Author Topic: Constant Acceleration at 1G and Beyond  (Read 99949 times)

Offline luinil

Re: Constant Acceleration at 1G and Beyond
« Reply #60 on: 07/03/2014 07:10 am »
Even if this is very interesting, I thing that solving constant 1G acceleration for interplanetary transport need to be solved before talking of 1G constant acceleration for interstellar transport

Offline cordwainer

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Re: Constant Acceleration at 1G and Beyond
« Reply #61 on: 07/03/2014 08:15 am »
With the term beamed propulsion one can make the point that if you are using ion beams then the propellant is "chemical". I believe the current limit for G-forces is up to around hundreds of G's for short durations with current technology. Charged particle beams do have trouble propagating in a vacuum but can still travel hundreds of thousands of kilometers if I'm not mistaken. Also, if you use an electron particle beam for the propulsive beam you can accelerate an object rather briskly so you wouldn't need to focus your beam over a long distance to high fractions of c. Several beams stationed in a track would be sufficient. The issue would be preserving the crew from the radiation of the particle beam and protecting them from the high g-forces.

Beamed propulsion could also be used to accelerate other propulsion beam "cannons" or chemical propellant depots along the path of the your space-crafts flight. Looking and Gerald Nordley's paper using a an electromagnetic launcher of beam drive to launch SRB's or low velocity beam riders similar to ion or helicon thrusters would allow a gentle acceleration of a vehicle at .01 c for a considerable amount of time and would be well within our current technology to build.

If the above figures stated our true then 21% the speed of light might be possible with the right materials technology and design to keep your ship from being destroyed by collision with the interstellar medium at those speeds.

Of course we could go with the constant 1G or higher but to do that with current technology we would need to build a chemical rocket so large that if built in LEO it's shadow would blot out the Sun for a small portion of the Earth's surface, it would also probably take at least a few decades or even scores of years to build and would tie up human launch capability for years to come. Building a gravitational mirror and/or EM launcher would not require nearly as much material and could be used to expand transportation to other places within the solar system rather than just a one-off vehicle for interstellar travel.

Offline cordwainer

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Re: Constant Acceleration at 1G and Beyond
« Reply #62 on: 07/03/2014 09:25 am »
Also, fusion and anti-matter is not "unproven physics" rather as methods of propulsion and power generation they are unproven engineering. Mag-sails actually work they just aren't as efficient as we would like them to be for the purposes of "mag-beam" propulsion.

On the other hand we don't even have a working fusion reactor yet and if we had one it would still be more efficient in terms of thrust to mass ratio for interstellar travel to probably use something like Focus Fusion to generate a charged particle beam for beam propulsion purposes. Fusion is great for interplanetary distances but you need to stretch your fuel paycheck even more for interstellar distances. 

We could build a probe sized vehicle powered by an anti-matter sail but the costs to produce enough antimatter for an interstellar flight of such a vehicle would be pretty high.(although, perhaps not insurmountably so)

Offline KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #63 on: 07/03/2014 12:05 pm »
I believe I have read that in space keeping a particle beam together is harder than a laser. in an atmosphere the bloom of a particle beam is partly mitigated by the surrounding atoms and molecules of the atmosphere. in space the electrical charges of the particles in the beam will repel each other and the beam will spread out. However i have also read an article some time back about a lab successfully creating a magnetically jacketed plasma in which case the particle beam could conceivably be kept together by such a jacket.

http://www.sciencedaily.com/releases/2013/04/130416151931.htm

Cool! Found this version which has a movie:
http://munews.missouri.edu/news-releases/2013/0415-plasma-device-developed-at-mu-could-revolutionize-energy-generation-and-storage/

I was thinking of a few ideas like this. Perhaps the goal should not be to create a plasma ring that remains compact across from projector to ship but instead a very faint, very large plasma lens halfway between the projector and the ship. One thing you will have in abundance is space! My guess is that at best the particles would not converge back to a single point but more of a line along the axis, but a collector extended along an axis would be far less massive than a collector disk of similar scale. (I haven't thought much about what configuration such a lens would require, let alone its shape evolving correctly during the ships entire flight.)

