### Author Topic: Constant Acceleration at 1G and Beyond  (Read 59269 times)

#### cjackson

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##### Constant Acceleration at 1G and Beyond
« on: 06/20/2014 04:50 AM »
Exactly what kind of technological leap and how much energy would be needed to accelerate/decelerate at 1g on a trip to another star system? I understand that, barring wormholes, constant 1g acceleration is the only way to achieve relativistic effects and get a spacecraft across significant distances in a human lifetime as measured aboard the spacecraft.

#### scienceguy

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #1 on: 06/20/2014 05:05 AM »
OK lets see. Say the craft has a mass of 10^4 kg. To accelerate at 1 G you need F = ma = (10^4 kg)(10 m/s^2) = 10^5 N. To get a force of 10^5 N over 10^16 m (10 ly), you would need (10^5 N)(10^16 m) = 10^21 J. Antimatter is the most energy dense material we know. To get that from antimatter you would need m = E/c^2 = 10^21 J/10^17 m^2/s^2 = 10^4 kg. Therefore your entire ship would have to made out of antimatter and react with some extra matter to propel itself at 1 G.
e^(pi*i) = -1

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #2 on: 06/20/2014 08:38 AM »
constant 1g acceleration is the only way to achieve relativistic effects and get a spacecraft across significant distances in a human lifetime as measured aboard the spacecraft.

Not really. I'd settle for measly 0.1g

#### john smith 19

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #3 on: 06/20/2014 10:29 AM »
In space 1g is actually a very high acceleration.

I cannot say about getting to the next star system but just to travel to say Saturn (about 30 AU) is a serious struggle.

What I have seen was a NASA study on a theoretical fusion ship to Saturn. In there the key metric to get to Saturn in < 1 year was that you needed to exceed the suns gravity at the Earths orbit.

The figure they gave for this was 0.6 milli g. It was stated above that the standard transfer ellipse orbits collapse to straight lines.

Maintaining such an acceleration over time is the tough part, but it's 1/1666x easier than 1g.

I'll leave others to comment if this problem is that much easier IRL.
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##### Re: Constant Acceleration at 1G and Beyond
« Reply #4 on: 06/20/2014 11:01 AM »
constant 1g acceleration is the only way to achieve relativistic effects and get a spacecraft across significant distances in a human lifetime as measured aboard the spacecraft.

Not really. I'd settle for measly 0.1g
I'm trying to do math in my head here. That would make for something like 12 years to get to Alpha Centauri, assuming you didn't want to blow through the system at .95C?
The difficulty of relativistic travel tends to be underestimated. Look at it this way. To get to the speed where time travels half as fast for the ship, you also end up doubling the mass of the spacecraft. That extra mass has to be paid for somehow. It's paid for by the energy you impart to the ship through acceleration. If you accelerated that ship by imparting energy from the outside with a perfect, 100% efficient system, you'd have to turn a kilo  of matter into pure energy with no losses for every kilo you increased the ships mass.
And it's much worse with a self contained rocket. You also need to accelerate the fuel that you haven't used yet.
So, it comes down to, to accelerate to a speed where time for the ship is 10% that measured by someone standing still and slow down again once you reach your destination, you'd need the most perfect imaginable system (with today's physics) and spend 99.99% of your initial mass to do it.
Anything better will need more than technology. It will take different physics than we understand now.
« Last Edit: 06/20/2014 11:23 AM by Nomadd »

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #5 on: 06/20/2014 11:44 AM »
I think three big parts of the solution could be
* Beamed power and reaction mass.
* Exploiting a LOT of solar energy.
* Self replicating machines to build stupendously large infrastructure.
eg, eat mercury to create a massive swarm of solar powered lasers, particle beams, or something like that.

The power/propellant you would need to beam from the sun would have to keep increasing, but this could also mean that you can launch before your array is at full strength.

... but there is plenty to do in this solar system before worrying about the next one. There are about 100,000 rocks > 50km in diameter, and each of those has a volume of about 3000 manhattans.. Also there were 178 episodes of Seinfeld. Thats enough room for 5.3 billion episodes of Seinfeld.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #6 on: 06/20/2014 12:00 PM »
constant 1g acceleration is the only way to achieve relativistic effects and get a spacecraft across significant distances in a human lifetime as measured aboard the spacecraft.

Not really. I'd settle for measly 0.1g
I'm trying to do math in my head here. That would make for something like 12 years to get to Alpha Centauri

At 1g, you get to relativistic speed in about 1 year.
At 0.1g, you won't even reach relativistic speeds on a a Cen trip (4.37ly). So, it'll take several times longer than 4.37 years to reach it.
Farther destinations would not take much longer, since relativistic time dilation would kick in. I estimate you can reach Milky Way core under 100 years of ship time.

BTW, I think 12 years to a Cen is very good. Fantastically short, in fact.
Most of today's astronauts waited longer than that to get to LEO!

#### aceshigh

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #7 on: 06/21/2014 11:08 PM »
what about Bussard Ramjet. Couldnīt it provide enough fuel mass for fusioning your way to another star system at constant 1g acceleration?

#### Burninate

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #8 on: 06/21/2014 11:39 PM »
Exactly what kind of technological leap and how much energy would be needed to accelerate/decelerate at 1g on a trip to another star system?
The entire time?  A big one.  A lot of energy.

Ignoring the rocket equation, in kinetic energy alone, to accelerate 1000 tons at 1G for 1 *month*, you would need about the same amount of energy as the human race consumed through all sources in 2013 - or around 400 terawatts of power.  That gets you to about 0.1C.  Somewhere around this point, interstellar gas starts to become dangerous ionizing radiation, and interstellar dust molecules become bullets.

Quote
I understand that, barring wormholes, constant 1g acceleration is the only way to achieve relativistic effects and get a spacecraft across significant distances in a human lifetime as measured aboard the spacecraft.
No, there's nothing *special* about 1G, that's just the default number for some science fiction scenarios because it provides a nice non-rotating habitable acceleration frame for the colony of humans on their magical schoolbus to the end of the universe.  Ignore them, as a practical matter.  Also ignore FTL, at least until a physicist demonstrates some theoretical principle under which it might work.

Interstellar craft are such an enormous engineering challenge that it is entirely possible that human flesh will never be a cargo, because by the time we develop the resources for it, humanity will be living in the cloud as uploads.  Controlled human cryogenic hibernation is a fairly reasonable expectation next to the implausibility of interstellar craft.  If we never get that, generational ships are the only option - propelled by extremely high ISP nuclear engines, which thrust at a small fraction of 1G (likely < 1 milli-G) for the entire mission, turning around at some point to match velocities.  We have some of these ideas down on paper, like the fission fragment rocket and nuclear pulse propulsion - but they're just paper designs for now.  We likely wouldn't launch even an unmanned probe-class mission to another star until we have invested perhaps 10,000 times as many resources in spaceflight, as we have up to this point - and a self sufficient manned mission is going to be still several orders of magnitude harder.  The solar system is a big place, and we have many generations of mission concepts yet to be invented before we start leaving it.

what about Bussard Ramjet. Couldnīt it provide enough fuel mass for fusioning your way to another star system at constant 1g acceleration?

Basically anything you or I can come up with that is definitely physically possible is likely to be 'necessary but not sufficient' - for example it might be the case that we'd never get to 0.001G without a Bussard Ramjet to provide motive mass without increasing initial mass up to intractable amounts.  1G is really a very large number.  But these kinds of questions are so far in the future as to not be worth qualifying.
« Last Edit: 06/21/2014 11:51 PM by Burninate »

#### Greg Hullender

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #9 on: 06/22/2014 12:19 AM »
Since no one else seems to have run the numbers, let me do that.

First, assume 1g acceleration from Earth halfway to Alpha Centauri and then 1g deceleration from there to the target. Total distance: 4.3 light-years.

Ship time: 3.6 years
Earth time: 5.9 years
Peak velocity: 95% c

Same thing but at 0.1g

Ship time: 12.7 years
Earth time: 13.6 years
Peak velocity: 57% c

Again, but at 0.01g

Ship time: 40.7 years
Earth time: 41.0 years
Peak velocity: 21% c

Now suppose you want to go exactly 27,000 light-years to the galactic core. I'll only do the 1g figures

Ship time: 19.8 years
Earth time: 27,002 years
Peak velocity about 77 cm/sec less than c.

Assuming a perfect anti-matter drive (exhaust is light-speed and all in the right direction), then the mass fraction for the 1g trip is 39.5. That is, for every kilo of payload delivered to Alpha Centuri, you would need 38.5 kilos of fuel (half matter and half antimatter).

