h a l f b a k e r yFaster than a stationary bullet.
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Start with a LARGE spherical He balloon with a small but high Isp ion drive. Power the engine with a ground based microwave power link by making the top third of the balloon from mylar to create a giant parabolic antenna pointed towards the ground and focused on a microwave receiver hanging inside the
balloon. Float the system to 30+km as a balloon then send power to the balloon from a large ground based microwave transmitting station. Use that power to fire the engine which will ionize the He from the balloon and then accelerate it to high velocities electrically and eject it out of the bottom as an ion rocket to lift the balloon the rest of the way to GEO or space.
Specific Impulse
http://en.wikipedia...ki/Specific_impulse
[MisterQED, Jul 12 2009]
Instructions for making a "lifter"
http://en.wikipedia.org/wiki/Ionocraft
[MisterQED, Jul 12 2009]
The limit of ion engine usefullness.
http://www.scienced...05/090527073023.htm
Haven't done the calculations, but 30 kms up still needs significant force to get escape velocity... [4whom, Jul 12 2009]
[link]
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//As opposed to a petite she balloon?// |
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Well, if there were two balloons... |
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So crazy it just might work! [+] |
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On the other hand, targetting is going to be a right old palaver. Your balloon isn't going to sit directly above your ground station as it rises through the various winds of the atmosphere. You could steer your ground dish to track it, but that's going to throw off the focus at the receiving end. |
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Perhaps your mylar dish and antenna can be separate from the balloon's skin, so they can rotate inside to track the ground station. |
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Nitpicking aside, I'm thoroughly impressed with the originality of this proposal. |
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//targetting// use the ion thruster to steer. |
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Other than that is there an ion drive that weighs little enough that the thrust can overcome gravity ?... and absorption spectra for aluminium and mylar ?... Inquiring minds want to know :) [+] |
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Well spherical reflector are steerable. The focal point stays on the axis of the incoming rays at r/2 away from the reflector. The rectenna is hung inside the balloon on adjustable lines so that it can be moved to the correct focal point for the incoming waves.
Sadly I didn't think of the inflatable spherical reflector. Just recently that a guy won a contest to use them for emergency communications.
As for whether this could make it to GEO, I'm not sure it probably can't but not because it is not as powerful as the shuttle. An ion drive is a magnitude more efficient than even the shuttles main engines, Shuttle=450s, Ion=3000s and will not be burdened with most of the excess weight the shuttle has to lug up to space. Add to that the fact that this system could use atmospheric gas when available to have a thoretically infinite specific impulse.
The problem is as [BH] states is creating a ion engine that can lift both its weight and the weight of the envelope. This can be done at sea level as shown by the "lifter" which is been created by lots of people which weighs 100g and takes a 100W to lift it's own weight. The difference between a lifter and an ion engine is the gas source. |
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//can focus down 1kW per square metre//
things that make you go "hmmmm..." |
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The sun is sending ~1.39 kW/m² of electromagnetic radiation constanly. Is a freynal lens the best way to bounce it down? considering that rectennas are supposed to get up to 90% effeciency? Yeah, I'm skeptical too... |
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Solar cells can only convert power at ~20% and have a fixed upper power input limit (solar radiation). Rectennas convert at 90% efficiency and are only limited by the transmitter power. |
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And they don't work at night. |
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Ion drives are efficient, but they produce a tiny continuous thrust. The question will be can you generate enough thrust to overcome residual air resistance, and to maintain altitude - let alone gain any - while you use up your lift gas. |
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Then you need to circularise your orbit. How do you plan to do that? |
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GOCE is doing this, admittedly it didn't attain its orbit with ion engines, but it is doing a reasonable job of maintaining it, so far...<see link> |
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I love the idea of a combined balloon/antenna construction, but the (existing) balloon+chemical rocket combination would possibly be better suited for the intended use. |
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The parabolic-antenna-in-ballloon might be a nifty idea for high altitude com-relays, though? |
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