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Old 08-13-2011, 08:39 AM   #31
cultureulterior
 
Join Date: Oct 2007
Default Re: TL9 Spaceships

Personally I like a beanstalk-and-motor attached to the spaceship itself, with a lander permanently attached to the end, so that you can descend down on strange worlds. Not sure how practical this is.
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Old 08-13-2011, 08:50 AM   #32
johndallman
 
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Default Re: TL9 Spaceships

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Originally Posted by cultureulterior View Post
Personally I like a beanstalk-and-motor attached to the spaceship itself, with a lander permanently attached to the end, so that you can descend down on strange worlds. Not sure how practical this is.
Not very. You need a ludicrously large ship to carry the mass of the stalk and act as a counterweight. The level of superscience involved usually comes with easier ways to do the job.
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Old 08-13-2011, 08:50 AM   #33
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Default Re: TL9 Spaceships

Good thing is that (the descent) reaching the ground part will happen pretty definitely. :P
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Old 08-13-2011, 09:17 AM   #34
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Default Re: TL9 Spaceships

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Originally Posted by cultureulterior View Post
Personally I like a beanstalk-and-motor attached to the spaceship itself, with a lander permanently attached to the end, so that you can descend down on strange worlds. Not sure how practical this is.
As John said it really isn't practical at all. There might be ways to get the same effect for small landing vehicles using a variant on a laser launching system. I half remember an article a few years ago during an outbreak of enthusiasm for SPS that speculated on using the output of a power satellite directly as an alternative to a ground based laser. If you can find that you might be able to bash the idea until it fits to get the same result though.
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Old 08-13-2011, 11:34 AM   #35
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Default Re: TL9 Spaceships

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Originally Posted by Nyarli View Post
They are not the most expensive of all drives, they don't require fuel and their only drawback is inability to start from planet. Am i right, or i have missed something?
Low thrust. Bad in combat, and my understanding is that in more nuanced systems, it should limit your choice of trajectories. That can have a major impact on your actual travel times vs. abstracted Spaceships travel times, due to launch windows and that sort of thing.

However, my physics education is very weak, so I may be right out of the ballpark here. This opinion mostly comes from playing games like High Frontier, where the sails are very powerful -- cheap/light/simple -- but need a head start to win a race vs. a costly/heavy/complex rocket once it's launched.
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Old 08-13-2011, 11:40 AM   #36
cultureulterior
 
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Default Re: TL9 Spaceships

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Originally Posted by Frost View Post
As John said it really isn't practical at all. There might be ways to get the same effect for small landing vehicles using a variant on a laser launching system. I half remember an article a few years ago during an outbreak of enthusiasm for SPS that speculated on using the output of a power satellite directly as an alternative to a ground based laser. If you can find that you might be able to bash the idea until it fits to get the same result though.
According to this, with carbon nanotubes they expected to be able to launch a reel reaching all the way down with just 20 tons:

http://web.archive.org/web/200905241..._020327-2.html
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Old 08-13-2011, 02:48 PM   #37
teviet
 
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Originally Posted by munin View Post
The heliopause is in the neighborhood of 100 AUs from the sun. For a magsail to maintain constant acceleration all the way out to there it would need to increase its loop circumference also by a factor of 100, implying that it only has 1% of its cable spooled out when traveling at 1 AU (it can't spool out more closer to the sun because there's a point where, as you said, the acceleration of a larger loop exceeds the cable's tensile strength). I don't think you would design a magsail that way, you'd have the whole thing spooled out all the time and just get less acceleration as you move further from the sun -- and I think the Spaceships magsail stats are based on having the entire mass of the system devoted to acceleration, and not spooled up. Thus the rule on p. 39 to divide the magsail's acceleration by (1/D)^2 (though it is weird it's not mentioned in the magsail's description, like the light sail).
Sorry, I did say that I was talking about magsails in reality, not GURPS magsails, so the assumptions will be different. Feel free to ignore me! :)

But if you're still interested... a real magsail would not deploy to its full radius in all environments, because it wouldn't be able to maintain a magnetosphere; it would collapse under stellar wind pressure. Instead it would deploy multiple loops of smaller radius. At larger distances it would deploy the same cable in fewer loops of larger radius.

Double-checking my notes, the net acceleration will not be constant, but will decrease as 1/D rather than 1/D^2.

I haven't read up as much on the M2P2 sail; maybe it can maintain constant acceleration, but it might also need more consumables as it expands.

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Old 08-13-2011, 08:38 PM   #38
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Default Re: TL9 Spaceships

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Originally Posted by cultureulterior View Post
According to this, with carbon nanotubes they expected to be able to launch a reel reaching all the way down with just 20 tons:

http://web.archive.org/web/200905241..._020327-2.html
When I read that article 20 tons is the load capacity of the beanstalk and the initial launch requirement to build the beanstalk, not the mass of the beanstalk when operational. The beanstalk proposed consists of two shuttle payloads plus extra material hauled up the cable over two-and-a half years from the full-scale high-tech industrial economy at the bottom. By the time it is robust enough to carry a 20-ton payload its total mass is hugely greater than 20 tons. So this is not something you can carry with you for landings.

Also, I note an implication that getting up or down this beanstalk will take a week.
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Old 08-13-2011, 08:56 PM   #39
Fred Brackin
 
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Default Re: TL9 Spaceships

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Also, I note an implication that getting up or down this beanstalk will take a week.
That's largely unaviodable. It's a 22,300 mile journey and I haven't heard any proposed speeds higher than 300 mph. For a week assume approx. half of that.

You'd also have to be pretty lucky to find out that the dynamics of a new planet were within the capacity of your Earth-scale beanstalk. That is not at all guaranteed and longer distances are easily possible.
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Old 08-14-2011, 03:39 AM   #40
cultureulterior
 
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Default Re: TL9 Spaceships

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When I read that article 20 tons is the load capacity of the beanstalk and the initial launch requirement to build the beanstalk, not the mass of the beanstalk when operational. The beanstalk proposed consists of two shuttle payloads plus extra material hauled up the cable over two-and-a half years from the full-scale high-tech industrial economy at the bottom. By the time it is robust enough to carry a 20-ton payload its total mass is hugely greater than 20 tons. So this is not something you can carry with you for landings.
Um, the Midnight Sun shuttle masses 300 tons, and uses 130 tons of rocket fuel. Even if it is hugely greater, a beanstalk for transporting 1 ton=A guy in a spacesuit- would fit into _some_ spacecraft. At least SM+9 and above.
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