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Old 08-11-2014, 07:49 PM   #11
mindstalk
 
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Default Re: Gas Station asteroids, I don't understand their use.

I suspect they don't make sense. SF has trained us to think of spaceships like cars, when in reality they may be more like railroads without rails. http://www.rocketpunk-manifesto.com/...-on-rails.html
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Old 08-13-2014, 08:41 PM   #12
dcarson
 
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Default Re: Gas Station asteroids, I don't understand their use.

If they have tethers and rotovators they can do momentum transfer. This might let you use less deltaV for a given speed trip.
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Old 08-14-2014, 11:46 AM   #13
Fred Brackin
 
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Default Re: Gas Station asteroids, I don't understand their use.

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If they have tethers and rotovators they can do momentum transfer. This might let you use less deltaV for a given speed trip.
These technologies are not attractive fro anyone who has a TS fusion pulse drive. Very little else in the way of hard science propulsion is.
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Old 08-18-2014, 01:48 AM   #14
Mailanka
 
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Default Re: Gas Station asteroids, I don't understand their use.

Correct me if I'm wrong, but aren't we also dealing with orbital mechanics?

Your delta-v is not just going to move you in a straight line out of the solar system, or from one world to another. You're going to be spending delta-v to transfer from a lower orbit to a higher one. That is, when a ship leaves earth to go into a GEO, it's not going to necessarily suddenly put on the brakes and "stop" when it gets there. It's usually going to spend exactly the delta-v necessary to get to that orbit.

The same applies when transferring from a solar orbit equivalent to Earth and into a solar orbit equivalent to the asteroids. When you go to the asteroids, you're not necessarily "putting on the brakes" when you get there and spending as much delta-v as when you started just to stop. You're increasing your speed because that increased speed is necessary to remain in that particular orbit. Then, you fuel up, and increase your orbit again and again while moving up.

When you want to move "back down," you're doing the opposite, slowing yourself down by spending delta-v to bring yourself safely down to a lower orbit. That might also require refueling.

Within a given frame of reference, or with sufficiently powerful engine, it's true that space travel is more like a railroad without rails, but with slower, less powerful engines and in a larger system, you're playing games with orbits and then the circumstances change. Or so my meager understanding suggests.
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Old 08-18-2014, 10:44 AM   #15
jeff_wilson
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Default Re: Gas Station asteroids, I don't understand their use.

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Originally Posted by Mailanka View Post
Correct me if I'm wrong, but aren't we also dealing with orbital mechanics?

Your delta-v is not just going to move you in a straight line out of the solar system, or from one world to another. You're going to be spending delta-v to transfer from a lower orbit to a higher one. That is, when a ship leaves earth to go into a GEO, it's not going to necessarily suddenly put on the brakes and "stop" when it gets there. It's usually going to spend exactly the delta-v necessary to get to that orbit.
Transfer orbits require delta-v be added in at least two steps. First, to change to the elliptical transfer orbit itself, then more at the destination orbit to remain there, instead of continuing to oscillate between the two.
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Old 08-18-2014, 10:49 AM   #16
mindstalk
 
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Default Re: Gas Station asteroids, I don't understand their use.

The point of "railroad without rails" is that you don't have much control once you're en route. You've got an origin and a destination and if there's a distress call off to the side on a different vector then there's nothing you can do about it. Physically, I think it's about delta-vee; if you spend half your delta-vee to start and half to stop, you can't do much. If you spent 90% of your delta-vee to start and 10% to match orbits, that's hardly increasing your flexibility. You'd need total starting delta-vee to be many times your manuever delta-vee to approximate a terrestrial car, ship, or plane.
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