Offline Nomadd

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Re: Constant Acceleration at 1G and Beyond
« Reply #64 on: 07/03/2014 04:21 pm »
Even if this is very interesting, I thing that solving constant 1G acceleration for interplanetary transport need to be solved before talking of 1G constant acceleration for interstellar transport
Very rough math I tried to do in what's left of my brain, but, at closest approach, I'm getting a little less than two days to Mars (including slowing back down) at 1g.
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Offline Hanelyp

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Re: Constant Acceleration at 1G and Beyond
« Reply #65 on: 07/03/2014 04:56 pm »
I was thinking of a few ideas like this. Perhaps the goal should not be to create a plasma ring that remains compact across from projector to ship but instead a very faint, very large plasma lens halfway between the projector and the ship. One thing you will have in abundance is space! My guess is that at best the particles would not converge back to a single point but more of a line along the axis, but a collector extended along an axis would be far less massive than a collector disk of similar scale. (I haven't thought much about what configuration such a lens would require, let alone its shape evolving correctly during the ships entire flight.)
There are magnetic and electric ion and electron lenses.  But the designs I've seen are sensitive to particle charge/mass ratio and energy.  Making a system that can focus the ion and electron components of a plasma beam to a common point strikes me as likely non-trivial.

Offline meekGee

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Re: Constant Acceleration at 1G and Beyond
« Reply #66 on: 07/03/2014 05:23 pm »
It strongly suggests we are entirely alone, or worse, the unknown hurdle is still before us and our chances of surviving to achieve 1000th of c. are very slim indeed.

That involves quite a few assumptions...

-maybe most intelligent species are in environments where developing spaceflight tech is unlikely (say, the majority of living worlds are Europa/Enceladus type, under ice, and they never even learn that space exists) or lack hands (say, dolphins or ravens or parrots become sapient instead of primates)

-or, maybe developing significant technology is simply rare (most of the human race's history was spent as hunter-gatherers)

-or, maybe most intelligent species don't have a 'drive to explore' and never get beyond the continent they originated on, much less into space

IMO we don't even know enough for the "Fermi Paradox" to be a meaningful problem.

EDIT: also, I don't think having the technology for interstellar travel implies exponential expansion through the galaxy, by a long shot. We aren't really colonizing the oceans or turning them into giant farms (eg Arthur C Clarke's "The Deep Range") though we totally could, or trying to turn the deserts into farmland, etc. --- because agricultural technology has more than kept pace with population growth*, and population densities are becoming higher with urbanization. We don't really need more room. Moon or Mars colonization will be driven "because it's there" if it happens IMO, by people like Elon Musk who are visionaries, rather than by pure economics.

*And most first world nations have below replacement birthrates, the 'demographic transition'. So assuming exponential growth for high tech civilizations doesn't seem supported by the one example we have - ourselves.

EDIT x2: Also, the universe is huge. Even if we really are the only sapient species in the galaxy or the Local Group, there could still be a huge number total (universe-wide). At say 1% of c there might not have been time to colonize from distant galaxy clusters.

True.

Maybe (and that's quite an assumption!) 99% of all intelligent species are trapped under ice or otherwise barred from expanding forth.

But if even one (not 1%....  1ea!) gets out, and starts populating the galaxy using a travel speed of 0.001c (and either multi-generational ships, seed ships, etc) then that species wins the game within a few hundreds of Millions of years.

More than we spent on that little evolutionary detour called "Dinosaurs".

And as far as we can tell, nobody still has.   So either we're first, or at least we're not lagging by more than a few hundreds of Millions of years.  Or there's a galactic ghoul, as some have speculated.

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Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #67 on: 07/03/2014 07:06 pm »
Even if this is very interesting, I thing that solving constant 1G acceleration for interplanetary transport need to be solved before talking of 1G constant acceleration for interstellar transport
Very rough math I tried to do in what's left of my brain, but, at closest approach, I'm getting a little less than two days to Mars (including slowing back down) at 1g.

Yeah, between ~2 and ~5 depending on orbital phase with Earth IIRC.

IOW, you don't need to wait for closest approach...

Offline Mark K

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Re: Constant Acceleration at 1G and Beyond
« Reply #68 on: 07/03/2014 07:48 pm »
Geoffrey Landis did wonderful simulations decades ago in the BIS Journal I believe, and showed that if the expansion phase for civilizations were  a few million years there could be many of them in the galaxy that we haven't seen.  The Fermi 'paradox' is an ill posed statement that assume constants for things like species lifetimes and interest in expansion that there is no good reason to assume are infinite. There is no reason  to think our assumption should be anywhere near what it that paradox would need it to be.