For the 0.1g trip, that falls to 3.7 and it's only 1.5 for the 0.01g trip.

For the trip to the galactic core, it's about 777 million, so funding may be difficult. :-)

Source for formulas: http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html
« Last Edit: 06/22/2014 12:26 AM by Greg Hullender »

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #10 on: 06/22/2014 02:05 AM »
Might be going rather off topic, but despite the mind boggling difficulty of interstellar travel when viewed in a single human lifetime, When considering the search for extraterrestrials the troubling problem is how mindboggly easy it appears.

Even at a thousandth of c. an exponentially growing civilization should have been able to colonize every star in the galaxy about a hundred times over. The time to stop and colonize each world become irrelevant due to the rapidly growing number of worlds willing to engage in the next wave.  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.

#### Vultur

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #11 on: 06/22/2014 08:09 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.
« Last Edit: 06/22/2014 08:18 PM by Vultur »

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #12 on: 06/23/2014 07:04 AM »
That involves quite a few assumptions...
Not really, you are just pointing out all the ways we might be a special case. Of course we could be, but we are unlikely to be. Postulating we are 'alone' does not make us a special case because that is just postulating the average distance between species is some large value. Anyway Im pulling this off topic. I will continue it in another thread if you want to start it.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #13 on: 06/23/2014 08:38 AM »
Might be going rather off topic, but despite the mind boggling difficulty of interstellar travel when viewed in a single human lifetime, When considering the search for extraterrestrials the troubling problem is how mindboggly easy it appears.

Even at a thousandth of c. an exponentially growing civilization should have been able to colonize every star in the galaxy about a hundred times over. The time to stop and colonize each world become irrelevant due to the rapidly growing number of worlds willing to engage in the next wave.  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.

The hurdle may be already behind us: maybe the appearance of *sentient* (or even just multicellular) life is very rare.

On Earth, it took less than 1 billion year after planet's creation for life to appear. And the environment was quite a bit harsher than now, maybe we should count from Late Heavy Bombardment? Then first life appeared even faster after that event.

But then it took almost 3 billion years for multicellular organisms to appear. It might have been a fluke!

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #14 on: 06/23/2014 03:53 PM »
multi cellular...fluke. Haaaa!
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##### Re: Constant Acceleration at 1G and Beyond
« Reply #15 on: 06/23/2014 04:17 PM »
Somebody has to be first. Might as well be us.

#### kevin-rf

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #16 on: 06/23/2014 04:20 PM »
The Fluke might be as simple as Mitochondria and Chloroplasts.

There is a train of thought that they are a bunch of bacteria that ended up being absorbed by large single cell organisms and instead of being digested wound up in a symbiotic relationship with the larger parent single cell organism.

In the case of of plants, Chloroplasts (Plant photosynthesis engines) may have evolved from the symbiotic relationship between the larger cell and cyanobacteria (Which evolved into Chloroplasts).

The odds of single cell life evolving may not be that low, but the odds of single cell organisms absorbing and then entering into symbiotic helper relationships with other single cell organisms that then allow for large multi-cellular organisms may be very, very, low.

See Endosymbiotic Theory: http://en.wikipedia.org/wiki/Endosymbiotic_theory
« Last Edit: 06/23/2014 04:22 PM by kevin-rf »
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#### Vultur

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #17 on: 06/24/2014 01:28 AM »
The odds of single cell life evolving may not be that low, but the odds of single cell organisms absorbing and then entering into symbiotic helper relationships with other single cell organisms that then allow for large multi-cellular organisms may be very, very, low.

Why should it be though?
It happened at least twice on Earth (mitochondria and chloroplasts) and organelles also get traded (the sea slug Elysia chlorotica has stolen chloroplasts from algae).

I think the origin of life (which we know basically nothing about -- there are hypotheses but testing them is incredibly difficult to impossible -- even if we could synthesize life from base chemicals in a lab, it wouldn't mean that's how it happened naturally) or the origin of intelligence is a much more likely point than the jump from single-celled to complex life.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #18 on: 06/24/2014 09:02 AM »
Going waaay off topic guys. Sorry if I started this. I think constant acceleration at 1g is a nice well defined problem despite the various reasons we probably wouldnt attempt it.

On topic, it could be worth noting that constant 1g acceleration would be pretty easy for a standard chemical rocket if there where depots strung out at just the right positions and velocities ahead of it.. of course that just pushes the problem onto how to get the depots there, but perhaps you have more options for unmanned depots than for a crewed ship. They could be shot with massive acceleration or take centuries to align.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #19 on: 06/24/2014 09:28 AM »
Somebody has to be first. Might as well be us.

Sure. Somebody has to be first. That's not what puzzles people in this regard.

The apparent contradiction is that Universe is 13 billion years old already and we don't see aliens coming to Solar System.
Our Galaxy has 100s of billions of stars, and there are many more galaxies close by. Why none developed starfaring civilization when evidently Earth needed only 4.5 billion years to get there? (almost. give us ~500 more years!)
There has to be a reason for that.

#### Bob Shaw

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #20 on: 06/24/2014 09:40 AM »
Might be going rather off topic, but despite the mind boggling difficulty of interstellar travel when viewed in a single human lifetime, When considering the search for extraterrestrials the troubling problem is how mindboggly easy it appears.

Even at a thousandth of c. an exponentially growing civilization should have been able to colonize every star in the galaxy about a hundred times over. The time to stop and colonize each world become irrelevant due to the rapidly growing number of worlds willing to engage in the next wave.  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.

Absolutely correct, sadly. Even assuming a wholly robotic, Von Neuman machine civilisation or post-Singularity ex-biological one (is there a difference?), it takes a reasonably short time to colonise an entire galaxy with rather slow ships. If you can colonise a galaxy, then you almost certainly manipulate the environment, increasing dust, decreasing dust, changing the percentage of stars with high metallicity, altering stellar rotation rates, emitting gravity wave signals and so forth. All these signs and portents can be observed at great distances, but to the best of my knowledge there are no results from astronomical observations of galaxies which suggest any statistical outliers liable to be the relics of distant civilisations. Such signs would be distant in both time, and space, and with a spread right across the development of the universe, too - our 'local' searches are not just local in terms of nearby stars, but are also recent in terms of time and so see only a tiny slice of the history of our own neighbourhood. In short, to seek out civilisations you have to look to the past, and far away for their lights and industrial wastes - and nothing has been seen.

Life, though, is a different matter. Were I a betting man, I'd lay money on life being everywhere. And I can easily extend that to the detection of life in the nearish future. The trouble is, it won't be big critters with eyes, brains and fur (or whatever) but will instead be the perfect life-form, highly adapted to its environment and really quite advanced. Well, advanced for slime, anyway...

So: no signs of relict industry across the observable universe, no signals locally, and lots of slime everywhere. Multi-cellularism may well be a real rarity, and us guys rarer still.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #21 on: 06/24/2014 09:53 AM »
I think constant acceleration at 1g is a nice well defined problem despite the various reasons we probably wouldnt attempt it.

On topic, it could be worth noting that constant 1g acceleration would be pretty easy for a standard chemical rocket if there where depots strung out at just the right positions and velocities ahead of it.. of course that just pushes the problem onto how to get the depots there, but perhaps you have more options for unmanned depots than for a crewed ship. They could be shot with massive acceleration or take centuries to align.

Isp is WAY too low.
The total mass of chem depots needed even for a small craft to reach any sort of interstellar-class speed is not feasible. Billions of tons.

If you have to have high accel, how about electromagnetic acceleration a-la maglev/railgun.

For a fixed length track and acceleration, final velocity is:
v = sqrt(2*a*l)

At a=10 (one gee), l=1million km, you'd attain 100km/s.
With ten gees and 10 million km track, it's 1000km/s (0.3%c)

#### john smith 19

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #22 on: 06/24/2014 03:03 PM »
The problem is not acceleration as such it's sustained acceleration and the energy you need to sustain it.  Look at the voyager science package, knock it down by a factor of 10 to allow for 40 years of improvements and work out how much energy it takes to accelerate that to even 1% of C. That would tell you quite a lot about any planets it found, but how would it tell us about them?

If I understand correctly this is the sort of thing some kind of quantum entanglement comms device would be perfect for.

Obviously if you can do higher g you can accelerate faster, possibly using remote power systems and beamed power while still in the solar system. The limits in the 50's seemed to be about 60g for 15 minutes in a water tank. People have also suggested ingesting oxygenated flourcarbons (actually used for breathing assist in patients with badly damaged lungs), possibly also introduced into the body cavity to support internal organs. 1g is 1C in 6 months but 60g?

