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How difficult is interstellar travel?

whiteyonthemoon said:
How long would it take to gather 1.5 gigawatts energy with the solar power station you propose?
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I think the conquest of space will be done by those who know the difference between power and energy. In the meantime, the only answer I can think of that might answer this question is "instantly the moment it's built".
 
Stitch said:
1 gram of rock travelling at a couple of times the speed of sound packs a pretty big punch!
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1 gram traveling at 87% the speed of light is about equal to a Hiroshima bomb.

Paul

:) :) :)
 
Paulhoff said:
1 gram traveling at 87% the speed of light is about equal to a Hiroshima bomb.

Paul

:) :) :)
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[OT]
And when you scale up to the size of a craft that would be needed for a reasonably capable probe or to transport complex lifeforms, this leads to an interesting conclusion.

Any civillization capable of non-generational interstellar travel is also capable of sterilizing the surface of a plantery body.

And another aspect of this: Any object travelling at a significant percentage of the speed of light is nearly un-interceptible, especially if it is capable of changes to its velocity. By the time your radar returns/gamma returns/light rays/whatever reach your detectors, the object has moved, so it's never in the same place you "see" it.

And, finally, the only way to determine is an incoming object is a ship or a missle is to see if it starts to deccelerate.

Sleep tight :D
[/OT]
 
I'm sure there are easier ways to sterilize the surface of a planet. Who are you trying to get even with?
 
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RY:

Actually, that's about the easiest. ANY object with mass that can be accelerated to a percentage of the speed of light becomes a massive explosive device. The addition of a warhead of any type (even antimatter) becomes almost superfluous. An object the size of a volkswagon hitting atmosphere at 90% light speed is going to produce a reaction that's very, very close to that of a matter-antimatter conversion.

Not trying to get even with anyone, this is simply a consequence of high-speed travel. Also a possible warning against broadcasting our presence too loudly, just in case there is another intelligence out there, at or above our level of technology, that's maybe a bit more xenophobic and/or paranoid than we are.

Just something else to think about. Maybe there's a reason we've detected no sign of another intelligent civillization, besides that life is uncommon :D
 
It occurs to me that if you could figure out a way to produce and contain anti-matter, a lot of the propulsion issues will go away.
 
rockoon said:
You do not truely understand relativity.

The ships mass will appear constant from the ships perspective (well, it will actualy decrease as it expends its energy store)

There is never a point where you say "omg i'm heavier!" However outside observers might say "omg he is heavier!" - thats relativity.
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The article specifically states that the power source can't be on board, and the use of a Sol satellite to collect (let me guess, those solar panels are 100% efficient) and send (once again, 100% efficient) the energy also implies that the power source won't be on the ship, so the relativistic mass of the ship is the proper one to consider.

You are right though, I don't understand relativity.

Not surprising since
rockoon said:
You do not truely understand energy and power units.

The Watt is a unit of power equal to 1 Joule per Second.

The Joule is a unit of energy.

So 1.5 gigawatts is 1.5 billion joules per second.

To put this in perspective, the typical lightbulb consumes 60 to 80 watts of power, or about 60 to 80 joules per second.

To answer your question, "1 second"
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I don't even get Newtonian physics right.
 
Meadmaker said:
It occurs to me that if you could figure out a way to produce and contain anti-matter, a lot of the propulsion issues will go away.
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We can do that now. Although creating and containing it in large neough quantities to be useful is a different story :)

Right now, the price for antimatter production is about 10 trillion a microgram (IIRC, been a while since I've read the studies). Not only that, but AM has some problems in the propulsion department, as well. Primarily the fact that matter/anti-matter reactions produce a large amount of gamma radiation, which is very hard to block. For short trips this isn't a big deal (gamma tends to be less damaging in an absolute sense than alpha or beta, although it's harder to block-those traits are related). Ut for long trips, you run serious risks of radiation damage. The shileding is going to add a lot of mass to the ship; oe you'll have to develop some sort of very lightweight material (monofibers come to mind) to have a long seperation betwwen the engine and crew compartment (the Valkyrie concept was based on this idea).

AM would solve the problem of fule storage, as you can pack a lot of go in a little package. But it still has some problems of it's own. Personally, I think that'll be our best bet for a fast (relatively speaking) interstellar craft.

If we can deal with going slow, something like a light sail or possibly an ion engine might be a better choice IMHO. Of course, I'm not a rocket scientist. Ask R. Mackey, I think he IS a rocket scientist :)
 
Meadmaker said:
It occurs to me that if you could figure out a way to produce and contain anti-matter, a lot of the propulsion issues will go away.
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Not really, it will take more energy to make it then it has. Also you still have to use has much energy in weight as you weigh to get to 87% the speed of light.

