Author Topic: Interstellar Spaceflight: Is It Possible?  (Read 17642 times)

Offline Martin FL

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Offline Justin Space

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #1 on: 12/07/2005 02:43 PM »
What a great read. There must be a way around Einstein's boundaries of travelling faster than the speed of light?

Offline Rocket Ronnie

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #2 on: 12/07/2005 02:58 PM »
Looks like the speed is not going to be impossible, but don't you simply lose acceleration, regardless how much power you throw at it, as you get closer to light speed, before never actually breaching it?

Offline To The Stars

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #3 on: 12/07/2005 06:41 PM »
Quote
Rocket Ronnie - 7/12/2005  9:58 AM

Looks like the speed is not going to be impossible, but don't you simply lose acceleration, regardless how much power you throw at it, as you get closer to light speed, before never actually breaching it?

Well yes, but I've never believed anything is impossible.

Offline publiusr

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #4 on: 12/07/2005 07:39 PM »

We could have a  starship soon. A launch vehicle like Sea Dragon that can loft 550 tons to LEO would be fueled by water broken down at sea by the reactor of an ARKTIKA type icebreaker. The payload would be a nuclear salt water rocket which would also require water. Such a craft would give steady 1g thrust and be more smooth than an Orion type starship.

So a super-HLLV/NSWR combination is what we should strive for after standard HLLV/NERVA type interplanetary ships.

Offline braddock

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #5 on: 12/07/2005 08:25 PM »
It's interesting reading up on some of this.

The isp of NERVA was apparently only around 1000 isp, while the calculated isp of Orion was 10,000 to 1 MILLION isp.  Apparently a controlled nuclear reactor like NERVA has to be throttled back to keep it from melting, so it's only about twice the isp of a chemical.
Here is an interesting site with these figures: http://www.astronautix.com/articles/probirth.htm

Does anyone know where to find worked Tsiolkovsky equations for an interstellar flight?  Like an Isp/Mass ratio/travel time graph for Alpha Centauri?  It would be interesting to see.

Offline Avron

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #6 on: 12/08/2005 03:56 AM »
Quote
Justin Space - 7/12/2005  10:43 AM

What a great read. There must be a way around Einstein's boundaries of travelling faster than the speed of light?

Yes .. have no mass to start with.. as you go faster mass increases F=ma good luck with the 'F' as the mass approaches infinity..

Offline CuddlyRocket

Re: Interstellar Spaceflight: Is It Possible?
« Reply #7 on: 12/08/2005 11:35 AM »
Quote
Justin Space - 7/12/2005  3:43 PM

There must be a way around Einstein's boundaries of travelling faster than the speed of light?
Do you want to travel faster than light? Or do you want to get somewhere faster than light can? These are not the same.

One way to achieve the latter is to simultaneously travel back in time (or travel forward in time less than you would otherwise). Providing you limit the time travel so that you can't arrive at your starting point before you left, there's no problems with causality.

Time travel is not against the laws of physics as currently understood. (Neither is FTL, although Einstein's special theory of relativity implies that doing so involves Imaginary quantities.) The details I'll leave as an engineering exercise for the interested student. :)

Offline darkenfast

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #8 on: 12/08/2005 04:51 PM »
It would only provide that thrust for a very short time.  While it would be an improvement over chemical propellants, it wouldn't be even a thousandth of what is required for a reasonable travel time to another star.
I believe that if nuclear-thermal rockets are ever used, it will be to lift a deep-space craft from Low Earth Orbit to either a high orbit or escape velocity to avoid the Van Allen belts.  Then, far more efficient (but lower acceleration) nuclear-electric propulsion will take over.  The same would probably be required on return as well.

Online nacnud

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #9 on: 12/08/2005 05:21 PM »
Quote
Looks like the speed is not going to be impossible, but don't yousimply lose acceleration, regardless how much power you throw at it, asyou get closer to light speed, before never actually breaching it?

No accelleration stays the same, its time that gets all weird. (as well as mass and lenght)


Offline Avron

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #11 on: 12/09/2005 04:45 AM »
Quote
nacnud - 8/12/2005  1:21 PM

Quote
Looks like the speed is not going to be impossible, but don't yousimply lose acceleration, regardless how much power you throw at it, asyou get closer to light speed, before never actually breaching it?

