3-2 Satellites

Natural vs. Artifical

When you think about a satellite, chances are you're thinking about one of these orbiting the Earth, doing something useful:

That is an artificial satellite, which humans put into orbit by lifting it on a rocket. However, did you know what's below is also a satellite of Earth?

(If you want a fantastic high-resolution version of this, go here and download the picture yoruself. There's a lot of fascinating detail here; if you look near the edges you can really see how the craters have depth to them.)

Our moon is a natural satellite of Earth: it's a natural object which orbits around something else which is natural. The moons of Jupiter -- the planet with the most confirmed moons right now, as this article describes -- are all satellites of Jupiter.

Similarly, Earth is a satellite of the Sun, and the Sun is a satellite of the Milky Way galaxy. We could keep going, but let's stop here.

A Brief History of Artifical Satellites

The Early Years

After World War II, a few countries around the world started rocketry programs: that is, strap something to a rocket, shoot it up into the sky, and see what happens. The earliest confirmed rocket launch of any kind happened before WW2, in 1926; below, Robert Goddard is posing with what is believed to be the first liquid-fueled rocket. It didn't go very high, but it proved that something like it could be done.

Just before and during World War II, Nazi Germany invented the V2 rocket, seen below. The rocket was precise enough so that it could be fired off in mainland Europe with bombs attached, cross the North Sea, and hit targets in England, hundreds of kilometres away.

Obviously, rocket technology has its possible drawbacks, much like other new types of technology:

• it was first developed for military use

• it can sometimes be used for destructive purposes

• these destructive purposes can sometimes directly hurt people

However, consider that all of the points above could equally be applied to electronic computers (which were first developed during World War II as well). Technology isn't necessarily "good" or "evil," but it's what you do with it that determines all of that.

After World War II

When Germany was defeated in 1945, a lot of their rocketry engineers faced a choice: willingly go with either the United States and its allies, the Soviet Union and its allies, or stay in Germany and face the consequences from having been involved with its Nazi government.

During the war, the United States had developed a nuclear bomb; two were dropped on Japan in 1945 from airplanes. However, flying an airplane and dropping a bomb is much more dangerous than attaching that same bomb to a rocket, and launching it from a long distance away.

So, both the United States (US) and the Soviet Union (USSR), who each had nuclear weapons, got into the Space Race to see who could build a rocket so powerful that it could be launched from one country and land in the other. Part of this was that the US was the most powerful "capitalist" country, and the USSR was the most power "communist" country, after the war.

Since those political systems didn't really work well together, and the two countries both wanted worldwide supremacy, both the US and USSR each wanted to defeat their enemy. However, since one country invading the other almost surely meant, at that time, nuclear weapons being used in battle, neither country actually invaded the other.

A term was invented to describe this kind of non-directly-shooting-at-each-other standoff: the Cold War. However, that didn't mean both of those countries weren't itching to develop intercontinental ballistic missiles (ICBMs) capable of carrying a nuclear weapon.

Sputnik 1

It was a pretty tense time in general from the late 1940s through the 1980s, but the 1950s saw things first come to a head with the USSR's launch in 1957 of the first artificial satellite, Sputnik 1, into orbit:

The word sputnik in Russian loosely translates to travelling companion; if it's in orbit around the Earth, it could be seen as Earth's companion, in a way. The round part of the satellite is about the size of a beach ball and contained a power source and the electronics. The parts sticking out are the antennas, which broadcast signals back down to Earth so scientists could track its position.

Nobody was really sure it would work, so this simple device broadcast an on-and-off electrical signal which made a receiver beep on Earth. It worked, and the U.S. government panicked: this was not just a scientific achievement. Rather, it was a way for the USSR to say, "Look at us, we have a big enough rocket that we can send this thing into space! Oh, and by the way, we could have just as easily strapped a nuclear bomb to this, fired it off in the USSR, and had it come down in your back yard. Sleep with one eye open, USA!"

The US quickly managed to get a satellite into orbit soon after, but the USSR had showed it was leading in the Space Race at that point.

