Author Topic: Constant Acceleration at 1G and Beyond  (Read 52581 times)

Offline 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.

Offline 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.

Offline 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.
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Offline 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.

So that means all your calculations about energy needed, are moot.

Offline 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.

Offline 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!


Offline 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!

Offline 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).

Offline 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).

Offline 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.

Online 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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Offline 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?

Offline 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 »

Offline 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?

Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? Well... have you heard of Zeno's paradox?

Offline 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.

Offline 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.
Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? Well... have you heard of Zeno's paradox?

Offline 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.

Offline 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!
Jeff Bezos has billions to spend on rockets and can go at whatever pace he likes! Wow! What pace is he going at? Well... have you heard of Zeno's paradox?

Offline 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 »

Offline 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 :D

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 »

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