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#33220 - 01/15/10 03:29 PM Orion, Mission to Alpha Centauri
Momos Offline
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Registered: 01/15/10
Posts: 48
Loc: Germany
http://www.scienceagogo.com/message_board7/messages/747.shtml

Ok, this thread is ancient smile

Nevertheless I'd like your opinion on using Nuclear Pulse Propulsion for manned interstellar travel (not for reaching orbit).

Let's assume a 100 year one-way journey to Alpha-Centauri A/B at 4.4 ly.
So the average speed should be 4,4 % c.

Deceleration could possibly be done by using km-long theters to produce an electric/magnetic field with many kilometers in diameter, once inside the heliopause of the target star.

Which figures could we assume?
(For start lets just say smooth deceleration, over 0.5ly during 5 years)

Energy could be provided by current day fission or "possible near future" fusion generator.

The ship would be assembled in space, maybe in one of the lagrange points. Let's assume a ship mass of 10.000 - 50.000 metric tons, which is half the mass of a Nimitz-class aircraft carrier.

So: if the plasma debris of a thermo-nuclear-explosion has a velocity of 2*10^7 m/s (?) and 40% of the blast could be used for momentum change: would this be possible?

And is there any other technology which might be better suited for such missions? With higher exhaust velocities? Maybe LAPPS?

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#33225 - 01/16/10 04:29 AM Re: Orion, Mission to Alpha Centauri [Re: Momos]
redewenur Offline
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Registered: 02/14/07
Posts: 1840
Always an interesting topic. Wisely, you use the Sci-Fi section, even though respected eggheads began working on such proposals many decades ago.

Try to get back. Need to check out the available info on the net when/if I get time. There's probably plenty of it.
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#33226 - 01/16/10 04:48 AM Re: Orion, Mission to Alpha Centauri [Re: Momos]
paul Offline
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Registered: 03/21/06
Posts: 4122
I think we should wait until we have the technology to travel to our closest planet before we take such a huge step.

dont worry if we survive the current oil age there are plenty of ways to get around to other planets and stars.

after the oil age is over those of us that have survived will be surviving using free energy or solar energy and travel to other planets will be more desireable if not necessary.

but for now you should concentrate on a way to travel to our closest planet using the only available fuel source we are allowed to use.

maybe try coal even or natural gas.

some feasible fuel supply that can be taxed.

that way no one will scoff at your ideas and there would be billions of funding dollars just waiting for you to waste them on your next idea.
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#33244 - 01/18/10 11:18 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
Momos Offline
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Registered: 01/15/10
Posts: 48
Loc: Germany
Originally Posted By: paul
I think we should wait until we have the technology to travel to our closest planet before we take such a huge step.


Well, by saying "the ship will be assembled in space" I meant "after we might have established an industrial capacity in space using/mining/refining resources in space".
Of course a One-Way-Mission to the nearest star (which hasn't got small planet in the habitable zone) implies we have to have the technology and experience to build and maintain a society in space.

My question is, if it is possible at all to reach the nearest Stars without referring to unproven hypothesis and technologies which probably will never be developed.
(Like FTL, "free Energy").

Originally Posted By: paul

some feasible fuel supply that can be taxed.


There is no such thing as nontaxable-stuff.
If need arises a parliament could invent taxes for IR-Emissions, regardless if the energy for this emissions comes from coal, nuclear fusion or "free energy"...


Edited by Momos (01/18/10 11:19 AM)

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#33347 - 02/05/10 08:59 PM Re: Orion, Mission to Alpha Centauri [Re: Momos]
paul Offline
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Registered: 03/21/06
Posts: 4122
Quote:
Quote:
My question is, if it is possible at all to reach the nearest Stars without referring to unproven hypothesis and technologies which probably will never be developed.
(Like FTL, "free Energy").



no , its not possible.

without using free energy theres no space travel to other stars.

using what we have now all at one shot might accelerate a ship carrying everything we now have on the earth such as oil , coal , natural gas , atomic fussion materials etc...

towards another star , but how big would that ship be?

remember the bigger it is the more energy will be needed for acceleration.

