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.
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?.
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....?