Do All Space Satellites Orbit The Earth In The Same Direction?

To answer this question simply first before going into more detail. Yes, all satellites that are on a sideways path west to east all move in that direction, they just move at different times and speeds.

What people tend to forget is that the Earth is spinning on its axis. A satellite that is in ‘geostationary orbit’ is moving despite it looking to remain still in the sky, it’s simply matching the speed of Earth’s orbit. 

If we look up to the moon it is easy to imagine it as a planet. A huge rock ball, made up of basalt plains and mountain ranges, with a gravitational pull that produces tides on Earth. 

Despite its huge gravitational effect, the moon does well not to crash into Earth. Why is this? It is because the moon is in orbit. 

The studies and concepts of gravity and orbits have been developed over time by great minds of science such as Galileo Galilei, Johannes Kepler, Isaac Newton and Albert Einstein. 

The satellites in the sky are mainly used for communication, imaging and navigation, but many people do not fully understand how these satellites stay in space and don’t come tumbling down into Earth. 

Moving Sideways

A big misunderstanding about space and weightlessness is that it occurs due to an absence of gravity. As the gravitational pull from Earth decreases the further you travel into space, it never totally disappears. If you were to drop a bottle 150,000km above Earth it would gradually fall. So how do satellites and moons not come crashing into Earth? 

They are going sideways. 

Although Newton may not have been the life and soul of the party, he could create a brilliant thought experiment. He created Newton’s Cannon to demonstrate the motion of satellites. 

If you were to fire a cannon horizontally, the cannonball would go a certain distance before falling to the ground due to gravity. Fire the cannonball faster and it would go further before falling to the ground. So imagine firing the cannonball at such a fast speed of 8 kilometres per second. The cannonball would fly around the curvature of the earth, being pulled towards Earth but never reaching the ground due to it going sideways. 

Moving Upwards  

Newton’s Cannon experiment remains one of thought, but in the 20th century, it became possible to travel at speeds of 8km per second. A rocket can travel more than 100km upwards and then accelerate to 8 kilometres per second in space. At this speed, it takes 90 minutes to circle the globe. 

When the rocket reaches orbit the engines can be switched off and the spacecraft can coast around Earth. The Earth’s atmosphere is incredibly thin at altitudes of 100-1000kilometers, so it would take days or years for a spacecraft to be dragged back to Earth by gravity with the engines switched off. When you are inside the spacecraft, gravity will still pull on you, but it’s so much weaker that you will feel weightless. 

Weightlessness occurs when you are being pulled by gravity without resistance from a surface or the air. 

Going Higher

What happens if you go even faster? If you go at speeds of 10 kilometres per second, instead of following the curvature of the earth, the spacecraft would follow a course that gradually takes it further away from Earth. As the spacecraft moves away from Earth, it starts to slow down due to the ‘conservation of angular momentum. Eventually, its peak altitude will be met, then it will begin to fall back to Earth.

The process now happens backwards, as the spacecraft picks up speed until it reaches minimum altitude. This process then repeats with the spacecraft following an ellipse around the Earth.  

If we now decide to go even wilder and fire up the rockets to get to 11 kilometres per second, things start to get crazy! The spacecraft will travel away from Earth and be slowed by the forces of gravity, but the pull of gravity has so little effect and drops so rapidly that you will leave Earth entirely, and be propelled into the depths of space. 

Not Moving

Some satellites are rapid and fly around the Earth in 90 minutes, others seem to be rather stationary. Weather and TV satellites are seen to be hovering above the equator. These satellites are in what’s known as ‘geostationary orbit’. As you orbit further from Earth, the speed required to stay in orbit decreases and the time required to complete an orbit goes up.

At an altitude of 36’000km, orbit takes 24 hours. The Earth spins on its axis once a day, so these satellites appear to be fixed in place from the spinning Earth, but this is an illusion.

If we travel even further from Earth then orbits take even longer. We call the moon a natural satellite, 384,000km from Earth and takes 27 days to complete one orbit, despite the moon travelling 1 kilometre every second towards the east, on Earth due to its spinning, the moon rises in the east and sets in the west. 

Passing By 

If you look up to the night sky then you will see satellites racing across the sky as they reflect sunlight towards the earth. Some satellites follow the rotation of the earth and travel west to east. Others have different orbits over the poles and travel north to south or vice versa. If you pick your night well, you will watch in awe as the International Space Station continually circles the globe like a slow-moving shooting star. 

Final Thoughts

To summarise, although when we look up at the night sky, it can seem like many satellites are remaining still over certain parts of Earth such as TV satellites, these satellites are simply matching the speed of Earth’s rotation on its axis. These satellites will be travelling west to east at the same speed as the earth is rotating, making it seem like they aren’t moving from Earth.

This is called geostationary orbit. Other satellites will be moving west to east but at different speeds, not the same as Earth’s rotation on its axis, these satellites are all moving west to east. There are exceptions to this, the satellites over the poles, which move north to south and south to north.

Pick a dark and clear night, with little to no moon, and gaze up at the sky, watch as you see various satellites race through space, in awe over the incredible progress humankind has made to achieve such wild dreams in space discovery.  

Gordon Watts