186 million miles per second.
thats travelling from the earth to our sun and then back to the earth in 1 second.
do that for 1 year and you have traveled 1 light year.


our closest neiboring star Proxima Centauri is 4.3 light years away.


the ship would eventually reach the star , if anybody survived the initial acceleration and nothing got in the way.

then you will need at least 1/4 the amount to slow the ship down.

unless you eject from the main ship and slow down a smaller landing ship.

not trying to burst the bubble just being realistic here.

thats why we should start going to our planets using our energy sources first.

then later maybe a better form of propulsion could be found made available.



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#33383 - 02/14/10 01:12 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
paul Offline
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Registered: 03/21/06
Posts: 4122
Quote:
186 million miles per second.
thats travelling from the earth to our sun and then back to the earth in 1 second.
do that for 1 year and you have traveled 1 light year.


should have been 186 thousand miles per second.
sorry must have been either a brain fart ot alzheimers.
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#34429 - 05/19/10 07:51 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: paul
Quote:
Quote:
My question is, if it is possible at all to reach the nearest Stars without referring to unproven hypothesis and technologies which probably will never be developed.
(Like FTL, "free Energy").



no , its not possible.

without using free energy theres no space travel to other stars.


Sorry, the above is just silly. Unmanned travel to other star systems is well within current technology, so long as you're not in a rush to get there. In fact, several human probes are already traveling faster than escape velocity and will (in thousands of years) pass other stars. No need for exotic energy sources, just 1960's rocket propulsion and the odd gravitation sling was all that was needed.

As for human travel, the generation ship idea's been around for a long time - out of our current technological capabilities, but is capable of moving a human colony using a Hohmann (minimal energy) transfer orbits that are well within the energy levels that could be provided by an orion drive, fusion drive, VASIMR, etc. Several other projects have been designed, but never implemented, that could potentially send humans to nearby stars within a human lifetime (Project Longshot and Daedalus, for example). These were based on existent tech, or tech expected to be developed in the near-term.

And people seem to forget, you can leave a significant portion of your "propulsion" at home - laser-powered solar sails are near tech that could "easily" get a space craft over the 1%C mark. Doesn't reduce the amount of energy needed to slow down on the other end (nor return, if that is your goal), but it does cut down on fuel use dramatically. It even makes a "fly buy" mission "fuel free" (ignoring reactors and steering).

BTW, what do you mean by "free energy"?

Bryan

EDIT: by "laser powered solar sails" I'm referring to where you have a solar-sail powered craft, and use orbital lasers to provide propulsion above what the sun provides. Because they lasers stay in earth orbit, the fuel needed to run them stays "at home" and need not be carried.


Edited by ImagingGeek (05/19/10 07:54 PM)
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#34536 - 05/26/10 08:45 AM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
Momos Offline
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Registered: 01/15/10
Posts: 48
Loc: Germany
"Unmanned travel to other star systems is well within current technology, so long as you're not in a rush to get there."

Well, I'm not very patient. So is the public, which has to do the funding.

I guess an unmanned probe (possibly a fly-by) would have a chance if the target is interesting enough and the necessary amount not to big.

My initial interest in this topic is the question if it is entirely impossible to get to the nearest star system broadly within the lifespan of a human.

Assuming a lifespan of 100 years for the carefully choosen crew.
A take-of-age of 25 years, "retirement age" of 85 years (!).
I would even consider a 1 to 2 Generation Ship, with new born childs replacing the aging crew.
Time for the journey could be 60 - 100 years.

Thats why I figured an average speed of 4.4% c should be sufficient to reach alpha centaury during a manageable time frame.

The crew would have to transport every machinery to build and sustain a space faring society around the target star, enough genetic material to allow for a stable population.... lot's of transportation smile

"laser powered solar sails" have several advantages, but the main disadvantage would be the political ramifications of Multi-Terrawat-Lasers in space.

Additionally I would kind of prefer to have the engine on board rather then depending on people billions of km away to maintain the equipment.

So far the only remotely feasible concept, given my wishes, seems to be nuclear pulse propulsion.
However I calculate the needed masses/energies are always to big.

Even the nearest stars are awfully far away :-/

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#34542 - 05/26/10 02:22 PM Re: Orion, Mission to Alpha Centauri [Re: Momos]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: Momos
"Unmanned travel to other star systems is well within current technology, so long as you're not in a rush to get there."

