Author Topic: Constant Acceleration at 1G and Beyond  (Read 59441 times)

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #40 on: 06/27/2014 02:10 AM »

... You are pushing directly against the moon for the whole trip...
...The big problem I see is what sort of beam you can focus on that range?
The big problems I see:
Wont it inflict the opposit push on the moon? How big is it considering the vast amount of energy mentioned before?
Can you point it to the same direction of the traveling ship, while the moon rotates around the earth and sun?

Well the total force, for example to push something the size of a skyscraper at 1g for 40 years, is the same as the force that such a skyscraper would apply to the earth by standing on it. That doesn't prove it is negligible however.

(1) My guess is that it would ultimately balance out and you would just bias the orbit a bit around the sun, but the orbit would remain stable. Ultimately you are pushing against the sun itself.

(2) One case where you could keep aiming in the same direction is if you were launching in a polar direction.

But a moon was just an example. I think such a 'cannon' might have to be extravagantly long depending on what you are launching. It is probably more likely you convert a portion of Mercury's mass into some huge mass driver, perhaps a ring around the sun out to a couple of AU.

The way I see it, you have a choice of two big problems:
(1) if you are launching very small particles, achieving greater final velocities than your manned vehicle are not hard. We easily do that today. However would it be possible to project such a beam with such accuracy as to not require some magical collector on the other end? Ideally it would arrive like merely hot gas and the bottom of the ship could be like a reentry shield.. Or can we come up with such a magical collector on the ship, such as a mini-magnetosphere. Could we exploit gravitational lensing to focus our beam? Could we somehow run a current through the plasma to get a z-pinch?

(2) If you are launching propellant objects of greater size, say fist sized, they could intelligently correct their course so accuracy is not a problem. We could rely on any getting close to safely evaporate as they fly up the vehicle's exhaust. But can you accelerate an object up to such incredible velocities within the solarsystem without destroying it's mechanisms? Also this would make it clear you need something like self reproducing machines to create probably billions of tons of smart propellant, but I personally find this much more acceptable than the assumptions of several other schemes.

The gains are huge:
# Escape the exponential rocket equation.
# No unobtainium at the vehicle end. The problem is comparable to mere chemical propulsion.

Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #41 on: 06/27/2014 04:46 AM »
Well the total force, for example to push something the size of a skyscraper at 1g for 40 years, is the same as the force that such a skyscraper would apply to the earth by standing on it.

Except that the skyscraper also exerts the exact same force in the opposite direction simply by being there, due to a little something called "universal gravitation".  Net thrust is zero.

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #42 on: 06/27/2014 05:12 AM »
Well the total force, for example to push something the size of a skyscraper at 1g for 40 years, is the same as the force that such a skyscraper would apply to the earth by standing on it.

Except that the skyscraper also exerts the exact same force in the opposite direction simply by being there, due to a little something called "universal gravitation".  Net thrust is zero.

Yes thats why I said it doesn't prove it is negligible. Im just guessing a moon's orbit would only be distorted a bit but remain stable, transferring that force to the sun. Maybe someone can confirm one way or another?

..but Im more interested in what you think of the two advantages and two problems I listed. Agree? disagree? Got an improvement? I think this is the right direction to search in.
« Last Edit: 06/27/2014 05:14 AM by KelvinZero »

Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #43 on: 06/27/2014 07:00 AM »
The particle beam idea has unrealistic cooling requirements, for starters.  Otherwise the beam spreads too much over interstellar distances.  A Z-pinch would result in ohmic heating of the beam, and wouldn't it be unstable to perturbations?

I've got to wonder how a fist-sized spacecraft would withstand a dust impact at these speeds...  The Doppler effect also means that once your starship starts moving fast enough to deserve the title, the units have to have been launched in very quick succession, at least if you want them to arrive at no more than several km/s...  How are they steering?  Onboard propellant?  Laser from home?  Both could be problematic...