No accelleration stays the same, its time that gets all weird. (as well as mass and lenght)

Wierd like the warping of space-time... small engineering challange...:) Humm from our view on earth, what would a spacecraft look like moving away from us at light speed?

Offline braddock

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #12 on: 12/09/2005 11:53 AM »
Quote
Avron - 9/12/2005  12:45 AM

Wierd like the warping of space-time... small engineering challange...:) Humm from our view on earth, what would a spacecraft look like moving away from us at light speed?

It couldn't move AT light speed, because that would require infinite energy.  But if it was moving away from you at a hair under light speed, I believe the light and other RF from the spacecraft would be red-shifted down to the extremely low frequency radio spectrum, so you wouldn't really be able to "see" it except with a radio telescope.

Perhaps it would be an interesting SETI test someday to look at extrasolar planet spectra and see if we see light/radio sources rapidly red and blue shifting in the spectrum, as high-speed spacecraft presumably buzz around.  :)


Offline CuddlyRocket

Re: Interstellar Spaceflight: Is It Possible?
« Reply #13 on: 12/10/2005 09:48 AM »
Quote
braddock - 9/12/2005  12:53 PM

It couldn't move AT light speed, because that would require infinite energy.
Not to be picky, but to be strictly accurate (OK, picky! :)), Einstein's equations don't apply at v=c and therefore say nothing at all about the energy of an object with non-zero rest mass travelling at c.

True, for all v less than c, as v approaches c, the energy becomes arbitrarily large, but is at all times finite and therefore never becomes anywhere near infinite.

Offline mikorangester

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #14 on: 03/25/2011 04:37 AM »
No

Offline Downix

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #15 on: 03/25/2011 04:44 AM »
No
Wrong.

Holy necro-thread batman!
« Last Edit: 03/25/2011 04:45 AM by Downix »
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline Joris

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #16 on: 03/25/2011 06:06 AM »
No

The whole point of project Deadalus was to show that interstellar spaceflight was possible. Even though it is unaffordable now, in one or two centuries the economy will have grown enough to afford a Deadalus.

But at that time there will probably have been a breakthrough. General relativity is really only an approximation of how gravity works. So there might be *glitches* that we will be able to use.

Lastly, as the biological singularity comes near, interstellar spaceflight becomes possible within a lifetime for a very simple reason.
JIMO would have been the first proper spaceship.

Offline Downix

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #17 on: 03/25/2011 06:13 AM »
No

The whole point of project Deadalus was to show that interstellar spaceflight was possible. Even though it is unaffordable now, in one or two centuries the economy will have grown enough to afford a Deadalus.

But at that time there will probably have been a breakthrough. General relativity is really only an approximation of how gravity works. So there might be *glitches* that we will be able to use.

Lastly, as the biological singularity comes near, interstellar spaceflight becomes possible within a lifetime for a very simple reason.
You don't even need to be so advanced as Daedalus, a Project Orion would fill the job fine.
chuck - Toilet paper has no real value? Try living with 5 other adults for 6 months in a can with no toilet paper. Man oh man. Toilet paper would be worth it's weight in gold!

Offline RanulfC

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #18 on: 03/28/2011 07:44 PM »
You don't even need to be so advanced as Daedalus, a Project Orion would fill the job fine.
Oh heck we've already started on "Interstellar" space flight and without even using an "Orion-Boom-Boom" vehicle! We used a couple of Titan-III/Centaurs in fact!
http://en.wikipedia.org/wiki/Voyager_1

Now if you want to get anywhere in less than a geological time frame....

Randy
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Offline mlorrey

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #19 on: 03/31/2011 05:23 AM »
You don't even need to be so advanced as Daedalus, a Project Orion would fill the job fine.
Oh heck we've already started on "Interstellar" space flight and without even using an "Orion-Boom-Boom" vehicle! We used a couple of Titan-III/Centaurs in fact!
http://en.wikipedia.org/wiki/Voyager_1

Now if you want to get anywhere in less than a geological time frame....

Randy

Starwisp is the interstellar space flight on the cheap that is affordable now, falls within current known physics, though it depends on its ultimate utility on the idea that humans will eventually either learn to upload their minds onto computers (which obviously means we can then have our minds beamed on laser or radio beams to interstellar distances with no subjective travel time, since no time passes at light speed) or we are replaced by artificial intelligence.

