000 miles away (or 380,000 kilometers). Everything else in orbit around the Earth is artificial or put there by people.

See also: That’s No Moon, It’s a Space Station

The first human-made satellite placed in orbit was Sputnik 1, a 184-pound ball of metal launched by the Russians in 1957 which carried only a battery, a thermometer, and a radio transmitter. Sputnik’s battery lasted a mere 3 weeks, but it was the beginning of huge change in the way we communicate and use the space around our planet.

Since Sputnik, an estimated 2,500 satellites of various sizes have been launched into space via rocket and placed into orbit around the Earth. These satellites have a range of uses, including weather monitoring, communication, television broadcasting, navigation, and, of course, scientific study. There are also military satellites, but most of those have missions that remain a secret to the rest of us.

You may have seen the gorgeous images of stellar nurseries or colliding galaxies from the Hubble Space Telescope, a satellite that has orbited Earth from 300 miles above since 1990. In 2018, NASA plans to launch the James Webb Space Telescope, Hubble’s $8 billion successor, which will view the universe in infrared light (compared to the mostly optical view of Hubble) with unprecedented sensitivity and resolution.

We have also launched scientific satellites into orbit around other planets, like the Mars Global Surveyor and the 2001 Mars Odyssey. Sometimes the Mars Rovers use these orbiters to uplink information to be transmitted to Earth.

How Do Satellites Stay in Orbit?

Satellites maintain their positions in orbit around the Earth thanks to a perfect balance between their velocities and the gravitational force pulling them towards the planet. If a satellite were to speed up, its motion would eventually overpower the force of gravity and it would fly off into distant space. If instead it were to move too slowly, gravity would take over and the satellite would fall back to Earth.

All human-made satellites will eventually fall back to Earth once they can no longer keep up to speed. That can occur because of either planned or accidental mechanical failure. But us Earthlings need not worry – as these objects fall back to Earth, they will burn up due to friction with the Earth’s atmosphere before they are able to make contact. The death of a satellite can take up to 100 years for those in the lowest orbits and up to 1 million years for those that are farther out.

There are 3 main types of orbits used for satellites: low Earth orbits, geostationary orbits, and highly elliptical orbits.

So what’s the difference between the 3 types of satellites….?

Satellites in low earth orbit are so close (300-1,250 miles up) that they have to move very quickly (more than 15,000 miles per hour) to balance the strong force of gravity. They can make one lap around the Earth in two hours and are usually tracked by antennae on the ground. Both the Hubble Space Telescope and the International Space Station are in low Earth orbits as are many weather-tracking satellite.

Satellites in geostationary orbits (or GEO satellites) appear fixed over one location on the Earth and can typically see around 1/3 of the Earth’s surface at once. In order to match the speed of the Earth’s rotation, GEO satellites are typically placed around 22,000 miles above the Earth and move close to 7,000 miles per hour at the equator.

The Geostationary Operational Environmental Satellites or GOES are examples of geostationary satellites that look for changes in weather patterns that can lead to storms as well as track ice and sea levels.

GPS (Global Positioning System) satellites are not usually geostationary which is why you sometimes have trouble getting a signal when you first start using a new GPS or when you take your GPS to a new location. Since GEO satellites have to be near the equator to stay fixed over a rotating Earth, they do not provide good coverage for locations farther north or south.

To provide coverage closer to the Earth’s poles, some satellites are placed in highly elliptical orbits that take the shape of a very stretched circle, or ellipse. These satellites move more slowly when they are farther from the Earth and so appear relatively stationary during that period of time from the Earth’s perspective. These satellites thus mimic geostationary orbits and can be placed at large angles askew from the equator so that they cover northern and southern areas. The use of highly elliptical orbits was pioneered by the Russians since they are so far north.

Space Junk

Once a satellite is no longer functional, it becomes orbital debris. NASA estimates that there are about 20,000 pieces of orbital debris larger than the size of a softball and about 500,000 pieces larger than a marble. Any orbital debris that is large enough to be tracked is dubbed “space junk.” NASA and the Department of Defense together track over 21,000 pieces of space junk.

However, the largest threat to astronauts and working satellites is actually the stuff that’s too small to track. Even something as small as a fleck of paint can cause major damage when traveling at speeds of 17,000 miles per hour.

The crowding of space with such debris is becoming a real issue (and not just a science fiction scenario like the one that endangered George Clooney and Sandra Bullock in the movie Gravity). In 2007, a Chinese mission to destroy a defunct satellite resulted in an estimated 3,000 additional pieces of orbital debris.

In 2009, a U.S. Iridium communication satellite (used for satellite phones) collided with a Russian satellite adding thousands more independent chunks to the orbital highway. A major effort to clean up space is needed to avoid endangering the working satellites we rely on, as well as future manned space missions.

Satellite Sightings

Thanks to the large numbers of working satellites in addition to all this space junk, with a little patience and a wide view of the sky, you should be able to see as many as 10-20 satellites per hour. In a comfortable, reclined position, scan the sky with a set of good binoculars just after sunset or just before sunrise, so that the Sun is no longer bright in the sky but is still high enough that its light reflects off passing satellites.

Look for bright points of light that streak across the sky and quickly fade out. You can easily tell them apart from planes which move much more slowly and steadily and are often accompanied by blinking lights.

One of the most searched for satellites by amateurs on the ground is the International Space Station (ISS). Launched in 1998 in a joint effort between the U.S. and Russia, the ISS is the largest artificial satellite weighing in at just under 1 million pounds. Orbiting at around 250 miles from Earth, ISS provides a microgravity environment good for studying biology, physics, and astronomy, and has been continuously occupied since November of 2000.

ISS is so large that you can actually see it with your naked eye. You just need to know where and when to look! Check out NASA’s Spot the Station web site for details.

That ends our show for today. In the meantime, you can become a fan of Ask Science on Facebook or follow me on Twitter, where I’m @QDTeinstein.

If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.comcreate new email or post it on my Facebook page.

Until next time, this is Dr. Sabrina Stierwalt with Ask Science’s Quick and Dirty Tips for helping you make sense of science.

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Space debris image courtesy of NASA.gov. Satellite image courtesy of Shutterstock.