Another option is a pulse systems would be to string out a series of mass driver rings across the solar system. The ship threads the needle of each one, which then recoils until brought to rest by either thrusters on the ring or by the repulsion of the approaching nearest neighbour.

Obviously the level of recoil depends on the relative masses of the accelerator ring to the payload it's accelerating but any way you slice it this would a massive project.

BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

#### Vultur

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #23 on: 06/24/2014 05:25 PM »
Absolutely correct, sadly. Even assuming a wholly robotic, Von Neuman machine civilisation or post-Singularity ex-biological one (is there a difference?), it takes a reasonably short time to colonise an entire galaxy with rather slow ships. If you can colonise a galaxy, then you almost certainly manipulate the environment, increasing dust, decreasing dust, changing the percentage of stars with high metallicity, altering stellar rotation rates, emitting gravity wave signals and so forth.

What if "mechanical" (as opposed to basically-biology-as-we-know-it-but-with-a-little-bit-different-chemistry) Von Neumann machines simply aren't possible or aren't invented? Living things won't do well in vacuum and I have a feeling that "nanotech" if it happens will be more like biology (viruses/bacteria) than really tiny robots and factories.

Also, that assumes the desire to both colonize the galaxy and change it in observable ways (a quadrillion O'Neill colonies orbiting a billion stars galaxywide would be a colonized galaxy, but not one that the colonization was detectable from a distance). I don't see why that is a natural assumption.

And what if there are lots of altered galaxies? Would we recognize them as artificial rather than just a different type of galaxy? We could have already seen them and they are simply not recognized.

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #24 on: 06/24/2014 06:00 PM »
one reason this may be a false paradox is we might not even be able to perceive or recognize the signatures of such civilizations. for example; what if such civilizations use slightly larger than plank length wormholes to spy on planets rather than go to all of them? there are cosmic ray signals that would be the only signature of such virtual probes. according to Dr Kramer there are cosmic ray events that would match the signature of such probes. this would not ordinarily bring to mind alien activity. how would we know the difference between natural cosmic ray signals and wormholes spying on us?

What if it's only mankind's arrogance to assume that we can predict what a more advanced civilization's signatures would be? they'd have to do this and this and this and have this or that... how in the heck do we know that?
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#### john smith 19

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #25 on: 06/25/2014 08:20 AM »
What if it's only mankind's arrogance to assume that we can predict what a more advanced civilization's signatures would be? they'd have to do this and this and this and have this or that... how in the heck do we know that?
And so we are back to Haldane's conjecture that "The universe is not only stranger than we know it is stranger than we can imagine"

Although obviously as we've learned more what we can imagine has expanded a lot.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #26 on: 06/25/2014 10:13 AM »
I think constant acceleration at 1g is a nice well defined problem despite the various reasons we probably wouldnt attempt it.

On topic, it could be worth noting that constant 1g acceleration would be pretty easy for a standard chemical rocket if there where depots strung out at just the right positions and velocities ahead of it.. of course that just pushes the problem onto how to get the depots there, but perhaps you have more options for unmanned depots than for a crewed ship. They could be shot with massive acceleration or take centuries to align.

Isp is WAY too low.
The total mass of chem depots needed even for a small craft to reach any sort of interstellar-class speed is not feasible. Billions of tons.

No ISP is not relevant in this example. The catch is that you have gotten all these depots up to speed ahead of you somehow. Thats where you have to put all your energy in. The chemical rocket becomes just a way of taking this energy from the depot and putting it into the vehicle. You could just bounce off each depot and steal their kinetic energy that way, but that would be a rough trip.

Its not something Im proposing to do, just thought it might spark some ideas. Myself I favor some sort of beamed propellant propulsion, which you can think of as an extreme case of the above idea.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #27 on: 06/25/2014 10:44 AM »
one reason this may be a false paradox is we might not even be able to perceive or recognize the signatures of such civilizations. for example; what if such civilizations use slightly larger than plank length wormholes to spy on planets rather than go to all of them? there are cosmic ray signals that would be the only signature of such virtual probes. according to Dr Kramer there are cosmic ray events that would match the signature of such probes. this would not ordinarily bring to mind alien activity. how would we know the difference between natural cosmic ray signals and wormholes spying on us?

What if it's only mankind's arrogance to assume that we can predict what a more advanced civilization's signatures would be? they'd have to do this and this and this and have this or that... how in the heck do we know that?

Maybe you are in a vat with neural feed sending you fake picture of the virtual reality. How in the heck can you know that?

See? Not a useful position.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #28 on: 06/25/2014 10:46 AM »
I think constant acceleration at 1g is a nice well defined problem despite the various reasons we probably wouldnt attempt it.

On topic, it could be worth noting that constant 1g acceleration would be pretty easy for a standard chemical rocket if there where depots strung out at just the right positions and velocities ahead of it.. of course that just pushes the problem onto how to get the depots there, but perhaps you have more options for unmanned depots than for a crewed ship. They could be shot with massive acceleration or take centuries to align.

Isp is WAY too low.
The total mass of chem depots needed even for a small craft to reach any sort of interstellar-class speed is not feasible. Billions of tons.

No ISP is not relevant in this example. The catch is that you have gotten all these depots up to speed ahead of you somehow. Thats where you have to put all your energy in. The chemical rocket becomes just a way of taking this energy from the depot and putting it into the vehicle. You could just bounce off each depot and steal their kinetic energy that way, but that would be a rough trip.

You missed the word "chemical" in the phrase "standard chemical rocket" in the post I replied to.

If it's "chemical", it means "chemical propulsion" for depots and for the rocket.
« Last Edit: 06/25/2014 10:47 AM by gospacex »

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #29 on: 06/25/2014 10:59 AM »
Nah, I was clear that the depot was not launched by the same means, or by explained means at all. It was just to give ideas, not a solution.

That magnetic rail idea could have promise, don't use it to launch your ship but your propellant that follows after. This way you can inflict much higher accelerations and build something a million times smaller and have it running for years instead of minutes.

I do think beamed propellant is the most promising. Even if you like antimatter, you could greatly increase your efficiency if you beamed the antimatter. It is easy for some sort of particle projector sitting on a moon to launch particles at a much greater fraction of light than you expect your ship to reach, so with beamed propulsion you escape the exponential problem of the rocket equation. 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? There is light of course, but then you have to postulate amazing materials for the sail, especially if you are postulating 1g. If you could focus a plasma or gas then from the vehicle's point of view it could be riding on a column of gas no hotter than a chemical rocket the whole way.

If it helps, the beamed material could probably be arbitrarily large. It would all ablate into plasma as it gets near the craft's 'nozzle' I expect.

#### gospacex

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #30 on: 06/25/2014 11:03 AM »
Nah, I was clear that the depot was not launched by the same means, or by explained means at all. It was just to give ideas, not a solution.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #31 on: 06/25/2014 11:15 AM »
Nah, I was clear that the depot was not launched by the same means, or by explained means at all. It was just to give ideas, not a solution.

Its absolutely clear which bit is chemical. It is the use of the word scheme that might be misleading because it implies solution. It was a principle to provoke ideas. If it didn't for you, thats fine.

It did for me, because it underlines how beamed propellant can push something at constant acceleration as comfortably as if it were pushed by a chemical rocket, only dealing with chemical-equivalent stresses. No unobtainium, at least on the vehicle end.

#### frobnicat

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #32 on: 06/25/2014 02:36 PM »
And what if there are lots of altered galaxies? Would we recognize them as artificial rather than just a different type of galaxy? We could have already seen them and they are simply not recognized.

Not on topic but for those interested the following serious research bubbled up in some forums about detection of large scale ET technologies :
Video quality of the talk is a bit lousy but content I find worth : "The WISE all-sky mid-infrared survey has dramatically improved our ability to detect such civilizations and to distinguish them from "natural" astrophysical sources"

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #33 on: 06/25/2014 05:33 PM »
one reason this may be a false paradox is we might not even be able to perceive or recognize the signatures of such civilizations. for example; what if such civilizations use slightly larger than plank length wormholes to spy on planets rather than go to all of them? there are cosmic ray signals that would be the only signature of such virtual probes. according to Dr Kramer there are cosmic ray events that would match the signature of such probes. this would not ordinarily bring to mind alien activity. how would we know the difference between natural cosmic ray signals and wormholes spying on us?

What if it's only mankind's arrogance to assume that we can predict what a more advanced civilization's signatures would be? they'd have to do this and this and this and have this or that... how in the heck do we know that?