Starwisp is a small interstellar ship, essentially a laser powered solar sail that carries as its cargo a communications system, lots of memory storage, and an ability to manufacture either robots, or artificial wombs and DNA sequencers, when it arrives at a habitable world. On arrival, it beams a message back to earth that its arrived, and people start beaming their minds and memories (if they were not preloaded on a starwisps memory at launch) to the destination for reception and installation in either a robot body, or a clone of their original body....

The propulsion concept is entirely doable at present. The cargo side of things, obviously is not, but given our current technological singularity, will likely be doable within the next few decades.
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Offline Patchouli

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #20 on: 03/31/2011 09:03 AM »
No

The whole point of project Deadalus was to show that interstellar spaceflight was possible. Even though it is unaffordable now, in one or two centuries the economy will have grown enough to afford a Deadalus.

But at that time there will probably have been a breakthrough. General relativity is really only an approximation of how gravity works. So there might be *glitches* that we will be able to use.

Lastly, as the biological singularity comes near, interstellar spaceflight becomes possible within a lifetime for a very simple reason.
You don't even need to be so advanced as Daedalus, a Project Orion would fill the job fine.

Project Orion or Daedalus are the only realistic concepts posted so far.

It's not likely the singularity fairy is going to make all the problems of space flight go away any time soon.

In fact Moore's law is starting to run into the problem of diminishing returns.
http://www.itbusinessedge.com/cm/blogs/cole/from-moores-law-to-the-law-of-diminishing-returns/?cs=44570

Besides nano tech might be just as susceptible to damage to GCR as organic beings which means no it probably can't sleep for millena and be expected to still work.

Even Voyager's old school 1970s memory chips have had issues with GCR http://www.space.com/8500-nasa-revives-voyager-2-probe-solar-system-edge.html


« Last Edit: 03/31/2011 09:07 AM by Patchouli »

Offline QuantumG

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #21 on: 03/31/2011 09:09 AM »
The propulsion concept is entirely doable at present.

A grand total of 2 solar sails have flown.. only one of them produced any thrust.  The laser beaming record is held by a bunch of guys at a startup company (Laser Motive) and none of that outside the atmosphere.  I know "doable" isn't exactly a strict measurement but so long as you refuse to enumerate the problems and address the development that is needed, we'll never get beyond "it's doable".
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline mlorrey

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #22 on: 04/01/2011 11:00 AM »
The propulsion concept is entirely doable at present.

A grand total of 2 solar sails have flown.. only one of them produced any thrust.  The laser beaming record is held by a bunch of guys at a startup company (Laser Motive) and none of that outside the atmosphere.  I know "doable" isn't exactly a strict measurement but so long as you refuse to enumerate the problems and address the development that is needed, we'll never get beyond "it's doable".


We are talking about in comparison to other concepts. Daedelus depends on fusion, which has not been proven to operate other than thermonuclear weapons, and Orion depends on a fuel source which is politically impossible. So neither of those is currently "feasible". Conversely, solar sails that have actually operated in interplanetary space (LEO is possibly the worst place for a solar sail, as the only "thrust" it will generate is drag from the thermosphere) actually have worked. So thats proven technology. laser propulsion is also proven technology that has been demonstrated.
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Offline Air Q

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #23 on: 04/01/2011 12:15 PM »
No accelleration stays the same, its time that gets all weird. (as well as mass and lenght)
Sorry for quoting such an old post but I thought it might be interesting. Instead of defining "rest mass" and "relativistic mass" many think that it is much better to keep in equations only one mass that is "rest mass". Instead change in momentum and energy should be applied. In this case:
-the faster we go the more energy we need to accelerate
or
-the faster we go the less acceleration we obtain by the same amount of energy
In v=c the amount of energy goes to infinity.

This is how Einstein wrote in 1948 his letter to Lincoln Barnett:
Quote
"It is not good to introduce the concept of the mass M = m/(1-v2/c2)1/2 of a body for which no clear definition can be given. It is better to introduce no other mass than 'the rest mass' m. Instead of introducing M, it is better to mention the expression for the momentum and energy of a body in motion."
More detailed discussion on that can be found in this article published in Physics Today:
worldscientific.com link removed

http://www.physics.rutgers.edu/ugrad/313/concept%20of%20mass.pdf
« Last Edit: 04/02/2011 06:09 PM by Air Q »

Offline Cinder

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #24 on: 04/02/2011 06:54 AM »
Getting a Chrome redirect warning on that link, going to worldscibooks.com instead of worldscientific.com
Wouldn't have mentioned it except for this news of massive redirect attack
« Last Edit: 04/02/2011 06:55 AM by Cinder »
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Offline Air Q

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #25 on: 04/02/2011 06:10 PM »
Getting a Chrome redirect warning on that link, going to worldscibooks.com instead of worldscientific.com
Wouldn't have mentioned it except for this news of massive redirect attack
Took that link from wikipedia. Anyway just in case I googled for another link and edited my previous post.