In regard to 1 G constant acceleration for large > 1000 hours there is currently no technology that we know how to build or even have an idea of how to do that could give that. Even nuclear bomb propulsion would have mass requirements at the start that we don't have a clue how to deal with. There no knowledge we have that would allow us to keep anti-matter at a density that would even approach what would be needed. We don't know if we could do it physically.

It isn't like super-luminal speeds where we have a theory that would need to be altered to allow it, but the energy considerations imply a "magical" technology at this time and there is no path we are pursuing that is making the time where we would have an answer any closer in a noticable way. This is even ignoring the relativistic issues of particle and dust collisions.

0.01 G is different, but the Subject does say 1 G constant acceleration.

Offline Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #69 on: 07/03/2014 08:12 pm »
Also, fusion and anti-matter is not "unproven physics" rather as methods of propulsion and power generation they are unproven engineering. Mag-sails actually work they just aren't as efficient as we would like them to be for the purposes of "mag-beam" propulsion.

On the other hand we don't even have a working fusion reactor yet and if we had one it would still be more efficient in terms of thrust to mass ratio for interstellar travel to probably use something like Focus Fusion to generate a charged particle beam for beam propulsion purposes. Fusion is great for interplanetary distances but you need to stretch your fuel paycheck even more for interstellar distances. 

We could build a probe sized vehicle powered by an anti-matter sail but the costs to produce enough antimatter for an interstellar flight of such a vehicle would be pretty high.(although, perhaps not insurmountably so)
well i read an article a few months ago about a new record of antimatter production and a scheme to provide antimatter samples to (off the production site) labs around the world as a result. it turns out the "trillions of dollars per gram" thing is bunkum. one of these production machines can do a gram a year. and these things are small. like nearly refrigerator sized. so there is no reason not to have hundreds or thousands of them.
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Offline KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #70 on: 07/03/2014 09:25 pm »
There are magnetic and electric ion and electron lenses.  But the designs I've seen are sensitive to particle charge/mass ratio and energy.  Making a system that can focus the ion and electron components of a plasma beam to a common point strikes me as likely non-trivial.
And that is before we even consider how the beam evolves the shape of the lens
Im speaking waaaay beyond my experience level here, but Im not sure any scheme may be able to focus back to a point. It might be enough to focus back to the axis and then have a very long one dimensional collector, which would be much less mass than a two dimensional collector like a sail.

The other direction to search is, can you get any tiny object (smart enough to correct its own course) up to velocity greater than your human craft's final velocity, in a single 'shot' from within the solar system

Offline Nomadd

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Re: Constant Acceleration at 1G and Beyond
« Reply #71 on: 07/03/2014 10:26 pm »
well i read an article a few months ago about a new record of antimatter production and a scheme to provide antimatter samples to (off the production site) labs around the world as a result. it turns out the "trillions of dollars per gram" thing is bunkum. one of these production machines can do a gram a year. and these things are small. like nearly refrigerator sized. so there is no reason not to have hundreds or thousands of them.
Nonsense. Nothing on the boards could even dream of producing a gram of anti-matter.
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Offline Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #72 on: 07/03/2014 10:40 pm »
well i read an article a few months ago about a new record of antimatter production and a scheme to provide antimatter samples to (off the production site) labs around the world as a result. it turns out the "trillions of dollars per gram" thing is bunkum. one of these production machines can do a gram a year. and these things are small. like nearly refrigerator sized. so there is no reason not to have hundreds or thousands of them.
Nonsense. Nothing on the boards could even dream of producing a gram of anti-matter.

back of the napkin type calculations said such a production rate was possible with this new technique.
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Offline Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #73 on: 07/03/2014 10:59 pm »
here is the article:

http://phys.org/news/2014-05-scientists-year-quest.html

and what i said about it in another forum will follow. now i probably cannot find where the 1 gram figure came from because i don't remember the forum where the discussion was held (its different from where i am posting the bellow quote) but elsewhere some thread participants posted calculations showing the quantities that could be produced.

Quote

    Holy Poop! i don't know how i missed the most significant implication of this whole story!

    the number of positrons made per shot? 6 orders of magnitude more antimatter production than the previous record. back of the napkin calculations seem to indicate that with the extremely short pulse lasers you could potentially create over a gram a year with just one machine.

