What’s a satellite? 

You might be surprised to find out that Earth is a satellite (and that bananas are berries). A satellite is anything that orbits another object: Earth orbits the sun, and also has a satellite of its own – the Moon (our one moon is a modest number compared with Jupiter’s 79 moons). 

The Moon remained Earth’s sole satellite for billions of years until Oct. 4, 1957. On that day, the Soviet Union launched the first ever artificial satellite – a beach-ball-sized hunk of metal, Sputnik I, that weighed 184 pounds and could orbit the Earth in 98 minutes.

What kinds of artificial satellites exist today? 

Today, 62 years after Sputnik, satellites are central to a densely interconnected world –from navigation and communication, to reconnaissance and scientific monitoring. When we talk about satellites, we usually mean the artificial ones of which there are currently 5102, positioned at different heights in space, according to the United Nations Office for Outer Space Affairs. 

Recently Amazon announced its plans to build a network of more than 3,000 satellites to provide a global internet access, comparable to Earth’s fiber optic networks. 

Satellites are not just for business. In pursuit of scientific accuracy, NASA launched a $1 billion Cloud and land Elevation Satellite in September 2018, which uses lasers to monitor changes in ice thickness. 

“In general, satellites provide the only means to monitor the Earth globally and continuously. Especially for the polar regions (with their harsh environment and remoteness) other measurements are very sparse,” Markus Thorsten, the head of NASA Goddard’s Cryospheric Sciences Lab and the project scientist for the ICESat-2 mission, wrote in an email. 

How do satellites reach their orbit? 

To receive and transmit signals, satellites are equipped with antennas and a transponder, a device that receives one type of signal and converts it to another. The energy is provided by fuel and by solar panels that also give satellites a metallic bird-like appearance.

Satellites are launched into space by rockets that have to accelerate to at least 25,039 mph (40,320 kph) – the so-called escape velocity that propels the satellite into space despite Earth’s gravity. Once the satellite’s desired height is reached, the rocket releases it.

Why doesn’t the satellite simply fall down or even speed off into open space? The answer has to do with gravity and speed. The momentum that the satellite gains from the launch maintains the movement, but gravity’s pull doesn’t let the satellite get away: the satellite is technically continuously falling towards Earth, but its speed ensures that it falls around the Earth, while remaining in the same orbit. 

“The Earth has been falling around the Sun for the past five billion years and that’s just what these things do,” Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, says.  “We are not used to this idea because we spend our lives in the murky atmosphere that has friction. So if I throw something at you, it will quickly be slowed down.” 

What are orbits? 

The spaces where satellites operate are separated into four orbits: low, medium, geostationary or high earth orbits. 

Particularly interesting is the geostationary orbit that floats some 22,236 (35,786 km) above the Earth’s equator. At this altitude the satellites are geosynchronous – they move at the same speed as the rotation of Earth, so they actually appear to be stationary, hanging over our heads at the same longitude.

One of the people credited with popularizing the idea of geostationary satellite communication is British science fiction writer Arthur C. Clarke (1917-2008). In 1945 he published an article titled Extra-Terrestrial Relays, where he outlined a method by which a satellite would be put 36,000 km above ground into geostationary orbit, making it revolve at the same speed as the Earth and thus remaining in the same position. Today the orbit, which is often referred to as the Clarke belt, contains over 400 active satellites. 

Are there too many satellites? 

It might seem that outer space is getting more crowded. That is most certainly true, but collisions are still rare. 

“So far we had one major accidental collision in 2009 when thousands of pieces of debris were generated in space,” says McDowell. “The reason why it doesn’t happen more often is because space is really really big.” 

He says that we are now running at about one collision every 10 years, but collisions increase exponentially, so if there are 10 times as many satellites in 10 years, then there will be 100 times as many collisions. 

The most recent but by no means the only example of space danger was when India destroyed one of its own satellites, creating 400 pieces of space debris and potentially putting the crew on the International Space Station in danger. 

Do satellites stay in space forever? 

Satellites have thrusters to ensure that their positions in an orbit can be adjusted if necessary, as satellites can remain in space for decades. The longest lived satellite is Vanguard I, an aluminum “grapefruit satellite” which has entered its seventh decade in space after its launch on March 18th, 1958. The International Space Station – a habitable satellite that can be occupied by up to 10 people – has been operating continuously for the past 20 years. 

Once a satellite completes its goals it has two ways to go: back down or higher up.

Large satellites in low orbits are lowered down into the Spacecraft Cemetery – a lonely place in the South Pacific Ocean, more than a thousand miles from any land, according to Business Insider. Satellites in higher orbits have a graveyard of their own – an orbit almost 22,400 miles above Earth. 

Smaller satellites in lower orbits are usually lowered down until they enter the Earth’s atmosphere. There, slowly, almost imperceptibly, the satellite continues its descent until it is finally met with so much friction that it burns up, creating a glorious streak of light across the sky.