Offline Johnnyd

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #26 on: 08/07/2011 12:54 AM »
Do we (humans) have the ability in any capacity to reach "light" speed?

After he asked I started to wonder if we did, do or will. I'd imagine with what little I know about conventional rocket engines (solids & liquid), it would be impossible to achieve that speed.

Can anyone elaborate?
« Last Edit: 08/08/2011 01:19 PM by Chris Bergin »

Offline pippin

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #27 on: 08/07/2011 12:56 AM »
It's theoretically impossible to reach light speed for anything that has a (rest) mass (like a human or a spaceship).
« Last Edit: 08/07/2011 12:58 AM by pippin »

Offline Johnnyd

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #28 on: 08/07/2011 02:23 AM »
In my feeble mind, I kinda "know" it's impossible to achieve 670 million some odd Mph... but I figured I'd ask. 

Offline Chris Bergin

Re: Interstellar Spaceflight: Is It Possible?
« Reply #29 on: 08/07/2011 02:27 AM »
Many threads on this. Someone link one up and I'll merge.

Offline nethegauner

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #30 on: 08/08/2011 08:31 AM »
Johnnyd, You can tell Your kid that You could reach 99 percent of lightspeed. Or 99,9 -- or even 99,99999999999. But whatever You try to to: the faster You go, the heavier You become, so to speak. And the more mass You have, the more energy You would need to accelerate further. So theoretically, You would have to put an infinite amount of energy into Your "star drive" in order to reach the speed of light. You have that amount available? Well -- then fine ...

;)

And if You compared the time on a watch You carry with You with that on a watch left behind, You would notice that mass is not the only parameter affected by Your light speed efforts. If You travel at very high speeds for an appropriate period, You actually gain time! There was this cute little scene in an episode of Carl Sagan's "Cosmso", where a boy is riding his scooter at relativistic speeds. When he returns to his village, his younger brother is an old man!

Of course, there is still the idea of opening gateways from one point in space-time to another very far away -- but that is strictly science-fiction. That is like in the movie "Contact" or TV'S "Star Trek, Deep Space Nine", for example.

Offline MarsInMyLifetime

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #31 on: 08/08/2011 06:38 PM »
Reading all this, I'm reminded of the street wisdom of beat poet Kenneth Patchen:

If you return
Before you go
Most fast shuffles
Will seem pretty slow
--The Walker Standing, by Kenneth Patchen

Isn't that a motif for "faster than light" in a nutshell?
Don

Offline mr. mark

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #32 on: 08/08/2011 06:58 PM »
Interstellar Spaceflight: Is it possible? Well, the two Voyager spacecraft are about to travel into interstellar space in a few more years so, the answer is yes... As for Star Trek like vehicles well.......

Offline DarkenedOne

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #33 on: 08/08/2011 09:44 PM »
First lets get the question right. 

Is Interstellar Spaceflight possible?  Yes we have probes in interstellar space right now.

The real question is whether or not humans will be able to make such trips.  Fact of the matter is to conduct meaningful interstellar spaceflight we will have to increase the life span of humans somehow.  Increasing human lifespans is much more doable from a physics perspective than faster than light travel.

Offline Andrew_W

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #34 on: 08/09/2011 04:29 AM »
When (if) we send out interstellar probes moving at a significant fraction of c, what method do people think is the most likely?
 Daedalus/Icarus is one possible method, but my favorite is lots of small rod shaped probes, each weighing in the tens of kilos, accelerated by powerful lasers. Each probe would have a small sail for the laser beam to push.

Laser propulsion is likely to have other applications apart from interstellar probes, so the technology is likely to be well advanced by the time we're seriously contemplating sending probes out to examine other star systems close up.
 