    EDIT! actually thats not a year! it a little over a minute to make a gram and just short of a year to make enough to power up an alcubierre warp drive.

    now that assumes that a quadrillionth of a second laser pulse would produce the same number as the pulses they used in this experiment. but if so...

    you know... there are some antimatter propulsion schemes that can do an entire mission on as little as one nanogram. for example AIMSTAR and ICAN proposals for hybrid systems. these schemes have been proposed for trips to the outer planets and as far out as the Oort cloud on a nanogram or a microgram of antimatter.

    Last edited by Darkblade; May 21st, 2014 at 7:00 pm.
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Offline IslandPlaya

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Re: Constant Acceleration at 1G and Beyond
« Reply #74 on: 07/03/2014 11:17 pm »
here is the article:

http://phys.org/news/2014-05-scientists-year-quest.html

and what i said about it in another forum will follow. now i probably cannot find where the 1 gram figure came from because i don't remember the forum where the discussion was held (its different from where i am posting the bellow quote) but elsewhere some thread participants posted calculations showing the quantities that could be produced.

Quote

    Holy Poop! i don't know how i missed the most significant implication of this whole story!

    the number of positrons made per shot? 6 orders of magnitude more antimatter production than the previous record. back of the napkin calculations seem to indicate that with the extremely short pulse lasers you could potentially create over a gram a year with just one machine.

    EDIT! actually thats not a year! it a little over a minute to make a gram and just short of a year to make enough to power up an alcubierre warp drive.

    now that assumes that a quadrillionth of a second laser pulse would produce the same number as the pulses they used in this experiment. but if so...

    you know... there are some antimatter propulsion schemes that can do an entire mission on as little as one nanogram. for example AIMSTAR and ICAN proposals for hybrid systems. these schemes have been proposed for trips to the outer planets and as far out as the Oort cloud on a nanogram or a microgram of antimatter.

    Last edited by Darkblade; May 21st, 2014 at 7:00 pm.
Producing anti-matter at 1 gram per minute would allow you to create a 43 kiloton bomb every minute.
At least 6×10^12 W of power would be required to do this assuming 100% conversion efficiency. That's 6 TW!
I can't imagine this to be feasible.
Well, I certainly hope it's not feasible for all our sakes...  :'(
« Last Edit: 07/03/2014 11:30 pm by IslandPlaya »

Offline aero

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Re: Constant Acceleration at 1G and Beyond
« Reply #75 on: 07/03/2014 11:54 pm »
Interesting.

This one is interesting, too.

http://nextbigfuture.com/2013/08/billionaire-peter-thiel-funds-positron.html

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Offline QuantumG

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Re: Constant Acceleration at 1G and Beyond
« Reply #76 on: 07/04/2014 12:06 am »
Neat.

Quote
Physicists Dr. Ryan Weed and Joshua Machacek conceived of a company that would enhance positron production and storage technologies during their doctoral research at the Australian National University. Bala Ramamurthy, Dr. Sean Casey and Mike Barrucco – engineers with experience in aerospace engineering projects, scientific equipment development and project management joined the Positron Dynamics team in 2012. Breakout Labs, part of the Thiel foundation, provided initial funding for their efforts in 2012. Positron Dynamics has patents in positron moderation techniques.

http://positrondynamics.com/

Their front page is a blog that hasn't been updated since November last year. :(

Seems they're based in Seattle. The CEO is a pilot in the USAF.

Mike Barrucco is an engineer at SpaceX.
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Offline KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #77 on: 07/04/2014 01:48 am »
We could probably start another thread just on the feasibility of storing useful amounts of this stuff. I guess something like an artificial magnetosphere would be too leaky?

(but again.. beamed propulsion to the rescue! That largely avoids the problem of storage)

Offline Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #78 on: 07/04/2014 04:58 am »
well to be fair...antimatter would definitely fill the requirement of the OP. so would mature fusion engine technology.
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Offline Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #79 on: 07/04/2014 05:11 am »

Producing anti-matter at 1 gram per minute would allow you to create a 43 kiloton bomb every minute.
At least 6×10^12 W of power would be required to do this assuming 100% conversion efficiency. That's 6 TW!
I can't imagine this to be feasible.
Well, I certainly hope it's not feasible for all our sakes...  :'(

well with antimatter you cannot get better than 50 percent conversion efficiency (absent some sort of "magic"  unknown physics based converter technology) so you have to automatically double your energy requirements. that's before you get into normal constraints on efficiency.
When antigravity is outlawed only outlaws will have antigravity.

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