ORBITS
Keywords: orbit, orbital speed, orbital period, geostationary, elliptical
So like we said before,
The object travelling in orbit is a called satellite. and there can be two types - natural satellites like the moon, comets, or planets, and man-made. [2] Man-made satellites are sent to space for a number of reasons. A few examples [3] include
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navigation (GPS)
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communication (satellite TV or telephone calls)
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scientific research
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observations on Earth (tracking weather forecasts, pollution)
Speaking of satellites, have a go at playing our Moon Landing game where you must tackle obstacles to land a space rover on the Moon!
an orbit is a regular path an object takes in space when it goes around a larger mass like a star, a planet or a moon. [1]
This picture shows you how the different planets in our Solar System orbit the Sun - this was
A long time ago....
Many many years ago, people actually thought that the Earth was at the centre of our solar system, and the Sun orbits in a circular path around the Earth. Thanks to people like Copernicus and Galileo, we actually discovered that this is not true at all and that in fact, all the planets orbit the Sun, not the Earth. This unlocked the door to more discoveries of space!
A neat way to visualise an orbit is an athlete doing a hammer throw, he spins the weight to a large velocity/speed before letting go. When he’s spinning the hammer, it’s moving in a circular path. It works like this because the athlete is creating a force F towards the centre of the circular path.
The Importance of Speed [4]
The speed of an object like a satellite when orbiting the Earth is really important. We call this object's speed its 'orbital speed'.
If its orbital speed is too large, the object will come out of orbit away from Earth, and travel outwards into outer space. If the orbital speed is too slow, the satellite will struggle to stay in orbit and will actually fall inwards, towards Earth, neither of which we want to happen! This is why the satellite needs to be at the right speed, so it can stay within the correct orbit around Earth.
What happens if the speed is too high or low?
When a rocket is orbiting the Earth, we can imagine two forces acting on it. The first is the force of gravity, which pulls the rocket towards the Earth. The second is the force that pushes the rocket forwards (thrust). That second force can change depending on the speed of the rocket.
So, if we speed up too much, the forward force pushing the rocket ends up being much larger than the force of gravity, which causes the rocket to fly away from Earth.
If the rocket is moving too slowly, the force of gravity becomes much larger than the forward pushing force, so the rocket gets pulled towards Earth. The way a rocket changes speed can be by increasing or decreasing the thrust from the engine. Go ahead and play around with the simulation to see this in action here!
Orbital Speed - Simulation
The simulation will show you what will happen if the rocket's speed is too low or high
This simulation shows you how orbital speed plays an important role for a satellite to stay in orbit. In this example, the satellite is the rocket and it is trying to orbit around the Earth.
Calculating Orbital Speed
The speed of orbit of a moon, planet or satellite can be related to the radius and time of orbit with the following equation:
where v is the orbital speed of the object, r is the radius of the orbit and T is the time taken for the object to travel one full orbit, back to its starting position (orbital period) [5]
This equation is a special form of speed = distance/ time. So when you think about it, imagine you are walking around a circle (like our circular orbit), the distance you moved would be the circumference of the circle. We know that the circumference of the circle (c) is given by c = 2π x r , so this is the distance in the speed = distance/ time formula.
orbital speed
time (orbital period)
radius of orbit
Types of Orbits
GEOSTATIONARY ORBITS
Satellites orbit the Earth in geostationary orbits. What is a geostationary orbit? This is an orbit where the satellite appears to be in the same position above the Earth when actually it is moving. So how can something appear to be still when it's actually moving? This is simple, we know that a day on Earth is 24 hours, so this means the Earth spins round once every 24 hours, the satellite is orbiting for 24 hours following the Earth's orbit, roughly 42000 km above Earth’s equator. So the satellite in a geostationary orbit moves around the Earth as fast as the Earth spins,. These types of satellite orbits are really useful for satellite communications, meteorology, navigations. For example, the GPS in your parents' car, works with this type of orbit! [6]
ELLIPTICAL ORBITS
If an object like a planet is orbiting the Sun, it is travelling at a constant speed, because the gravitational pull is always at a right angle to the planet's path. However, the planet is not moving at a constant speed. This is because the Sun has a strong gravitational pull. The closer you are to the Sun, the stronger this force of gravity is going to be. This also means that your speed as you orbit the Sun will increase. The opposite happens as you orbit further away from the sun, the gravitational pull will be weaker, meaning you will travel slower. This creates an oval-shaped path for the planet's orbit. [7]
This graphic shows you what a geostationary orbit looks like. The Earth is in the centre of the orbit and the satellite is the grey circle. As the Earth spins on its axis and rotates, the satellite will move as fast as the Earth's spin.
B
A
This is what an elliptical orbit looks like. This time, we have the Sun in the centre of the orbit and the Earth moving in orbit. At position A, since the Earth is further away from the Sun, its gravitational pull isn't as strong, so it moves at a slower speed. At position B, the Earth is much closer to the Sun, so it'll move at a faster speed.
Moon Landing - Game
So now that you have learnt a bit about orbits and satellites, try out this Moon Landing Game!
YOUR MISSION
To safely move the space lander to the green landing base without damaging the lander.