And if you insist on chemical-like interaction energies between the starship and the beamed propellant, I insist on seeing some calculations regarding how much reaction mass and kinetic energy it takes to pull this off.  Eliminating the rocket equation doesn't automatically mean you're home free...

Personally I don't like beamed propulsion, except perhaps as a short-term boost getting out of system.  To do much better than that, you have to assume monstrously unrealistic infrastructure parameters.  I prefer pulsed fusion plus magsail brake as a baseline, with antimatter as a performance upgrade if available (safely) and Mach effect as a hopeful.  That gives you the nearest stars in less than a century for sure, a couple decades maybe, and just possibly several years.

Speaking of which, everyone's been studiously avoiding mentioning this, but a Mach-effect vehicle with sufficiently advanced thrusters could do 1 gee for an arbitrary period of time, barring mechanical breakdown...  and if M-E works, there's an outside shot at warp drives and wormholes, which basically gives you Star Trek...

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #44 on: 06/27/2014 10:27 AM »
I think we should ban any unaccepted physics from the conversation. I think the point of this thread really is to avoid that. Lets treat it as an engineering problem.

Im not going to justify things like using z-pinch. All I meant was, can we brainstorm some method of directing particles accurately over these vast distances? I can come up with lists of ideas for you to dismiss but I would much rather see you apply some imagination to it.

I accept the point about fist sized craft. I will have to think about that.

Im not sure where you are coming from with cooling issues. Could you expand on that some more? Naively, it seems much easier to consider dealing with such energy levels on a stationary object of arbitrary mass than on your vehicle.. or are you talking about a relationship between temperature and the spread of the beam?

The major point is that beamed propulsion allows you to exploit a velocity squared relationship instead of an exponential one. My position is that you would need and extremely good argument to throw that away. Of course it will beat carrying the fuel with you if you can overcome these niggly problems of actually hitting the craft with the beam. Think harder!

ps: the reaction mass is pretty easy to calculate isnt it! I mean. Take the mass per second of the fuel that passes though a chemical rocket, and multiply that by 40 years or so. That is about the mass your projector has to handle, give or take an order of magnitude, but the velocity of that beam has to keep increasing. I hope it is clear that what I mean by chemical-like includes NTR-like at an extreme end. It is what we can handle without unobtainium.

pps: Pulsed fusion is fine.. but if it were possible to launch those pellets from home, ie exploit beamed propellant, you would have all the same advantages but have converted the fuel requirements from exponential to n^2. When you are talking about interstellar velocities the difference has to be boggling. It just has to be.
« Last Edit: 06/27/2014 10:44 AM by KelvinZero »

Online Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #45 on: 06/27/2014 05:56 PM »
eh; i know that some board member shy away from unproven physics like a vampire back pedalling from a crucifix but what about when this happens?

http://phys.org/news/2014-06-physicist-slower-thought.html

if we got that wrong it shakes settled science to the core. the number of ways the speed of light figures into settled science across many disciplines. the speed of light is in so many theoretical frameworks that if it is wrong most of modern physics is as well; not to mention astronomy and cosmology.

or what about the problem recently discovered WRT dark matter and dwarf galaxies?

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Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #46 on: 06/28/2014 01:24 AM »
or are you talking about a relationship between temperature and the spread of the beam?

It's startling how fast a particle beam spreads out over interstellar distances when it's not really really close to absolute zero.  The beam energy has to be ridiculously high for it to be even a little bit useful at a significant fraction of a light year.

Lasers have a different problem, that boils down to the same thing:  your initial focus has to be unreasonably good for you to be able to get enough of the beam on target for it to be worth it.

Unless, again, you're just using it for boost out of the solar system, like a really big starwisp...

Quote
I hope it is clear that what I mean by chemical-like includes NTR-like at an extreme end. It is what we can handle without unobtainium.