Maybe you are in a vat with neural feed sending you fake picture of the virtual reality. How in the heck can you know that?

See? Not a useful position.
actually... that depends. in the same way you aren't paranoid if people really are out to get you. if advanced societies develop forms and methods that we cannot extrapolate from our own stuff then we might not be able to recognize the signs of their existence.

it is useful because it reminds us we aren't the be all and end all of technology or biology. it tells us to look at things with a different perspective from time to time. it's not the cave men looking at a rock that advances stuff. it's the caveman that picks up the rocks and bangs them together.
When antigravity is outlawed only outlaws will have antigravity.

#### JasonAW3

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #34 on: 06/25/2014 06:01 PM »
Since no one else seems to have run the numbers, let me do that.

<SNIP>

Now suppose you want to go exactly 27,000 light-years to the galactic core. I'll only do the 1g figures

Ship time: 19.8 years
Earth time: 27,002 years
Peak velocity about 77 cm/sec less than c.

Assuming a perfect anti-matter drive (exhaust is light-speed and all in the right direction), then the mass fraction for the 1g trip is 39.5. That is, for every kilo of payload delivered to Alpha Centuri, you would need 38.5 kilos of fuel (half matter and half antimatter).

For the 0.1g trip, that falls to 3.7 and it's only 1.5 for the 0.01g trip.

For the trip to the galactic core, it's about 777 million, so funding may be difficult. :-)

Source for formulas: http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

I assume that you're talking constant acceleration without midpoint turn over and deceleration.  In the case of the 1g acceleration, I would figure that it would take about 4 as long objectively, as you'd never reach peak velocity, but only about half of that.  Unfortunately, I don't have the formula to figure out the time dilation subjective for the ship.  I figure at best, they'd reach about .5c in velocity.
My God!  It's full of universes!

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #35 on: 06/25/2014 07:38 PM »
Since no one else seems to have run the numbers, let me do that.

<SNIP>

Now suppose you want to go exactly 27,000 light-years to the galactic core. I'll only do the 1g figures

Ship time: 19.8 years
Earth time: 27,002 years
Peak velocity about 77 cm/sec less than c.

Assuming a perfect anti-matter drive (exhaust is light-speed and all in the right direction), then the mass fraction for the 1g trip is 39.5. That is, for every kilo of payload delivered to Alpha Centuri, you would need 38.5 kilos of fuel (half matter and half antimatter).

For the 0.1g trip, that falls to 3.7 and it's only 1.5 for the 0.01g trip.

For the trip to the galactic core, it's about 777 million, so funding may be difficult. :-)

Source for formulas: http://math.ucr.edu/home/baez/physics/Relativity/SR/rocket.html

I assume that you're talking constant acceleration without midpoint turn over and deceleration.  In the case of the 1g acceleration, I would figure that it would take about 4 as long objectively, as you'd never reach peak velocity, but only about half of that.  Unfortunately, I don't have the formula to figure out the time dilation subjective for the ship.  I figure at best, they'd reach about .5c in velocity.
time dilation effects are negligible until you get really close to light speed in terms of the crew's perception of trip time. it mucks with electronic timing and stuff long before it get's to be useful to humans. at .5 c the crew would basically spend the full trip time and consume the full trip time's consumables like water air and food and wear and tear on equipment and clothing and stuff like that. if they were going .9 c they would begin to reap the benefits of time dilation.
When antigravity is outlawed only outlaws will have antigravity.

#### aceshigh

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #36 on: 06/25/2014 08:49 PM »
well, the borehole however was a straight drilled hole downwards. If we mine like an inverted pyramid, we could go much further, without the rock pressure problems (although atmospheric pressure itself will get stronger.

#### kch

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #37 on: 06/25/2014 09:07 PM »
well, the borehole however was a straight drilled hole downwards. If we mine like an inverted pyramid, we could go much further, without the rock pressure problems (although atmospheric pressure itself will get stronger.

#### RanulfC

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #38 on: 06/26/2014 04:53 PM »
On the notion of "Where is Everyone?" I recall one proposal that we might be part of a cycle of "waves" of intelligence around the galaxy. In a short story the background of the planet being colonized it was mentioned that it showed "layers" of possible alien civilizations followed by a "sterilized" period after which it was "reseeded" back to its original bionome. The general "theory" was that civilizations would colonize the planet and then grow to the point where they decided to leave and "reset" the planets biosphere for the "next" wave.

I think the main "issue" with the idea that someone would have "colonized-the-galaxy" by now is rather self-centerered and really unsupported by the evidence of our own civilization. When most of these thought-problems were introduced the general idea was populations and civilizations that COULD would continue to expand indefinitly both in population and area. That doesn't seem as "true" as it did then, and coupled with the fact that "space" is hard to get to, much harder than it would be to "colonize" still open "areas" of our own planet it doesn't seem the "incentive" to expand at "all-costs" is as logical as it might have been assumed.

Randy
From The Amazing Catstronaut on the Black Arrow LV:
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?

#### dror

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #39 on: 06/26/2014 10:02 PM »

... 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?
"If we crave some cosmic purpose, then let us find ourselves a worthy goal. "
Carl Sagan, Pale Blue Dot

#### 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.

#### 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.

#### 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 »

#### 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...

#### 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 »

#### 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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#### 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...

#### 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.

#### 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 »

#### 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.

#### 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 »

#### 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.

#### 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.

#### 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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#### 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.

#### 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

Randy
From The Amazing Catstronaut on the Black Arrow LV:
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?

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #56 on: 07/01/2014 03:09 AM »

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.

#### IslandPlaya

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #57 on: 07/01/2014 10:09 PM »

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.

#### Lampyridae

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #58 on: 07/02/2014 06:31 AM »

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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#### 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.  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
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#### 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

#### 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.

#### 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)

#### 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.)

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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.

#### 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.

#### 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.

ABCD - Always Be Counting Down

#### 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...

#### 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.

#### 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.
When antigravity is outlawed only outlaws will have antigravity.

#### 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

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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.

#### 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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#### 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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#### 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 6Ũ10^12 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 »

#### 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

Create and capture.
Retired, working interesting problems

#### 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.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

#### 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)

#### 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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#### 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 6Ũ10^12 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.
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#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #80 on: 07/04/2014 05:13 AM »
and another caveat...

positrons are not the best type of antimatter to use for propulsion. you need anti-protons... which take thousands of times more energy to make.
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#### Soralin

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #81 on: 07/04/2014 09:11 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
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...
2-5 days at 9.8m/s2 means that you would need about 1700-4230 km/s of delta-v.  As compared to something like 14km/s to get from the surface of the Earth into a Hohmann transfer orbit to Mars for the slow trip.  Or around 10 km/s to get from the surface of the Earth into low Earth orbit (atmospheric/gravity drag would add a bit more)

#### cordwainer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #82 on: 07/04/2014 09:16 AM »
Depends on what you want to do with positrons vs. antiprotons for their efficacy as a propulsion component. Antiprotons are better for catalyzing fission while positrons are better for catalyzing fusion. Antiprotons are cheaper to store energy-wise in a Penning trap while positrons require novel storage approaches for long term storage like "stable" exotic atom states in positronium or colliding beam rings. Anti-protons are better for condensing into anti-matter while positron annihilation is more energetic. More energetic annihilation means that positrons would be more suitable for power generation although not necessarily propulsive energy. Like fission versus fusion you get higher reaction mass with anti-proton annihilation than positron annihilation, although the increase is hardly worth noting.

Yes, you heard it you get better reaction mass with fission not fusion, fusion reaction plasma has less molecular weight both because the atoms being fused have less atomic weight than fissionable materials but also because the reaction produces a much hotter plasma with a higher specific impulse or "flow rate". In other words it's more like a plasma and less like a cloud of hot gasses so the density of the reaction mass is more tenuous.

That's why the Pulsed Fission-Fusion Propulsion by Rob Adams is looking into using thorium or uranium fissionable liners for a concept similar to MSNWR's lithium liner fusion propulsion system.