If the probes were accelerated by the lasers at 100g they'd get to 0.33c at a distance of 33AU, acceleration would take 27.5 hours.
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Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #35 on: 08/09/2011 05:03 AM »
When (if) we send out interstellar probes moving at a significant fraction of c, what method do people think is the most likely?
 Daedalus/Icarus is one possible method, but my favorite is lots of small rod shaped probes, each weighing in the tens of kilos, accelerated by powerful lasers. Each probe would have a small sail for the laser beam to push.

I think a prerequisite is an ability to decelerate at the target system.  A relativistic flyby mission would spend too little time near any interesting targets to be worthwhile compared to advanced long range telescopes.

That said, I do like the idea of accelerating many laser sails.  However, they are used for propulsion rather than flyby probes.  The main spacecraft is a superconducting magnetic loop with two compact equipment modules strung on it like two necklace beads.

Outward acceleration is done in the fairly obvious way (see Jordin Kare's Sailbeam).  The relativistic laser sails are vaporized by collision with a thin puff of gas and the resulting plasma bounces off the probe's magnetic field.

Braking acceleration is done in a non-obvious way.  The relativistic laser sails are vaporized by collision with a somewhat "thicker" puff of gas--but this collision takes place just after the sailbot passes through the magloop.  As a result, the exploding plasma pushes the magloop back toward the source of the laser sails (back toward our solar system).  This allows the probe to decelerate at the target system.

I call this propulsion system "Single Stream Impact Powered Propulsion", and it requires significant amounts of on board propellant.

Another possibility is "Double Stream Impact Powered Propulsion", which does not require significant amounts of on board propellant.  With double stream propulsion, two different streams of sailbots are used.  They are moving along parallel lines, but at very different velocities.  Collision with a very thin puff of gas vaporizes the sailbots just as they approach the spacecraft.  This turns them into expanding puffs of plasma which then collide with each other just after passing the magloop.

Unlike single stream propulsion, double stream propulsion does not require much on board propellant.  However, I think that generally single stream propulsion is superior.

Offline indaco1

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #36 on: 08/10/2011 04:53 AM »
...

I think a prerequisite is an ability to decelerate at the target system.

...


Are we certain passive braking is so difficult, relatively speaking?

What is really difficult is to accelerate to relativistic speed.

But to brake in theory you don't have to provide energy nor reaction mass.

Interstellar medium is relatively slow (few hundreds m/s) and solar wind of the approaching star moves in the opposite direction.

Any form of magsail has the potential to use them to brake.

They need a power supply, but when you are moving so fast respect the surrounding mean in theory you have a lot of energy.

In fact there are proposals to use solar wind to produce power.

Eg this: http://news.discovery.com/tech/solar-wind-energy-power.html

Deceleration could begin very far from destination, it can take years, you don't need a big sail.


In brief:

Some form of beamed propulsion to accellerate a probe.

Passive magsail braking to decelerate during the approach to the destination.



Return is another story, of course. :)
« Last Edit: 08/10/2011 04:56 AM by indaco1 »
Non-native English speaker and non-expert, be patient.

Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #37 on: 08/10/2011 05:18 AM »
Zubrin has done calculations on large magnetic sails for interstellar medium braking.  It does require an very large and lightweight sail (read as "speculative performance"), and the braking time is on the order of decades.

So, if the ISM mag-brake is the best thing you can come up with, the flight plan looks like a sharp acceleration up to maximum speed followed shortly by the deployment of the mag-brake.  The probe initially bleeds off speed quickly, but deceleration scales with the cube of the current speed.  The probe then spends the next several decades gradually slowing down like a heavy curling stone inexorably sliding along nearly frictionless ice.

Hopefully the probe has JUST enough momentum to stop at the destination star system.  Any miscalculation in the ISM means that the probe either fails to reach the destination system or it goes sliding past the destination with the mag-brake powerless to stop it.  The risk of this isn't such a big deal if the probe has another propulsion system--but if such a potent propulsion system is available it should probably be used for braking in the first place.

Offline Tass

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #38 on: 08/10/2011 09:35 AM »
Zubrin has done calculations on large magnetic sails for interstellar medium braking.  It does require an very large and lightweight sail (read as "speculative performance"), and the braking time is on the order of decades.

So, if the ISM mag-brake is the best thing you can come up with, the flight plan looks like a sharp acceleration up to maximum speed followed shortly by the deployment of the mag-brake.  The probe initially bleeds off speed quickly, but deceleration scales with the cube of the current speed.  The probe then spends the next several decades gradually slowing down like a heavy curling stone inexorably sliding along nearly frictionless ice.