Orbits: Low, Medium and Geostationary

Depending on what you want your artifical satellite to do, you will want to put it into some kind of orbit around Earth. Three of the main types of orbits are described below, but this can give you some sort of an idea about the scale of these orbits:

Low Earth Orbit (LEO)

• Satellite height above the ground: 400 to 1500 km

• Time taken to orbit the Earth: 1 to 3 hours

• Good for: taking readings of Earth, taking pictures of Earth

• Disadvantages: moves around a lot, drag force from upper atmosphere

• Example: International Space Station, weather satellites

Medium Earth Orbit (MEO)

• Satellite height above the ground: 5000 to 20 000 km

• Time taken to orbit the Earth: 3 to 10 hours

• Good for: similar to LEO satellites, but a bit less detail

• Disadvantage: located in Van Allen Belt, an area of intense radiation surrounding Earth

• Example: GPS satellites

Geostationary Orbit (GEO)

• Satellite height above the ground: 35 800 km

• Time taken to orbit the Earth: exactly 24 hours

• Good for: things that need to stay in the exact same place in the sky

• Disadvantage: very far away, costly to launch

• Examples: telecommunications and broadcasting

("HEO" on the picture above stands for "Highly Elliptical Orbits," but we won't be talking about them here.)

Prominent Examples

International Space Station

The International Space Station (ISS) is an orbiting research laboratory in Low Earth Orbit (LEO).

Its orbit is roughly circular, and is about 450 km above Earth's surface. It was built in pieces, with the Space Shuttle taking the large parts up into orbit so it could be assembled by astronauts in space.

Its main goal is to act as a scientific research laboratory, with various experiments in astronomy, physics, biology and chemistry taking place on it. The first part of the ISS was launched in 1998, and it was essentially completed in 2011, although new small pieces are being added to this day.

There are five space agencies that collaborated on building it, and are continuing to maintain it:

• NASA (United States)

• Roscosmos (Russia)

• ESA (European Space Agency)

• JAXA (Japan)

• CSA (Canadian Space Agency)

Look at that list, and realize that Canada is, by far, the smallest country (or group of countries) on that list. Definitely something to be proud of!

The Canadian Space Agency built and runs two robotic arms: Canadarm2, and the slightly smaller Dextre.

As you may know, CSA astronaut Chris Hadfield became the second non-American or non-Russian to be the commander of the ISS. This happened in 2013, and it turned Hadfield into a minor celebrity.

Global Positioning System (GPS)

These days, most cell phones have a Global Positioning System (GPS) device built into them, so they can connect to satellites to accurately determine your position on Earth.

Your phone, or a separate hand-held GPS device, bounces signals off at least three of the "constellation" of dedicated GPS satellites in Medium Earth Orbit (MEO). The round-trip times are measured, and your location can be determined from tiny differences in those times.

This technology was original developed for the US military, but it eventually found its way into products designed for the general public. As of 2022, there were 31 satellites in the system, some launched as far back as 1997.

How accurate are GPS satellites? It depends on what type of device you're using.

• On cell phone, it's typically accurate to within about 5 metres.

• On a dedicated GPS device (used by boaters and campers), it can be accurate to about 2 metres.

• Military GPS devices can be within centimetres of your location.

Pretty impressive for something about 20 000 km above your head, travelling about 14 000 kilometres per hour!

Practice

The Basics

1. Describe the difference between a natural satellite and an artificial satellite.

2. What was the first artifical satellite called? When was it launched, and who launched it?

3. Which has a higher orbit above the Earth's surface, a GPS satellite or the International Space Station?

Extensions

1. If you've ever watched satellite TV, that signal has bounced off a geosynchronous satellite. The signal travels at the speed of light, 300 000 km per second, and the satellite is 35 800 km above you. Determine how long it takes, in seconds, for a signal to travel from Earth's surface up to a geosynchronous satellite and back. The formula is speed (v) = distance (d) divided by time (t), or v = d/t; rearrange to solve for t here. (You might need some help from the internet on this, if you can't figure out the calculation.)

2. Look at the length of time it takes for LEO, MEO and GEO satellites to orbit the Earth. Can you see a pattern here which relates its length of time taken for one orbit, and its altitude?