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Ion Propulsion: Fuel-efficient Technology for High Velocities

Understand how ion propulsion works, its advantages, limitations, and potential for future space travel. Learn about the need for a new propulsion system and the use of charged particles for higher velocities.

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Ion Propulsion: Fuel-efficient Technology for High Velocities

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  1. Goal to understand how Ion Propulsion works. Objectives: To recap the need for a new propulsion system To learn about what Ion Propulsion is To understand how Ion Propulsion allows for higher velocities To examine the limitations to Ion Propulsion

  2. Chemical Propulsion • Takes lots of mass • Only good for humans in the region of the Earth • Once we try to get to Mars it gets dangerous and expensive.

  3. What is Ion Propulsion • Ion Propulsion is similar to chemical rockets in that it throws something out the end so that it can go forward • However, instead of tossing out gas it tosses out protons and/or electrons (aka charged particles)

  4. How it works • If you have a charged particle in an Electro-magnetic field the charge will be accelerated. • The stronger the field the greater the acceleration. • Therefore the particles can be thrown out at much higher velocities (up to 100,000 times higher). • Since the fuel has a higher velocity you need a lot less of it.

  5. Current Ion Propulsion • Deep Space 1 • encountered Comet Borrelly • $150 million • Used solar panels to power the 2100 Watt Ion Propulsion engines (Xenon) • However, this engine ran for 678 days

  6. Result • Due to the 40 km/s fuel the craft accelerated by 4.3 km/s over the 2 years. • If this had been put into Earth orbit initially then set off it would almost be enough to get to Mars. • All for 74 kg of fuel.

  7. From NASA.gov • Ion propulsion could be used for a manned mission to Mars. The decision on whether that would be the preferred approach would involve many questions such as which technique might get the crew there the fastest (independent of how fuel efficient the trip might be) in order to reduce the radiation exposure and effects of long periods of near weightlessness.

  8. Current limitations • Design limits fuel speed to 40 km/s. • This could be vastly improved in the future • Low thrust – have to put it into space. • Takes a long time to speed up.

  9. But • If you used a $500 million conventional rocket to put a space shuttle sized ion propulsion craft into Earth orbit you could blast off from orbit for a LOT less cost wise. • Does not require expensive or exotic fuel.

  10. What Ion Propulsion holds in the future: • Now lets design a more ideal futuristic Ion Propulsion vehicle: • Two possibilities • 1) straight acceleration • 2) particle collider like set up

  11. Straight. • Requires a large electric field for the length of the ship. • Could use Xenon but lighter elements will go faster. • We trade thrust for fuel efficiency

  12. For Hydrogen: • Acceleration = Electric field * e / Mp • e = charge of proton and Mp is mass • Velocity = (2 * Acceleration * length)1/2 • Examples: • 1 km long ship with a 1* 109 V/m electric field • Exhaust velocity = 99.95% the speed of light • 100 m long ship with a 10,000 V/m electric field • Exhaust velocity = 140,000 km/s (almost half the speed of light) • 10 m long ship with 200 V/m electric field • Exhaust velocity = 60,000 km/s (20% the speed of light)

  13. Notes • Xenon gets 1/10th the velocity but gives 10 times the thrust • Energy is going to be the key though as to how much Hydrogen you can ionize and eject and how fast. • Also, powering that large of an electric field can use a lot of energy.

  14. Ship 2: Magnetic • This would involve a more circular shaped ship which would slowly accelerate up the Hydrogen ions. • As the ions speed up they circle around a central magnetic field. • The faster they go the bigger a circle they make. • R = mv/qB • Where q is the charge and B is the magnetic field

  15. Velocity • So, the exhaust velocity now becomes: • V = qBr / m Examples: 1 km in diameter ship with 15 Tessla magnets Exhaust velocity = 99.99% speed of light 100 meter in diameter ship with 1 Tessla magnets Exhaust velocity = 98% the speed of light 10 meter in diameter ship with 0.002 Tessla magnets (hair dryer) Exhaust velocity = 2000 km/s (almost 1% the speed of light)

  16. So what is the hold up? • Energy • How do we produce the energy? • Solar power only does so much • Ten times velocity means ten times the energy overall (100 times energy per mass but 10 times less mass). • Nuclear power? Fusion power?

  17. Take the example… • Get a 100 metric ton spacecraft to 20 km/s using Hydrogen we speed up to 2000 km/s (need 1% of mass of ship as fuel). • Energy needed: • 2 Quintillion Joules (amount of energy USA uses in 12 minutes) • Cost: $56 million dollars • Would require a 63 Megawatt power generator to work non stop for a year

  18. 73 Megawatt power plant in Thailand

  19. 60 Megawatts

  20. Conclusion • Ion Propulsion is a CURRENT technology • It is very fuel efficient • It can get is to much greater velocities • However, it cannot currently launch itself • And the ultimate problem is that it takes a lot of energy.

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