Hopefully the probe has JUST enough momentum to stop at the destination star system.  Any miscalculation in the ISM means that the probe either fails to reach the destination system or it goes sliding past the destination with the mag-brake powerless to stop it.  The risk of this isn't such a big deal if the probe has another propulsion system--but if such a potent propulsion system is available it should probably be used for braking in the first place.

I guess you'd have a safety margin. Losing speed too fast? Reduce the field strength. Going too fast, put it back up.

Not saying this is at all a good idea though, spending most of the time at low speed because of the v cubed scaling sort of defeats the point of going fast in the first place.

By the way how do you get that cube anyway? Does the fields cross section increase with increased speed? On the contrary high speed should allow some particles to make it through the outskirts of the field with less deflection. 

Offline RanulfC

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #39 on: 08/10/2011 03:07 PM »
Zubrin has done calculations on large magnetic sails for interstellar medium braking.  It does require an very large and lightweight sail (read as "speculative performance"), and the braking time is on the order of decades.

So, if the ISM mag-brake is the best thing you can come up with, the flight plan looks like a sharp acceleration up to maximum speed followed shortly by the deployment of the mag-brake.  The probe initially bleeds off speed quickly, but deceleration scales with the cube of the current speed.  The probe then spends the next several decades gradually slowing down like a heavy curling stone inexorably sliding along nearly frictionless ice.

Hopefully the probe has JUST enough momentum to stop at the destination star system.  Any miscalculation in the ISM means that the probe either fails to reach the destination system or it goes sliding past the destination with the mag-brake powerless to stop it.  The risk of this isn't such a big deal if the probe has another propulsion system--but if such a potent propulsion system is available it should probably be used for braking in the first place.
The "Mag-Sail" shouldn't ever hit the point where it won't be able to accelerate or decellerate since it can ride the target stars solar wind as per the basic "Mag-Sail" concept. (It was proposed as an interplanetary "drive" originally after all)

"Better" would probably be to use the effect to swing the vehicle around and bring it back towards the target star from "behind" thus allowing the vehicle to simply intercept another "beam" of sail-bots using the exact same propulsion system to slow down. While your overall "trip-time" just about doubles your accelleration and braking phases are very much shorter.

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Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #40 on: 08/10/2011 08:47 PM »
By the way how do you get that cube anyway? Does the fields cross section increase with increased speed?

The diameter of the bow shock increases with speed.

Offline IsaacKuo

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #41 on: 08/10/2011 08:56 PM »
Hopefully the probe has JUST enough momentum to stop at the destination star system.  Any miscalculation in the ISM means that the probe either fails to reach the destination system or it goes sliding past the destination with the mag-brake powerless to stop it.  The risk of this isn't such a big deal if the probe has another propulsion system--but if such a potent propulsion system is available it should probably be used for braking in the first place.
The "Mag-Sail" shouldn't ever hit the point where it won't be able to accelerate or decellerate since it can ride the target stars solar wind as per the basic "Mag-Sail" concept. (It was proposed as an interplanetary "drive" originally after all)

The ISM mag-brake would have different characteristics than a mag-sail designed for stellar wind.  But that's not the point.  The point is that it can only provide a certain amount of braking.  If the probe enters the destination star system at 1% c (3000km/s), it doesn't really matter that the mag-brake can provide a small amount of braking all the way through the system and beyond.  What matters is that this small amount of braking simply isn't enough to stop it.  It might be able to provide on the order of 100km/s delta-v, which is inadequate.

Quote
"Better" would probably be to use the effect to swing the vehicle around and bring it back towards the target star from "behind"

Use what effect?  Zubrin's ISM mag-brake can't swing the vehicle around.

Online KelvinZero

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #42 on: 08/10/2011 09:11 PM »
The holy grail of manned interstellar flight is imo 1 g acceleration and deceleration for most of the voyage.
Prepositioning propellant at correct velocity and/or beamed propulsion have always been a favorite of mine. Isaac‘s zillions of tiny sails sound like a good way of delivering intelligent beamed propulsion that remains on target across lightyears and can even dash ahead then slow down near the destination for braking.
perhaps some sort of cannon on the moon or in orbit could launch these at a significant fraction of light speed, or more conventional beamed propulsion could accelerate them before leaving our system.

