# Chapter 11

Chapter 11 – Artificial Satellites. If there is anything you notice that looks a bit wrong, let me know via comments. Remember… I’m learning! 😀

1. a) What is meant by escape velocity? What is the escape velocity of the Earth?
The escape velocity of something, is the velocity needed to escape the gravity force that pulls it back. For instance, the Earth’s escape velocity is 11.8 km per second. That means, when something is thrown upwards at that speed, then the gravity of the Earth is not strong enough to pull it back.

1. b) What effect does the escape velocity of a planet have upon the extent and composition of the planet’s atmosphere?
If a planet has a high escape velocity, then all of the original matter collected at the planet building stage has not been able to escape, including the lightest of matter. Such as Jupiter; it has a high escape velocity and therefore, has kept all of the original matter, even Hydrogen which is the lightest atom which also be why we could never survive there. If a planet has a low escape velocity, then all of the original matter will have had a chance to escape. Like the Moon which has very little atmosphere, because there is nearly no gas left.

1. c) If the Earth’s escape velocity were ten times as great as it actually is, would we be able to live here? Give reasons for you answer.
No (unless evolution had managed to allow us to breath a different gas). Because we need oxygen to breath, if the ratio of oxygen and other gases vary we would not be able to survive. If the escape velocity were ten times greater, then none of the lighter atoms will have been able to escape and the air would be a higher ratio of all the lighter atoms, such as hydrogen and helium. We cannot breath hydrogen and helium. Also, the Earth’s escape velocity remains the same, so we life was beginning on Earth, had it been 10 times higher, then we might not have evolved.

2. a) Using diagrams, explain the principle of the rocket.
A propellant and oxidant are present in a rocket and the propellant is then combined with the oxidant. They then turn to gas and want to escape and so can only leave through the bottom. Because of Newton, we know that for every force, there is a reverse force. If there is a force leaving the rocket going down, the the rocket must go up.

2. b) Why can a rocket be used to send vehicles beyond the atmosphere, whereas a projectile fired from a space-gun cannot?
This is quite simple. A rocket sent up into space has many stages, whilst a space-gun hasn’t. If a space gun was used, then sending it up at the escape velocity immediately would cause so much friction in the air that the vehicle would most likely burn up. Because rockets have stages, the velocity doesn’t cause as much friction reducing the burning which also means it can be sent up safely.

2. c) Explain the step principle of launching probes, and show why it has to be used.
The general build of a rocket, there are many stages. The first big stage is what takes it off the ground and starts of some momentum. When the fuel has run out on that stage, then it separates and the next stage starts. This stage are smaller rockets to maintain velocity going up and get it either into space, or very close. More stages often occur and as many stages can be used.

3. a) Two satellites, X and Y, are in orbit round the Earth. X has a eccentric orbit, so that its height above sea level ranges between 120 and 550 km; Y has an almost circular orbit at a mean height of 400 km above sea level. Which satellite will remain in orbit for longer, and why?
Because of friction in the Earth’s atmosphere, the one which keeps going in and out of the atmosphere will be damaged the most. The satellite that remains at a steady height will be have less friction as it isn’t changing height all the time. Therefore, satellite Y will remain in orbit longest as it won’t burn up in the atmosphere.

3. b) Why is zero gravity experienced by an astronaut travelling round the Earth in free fall?
Zero gravity is experienced by an Astronaut travelling round the Earth in free fall because as the astronaut and vehicle travel at the same speed in free fall around the Earth, there is no pressure upon the astronaut who therefore experiences zero gravity. It is NOT because they have escaped the Earth’s gravity force, they are both still well in the force.

3. c) If an astronaut goes outside his space-craft while orbiting the Earth, will he fly away from it? If not, why not?
When an astronaut leaves his space craft, he is still in the same orbit, so he will not fly away. But it is always advisable to have a safety line and to keep hold of any tools you may have outside with you. 🙂

4. a) Give four practical uses of artificial satellites.
One good use of satellites is that they are good for experimenting with industrial processes. Another good use is to research certain aspects of the Universe which cannot be investigated on the surface of the Earth. An advantage of satellites is also that we can explore the Earth with a better view and see natural and human events. A final advantage of satellites are that depending on what we want them to do, we can place them in the needed orbit.

4. b) What were the wavelength studied by IRAS, IUE and Chandra?

These satellites investigated X-rays emitted from around the Universe.

4. c) Why does a satellite in geosynchronous orbit have to be at a height of 36,000 km above the Earth?
A satellite in geosynchronous orbit must have an orbit height of 36,000 km, so it can orbit at the same rate that the Earth spins upon it axis.

5. a) What are the Van Allen zones?
The Van Allen zones are zones of harmful radiation such in small pockets inside the magnetosphere.

5. b) What are aurorae, and how are they produced?
The aurorae occur at the poles of the Earth. They look like ribbons of light in the sky. They are produced by cosmic rays being diverted by the Earth’s magnetic force to the poles, where the rays ionise atoms in the air. To create lights that often witnessed, gases such as Argon and Neon are ionised.

5. c) If you spent a year on a space station without returning to Earth, would you feel any discomfort when you finally came down? If so, why?
Yes, there would be some discomfort. This is because you have become accustomed to the weightless feeling, and being back on Earth with a stronger force of gravity, you will feel quite heavy and slow. There may also be some muscle fatigue as your muscles will have to work harder than when you were in space.