Now you're the one being uncreative.  What's wrong with an electromagnetic receiver/nozzle?  If we can handle beamed-core antimatter with a dozen or so tesla in a modestly-sized device, we should be able to handle just about anything on the scale of an O'Neill-type starship...

And I repeat:  Do the math.  I did.  If you confine yourself to chemical-like interaction energies, the base station requirements in terms of both mass per second and power become utterly silly.  Think about it - if you cap the arrival velocity at 10 km/s, then at just 0.1c, 99.97% of the momentum and 99.99999% of the energy you put into the propellant is simply not seen by the starship at all.  And the mass flow rate, already pretty significant for a 1 gee starship, is multiplied by a factor of 3000 at the base station due to the Doppler effect.  To first order, doubling the arrival velocity cuts your base station mass and energy requirements in half, and quarters the mass flow rate and power requirements, without affecting system performance, and this remains approximately true for increases of more than two orders of magnitude.

That's for a starship moving at a speed attainable by a thermonuclear Orion or Medusa without magsail braking.  At higher speeds it would be worse.

Quote
pps: Pulsed fusion is fine.. but if it were possible to launch those pellets from home, ie exploit beamed propellant, you would have all the same advantages but have converted the fuel requirements from exponential to n^2. When you are talking about interstellar velocities the difference has to be boggling. It just has to be.

Not unless you go to very high speed.  In the vicinity of 0.1c, mass ratios for advanced fusion pulse schemes are in the range of single chemical rocket stages, if not lower, so the savings for using beamed power are modest and not enabling.

...

It could be argued that a reasonably fast pulse unit doesn't add as much boost with the nuclear explosion as it does with its own momentum, so it might be better to just use inert pulse units and crash them into small sacrificial probes from the starship (this is not my idea; it was suggested by another forum member).  This uses modestly more total energy than the slow-arrival/active-package scheme, but could make up for it in increased Isp and better logistics.  Alternately, very precise detonation timing could allow a combination of both and eliminate the sacrificial mass requirement, though a misfire could be bad...

Either way it wouldn't take much of a malfunction for a pulse unit to get slightly off course and smash into the starship...

...

I maintain that beamed propulsion would be best used as a boost to get out of the system fast, supplemented by pulsed fusion for additional speed and complemented by magsail braking on the far end (which also requires pulsed fusion for terminal braking because it only works when you're going fast).  The logistics of doing the whole trip on beamed propellant are too dubious for me.

If antimatter works out, the performance on internal propellant is good enough that the extra effort to add beamed propulsion is likely not worth it.

The Bussard ramjet is of course another possibility, and it does require a boost to get going.  When Bussard was asked about the practical limitations complained about by others, he responded with something along the lines of 'there are plenty of ways to design one so that it doesn't work'...  Some of the calculations do silly things like arbitrarily capping the exhaust velocity without considering energy recovery from the intake stream...

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #47 on: 06/28/2014 03:17 AM »
eh; i know that some board member shy away from unproven physics like a vampire back pedalling from a crucifix but what about when this happens?
Lets just at least shy away from it on this thread. Imagine you called your mates over to help wrestle a piano up a flight of stairs and they sat at the bottom offering suggestions that relied on unproven physics.

Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #48 on: 06/28/2014 03:28 AM »
That's a terrible analogy.

Better: how about if you proposed a maneuver with said piano that would take roughly half an hour and some delicate heavy lifting to get it around a corner or something, and one of your friends suggested an expedient way to do it much more easily that might or might not work, but would take two minutes to check without damaging the piano?

It is extremely likely that M-E will be either a known quantity or a bust long before we'd have the will or resource base, or technology for that matter, to build a conventionally-powered relativistic starship.

If you don't want to discuss it, fine.  But I will point out that it is not your thread.
« Last Edit: 06/28/2014 03:31 AM by 93143 »

Offline A_M_Swallow

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Re: Constant Acceleration at 1G and Beyond
« Reply #49 on: 06/28/2014 03:49 AM »
We may not be able to build constant acceleration spacecraft but by using nuclear power we can come close to constant energy.