Paul

:) :) :)
 
Huntsman said:
RY:

Actually, that's about the easiest. ANY object with mass that can be accelerated to a percentage of the speed of light becomes a massive explosive device. The addition of a warhead of any type (even antimatter) becomes almost superfluous. An object the size of a volkswagon hitting atmosphere at 90% light speed is going to produce a reaction that's very, very close to that of a matter-antimatter conversion.

Not trying to get even with anyone, this is simply a consequence of high-speed travel. Also a possible warning against broadcasting our presence too loudly, just in case there is another intelligence out there, at or above our level of technology, that's maybe a bit more xenophobic and/or paranoid than we are.

Just something else to think about. Maybe there's a reason we've detected no sign of another intelligent civillization, besides that life is uncommon :D
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Similar themes:

"Run To the Stars" Michael Scott Rohan

"Orbit Unlimited" Poul Anderson (IIRC)

The "Revelation Space" series by Alistair Reynolds...

Read any of them, anyone?
 
RecoveringYuppy said:
I

To give a different perspective on those numbers, his power requirement works out to about 1.5 gigawatts when the energy is spread over the duration of the mission he is describing. A solar power stations based near the orbit of Mercury would need under a square kilometer to catch that energy.

The energy isn't even outrageous, let alone impossible.

* BTW the design for the rocket capable of using that energy source has been sitting around unused for 40 years also.
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It would probably be easier to use the moon. Silicon from regolith?

Of course I wwouldn't want tho be standing anywhere where the reflected light from a GW light sail was pointing... (just out of interest, what happens to the Boeing Airborne laser aircraft, if it targets an adaptive mirror that refocusses the light back onto the pilot? Even at a 4th power attenuation that would probably smart a bit).

Scientific American had an article about advanced propulsion in about 1996? Can't find my copy...
 
Paulhoff said:
Not really, it will take more energy to make it then it has. Also you still have to use has much energy in weight as you weigh to get to 87% the speed of light.

Paul

:) :) :)
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details, details.

Still, it might take a great deal of energy to make, but the key is that you wouldn't have to propel nearly as much antimatter fuel as you would fusion or fission fuel. So, to get to 0.87 c, you would have to propel twice as much, instead of many times as much.

Of course, if you could make those bussard ramjets work, you wouldn't have to propel any fuel, but the latest calculations are that there is not enough hydrogen in deep space.
 
jimbob said:
Of course I wwouldn't want tho be standing anywhere where the reflected light from a GW light sail was pointing.
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The energy densities don't have to be outrageous. Bright sunlight is about a GW per square kilometer which I expect would work for a sail. Not sure if a sail would work for interstellar travel though.
 
BlackKat said:
I imagine that whenever possible planetary life is always going to be more desirable than life in an orbital colony.
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Perhaps, but if you start including O'Neill's largest ideas for space colonies (paired cylinders, each four miles in diameter and twenty miles long) then life on a colony isn't much different than a planetary one.
 
Corsair 115 said:
Perhaps, but if you start including O'Neill's largest ideas for space colonies (paired cylinders, each four miles in diameter and twenty miles long) then life on a colony isn't much different than a planetary one.
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Assuming that one could rail launch the materials for the ONeill structures from the Moon, which seems plausible, the ONeill structure should wind up being the very best human environment: Because you build it for exactly the intended purpose, instead of struggling to adapt to it.

Arguably, an ONeill structure could be better than Earth.
 
IIRC the Sci Am article was talking about focussing a TW laser to a 1km diameter laser...
 
whiteyonthemoon said:
The article specifically states that the power source can't be on board, and the use of a Sol satellite to collect (let me guess, those solar panels are 100% efficient) and send (once again, 100% efficient) the energy also implies that the power source won't be on the ship, so the relativistic mass of the ship is the proper one to consider.

You are right though, I don't understand relativity.
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In that case, you realize that the collecting station wont be supplying force, right?

The force will be applied by the energy "beam" or whatever (laser?) .. which will be traveling at the speed of light relative to everything that isnt.

Wavelengths will change based on the relative motion of the emitter to the reciever (red shift) and that will effect efficiency in some manner, but probably not nearly as much as distance will.

The relativistic mass of the ship still shouldn't apply... *shrug*

I would argue that this methodology is flawed. How do you decelerate?
 
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