Offline Downix

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #43 on: 08/10/2011 10:00 PM »
The most obvious answer is to use an Orion putt-putt.
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Offline Tass

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #44 on: 08/11/2011 04:47 PM »
By the way how do you get that cube anyway? Does the fields cross section increase with increased speed?

The diameter of the bow shock increases with speed.

Ah. I thought the medium would be so thin on the scale of an artificial sail that it was basically individual particles hitting a magnetic field, getting deflected and leaving. If you actually get significant plasma effects on the field then of course it changes things.

Offline mlorrey

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #45 on: 08/12/2011 02:38 AM »
The most obvious answer is to use an Orion putt-putt.

nuke pulse propulsion gets you to 5% of C at most.
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Offline Lampyridae

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #46 on: 08/12/2011 08:49 AM »
The most obvious answer is to use an Orion putt-putt.

nuke pulse propulsion gets you to 5% of C at most.

True but it gets you there in less than geological time. Use hibernation, extended lifespan or generation ship technology to get humans there alive. ISM does most of the deceleration; a combination of reserve nukes and sailing into the stellar wind slows the vehicle into orbit.

Nukes would most likely be those pellets for ICF, with the lasers running of an onoard nuke plant.

You'd probably want a nice big ship anyways. If it's a proper ORION with pusher plate, then the required yield is something like megatonnes and the pusher plate is 400 metres acros. When you get to the target star, at least you have a large enough ship to be self-sustaining and self-replicating with help from a few asteroids if for whatever reason surface colonisation doesn't pan out or is delayed.
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Re: Interstellar Spaceflight: Is It Possible?
« Reply #47 on: 08/12/2011 09:50 AM »
The holy grail of manned interstellar flight is imo 1 g acceleration and deceleration for most of the voyage.
Prepositioning propellant at correct velocity and/or beamed propulsion have always been a favorite of mine. Isaac‘s zillions of tiny sails sound like a good way of delivering intelligent beamed propulsion that remains on target across lightyears and can even dash ahead then slow down near the destination for braking.
perhaps some sort of cannon on the moon or in orbit could launch these at a significant fraction of light speed, or more conventional beamed propulsion could accelerate them before leaving our system.

No kidding! 1g constant acceleration will get you to anywhere in about 20 years with relativistic effects. Altair (18 ly) and Andromeda (2.5 million ly) are the same amount of ship time.

Offline DLR

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #48 on: 08/12/2011 11:23 AM »
The long deceleration time is a good argument for not using magsails as brakes, but we may have no other option if we want to put probes into other star systems.

What about deploying the mag-sail much closer to the target star than proposed by Zubrin, so rather than using drag from interaction with interstellar medium to slow down you utilize the more powerful solar wind and the denser particles in the target solar system? Would it make sense to use a magsail to brake from, say, 0.2c to 0.05c or so and use fusion or antimatter propulsion to complete deceleration, reducing the overall trip time?

Offline indaco1

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #49 on: 08/12/2011 08:16 PM »
Zubrin estimate is based on a "conventional" magsail?

Why not an M2P2? The plasma suppy to feed the magnetosphere will not sufficie?

I wonder if are possible other designs to improve mass/drag ratio, possibly steerable during deceleration to adjust trajectory.

A relatively good start for interstellar travel could be a M2P2 mission braked and steered beyond the heliopause to fly by one or more TNOs.


 
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Offline qraal

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Re: Interstellar Spaceflight: Is It Possible?
« Reply #50 on: 09/07/2011 12:11 PM »
Zubrin estimate is based on a "conventional" magsail?

Why not an M2P2? The plasma suppy to feed the magnetosphere will not sufficie?

I wonder if are possible other designs to improve mass/drag ratio, possibly steerable during deceleration to adjust trajectory.

A relatively good start for interstellar travel could be a M2P2 mission braked and steered beyond the heliopause to fly by one or more TNOs.

Contrary to all the old material that Googles up when you do a search on M2P2, the more recent papers on the concept will tell you it doesn't work. Seems Winglee et.al. violated certain MHD assumptions that they had taken for granted. When the real plasma dynamics is computed, the thrust is much, much lower. M2P2 doesn't work as advertized. The Japanese are still working on a hybrid concept - mag-sail plus a plasma sail system - but the pure M2P2 is a dud.

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