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #50 on: 06/28/2014 04:37 AM »
or are you talking about a relationship between temperature and the spread of the beam?
It's startling how fast a particle beam spreads out over interstellar distances when it's not really really close to absolute zero.  The beam energy has to be ridiculously high for it to be even a little bit useful at a significant fraction of a light year.
Quote
I hope it is clear that what I mean by chemical-like includes NTR-like at an extreme end. It is what we can handle without unobtainium.

Now you're the one being uncreative.  What's wrong with an electromagnetic receiver/nozzle?  If we can handle beamed-core antimatter with a dozen or so tesla in a modestly-sized device, we should be able to handle just about anything on the scale of an O'Neill-type starship...

And I repeat:  Do the math.  I did.  If you confine yourself to chemical-like interaction energies, the base station requirements in terms of both mass per second and power become utterly silly.

...

Quote
pps: Pulsed fusion is fine.. but if it were possible to launch those pellets from home, ie exploit beamed propellant, you would have all the same advantages but have converted the fuel requirements from exponential to n^2. When you are talking about interstellar velocities the difference has to be boggling. It just has to be.

Not unless you go to very high speed.  In the vicinity of 0.1c, mass ratios for advanced fusion pulse schemes are in the range of single chemical rocket stages, if not lower, so the savings for using beamed power are modest and not enabling.
...

Either way it wouldn't take much of a malfunction for a pulse unit to get slightly off course and smash into the starship...
...


Interesting about the temperature. I had already assumed focusing a particle beam would be harder than a light beam though. There may be ways around this but none I can justify. The particle example still demonstrates that a single shot can put more velocity into a fragment of mass than your vehicle's ultimate velocity, which is important.

(Off topic, I wonder if light sail proponents ever considered using gravitational lensing to get a better focus?)

Re the magsail. I have thought of that and I expect it would be a vast improvement, and provide a method of stopping. The problem is that the moment I add a single detail people jump on that and use it to dismiss the entire idea if I cannot defend that detail. What I am arguing is a much more general principle that must win out, if certain niggly details can be solved. I dont have all those solutions, but the same can be said for any device that does not exist today.

I accept it would be ludicrous to actually use only chemical levels of energy, for example at your top velocity you would have to project equal mass at that top velocity every few minutes. If we could really do that, it would be far more efficient to collect all that mass arriving at your tail pipe and use it to build a massive craft in flight.. but..

.. remember that the title of this thread is "Constant acceleration at 1G and beyond"!

 I don't think any of what you would call sensible ideas come close to that. Firstly my position is that for such a problem you have to grab the chance of reducing an exponential requirement down to a n-squared one. Secondly, as of today chemical (or at a stretch NTR) are the only demonstrated technology that can generate 1G thrust. It is not at all clear that these higher energy drives will ever achieve this. It is not that you have to stick with chemical, the higher you can go the better, but it means you have these two "points on the graph" where solutions actually exist:

* We can launch mass at a faster velocity than our ultimate vehicle velocity.
* We can achieve 1G sustained acceleration with this approach.

On an independent topic, I would also like to argue projected propellant would also aid any reasonable plan but we would have to define the parameters for that.

(edit)
There would be a limit to the velocity at which this could support continual acceleration. I guess I should try and come up with a guess for that.
« Last Edit: 06/28/2014 04:49 AM by KelvinZero »

Online KelvinZero

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Re: Constant Acceleration at 1G and Beyond
« Reply #51 on: 06/28/2014 04:59 AM »
If you don't want to discuss it, fine.  But I will point out that it is not your thread.
Ok and thanks :)

On far out topics, I quite like the notion that you could lower the mass of an object while keeping its structure, perhaps related to those zero point energy experiments with plates etc. I don't have any reason to believe this is possible, but so long as this mass is transferred somewhere, you are not violating any laws.