Well, I'm not very patient. So is the public, which has to do the funding.


Sad, but true...

Originally Posted By: Momos
I guess an unmanned probe (possibly a fly-by) would have a chance if the target is interesting enough and the necessary amount not to big.


Not to mention the most practical. People need a lot of support equipment to survive, machines generally do not. So a lot of the mass issues become less when talking about unmanned missions.

Originally Posted By: Momos
My initial interest in this topic is the question if it is entirely impossible to get to the nearest star system broadly within the lifespan of a human.


With current tech I doubt it, but I'd bet some of the proposals out there could do it in the near-ish future (assuming enough money is spent on the R&D side of things).

Originally Posted By: Momos
"laser powered solar sails" have several advantages, but the main disadvantage would be the political ramifications of Multi-Terrawat-Lasers in space.


Stupid politics, getting in the way of our fun smile

Originally Posted By: Momos
So far the only remotely feasible concept, given my wishes, seems to be nuclear pulse propulsion.
However I calculate the needed masses/energies are always to big.


Did you look into some of the other techs like VASIMR? I believe they get ISP's similar to that (maybe even better) than that of orion.

Bryan
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#34599 - 05/28/10 08:40 AM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
Momos Offline
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Registered: 01/15/10
Posts: 48
Loc: Germany

well, somewhere I found the following figures, but I don't know how representative they are:

* Nuclear: 20.000 m/s – 50.000 m/s
* Ions (HiPEP, VASIMIR): 30.000 m/s – 50.000 m/s
* Ablative Laser Propulsion (ALP: LAPPS): 200.000 m/s - 32.000.000 m/s
* Anti-Matter (AIMStar): 600.000 m/s
* Nuclear Puls Propulsion (Orion, Deadalus): 100.000 m/s – 10.000.000 m/s

My first try was use of an engine with exhaust speed of 200.000 m/s:

For 100t of ship mass and 60 year flight time I got a 3,5*10^100 kg of reaction mass. ouch. eek

Second try with 32.000.000 m/s (which is itself 10% c, an extraordinary and probably unreliable value):
405 t of propellant (which, at present, is gold laugh )

for 60 years the needed acceleration/deceleration is: 2,322252 * 10^-2 m/sē, which seems pretty small.
But to accelerate the overall mass of ~500 t we would need ~ 11.6 kN ? (at the beginning).

Somewhere it was stated LAPPS could achieve a thrust of 0,031 N per MW, I'm hard wishing for an advancement of the factor 100 (! blush )
So we get 3 N per MW, which means we would need ~366GW.

A nuclear reactor for 1.6 GW already has a mass of more then 10.000 t, 100times the load capacity, let alone the fission material for 60 years. cry


I don't know the figures for VASIMIR and co, but it all sounds very unlikely. Either we need lots of propellant or a really big nuclear power plant.

Thats why I thought an orion style propulsion, without the need for external energy might be more feasible.



Edited by Momos (05/28/10 08:43 AM)

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#34608 - 05/28/10 02:20 PM Re: Orion, Mission to Alpha Centauri [Re: Momos]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: Momos

I don't know the figures for VASIMIR and co, but it all sounds very unlikely. Either we need lots of propellant or a really big nuclear power plant.


But that's the point of vasimr - you use a nuclear reactor to provide the kinetic energy you impart on your fuel. You can get extremely high ISP's that way, thus cutting your fuel bill. At the highest efficiency settings (low-thrust, but high exhaust velocity), I've read predictions that VASIMR may have higher ISP's than any other potential tech aside from anti-matter.

Bryan
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#34616 - 05/28/10 11:33 PM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
paul Offline
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Registered: 03/21/06
Posts: 4122
Originally Posted By: momos
I'd like your opinion on using Nuclear Pulse Propulsion for manned interstellar travel


Originally Posted By: paul
no , its not possible.