Because anti-protons are less energetic you get a slower annihilation reaction that tends to produce more side reactions and reactive subatomic by-products that make anti-protons more suitable for catalyzing fission and in producing higher reaction mass with certain reactants like hydrogen and water. For ablation of solid materials positrons probably produce a slight improvement in performance, but as I said it's hardly worth noting. What is cool about positrons is that if the current research is right we could make them in large quantities with relatively little energy. This could have big implications for terrestrial power generation if you annihilated the positrons shortly after capture and are not worried about long term storage of the positrons. Issues with using them for propulsion would not necessarily be the mass of the equipment needed to produce the positrons but rather the fact that you would need to store the positrons for some time have a large enough "hohlraum" of them to propel a craft massive enough to produce it's own positrons. You could always store the positrons in a "positron storage ring" or as a stable onium inside a toroid similar to those used in fusion reactors, but that means a very large payload for an anti-matter "fuel tank" that you have to transport to LEO. If you go with the latter concept you wouldn't need to have one large hohlraum or as massive a craft in LEO so the danger of things blowing up is minimal and the energy required to maintain storage might be minimal once you get the storage tank aboard your craft. Problem is you don't have an extension cord long enough to maintain storage of your anti-particles while they make the flight to LEO so this further increases the mass of your payload to LEO. Penning traps work more efficiently for storing anti-protons if I'm not mistaken so the energy needed for transport to LEO might not be prohibitive.

#### IslandPlaya

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #83 on: 07/04/2014 10:53 AM »

Producing anti-matter at 1 gram per minute would allow you to create a 43 kiloton bomb every minute.
At least 6Ũ10^12 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.
That was already taken into account in the figures above. I was talking about other conversion losses.

#### Hanelyp

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #84 on: 07/04/2014 09:21 PM »
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
How long of a coil gun can you build in deep space, delivering how much acceleration to the probes it launches?

#### cjackson

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #85 on: 07/08/2014 01:57 PM »

Is it safe to say, that regardless of technological advances constant 1g acceleration will be infeasible?

#### 93143

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #86 on: 07/08/2014 08:40 PM »
Is it safe to say, that regardless of technological advances constant 1g acceleration will be infeasible?

No.

Like I said earlier, a space drive like M-E could potentially do it.  Easily, even, to the point that shielding the vehicle against interstellar gas and dust becomes by far the biggest problem.

And even with conventional ideas, beamed propulsion could work in principle, though I'm not sure how feasible it could ever get across interstellar distances, and it would use an awful lot of propellant...

"Regardless of technological advances" is very strong phrasing...
« Last Edit: 07/08/2014 08:45 PM by 93143 »

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #87 on: 07/09/2014 09:18 AM »
This is a fairly silly side thought, but beamed propulsion might even be able to support constant propulsion indefinitely.. given all those niggly problems of hitting the target over great ranges are solved of course.

This is because assuming any constant rate of expansion, the volume a race has colonized can grow proportional to time cubed. This volume is also proportional to the number of stars or galaxies it controls and thus it has at least this much power at its disposal. It may have discovered something even better of course.

To propel a vehicle with beamed propulsion, the energy need only grow as the square of the time, so a growing race would have enough energy to push not just one craft perpetually, but a number of craft proportional to the races age. (I have no idea if considering relativity changes this result or how)

(edit)
You could have some fun thinking up reasons why a race would be so determined as to devote a constant fraction of its output forever to essentially pushing a select few pretty much into the next universe. The traveller's ancestors might actually see the heat death of this one.
« Last Edit: 07/09/2014 09:30 AM by KelvinZero »

#### A_M_Swallow

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #88 on: 07/10/2014 01:33 AM »

Is it safe to say, that regardless of technological advances constant 1g acceleration will be infeasible?

Practically anything is possible but the costs and timescales can be large.

As propellant is used up the spacecraft's acceleration will increase unless the fuel flow rate is reduced.

for constant mass m

Next delta-E = 0.5 * m * (v22 - v12)

So as the velocity v increases the energy required to increase speed by 1 m/s increases non linearly.

When the spacecraft approaches the speed of light relativity has effects as well.

#### Bob Shaw

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #89 on: 08/14/2014 09:02 PM »

...a quadrillion O'Neill colonies orbiting a billion stars galaxywide would be a colonized galaxy, but not one that the colonization was detectable from a distance). I don't see why that is a natural assumption.

The IR signature would change. The stars would be in the wrong places on the H-R diagram, probably most visibly so in globular clusters.

#### JasonAW3

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #90 on: 08/14/2014 09:12 PM »

Producing anti-matter at 1 gram per minute would allow you to create a 43 kiloton bomb every minute.
At least 6Ũ10^12 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.

Excuse me?  if matter and antimatter completely convert to energy, that is a 100% conversion effeciency, or am I somehow having problems with my math?
My God!  It's full of universes!

#### aero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #91 on: 08/14/2014 10:25 PM »
Or is it 100% of the matter and 100% of the antimatter, for 200%? It depends, doesn't it! Just like fuel and oxygen, count the mass of the fuel but ignore the mass of the oxygen when toting up energy.

But unlike fuel/oxygen, matter and antimatter each supply energy to the annihilation so 100% of 2 times the mass of real matter sounds good, or 100% of the total mass.
Retired, working interesting problems

#### Mark K

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #92 on: 08/15/2014 02:32 AM »
positrons require novel storage approaches for long term storage like "stable" exotic atom states in positronium or colliding beam rings.

Exotic to be sure. I would like someone to propose any technology that could usefully hold even a few grams of naked electrons (let alone positrons) in a volume that would be reasonable. Heck if you can do that forget the antimatter positrons and the even nastier problems of their confinement. The potential energy of the electrons would be enormous. That is several thousand moles of electrons. If you have  the power to confine then even in 100 cubic meters the power to do that alone would be better spent on propulsion I think. Just thinking about the potential energy is giving me a headache we are talking gazillions (technically accurate there...) of Joules.

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #93 on: 08/15/2014 03:06 AM »
well they are charged particles. you could hold them in voids between arrays of charged or magnetized elements in what is essentially a fancy hard drive or SSD with fine enough scale elements. with the right architecture you should be able to load them. hold them and direct them as needed out of the Storage device.

or you could make them only as needed for reaction and only in the exact quantity needed for maintaining the proper reaction rate.

of course there is the idea of making atoms out of them then cryo freezing the result into a slush or solid in an evacuated chamber and suspended with magnets when the cryo freeze transitions to dimagnetic properties.

or more fanciful you could make materials with odd quark make ups such that the proper quarks and anti-quarks do not ever meet. antimatter matter annihilation actually only happens at the quark level. actually matter and antimatter collisions only result in annihilation 1/3 or 2/3s of the time. the other 1/3 or 2/3s of the time the wrong part of the particles bump and the particles recoil without annihilation.

more fanciful still you could make containers out of monopoles. no quark meet up equals no earth shattering kaboom. if you had something like that you'd only need to maintain a vacuum in the container to store antimatter safely.
« Last Edit: 08/15/2014 03:24 AM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

#### Scylla

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #94 on: 08/15/2014 03:12 AM »
Comparison of Fusion/Antiproton Propulsion Systems
for Interplanetary Travel
Stanley K. Borowski*
Lewis Research Center
Cleveland, Ohio 44135
http://web.archive.org/web/20080528030524/http://gltrs.grc.nasa.gov/reports/1996/TM-107030.pdf
I reject your reality and substitute my own--Doctor Who

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #95 on: 08/15/2014 03:19 AM »
say... riffing off on what i was saying about the necessity of the right quark anti-quark pairs bumping for annihilation to occur...

(I Love using the force...)

i wonder if there is a way to polarize, entrain or otherwise muck with the particles so the naughty bits of the matter and antimatter particles never line up.
When antigravity is outlawed only outlaws will have antigravity.

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #96 on: 08/15/2014 03:29 AM »

Producing anti-matter at 1 gram per minute would allow you to create a 43 kiloton bomb every minute.
At least 6Ũ10^12 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.

Excuse me?  if matter and antimatter completely convert to energy, that is a 100% conversion effeciency, or am I somehow having problems with my math?

It's actually not 100 percent efficient. the right quarks have to meet for annihilation to occur. when they don't the particles just bounce off one another but you could capture them and redo the collision until they do annihilate. also no way to make antimatter with better than 50 percent efficiency is known to science currently.

EDIT:  there may be ways to make antimatter with 100 percent efficiency though. we just don't know how yet. if a regular neutron can become a mirror neutron. with a fancy magnetic trick there may be a analogous way to convert matter to antimatter.

EDIT2: @IslandPlaya antimatter would be much more easy to keep out of the wrong hands than "easy" EM or gravitic tech that allows any idiot or psychopath or intoxicated or clumsy person to have a Relativistic Velocity Missile for the price of a radio shack raid.

