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Duration: 04:04 minutes Upload Time: 2007-11-25 19:03:25 User: BrunoTheQuestionable :::: Favorites :::: Top Videos of Day |
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Description: Ion Propulsion - Transport System to the Planets The efficiency of a rocket engine can be described by its specific impulse, which is the change of momentum gained from a 1 kilogram weight of propellent. The Space Shuttle main engines have a specific impulse of 453 seconds which is typical of a liquid fuelled rocket engine. An Ion thruster has a specific impulse of more than 3000 seconds and so requires less than a sixth of the fuel of a liquid fuelled engine. Gridded electrostatic ion thrusters commonly utilize Xenon gas. The gas is first ionized by bombarding it with electrons. The positively charged ions then diffuse through the positive grid and enter a potential difference between the positive and negative grids. The potential difference accelerates the ions to high velocities, which then leave the engine to create thrust. An electron emitter, on the exterior of the engine, neutralizes the ion beam to prevent charge build-up. The typical thrust of an ion engine is equivalent to a weight of 10 grams - about the weight of a sheet of paper. This means ion thrusters need to provide continuous thrust for a very long time in order to achieve a reasonable change in velocity. Electrostatic ion engines have been tested for 3.5 years of continuous thrust at full power. Collision of ions with the charged grids causes their erosion and will lead to eventual failure. Ion engines consume more than 2 kilowatts of electrical power, which may be generated by solar arrays or nuclear generator. NASA has developed a Xenon ion thruster called NSTAR for use in their inter-planetary missions. This thruster was tested in the space probe Deep Space 1, launched in 1998. The Dawn mission was launched in September 2007 to explore the dwarf planet Ceres and the asteroid Vesta. To cruise from Earth to its targets it will use three Deep Space 1, heritage, NSTAR thrusters, firing only one at a time, to take it in a long outward spiral. The three thrusters are required to meet the lifespan requirement of the engine. |
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| henrihead ::: Favorites 2007-12-25 23:03:39 I really enjoy watching videos like this. Gives my little mind something to think about. :) __________________________________________________ | |
| wallasky ::: Favorites 2007-12-15 18:21:22 What about the Bussard Interstellar Ramjet mentioned in Carl Sagan's book, COSMOS? __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-05 19:30:53 I've done a little research on sails and apparently a 1km^2 sail with a mass of 1kg at 1AU from the Sun has an acceleration of about 1g ! It will be tricky but I think I'll have a go at working out what velocity can be acheived from a Sun fly-by maneuver. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-05 19:03:17 I had also imagined that solar sails worked using the solar wind, but apparently this is not the case - the force due to radiation pressure is about 500 times greater than the force due to the solar wind. However, your general point that solar sails are only effective when close to a star is correct. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-05 09:57:59 The exhaust velocity for an ion engine is about 100km/s giving a journey time to the nearest star of at least 10,000 years. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-05 09:53:15 For a rocket engine, to maintain fuel efficiency it is necessary to keep the maximum spacecraft velocity below the exhaust velocity. Take as an example a spacecraft moving away from us at a speed equal to the exhaust velocity - recently expelled fuel will be stationary relative to us - it contributes zero momentum overall to the spacecraft ! The momentum gained when it was expelled is equal to the momentum absorbed by the fuel earlier in the flight. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-03 08:56:18 I had the same thought. Perhaps with some close flybys of the Sun to boost velocity using the sail, and a few planetary gravitational assist maneuvers. The ion engine would also be useful for course control while in the solar system. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-12-03 08:44:10 How about a mission to seed a suitable planet of a nearby star with cyanobacteria ? There's good reason to do this as quickly as possible before our civilization collapses and we miss the chance. The journey time is then irrelevant. __________________________________________________ | |
| baley7 ::: Favorites 2007-12-01 06:43:04 One viable option could be a combination probably of more propulsion types for interstellar travel. Eg a sail for the initial push close to the sun and deceleration, electric engines powered by nuclear fission (or fusion if it is in the future). I __________________________________________________ | |
| heroman9900 ::: Favorites 2007-11-27 22:22:17 A problem with solar sails is that they would be ineffective past the heliopause. Additionally, to be really effective solar sails need to venture close to the Sun, where radiation makes it very dangerous for human travel (if not impossible). __________________________________________________ | |
| heroman9900 ::: Favorites 2007-11-27 22:18:57 The RTGs used on Cassini and New Horizons were designed to survive reentry. I'm willing to bet that similar designs could be implemented to ensure the safety of the public when using something like the VASIMR. __________________________________________________ | |
| trondreitan ::: Favorites 2007-11-27 08:29:15 Thanks Bruno. Solar sails may eventually reach high velocities, but would use an enormous amount of time to get to such velocity (I would think, as I would think the acceleration would be very low). So it's not clear to me what would be the best technology (of today) for reaching Alpha Centauri. There's always the lure of new technology right over the horizon, but I'm curious about what we could achieve right here and now if we put a little elbow grease on. __________________________________________________ | |
| trondreitan ::: Favorites 2007-11-27 08:27:20 Thanks both to you KickAssClown and Bruno. But can we really make anything that reaches 0.5c on a distance of 4 lyr with todays technology? How much time would it take to accelerate to that velocity? (PS: Don't use to much time answering this. This is pretty idle speculation from my side.) __________________________________________________ | |
| KickAssClown ::: Favorites 2007-11-27 00:33:12 To Trondreitan, It depends on what the maximum thrust is for this engine. I have done calculations for going to Alpha Centauri, our closest neighboring star system. Alpha Centauri is located 4.1 light years away from our Solar System; thus, with a constant acceleration resulting in an average velocity of 50% of the speed of light (.5c) it would take us 28 years to get there. __________________________________________________ | |
| BrunoTheQuestionable ::: Favorites 2007-11-26 17:34:59 You would have to take a fission reactor along to power the ion engine, but it seems do-able. It would take quite a while though. I believe solar sails can achieve much higher velocity. I'm sure we could launch something in 10 years time that would overtake anything we launch now. __________________________________________________ | |
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