Originally Posted By: imagegeek
Sorry, the above is just silly. Unmanned travel to other star systems is well within current technology,


manned interstellar travel

and how fast can you accelerate the ship , that is manned?
how many generations will pass before the ship approaches
the deceleration point?

the probes we launched in the 60's and 70's
pioneer 10 was passed by voyager 2 in 1998 becomming the
furtherest man made object in space.



it has just passed our planetary system.

what new magical propulsion do we now use that was not
used then that would get us there faster?

solar wind? not hardly.

solar power? !!! but the suns sooooo tiny there.


dont forget if your going to use nuclear power to do the
job... how much fuel will you need?

do we have that much fuel?

so one false move and its lights out.
do we already have a nuclear power station in space?

just what would you use to power such a short lived journey if you dont use free energy?

just suppose your distant future family members are still
living and actually have succeded in keeping there muscle and bone structure in tact , what would the effects of slowing the spacecraft down have on them , as for the last 30 or 40 generations in your family have never experienced any deceleration on their bodies.

and for the next 30 or 40 generations they will all
experience deceleration.

then they arrive and no deceleration.

will they never get a cold or a virus in the thousands of years that would wipe them all out?

what would be the odds that any of them would survive the first year?

now or course there are no supply shipps trailing them or manufacturing ships or farm ships.

so your going to have to make everything that might break down as you travel.

this includes every manufacturing process on earth.

again

no its not possible.

im jst being realistic , thats all.

_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

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#34631 - 05/30/10 02:06 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: paul
manned interstellar travel


Paul, I was referring to this comment:

"without using free energy theres no space travel to other stars."

That is, as I pointed out, silly. Even with 1960's tech we could send stuff to other stars - it just takes an eternity to get there. No need for any magical free energy, just chemical rockets, gravity and time.

I'd also point out that you've never defined what you mean by "free energy". I have a hunch, but I don't want to put words into your mouth.

Originally Posted By: paul
and how fast can you accelerate the ship , that is manned?


3-5G's is sustainable for modest periods of time, 1G for eternity.

At 1G acceleration you get to the authors asked for 4.4%C in just shy of 16 days.

Originally Posted By: paul
how many generations will pass before the ship approaches the deceleration point?


Depends on your speed of travel. At a fast enough speed, anywhere is reachable in a human's life-time, as measured by ship-time. Acceleration to near-C, at a constant 1G, takes about 1 year.

Originally Posted By: paul
what new magical propulsion do we now use that was not used then that would get us there faster?


We've had working ion engines for over a decade, and vasimr has been demonstrated. Both of those are far more fuel efficient, and enjoy ISPs thousands of times better, than chemical rockets. Heck, Orion was considered possible with 60's tech - and was developed to the point of experimental models flown on conventional explosives.

And I'd point out that this thread was never about today's tech, but rather the orion system and potential alternatives. There is no reason an orion drive couldn't reach 4.4% c, all using conventional fissile materials. You'd need a lot of it, but you could get there.

Originally Posted By: paul
dont forget if your going to use nuclear power to do the job... how much fuel will you need?


Fusion, fission or RTG's?. The answer varies wildly, depending on which one, and what fuel. And what drive you're using, how fast you're flying, how big your ship is, how far you're going, etc.

Originally Posted By: paul
do we have that much fuel?


Yep.

Originally Posted By: paul
so one false move and its lights out.
do we already have a nuclear power station in space?


Several RTG's.

Originally Posted By: paul
just what would you use to power such a short lived journey if you dont use free energy?


What free energy?

Originally Posted By: paul
just suppose your distant future family members are still living and actually have succeded in keeping there muscle and bone structure in tact , what would the effects of slowing the spacecraft down have on them , as for the last 30 or 40 generations in your family have never experienced any deceleration on their bodies.


What keeps you from generating centripetal force? Centripetal force = "artificial gravity" for all eternity when you're spinning in a vacuum.

Originally Posted By: paul
will they never get a cold or a virus in the thousands of years that would wipe them all out?


Almost guaranteed to be zero. Pathogens evolve in very well understood fashions, usually requiring passage between several separate populations or even multiple species. A small isolated population is not one which'll breed new pathogens. Small isolated populations make good victims of existing diseases, but poor incubators for making new ones.

Originally Posted By: paul
what would be the odds that any of them would survive the first year?


Depends on how well things are built, etc.

Originally Posted By: paul

now or course there are no supply shipps trailing them or manufacturing ships or farm ships.