EDIT3: a electron and a positron have two bits in them and together they form a magnetic dipole. i beleive i just read an article about them measuring the magnetic moment of the electron. should be able to cage them magnetically taking advantage of the dipole thing so that the quark anti quark annihilation is impossible because the quark anti-quark bits are kept away from each other. that would probably be easier in a 2 quark particle rather than baryonic particle.
« Last Edit: 08/15/2014 03:53 AM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

#### Dave G

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #97 on: 05/02/2015 04:17 PM »
Assuming issues with power and friction could be worked out, here are some examples of how far you can travel at 1g acceleration:
http://www.daviddarling.info/encyclopedia/O/one-g_spacecraft.html

Note that these are round trip times, which would consist of 5 parts:
1) accelerate at 1g half way toward the destination
2) decelerate at 1g until the destination is reached
3) explore the destination
4) accelerate at 1g half way back toward earth
5) decelerate at 1g until earth is reached

Also note that, for longer trips, returning home may be somewhat pointless, since things would have changed considerably.
« Last Edit: 05/02/2015 04:29 PM by Dave G »

#### cosmicvoid

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #98 on: 05/03/2015 02:31 AM »
... Also note that, for longer trips, returning home may be somewhat pointless, since things would have changed considerably.

If your destination was not compelling enough to stay, I think it would be very interesting to come back to see how earth had changed over many 1000's of years.
Infiinity or bust.

#### aminordisaster

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #99 on: 05/03/2015 05:24 AM »
I believe these are the formulas used for anyone interested (there was a link provided earlier).

Time on ship = (c/a) sinˉđ(at/c)=(c/a) cosˉđ[as/cē+1]
Time on earth = (c/a) sin(aT/c)=√[(s/c)ē+2s/a]

Where;
a = 1g or 9.80665 m/sē
s = displacement
c = speed of light in vacuum

Any quick search for "relativistic rocket equations" should give you other derivatives.
"Feynman, I know why all electrons have the same charge and the same mass" "Why?" "Because they are all the same electron!"

#### tea monster

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #100 on: 05/03/2015 12:32 PM »
There were various proposals for using the original nuclear pulse Orion ships for interstellar journeys. Before you condemn it for using nuclear bombs, and thus being dangerous, I think that once the general public find out how dangerous antimatter really is, they will embrace pulse ships with open arms.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #101 on: 05/03/2015 01:11 PM »
That ridiculous scheme is not ridiculous enough for this particular goal

You might also want to look up Robert Zubrin's Nuclear Salt Rocket as a fun thing to try some day.

#### Stormbringer

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #102 on: 05/03/2015 01:57 PM »
There were various proposals for using the original nuclear pulse Orion ships for interstellar journeys. Before you condemn it for using nuclear bombs, and thus being dangerous, I think that once the general public find out how dangerous antimatter really is, they will embrace pulse ships with open arms.
The latest proposed Orion derivatives don't use bombs. they use deuterium pellets fused by lasers. so no proliferation hazard and little in the way of environmental risk if a carrier rocket malfunctions or otherwise crashes and burns.

Also the type of antimatter ship likely to be available to us near to medium term would be hybrid systems that require either a nanogram or a microgram depending on which scheme is selected. E.g; AIMSTAR. Either quantity is essentially without risk.
When antigravity is outlawed only outlaws will have antigravity.

#### Esteban

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #103 on: 12/14/2017 07:44 AM »
I didn't expect this from a NASA forum. I figure you mostly aren't scientists, but neither readers of science fiction?

The key is "constant" acceleration. When in your car you stop going faster and maintain your speed, _irrespective_ of it, you'll feel about 0g from acceleration. Keep in mind that maintaining speed or acceleration aren't synonymous. To keep feeling 1g, you need to never stop accelerating *at 1g" and spend ever more energy, because  as Einstein said, you'll have more mass the faster you go. You'll reach c very fast, if only were impossible of course.

And that is really the difficulty, 1g is not a speed, as 80km/h, but a rate of acceleration. Your speed will forever increase, but your acceleration will remain constant.

#### Nilof

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #104 on: 12/14/2017 07:51 PM »
http://www.projectrho.com/rocket/supplement/dvNomogram01.pdf

Fusion can do interplanetary 1g brachistochrones with somewhat reasonable mass ratios. It definitely can't do interstellar brachistochrone trajectories. You need antimatter or laser sails for that.

It gets better at ultrarelativistic speeds because proper acceleration isn't the same thing as coordinate acceleration, and proper velocity increases exponentially with rapidity in that range. But getting to that speed range is a pure fantasy to begin with.

Edit:

Ah, this got lifted by necroposting.

I didn't expect this from a NASA forum. I figure you mostly aren't scientists, but neither readers of science fiction?

This isn't a nasa forum. It's a spaceflight forum that has nasa in its name because most of it is devoted to US spaceflight.
« Last Edit: 12/14/2017 07:54 PM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

#### Esteban

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #105 on: 12/16/2017 03:56 AM »
http://www.projectrho.com/rocket/supplement/dvNomogram01.pdf

Fusion can do interplanetary 1g brachistochrones with somewhat reasonable mass ratios. It definitely can't do interstellar brachistochrone trajectories. You need antimatter or laser sails for that.

It gets better at ultrarelativistic speeds because proper acceleration isn't the same thing as coordinate acceleration, and proper velocity increases exponentially with rapidity in that range. But getting to that speed range is a pure fantasy to begin with.

Edit:

Ah, this got lifted by necroposting.

I didn't expect this from a NASA forum. I figure you mostly aren't scientists, but neither readers of science fiction?

This isn't a nasa forum. It's a spaceflight forum that has nasa in its name because most of it is devoted to US spaceflight.

Humm, I've always assumed orbits to be brachistochrone enough to be worth mentioning, but of course you're right and they're different.
And I'd truly be amazed the day we have the capacity to "set brachistochrone curve to yonder star, Mr. Sulu!" in the actual definition of the word.

Sorry, didn't know necroposting was bad form.

Ah, I see, the name fooled me, thanks!

#### D_Dom

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #106 on: 12/16/2017 03:47 PM »

Sorry, didn't know necroposting was bad form.

Not bad form, merely an observation. Often threads like this are inactive because the interest level has dropped off. No reason to not bring it back into discussion if you have a question or something else to add. I learned a new term today, thanks for that!

Looking into this I found Wolfram Alpha solving the problem "Find the shape of the curve down which a bead sliding from rest and accelerated by gravity will slip (without friction) from one point to another in the least time...
In the solution, the bead may actually travel uphill along the cycloid for a distance, but the path is nonetheless faster than a straight line (or any other line)."
http://mathworld.wolfram.com/BrachistochroneProblem.html

Sun is our closest star, wonder what the solution is to Alpha Centauri?
« Last Edit: 12/16/2017 04:05 PM by D_Dom »
Space is not merely a matter of life or death, it is considerably more important than that!

#### cyg

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #107 on: 03/08/2018 07:08 PM »
imo VR is the only "sensible" resolution of the Fermi paradox (& countless other issues). Stars are just lights in the sky. Only a few bits each to render(for a naked eye). A few million(if looking through a telescope). & none if nobody's looking etc. The "physical" universe may only be for us(at least for the time being).

#### JQP

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #108 on: 04/12/2018 06:23 PM »
imo VR is the only "sensible" resolution of the Fermi paradox (& countless other issues). Stars are just lights in the sky. Only a few bits each to render(for a naked eye). A few million(if looking through a telescope). & none if nobody's looking etc. The "physical" universe may only be for us(at least for the time being).

I think some combination of the time scales of evolution + rarity of potentially spacefaring species works okay. As someone else mentioned, it took something like 4 billion years for evolution to get from earliest life to modern humans. That's a little less than 1/3 of the lifespan of the universe (and much of the early life of the galaxy was spent cooling off, forming stars and star systems, etc.). Combine that with a few substantial hurdles along our (humans') evolutionary path, and you get a virgin galaxy, waiting to be colonized (or less likely, so recently colonized that the evidence hasn't reached us yet). The evidence definitely seems to point to a galaxy with very few spacefaring species candidates; nothing else satisfies the problems of scale (the less rare the candidate species, the more explaining one has to do, and the less explanatory power special case explanations have). It could all be down to our 4 billion years evolving being at the very short end of the bell curve (the explanatory power of these kinds of explanations increases as candidate species become rarer).

#### Mr. Scott

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #109 on: 04/12/2018 09:09 PM »
What is a virgin galaxy?
« Last Edit: 04/12/2018 09:14 PM by Mr. Scott »
I've already asked to have my NSF account deleted, but they keep wanting me to do this.

#### whitelancer64

##### Re: Constant Acceleration at 1G and Beyond
« Reply #110 on: 04/12/2018 09:23 PM »
What is a virgin galaxy?

Virgin meaning "untouched;" i.e., "virgin forest." In this context, it means "un-colonized," in other words, that no species has moved from their home star system to another.
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#### aceshigh

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #111 on: 04/12/2018 10:17 PM »
What is a virgin galaxy?

one whose central black hole remains untouched by advanced civilizations?

