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Goal: To understand the limitations to the current method of space travel

Goal: To understand the limitations to the current method of space travel. Objectives: To understand how and why rockets work To learn about why rockets have a limitation on the speed they can go To understand how the size of a rocket affects its cost. Newton’s 3 rd law.

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Goal: To understand the limitations to the current method of space travel

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  1. Goal: To understand the limitations to the current method of space travel Objectives: To understand how and why rockets work To learn about why rockets have a limitation on the speed they can go To understand how the size of a rocket affects its cost

  2. Newton’s 3rd law • For every action there is an equal and opposite reaction. • If I push you then you push me back automatically. • If you are on the side of a pool and you push the side it pushes back and you move away from the side.

  3. Application to rockets • The following will be a bit in depth… • In the rocket (depending on which one) you have 2 separated materials. • One is either ammonium perchlorate or oxygen. • The 2nd is either aluminum or hydrogen

  4. Ignition • The two substances are brought together (to make either Aluminum oxide or water) • This chemical reaction heats the material making it hotter.

  5. The purpose of heat • Heating a fluid increases its PRESSURE • Pressure is how much the fluid pushes on its surroundings. • This creates a force. • Force = difference in pressure * area

  6. The result • The rocket exerts a pressure force on the fluid/gas which pushes it downwards out of the end of the rocket. • Newton’s 3rd law now comes into effect and the fluid/gas now exerts an equal force but in the opposite direction. • If the force exceeds the weight (gravitational force) of the rocket then the rocket lifts off!

  7. What is the catch? • Well the catch is that you have to limit how quickly you can lift off. • If you push the rocket too fast it will either blow up (you are on a guided bomb after all) or you will kill the passengers.

  8. And so • You don’t throw out all the gas at once. • So, the initial gas has to move the entire rocket. • The next part has to move the rocket minus the gas it has lost so far. • And so forth.

  9. The result • Most of a spacecraft is FUEL, and not payload. • Also, since the gas can only be shot out at a certain speed….

  10. Momentum conservation • The momentum (mass * velocity) the spacecraft gets • Cannot exceed the momentum given to the fuel in the opposite direction. • Since a lot of the fuel is moved with the craft and the craft at the end will move 10 times faster than the fuel can be pushed a lot of the fuel ends up with a velocity in the same direction as the craft, but a bit slower. • Ooops…

  11. Speed limit • This creates an upper limit to the speed of a rocket. • You want to go 2 times faster it takes about 10 times more fuel from a math stand point (so you put a rocket on a much bigger rocket) • This gets COSTLY

  12. Space Shuttle • Goes into low Earth orbit (8 km/s) • Cost: $450 million (from NASA) • To go to the moon, simply, would take a about 30% faster velocity. • Fuel mass = Spacecraft mass * e(Vcraft/Vfuel) • So, if for Vcraft to be 30% more the fuel mass needs to be about 3 times greater. • Cost: $1.3 billion.

  13. Mars • To get to mars we need about double the velocity than to get into orbit around the earth. • That means 15 times more fuel at a cost of $7 billion • And if you want to get back, well you need to make it even bigger (another 10 times bigger, so now we are up to $70 billion for just the rocket).

  14. And so… • The current method of space travel is sadly limited to our inner solar system. • If we want to go anywhere other than low earth orbit or to the moon then we need to either: • 1) spend a LOT of money • 2) use a new form of propulsion

  15. Quick question: • If this is so bad for outer solar system exploration then how were we able to send probes to the outer solar system (such as Voyager, New Horizons, ect)?

  16. Solution • Robotic probes don’t need to be as big. • They don’t need to keep air or food or water • They don’t have humans on them • They don’t need to come back • So, they can be a lot smaller and a lot lighter. • Space shuttle fully loaded: 120 tons • New Horizons probe: 0.5 tons

  17. Gravity assist • If a spacecraft flies behind a planet (in the planets direction of orbit around the sun) then the gravity of the planet will give the craft a boost • Example, New Horizons got a 4 km/s boost from Jupiter.

  18. Conclusion • The current form of rocketry is useful for inner solar system • However, it is limited by speed and by cost • This makes human space travel using this method limited at best and therefore we need other designs if we want to go to the outer solar system and beyond.

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