EARTH & SKY : SPACE
The solar systemʼs biggest junkyard
By Stephen Ornes / September 23, 2008
On a clear night, you can look in the sky and see the moon and stars. You might even see the
blinking light of a working satellite as it flies past, on its way around the Earth.
And, even though you cannot see it, you are also looking at the largest junkyard in the solar
system.
Higher than the highest clouds but much closer than the moon, the bulk of the junkyard stretches
from the Earthʼs surface to 20,000 miles overhead. There are tens of millions of pieces of rubbish
there. Some of the pieces are rocks and dust from passing comets, but most of them are
manmade and called “orbital debris” (pronounced duh-BREE).
There are some unusual things up there, like a camera that floated away from astronaut Sunita
“Suni” Williams in December 2006. Other astronauts have lost tools like wrenches and
screwdrivers. In 1965 astronaut Ed White even lost a spare glove. Most of the junk, however,
comes from large satellites and rockets that fell apart after they stopped working.
Together, all the space junk would weigh about 11 million pounds on Earth, or more than 3,000
cars. The largest piece is a part of a rocket about the size of a minivan. The smallest piece would
fit on your pinkie fingernail with room to spare.
“Itʼs like a classic environmental problem, like water pollution or air pollution,” says Nicholas
Johnson. Johnson is the Chief Scientist for Orbital Debris at the NASA Johnson Space Center in
Houston. His job is to keep track of the orbiting garbage.
The junkyard is a serious problem for the future of spaceflight.
“Youʼve got multimillion satellites in orbit all the time, and manned space flights,” says Joe
Gambrell, who helps keep track of both working and broken-down satellites. His main tool is the
U.S. Space Surveillance Network, which is part of the U.S. military. Gambrell works at the
Peterson Air Force Base in Colorado Springs, Colo. “If you donʼt track debris, you risk some kind
of collision,” he adds.
In 2007, the space junkyard grew by more than 100,000 pieces. Thatʼs more than any other year
since people started launching satellites into space. The problem of space junk is not going
away, and scientists are watching closely.
Danger in Orbit
A “satellite” is any object that orbits another object, held close by gravity. The moon is a satellite
of the Earth, and the Earth is a satellite of the sun. These are natural satellites. Manmade
satellites, which are built on Earth and launched into space, are used for communications,
scientific studies and military applications.
In the last 50 years, human beings have launched thousands of artificial satellites into space.
When a satellite stops working, it usually falls back toward the Earth and burns up in the
atmosphere. Satellites at high altitudes, however, sometimes remain in Earthʼs orbit.
Later, they may fall apart or explode into thousands of smaller pieces. The higher the satellite,
the longer it stays in orbit, and the more likely it is to break apart. The pieces may stay in orbit for
years, decades or even centuries.
Space junk races around the Earth at breakneck speeds. Most pieces fly through space at more
than 20 times the speed that sound travels on Earth. Going that fast, even the smallest pieces
mean big trouble for spacecraft. For example, a tiny marble in orbit around the Earth can have as
much energy as a bowling ball going 500 miles per hour, or a car going 30 miles per hour.
In 1983, a small gouge appeared in one window of the space shuttle Challenger while it was in
space. When the shuttle returned to Earth and scientists analyzed the window, they found that
the crack was caused by a tiny, orbiting fleck of paint. If the shuttle had been struck by a larger
piece of junk, the astronauts may have been in danger.
Many other satellites and space shuttles have also shown damage from tiny pieces of trash.
When the space shuttle Endeavour returned to Earth last August, its radiator panels had small
holes from space garbage. Last year, two satellites had to be redirected to avoid collisions with
big pieces of junk.
The U.S. Space Surveillance Network and NASA work together to keep track of the largest
pieces. When the shuttle is in orbit, for example, their attention is on nearby junk that may get in
the way. If there is even a small chance of a collision, then the shuttle changes direction.
Watching the garbage
About 17,000 pieces of garbage are larger than 4 inches, which is slightly smaller than a softball.
The Space Surveillance Network keeps a list of all these pieces, using dozens of telescopes and
antennas on Earth and in space to watch them. Because all the pieces are in motion all the time,
keeping track is difficult (but not impossible).
Monitoring the space junk is a problem of energy and motion. To keep track of the junk, the
scientists have to know two things: where the garbage is now, and where it is going to be in the
future.
To find out where a piece is now, scientists use telescopes and high-powered antennas to watch
it fly through space. Every day, scientists must make sure each piece is where they expect to
find it. A “lost piece” could mean serious danger for a working satellite or space shuttle.
To find out where the piece is going, scientists measure its speed and direction as it crosses the
sky. Some of the pieces move in an almost perfect circle around the Earth. Other pieces move in
elliptical orbits, which means they are sometimes closer to Earth and sometimes farther as they
fly. The measurement of direction is complicated because junk can move north or south, east or
west, and up or down.
By knowing the location, speed and direction of each big piece of junk, the scientists can predict
where all the pieces will go. (Similarly, in baseball, an outfielder has to predict where a pop fly will
land, if she wants to catch it. In soccer, a goalie has to predict where a ball will go, so he can
block it.)
“Weʼre always looking about four days into the future, tracking objects which might come close,”
says Johnson.
There are tens of millions of pieces smaller than softballs. Because there are so many small
pieces, “We canʼt [keep track] of them all,” Johnson says. Instead of watching each piece
individually, scientists use telescopes and antennas to watch one patch of sky and count the
number of pieces that pass overhead. With that small measurement, they can use a computer
program to get a good idea of what the whole sky looks like.
Keeping track of all the junk is necessary to ensure that astronauts and working satellites can be
safe. Like other environmental problems, space junk will get worse without careful monitoring
and attention. In the future, pieces of junk will probably hit each other, making even more trash.
The more garbage that remains in orbit, the greater the risk to space flights. What can be done
about the problem of space junk? The large pieces of junk cannot be brought back to Earth,
Johnson says, because the technology is too expensive. Instead, he says, we should try to stop
adding new garbage. For example, engineers are changing the way they build spacecraft.
“How you build your satellite can minimize debris,” Gambrell says.
A solution will require international cooperation. Last year, the United Nations General Assembly
approved guidelines for how to reduce the risk of space junk. Johnson says that spacefaring
countries came together because “the environment was getting worse every year.”
If countries work together to control the amount of trash we send into space, Johnson says, we
can keep the problem under control. In the future, perhaps we can even clean up the mess.
“In time, either technology or economics will allow us to go out and [improve] the environment,”
he says.