#### JQP

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #112 on: 04/13/2018 12:16 AM »
What is a virgin galaxy?

Virgin meaning "untouched;" i.e., "virgin forest." In this context, it means "un-colonized," in other words, that no species has moved from their home star system to another.

Or, to quibble, nobody has gotten to the point of colonizing in a way that we couldn't help but see. We could easily miss somebody colonizing their own system (edit: just saw you said home system, not home planet), or nearby systems, without Dyson swarms. Or large colonization efforts by a civilization afraid to advertise the way a Dyson swarm would (which again points to rare candidates; the fewer the candidates, the more explanatory power this sort of thing has).
« Last Edit: 04/13/2018 12:17 AM by JQP »

#### QuantumG

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #113 on: 04/13/2018 01:00 AM »
The whole "we should be able to see type II civilizations" thing is sooooo 20th century. Even the argument for Dyson spheres seems weird when you imagine working nuclear fusion. Why bother with bottling a star if you can engineer an artificial one that is better?

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

#### Mr. Scott

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #114 on: 04/13/2018 02:11 AM »
What is a virgin galaxy?

Virgin meaning "untouched;" i.e., "virgin forest." In this context, it means "un-colonized," in other words, that no species has moved from their home star system to another.
OK.  That explains the euphoric feeling after landing a probe on Mars.

Make your own star... QuantumG has an excellent idea.  I've been thinking about how to steer them around the galaxy.

I've already asked to have my NSF account deleted, but they keep wanting me to do this.

#### QuantumG

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #115 on: 04/13/2018 02:14 AM »
Make your own star... [and] steer them around the galaxy.

Like you're on some kind of star trek.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #116 on: 04/13/2018 03:20 AM »
The whole "we should be able to see type II civilizations" thing is sooooo 20th century. Even the argument for Dyson spheres seems weird when you imagine working nuclear fusion. Why bother with bottling a star if you can engineer an artificial one that is better?
I don't think Dyson swarms were intended as a reliable speculation on future technology. They are about defining a lower bound. At LEAST that.

The quandary is that every technology that exceeds the most trivial ( Dyson swarms ) will increase the probability of exponential growth, and increase the high entropy signature. It is only for Dyson swarms that the energy is limited to the star's output. Better technology than collecting sunshine takes away that limit.

The star is still the largest cache of matter in each solarsystem. Why are they not star-lifting? If they have fusion, why are not even gas giants hosting civilisations that glow in infra-red just as if they were Dyson swarms? Or even colder. Growing regions of cold that swallow galaxies. Maybe they have warp drive and travel is so trivial that they pick and choose their worlds? Boom, you have just exploded their potential growth, and they could eat the entire universe in only tens of thousands of years of exponential growth.

We know how much baryonic matter there was in the distant past. We can see it there. We know a lot of the physics of what a universe that evolved from that past would look like, and that matter all seems to still be here, exactly matching the signatures of what we expect dumb matter to look like.  There should be obvious anomalies covering vast swathes of the universe and growing. We don't need to know what an alien looks like to spot a divergence from what dumb matter looks like, which in many cases we have modelled to exquisite accuracy.

You end up having to postulate some weird transcendence where they just don't care about energy or matter, yet still take care to leave the universe looking exactly as wasteful as an empty universe, with stars just pouring their light into the void.

#### QuantumG

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #117 on: 04/13/2018 03:26 AM »
We know a lot of the physics of what a universe that evolved from that past would look like, and that matter all seems to still be here, exactly matching the signatures of what we expect dumb matter to look like.

No it doesn't. Our models of "what the universe should look like" are based on what we can see. If we were looking at a living universe we'd make completely wrong predictions and be surprised over and over again as we observed more and more - and that's basically a short history of modern cosmology. The only way our models work is by introducing matter and energy we can't observe!
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #118 on: 04/13/2018 12:57 PM »
We know a lot of the physics of what a universe that evolved from that past would look like, and that matter all seems to still be here, exactly matching the signatures of what we expect dumb matter to look like.

No it doesn't. Our models of "what the universe should look like" are based on what we can see. If we were looking at a living universe we'd make completely wrong predictions and be surprised over and over again as we observed more and more - and that's basically a short history of modern cosmology. The only way our models work is by introducing matter and energy we can't observe!
Sorry, that is so mindbogglingly far off what science is I really don't think this is worth continuing. You are stating that science is just curve fitting, that if scientists see a mystery they just add a parameter to tweek and call that understanding and move on. That is not science.

(edit) and even if all astrophysics was just book keeping and curve fitting, an anomaly from aliens would still be blatant.. barring the one case of aliens so pervasive that we in effect exist only as a specimen in a zoo of virtual reality physics created by them, where everything we see from the beginning of time was already dictated by aliens. One of the most basic questions of physics is whether a principle is the same in different coordinates of time and space.
« Last Edit: 04/13/2018 02:33 PM by KelvinZero »

#### tea monster

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #119 on: 04/13/2018 02:21 PM »
QuantumG is talking about 'dark matter' which is exactly what he described, and yes, it's a real scientific theory. Look it up

Oh, and the 'ridiculous scheme' Orion drive underwent flight testing with conventional explosives and it worked.

« Last Edit: 04/13/2018 02:23 PM by tea monster »

#### Frogstar_Robot

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #120 on: 04/13/2018 02:25 PM »
A criticism of Inflation theory is that it is tweekable to fit any observable universe, and several other advanced cosmology and quantum theories have similar testability issues.

Clearly, science isn't just curve fitting, but we are not yet able to prove every theory, so I think it is fair comment. It is certainly an assumption that we are observing a pristine universe, and that may not be true.

On one hand SETI assumes that alien civilisations are abundant and should be detected easily due to their impact on the universe, on the other, cosmologists assume that everything they see is "natural" and not due to alien artifacts. Of course extraordinary claims would require extraordinary evidence, but there is ground on the middle.

Or has cosmology already proved advanced alien civs do not exist, in which case we can cancel SETI?

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #121 on: 04/13/2018 03:12 PM »
QuantumG is talking about 'dark matter' which is exactly what he described, and yes, it's a real scientific theory. Look it up

(edit)
Firstly, I was talking about baryonic matter. We know that dark matter did not arise from aliens converting baryonic matter to another form, because we can look into the past and see how much baryonic there was originally, and that it matches with what we can see now.

It is pointless to discuss aliens that existed for all time in all places and independent of baryonic matter for the same reason it is pointless to discuss God. Unless people specifically want to discuss angels on heads of pins it should go without saying that is not the topic.
(end edit)

Sorry it is really depressing to read these statements. Dark matter and inflation theory are the opposite of supporting that assertion. They highlight exactly that scientists do not just curve fit and then ignore the search for an underlying explanation. This is precisely why they are major topics. Only MOD conspiracy theorists think of science that way. "Oh, they just called it dark matter because they don't want to think about it any more."

Maybe you guys have just not understood the context. The context is could astrophysicists see aliens and think they are just seeing physics? Just tweek their understanding of what they expect to see and call it nature?

This misses the fantastic effort that physicists make to confirm that physics works the same everywhere, that the behaviour of stars across space and observable history matches physics that can be confirmed right here on earth.

This misses the absurdity of physicists, not only being incurious of the inconsistency with physics on earth, also being incurious of their tweeks not being uniform across space and time, but having an origin at a specific point and a specific time after the universe had produced the elements necessary for chemistry, and then radiated outward from there.

No, apart from aliens as god, existing before atoms and everywhere after, physicists absolutely would NOT observe alien anomalies and just tweek physics to accept them.

(edit2) Should we move this to some SETI thread?
« Last Edit: 04/13/2018 03:38 PM by KelvinZero »

#### meberbs

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #122 on: 04/13/2018 03:45 PM »
Sorry it is really depressing to read these statements. Dark matter and inflation theory are the opposite of supporting that assertion. They highlight exactly that scientists do not just curve fit and then ignore the search for an underlying explanation. This is precisely why they are major topics. Only MOD conspiracy theorists think of science that way. "Oh, they just called it dark matter because they don't want to think about it any more."
I have had discussions with "MOD conspiracy theorists" and the like in the new physics section. The people on this thread are not in any way making comments like those people. Your comparison is unfair at the minimum. Your assertions go beyond what is actually known and take current best guesses as gospel in areas where physicists who study those areas will clearly admit we aren't 100% sure what is going on.

