05-19-2012, 07:04 AM | #31 | ||||
Join Date: Aug 2004
Location: traveller
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Re: TL9 Antimatter pion rockets
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Moreover, investing in the infrastructure to produce the required quantities of antimatter pays immediate benefits, in the form of less-energetic antimatter reaction drive options. A network of lasers or masers to drive a lightsail is less flexible overall, and again will be tied up throughout the acceleration phase rather than becoming fully available immediately upon departure. Social engineering requirements may favor an antimatter rocket over a lightsail, even given the differences in efficiency. |
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05-19-2012, 08:23 AM | #32 |
Join Date: Aug 2004
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Re: TL9 Antimatter pion rockets
How do magnetic sails stack up? My understanding is that they'd be less dependent on social engineering, as you put it; there's also the fact that the force that they generate falls off more slowly than it does for lightsails, making them more attractive for outer-system maneuvering. The only downside I know of is that they can't exceed the speed of the solar wind, putting an absolute upper cap on how fast they can travel through interstellar space.
(I'm not quite so fond of plasma sails; while they apparently get better performance characteristics than magnetic sails, the need to replenish the plasma that leaks out pretty much kills them as a "fuelless propulsion system". But maybe I'm wrong?) |
05-19-2012, 08:35 AM | #33 |
Join Date: Aug 2007
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Re: TL9 Antimatter pion rockets
Any time the local charged particles aren't going at least as fast as your ship and in the direction you want, you start losing speed as momentum transfers from your sail to those particles rather than the other way around.
The mag sail generally makes a better brake than an accelerator. Places whre there is a convenient solar wind are about the only places it does make even a little sense.
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Fred Brackin |
05-19-2012, 08:39 AM | #34 |
Join Date: Aug 2004
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Re: TL9 Antimatter pion rockets
Right; but don't all stars have "a convenient solar wind" blowing in an outward direction?
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05-19-2012, 01:11 PM | #35 |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: TL9 Antimatter pion rockets
It's not really possible to focus a driver beam at the required ranges. If you could, it would be somewhat more efficient, because you can use a driver beam at 0.2c or so. The solar wind is much much too slow to be relevant to this discussion.
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05-19-2012, 05:50 PM | #36 | |
Join Date: Aug 2007
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Re: TL9 Antimatter pion rockets
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I also seem to real that te solar wind slows down as it goes outward so you'd probably stow your mag sail even before you got to the heliopause. That leaves you accelerating at a slow rate for only a very small period of your trip. Hard to make that look efficient. I know of soem designs that accelerate by another means that use a mag sail to brake with. It is better at that than acceleraing.
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Fred Brackin |
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06-12-2012, 10:45 PM | #37 | |
Join Date: Aug 2004
Location: In the UFO
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Re: TL9 Antimatter pion rockets
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I'd think increasing the exhaust velocity would quite likely reduce the acceleration, though, by at least half and possibly more. (High-impulse antimatter pion rocket?) On TL, while making antimatter is a big problem, it can be dealt with with appropriate engineering projects (cover mercury with solar collectors, whatever). But the biggest problem is the storage of antimatter. A pion drive relies on 1-1 ratio mix of matter-antimatter. However, storage facilities for antimatter currently mass a great deal to hold even sub-nanogram levels, and even the future generation versions quoted are things like "mass of a space shuttle tank to hold a few micrograms." Since half your fuel is antimatter, if your fuel tank ends up weighing vastly more, or even a little more, than your fuel, you are utterly out of luck. You'll have to get the fuel tank mass from a future speculative "tons per microgram" down to "micrograms per microgram" if you don't want your starship to have the acceleration of a flashlight. (There are possible ways to do this, maybe, like antihydrogen ice storage, but the road to them is probably TL10+). . Also, it's not just the storage - you have to find a way of moving the antimatter from whatever tank you have to the engine, which means the engine has to incorporate this technology. The most sensible approach I saw had the antimatter hydrogen stored as solid pellets and the hydrogen liquid. (Incidentally, while the 3e version was TL9 - but in 3e TL scale. Most 3e technologies specified as TL9 became either TL10 or TL11 in 4e (blasters, for example)).
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06-13-2012, 12:46 PM | #38 |
Join Date: Nov 2008
Location: Florida
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Re: TL9 Antimatter pion rockets
@ David Pulver: So when's the next Spaceships book coming out ;-), I got the $$ right here!
Seriously, I would love a Spaceships treatment on Current & Expected Tech in the next few decades, and fiddly numbers on things like Vasmir, M2P2, NERVA/LANTRN... broken down in Experimental through Mature TECH crunchy numbers. Anyways, got the $$$ right here... just sayin' :) |
06-13-2012, 12:48 PM | #39 |
Join Date: Aug 2004
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Re: TL9 Antimatter pion rockets
That strikes me as being in the domain of the Vehicle Design System rather than the Spaceships series.
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06-13-2012, 01:57 PM | #40 |
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Join Date: Oct 2004
Location: Forest Grove, Beaverton, Oregon
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Re: TL9 Antimatter pion rockets
I just can't see why anyone would do it when it would be infinitely cheaper and safer to use a multi-stage fusion drive ship.
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antimatter, hard sf, spaceships |
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