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When the Soviet Union launched a little satellite called Sputnik in October 1957, they beat America into space (we launched Explorer 1 the following January) and energized the Cold War “space race” that led to the creation of NASA. The beach ball-sized Sputnik was visible through binoculars and transmitted a repeating beep picked up by amateur radio operators. After three months in orbit, Sputnik lost battery power and burned up as it fell through Earth’s atmosphere. (Fun fact: the word “Sputnik” inspired the term “beatnik” to describe the mid-century Beat generation.)
Sputnik and Explorer 1 were launched during the International Geophysical Year (IGY), a global collaboration of scientists studying earth and space from July 1957 to December 1958. Since then, several thousand artificial satellites have been launched into orbit, the majority by government and private organizations in the United States and Russia.
Spies and Science in the Sky
From their sky-high perspective, satellites can observe Earth in ways not possible using ground-based instruments. They serve such purposes as relaying radio, television and cell phone signals; weather tracking; ground and climate research; astronomy; military reconnaissance (so-called “spy satellites”); and navigation via the network of 32 satellites that make up the Global Positioning System (GPS).
Between their antennae, power source (batteries, solar panels), sensors, cameras and other scientific or communications equipment, satellites can be as small as a shoebox or as big as a bus, weighing from 20 pounds to six tons. A notable exception is the International Space Station (ISS), the habitable space research lab that is as wide as a football field and weighs 462 tons.
Orbits and Altitudes
Rockets carry satellites into space and boost them to the correct speed, or “orbital velocity,” for their altitude: too slow and they fall to earth, too fast and they fly off into space. The ISS, Hubble Space Telescope and other observational satellites fly in low earth orbit (LEO) 200 to 1,200 miles above sea level, zipping around Earth in just 90 minutes at 17,000 miles per hour. GPS satellites are placed some 12,500 miles up in medium earth orbit (MEO), traveling 8,500 mph on a 12-hour cycle or “orbital period.”
Communications and weather satellites are positioned 22,000 miles up and fly at 6,800 mph, circling Earth every 24 hours in a “geosynchronous” (in sync with Earth’s rotation) orbit. Many geosynchronous satellites are placed directly above the equator and appear motionless from the ground because they move at the same rate as Earth is rotating. Earth-based antennae and satellite dishes can be permanently pointed at these “geostationary” satellites. (Cosmic fact: Arthur C. Clarke, author of “2001: A Space Odyssey,” first proposed geostationary orbit for communications satellites, so it is also called the Clarke Orbit.)
Satellites don’t have lights, but they reflect sunlight and look like a moving star when visible. The ISS often shines brightly at night and is easy to spot traveling across the sky. (Go to spaceweather.com/flybys/ to see when ISS and other satellites – including spy satellites. – will be passing overhead.) Any unblinking light moving through the stars is most likely a satellite or a piece of plentiful orbital debris, also known as “space junk.”
Celestial Flotsam and Jetsam
Space junk is the detritus of human space exploration – an accumulation of dead satellites, rocket bodies, debris ejected during mission operations, the remains of explosions and collisions, and even flecks of paint – caught in orbit around Earth.
The Space Surveillance Network (SSN) tracks more than 20,000 pieces of space junk larger than a baseball, and NASA estimates there are at least a half million more smaller fragments. Most hurtle through low earth orbit at 17,000 mph but can impact another object at twice that speed, so even a small piece could seriously damage a satellite or manned spacecraft, according to NASA. Occasionally the ISS maneuvers out of the path of orbital debris if the SSN sees the potential for a collision.
A Cascading Problem
One champion of the space junk conundrum is Donald J. Kessler who, as NASA’s first senior orbital debris research scientist, helped establish their Orbital Debris Program Office in 1979. Mr. Kessler uses the term “collisional cascade” – dubbed Mr. Kessler Syndrome by one of his colleagues – to describe the growing amount of space debris. When orbital objects collide at high speeds, Mr. Kessler explains, they create a large number of fragments that go on to collide with other objects, creating even more fragments and so on.
Space programs in the United States, Britain, Europe and Japan are developing plans to de-orbit satellites and remove space debris. Some ideas involve pushing, dragging or even laser blasting objects into lower orbit, where they will eventually slow down and fall through Earth’s atmosphere. Removal is expensive and slow to implement, Mr. Kessler says, so debris is generated faster than it can be cleaned out of the atmosphere. Eventually it may endanger the space-based systems that support our everyday lives.
“Space has become our infrastructure,” says Mr. Kessler, “we depend upon it in so many ways, and the military says they rely on it even more. So it’s not just the military, it’s all of our satellites, our GPS, communications, and internet could be dependent on space. If we don’t protect that environment we lose our ability to operate within it.”