Maybe you guys have just not understood the context. The context is could astrophysicists see aliens and think they are just seeing physics? Just tweek their understanding of what they expect to see and call it nature?

This misses the fantastic effort that physicists make to confirm that physics works the same everywhere, that the behaviour of stars across space and observable history matches physics that can be confirmed right here on earth.
You apparently don't understand the context. They have found things that vary with time that are also difficult to explain why they vary with time. That is what accelerating expansion of the universe is. You are making unsupported assumptions about what alien presence would look like, including whether it would be detectable at all. These assumptions are the most unscientific part of this entire conversation.

This misses the absurdity of physicists, not only being incurious of the inconsistency with physics on earth, also being incurious of their tweeks not being uniform across space and time, but having an origin at a specific point and a specific time after the universe had produced the elements necessary for chemistry, and then radiated outward from there.
They are quite curious about variations in things like the Hubble constant. Current measurements do not have anywhere near the resolution in space, time, or accuracy to detect the kinds of things you are describing.

No, apart from aliens as god, existing before atoms and everywhere after, physicists absolutely would NOT observe alien anomalies and just tweek physics to accept them.
Scientists are not omniscient god-like beings who magically would be able to tell natural changes in the universe from deliberate ones. They most certainly will develop models that allow for any variations they detect, and will check various models for underlying explanations. The way you talk about scientists here is simply fodder for getting twisted by conspiracy theorists.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #123 on: 04/13/2018 04:09 PM »
Or has cosmology already proved advanced alien civs do not exist, in which case we can cancel SETI?
The start of this off-topic was what I consider a mistake by another poster, to assume that "The Dyson Dilemma" implies an assumption that aliens will not master superior power sources. Im saying that is not the meaning at all. It simply defines a lower bound of what a civilisation should AT LEAST be able to achieve. Postulating superior power sources only increases the potential of exponential expansion to make it's presence blatantly obvious, increasing the problem of the Dyson Dilemma.

So the Dyson Dilemma remains real. Does this mean we should cancel SETI? Not even do the most basic checks? No. Of course not. It means exactly what the average astronomer has already decided it means: SETI is a fairly long shot in the short term, only deserving of a fairly small fraction of scientist's attention.

Also I guess I am arguing that one of the most powerful tools for finding aliens is the non-SETI astronomer and astrophysicist community just doing its thing, comparing observation to theory. I think that if/when we spot aliens they will first appear as a "well that's odd". The first million or so of these phenomena will probably prove to not be aliens.. and then one will turn out to be aliens. SETI can really only add a few stabs in the dark beyond that, often using dubious guesses of what alien technology might specifically look like.

#### JQP

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #124 on: 04/13/2018 04:29 PM »
The whole "we should be able to see type II civilizations" thing is sooooo 20th century. Even the argument for Dyson spheres seems weird when you imagine working nuclear fusion. Why bother with bottling a star if you can engineer an artificial one that is better?

Because the energy is wasted otherwise. Again, if candidate life were plentiful, some of them should be "bottling" stars. The rarer candidates become, the more explicable the observed dearth becomes.

#### KelvinZero

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #125 on: 04/13/2018 05:19 PM »
Sorry it is really depressing to read these statements. Dark matter and inflation theory are the opposite of supporting that assertion. They highlight exactly that scientists do not just curve fit and then ignore the search for an underlying explanation. This is precisely why they are major topics. Only MOD conspiracy theorists think of science that way. "Oh, they just called it dark matter because they don't want to think about it any more."
I have had discussions with "MOD conspiracy theorists" and the like in the new physics section. The people on this thread are not in any way making comments like those people. Your comparison is unfair at the minimum. Your assertions go beyond what is actually known and take current best guesses as gospel in areas where physicists who study those areas will clearly admit we aren't 100% sure what is going on.
I have been careful in my claims and explanations. You haven't given me points I can address. You have not dealt with any of my points. You are asserting the onus is on me to prove a universe full of aliens could not happen to exactly match and empty one. This implies a total lack of context.

This is the context of what I am arguing:
* The Dyson Dilemma does not rest on the assumption that solar power is likely.
* Scientists are highly unlikely to accidentally fold evidence of aliens into a tweeked physics.. and dark matter and inflation are examples of NOT dismissing unknowns, but FOCUSING on them.

I will address one point, indirectly:
You apparently don't understand the context. They have found things that vary with time that are also difficult to explain why they vary with time. That is what accelerating expansion of the universe is. You are making unsupported assumptions about what alien presence would look like, including whether it would be detectable at all. These assumptions are the most unscientific part of this entire conversation.
Im prepared to strongly argue that aliens would almost certainly vary parameters, that a universe that merely appears empty would be like rolling snake eyes 100 times in a row, but the wording here suggests you think the context is a claim that aliens can be disproven. The context is that the Dyson Dilemma is not based on the assumption of solar power.. and surely never was. That would be expecting many decently intelligent people to show zero common sense.
« Last Edit: 04/13/2018 05:20 PM by KelvinZero »

#### meberbs

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #126 on: 04/13/2018 06:08 PM »
Sorry it is really depressing to read these statements. Dark matter and inflation theory are the opposite of supporting that assertion. They highlight exactly that scientists do not just curve fit and then ignore the search for an underlying explanation. This is precisely why they are major topics. Only MOD conspiracy theorists think of science that way. "Oh, they just called it dark matter because they don't want to think about it any more."
I have had discussions with "MOD conspiracy theorists" and the like in the new physics section. The people on this thread are not in any way making comments like those people. Your comparison is unfair at the minimum. Your assertions go beyond what is actually known and take current best guesses as gospel in areas where physicists who study those areas will clearly admit we aren't 100% sure what is going on.
I have been careful in my claims and explanations.
No, you really haven't. For example:
Postulating superior power sources only increases the potential of exponential expansion to make it's presence blatantly obvious, increasing the problem of the Dyson Dilemma.
Stars are the most powerful energy source that we know of within the confines of modern physics.  Superior power sources would fall into the "indistinguishable from magic" category, so there is no reason to think that they would be either more or less detectable than dyson spheres.

You haven't given me points I can address. You have not dealt with any of my points. You are asserting the onus is on me to prove a universe full of aliens could not happen to exactly match and empty one. This implies a total lack of context.
Burden of proof is on the one making assertions. You are making unsupported assertions about the detectability of alien life. Burden of proof is not on me, because as you say I am not making any major points other than that your statements lack support.

This is the context of what I am arguing:
* The Dyson Dilemma does not rest on the assumption that solar power is likely.
You have only pointed out that it rests on a slightly broader assumption that anything better would somehow be more detectable.

* Scientists are highly unlikely to accidentally fold evidence of aliens into a tweeked physics.. and dark matter and inflation are examples of NOT dismissing unknowns, but FOCUSING on them.
The 2 parts of this bullet are unrelated to each other. The first part is based on unfounded assumptions about what alien life would look like. The second part is obvious, scientists try to fill in the gaps in knowledge, but that does nothing to explain why they should decide that discovery of variations in some universal parameters should be anything other than naturally occurring, when so far they have always primarily weighted "naturally occurring" as the most likely explanation.

Im prepared to strongly argue that aliens would almost certainly vary parameters, that a universe that merely appears empty would be like rolling snake eyes 100 times in a row, but the wording here suggests you think the context is a claim that aliens can be disproven.
If you are prepared to argue that, then stop making assertions, and provide some support for your claims. Before you do, I recommend you go revisit your assumptions. As I pointed out, the main claim you made about the Dyson dilemma is based on a clearly faulty assumption. Disproving aliens clearly falls into the category of "proving a negative" which isn't practically going to happen.

The context is that the Dyson Dilemma is not based on the assumption of solar power.. and surely never was. That would be expecting many decently intelligent people to show zero common sense.
Now you are making an assumption that there is a correlation between intelligence and "common sense"

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #127 on: 04/14/2018 03:33 AM »
Why exactly do aliens need this level of power?
If Someone here figured out how to build a zero point energy source out of banana peels and an old toaster tomorrow, what would we do with it?

#### nacnud

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #128 on: 04/14/2018 04:35 AM »

#### tea monster

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##### Re: Constant Acceleration at 1G and Beyond
« Reply #129 on: 04/14/2018 08:26 AM »
Why exactly do aliens need this level of power?
If Someone here figured out how to build a zero point energy source out of banana peels and an old toaster tomorrow, what would we do with it?

This is like asking why would someone in the 1800's need a nuclear power plant? "Thousands of megawatts of electricity, what's the point in that?" Fast forward a few centuries and suddenly it makes sense.

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