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Propulsion Technology

LucyR said:


I suggest that you take a few steps back and consider the difference between constant and non-constant acceleration.

Lucy.
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Why? Why would you want to accelerate at 1 milli-g the first week, 2 mg the second, 4 the third? If you can accelerate at higher g forces, why not do it all the time? A Bussard ram is the only drive proposal i'm aware of which would plausibly follow such a scenario, and as has been pointed out in previous posts, Bussard rams aren't feasible in this neck of the galaxy (the Sol system seems to be inside a particularly empty region of space).
 
Just accelerating would be difficult, but one would also have to start decelerating about half-way to the destination, eh?
 
I like the idea of light sails: you don't have to carry your fuel with you and thus some aspects of the rocket equation can be got around. It's still true that the light has to reach you, and the faster you go the more red shifted the light will be from your perspective, and thus the less impulse it will apply to your ship. Still, a laser on the earth, or moon, or one that stays in orbit around the earth, or just somewhere in the solar system that is suitable, seems to be me to be perhaps the most efficient way to accelerate an interstellar spacecraft.

If you are just staying in the solar system then sunlight may be enough for your purposes. The problem of course if building the solar sails and preventing them from falling apart I guess. Reasonable amounts of acceleration will require very large surface area and very low mass material.
 
Roboramma said:
I like the idea of light sails: you don't have to carry your fuel with you and thus some aspects of the rocket equation can be got around. It's still true that the light has to reach you, and the faster you go the more red shifted the light will be from your perspective, and thus the less impulse it will apply to your ship. Still, a laser on the earth, or moon, or one that stays in orbit around the earth, or just somewhere in the solar system that is suitable, seems to be me to be perhaps the most efficient way to accelerate an interstellar spacecraft.

If you are just staying in the solar system then sunlight may be enough for your purposes. The problem of course if building the solar sails and preventing them from falling apart I guess. Reasonable amounts of acceleration will require very large surface area and very low mass material.
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Also you always need someone in the Crow's nest to watch for Pirates!!!!!
 
A steady one-g acceleration, ignoring relativity for the moment, would get you just over the speed of light after a year. When we don't ignore relativity, one year's one-g acceleration still gets you up to very near light speed.
 
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ceptimus said:
A steady one-g acceleration, ignoring relativity for the moment, would get you just over the speed of light after a year. When we don't ignore relativity, one year's one-g acceleration still gets you up to very near light speed.
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Sounds great, but how do you propose to maintain one-g acceleration for a year? What sort of fuel are you going to use, for instance?
 
Roboramma said:
Sounds great, but how do you propose to maintain one-g acceleration for a year? What sort of fuel are you going to use, for instance?
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It reminds me of the complaints I saw at the start of the SyFy miniseries "Ascension". A generation ship that had been traveling for 50 years, powered by an Orion drive, with a constant 1G internal gravity and no spinning gravity decks.
Of course, the end of the first episode revealed how they achieved it.

The crew only thought they were in space. The ship was actually in an underground bunker, part of a decades-long scientific study on how people would react to long-term space travel.
 
One is still going to need a great deal of food, water, air, and other such supplies during these very long one G trips.
 
Crossbow said:
One is still going to need a great deal of food, water, air, and other such supplies during these very long one G trips.
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We can do air and water even today, nuclear subs can be months under water using recycled air and cleaned saltwater. ISS can recycle water. Food is more of a problem. First there is energy demand .. but that we could do even today, and the propulsion will most probably use electricity too, and lot more, so that should be no problem. But growing food will take tons of space (and yes, I know ton is not unit of volume).
 
Dr.Sid said:
We can do air and water even today, nuclear subs can be months under water using recycled air and cleaned saltwater. ISS can recycle water. Food is more of a problem. First there is energy demand .. but that we could do even today, and the propulsion will most probably use electricity too, and lot more, so that should be no problem. But growing food will take tons of space (and yes, I know ton is not unit of volume).
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Even if one can extend the use of the air, water, and food to a ratio of ten to one, then the problem of developing an adequate amount of air, water, and food supplies will still be a very considerable problem indeed.
 
Crossbow said:
Not quite.

After all, we Earthlings also have that big hot thing called the Sun which really helps to support life here on Earth.
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If the ship can sustain 1g acceleration long term energy for life support isn't going to be an issue as the drive requires fantastic amounts of energy and unless it is 100% efficient the biggest problem with using it as an artificial sun will disposing of the excess energy so as not to quite literally melt the ship
 
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