Offline 93143

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Re: Constant Acceleration at 1G and Beyond
« Reply #52 on: 06/28/2014 05:29 AM »
.. remember that the title of this thread is "Constant acceleration at 1G and beyond"!

 I don't think any of what you would call sensible ideas come close to that.

Fair point.

Online Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #53 on: 06/28/2014 07:03 AM »
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
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Offline IslandPlaya

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Re: Constant Acceleration at 1G and Beyond
« Reply #54 on: 06/28/2014 10:47 AM »
In a vacuum photons will spread due to their 'temperature'
I don't know when this becomes an issue wrt to beamed power.
I'm sure it is an issue however.

Offline RanulfC

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Re: Constant Acceleration at 1G and Beyond
« Reply #55 on: 06/30/2014 12:48 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

Particle beams (charged and neutral), lasers, etc all have some issue in space but I keep having to go back and refer to my "source" since I keep getting what works best where wrong...
http://www.projectrho.com/public_html/rocket/spacegunconvent.php

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British physics, old chap. It's undignified to belch flames and effluvia all over the pad, what. A true gentlemen's orbital conveyance lifts itself into the air unostentatiously, with the minimum of spectacle and a modicum of grace. Not like our American cousins' launch vehicles, eh?

Online Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #56 on: 07/01/2014 03:09 AM »
get out your crucifixes! ;)

http://physicsworld.com/cws/article/news/2014/jun/26/dwarf-planet-could-illuminate-the-dark-sector

Synopsis: a testable alternative theoretical model that allows for anti-gravity, does away with the need for dark matter, inflation and other more standard concepts.

Antigravity iz reel!

Noooooes! arrrgh!
When antigravity is outlawed only outlaws will have antigravity.

Offline IslandPlaya

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Re: Constant Acceleration at 1G and Beyond
« Reply #57 on: 07/01/2014 10:09 PM »
get out your crucifixes! ;)

http://physicsworld.com/cws/article/news/2014/jun/26/dwarf-planet-could-illuminate-the-dark-sector

Synopsis: a testable alternative theoretical model that allows for anti-gravity, does away with the need for dark matter, inflation and other more standard concepts.

Antigravity iz reel!

Noooooes! arrrgh!
Great science! Let's test it! Hopefully it or something like it can do away with the the Rube-Goldbergesque current theories.

Offline Lampyridae

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Re: Constant Acceleration at 1G and Beyond
« Reply #58 on: 07/02/2014 06:31 AM »
get out your crucifixes! ;)

http://physicsworld.com/cws/article/news/2014/jun/26/dwarf-planet-could-illuminate-the-dark-sector

Synopsis: a testable alternative theoretical model that allows for anti-gravity, does away with the need for dark matter, inflation and other more standard concepts.

Antigravity iz reel!

Noooooes! arrrgh!

Even if there is a discrepancy in precession, this only means the theory is one of many possibilities.

Exciting new physics, like vampires, tend to vanish in a puff of smoke in the light of day.

But even current physics gives us some clues as to possible new engine designs. The new antimatter nozzle was a matter of a simple conceptual design. Perhaps we will figure out how to collect and fuse dark matter, giving us a true Bussard ramjet, or just figure out a way to make the Bussard ramjet work.
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Online Stormbringer

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Re: Constant Acceleration at 1G and Beyond
« Reply #59 on: 07/02/2014 06:39 AM »
i found a really weird one.  :D dunno if i should even post it. but it's about electrostatic force fields. i mean "invisible wall of force" type science fantasy fiction style force fields. apparently (or perhaps allegedly) 3M accidentally made one in one of their factories. There is an extremely high giggle/Ko0k factor on this one... but i'm thinking cargo/shuttle bay open to hard vacuum but shirt sleeve environment any way type applications :)
When antigravity is outlawed only outlaws will have antigravity.

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