Why not? If you can launch 1 frigging huge ship into space, there is no reason you cannot launch more.

Originally Posted By: paul
so your going to have to make everything that might break down as you travel...this includes every manufacturing process on earth.


Not really. You only need those manufacturing processes required to replace ship-board items. No need for 747 manufacturing on the ship. By standardizing parts as much as possible, manufacturing capacity can be minimized.

And you forget the possibility of self-replicating prototypers (simple version of which have been demonstrated several times in the 2000's). These devices produce any parts needed, and assemble them - including what is required to replicate themselves. All you need is energy and raw material.

Bryan
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#34657 - 05/31/10 05:39 PM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
paul Offline
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Registered: 03/21/06
Posts: 4122
Quote:
Acceleration to near-C, at a constant 1G, takes about 1 year


how much fuel will that acceleration cost?

what happens when you encounter a grain of sand traveling at
near c.

how much energy would it cost to detect that grain of sand
at a distance far enought to allow for a course change.

and we dont yet know if there is anything in the void between the solar systems that would allow for a course change.

how do you know that there are even enought ions in the void?
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#34658 - 05/31/10 06:13 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: paul
Quote:
Acceleration to near-C, at a constant 1G, takes about 1 year


how much fuel will that acceleration cost?


Depends on the mass of the vessel, and how close to C you try to get.

Originally Posted By: paul
what happens when you encounter a grain of sand traveling at
near c.


Depends. If you have a waffle shield, it gets a hole in it and the particle is deflected. If not, your ship experiences a collision with the force of a small nuclear explosion.

Originally Posted By: paul
how much energy would it cost to detect that grain of sand
at a distance far enought to allow for a course change.


Why bother? Deflecting a particle of sand is a much lower-energy option than moving the whole ship, and if a passive shield is used, requires no pre-detection of anything other than large objects.

Originally Posted By: paul
and we dont yet know if there is anything in the void between the solar systems that would allow for a course change.


You don't need anything to "allow for" a course change - its all Newton's 3rd law: every reaction has an opposite and equal reaction. So you throw some propellant out with a force of 1N, your ship'll experience an equal force in the opposite direction and thus be accelerated in a direction opposite that of the propellant.

That propellant doesn't need anything to "allow" for it to provide that opposite reaction.

Originally Posted By: paul
how do you know that there are even enought ions in the void?


Why do I need ions?

BTW, the density of hydrogen in interstellar space is already known, to a point where we've mapped its density both locally, and across much of the milky way:
http://en.wikipedia.org/wiki/Local_Bubble


Bryan
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#34659 - 05/31/10 06:33 PM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
paul Offline
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Registered: 03/21/06
Posts: 4122
Originally Posted By: ImagingGeek
If you have a waffle shield,


what is a waffle shield , and if it deflects an object while traveling at near c , how much energy is drained from the achieved acceleration that will need to be replaced.

you mentioned using centripetal force for artificial gravity,what if someone walks in the other direction of rotation?
wouldnt this force that they apply for propulsion detract from the rotational velocity?

sure if nothing moves inside the centrifuge of theship , you can have eternal rotation , but if nothing is going to move , then why have the centrifuge?

for every action there is a equal and opposite reaction.

so for every step taken , every item moved within the centrifuge more energy will be required to maintain a precise artificial gravity.

Quote:
Depends on the mass of the vessel, and how close to C you try to get.


apx how much mass are you sudgesting?

toothpaste , porknbeans, french fries, cheesburgers,new underwear,socks,etc....

because they will be moving so they will wear down there clothes.
because we cant suspend life yet.

how many crew members would there be?
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3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

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#34660 - 05/31/10 06:46 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
paul Offline
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Registered: 03/21/06
Posts: 4122
Quote:
You don't need anything to "allow for" a course change - its all Newton's 3rd law: every reaction has an opposite and equal reaction. So you throw some propellant out with a force of 1N, your ship'll experience an equal force in the opposite direction


why do you need to throw something outside the ship?
why not just throw it out inside the ship.

the same reaction would occur.

and you still have your propellant.

you would only need a compressor and a nozzle that vectors
inside a compartment that has a lower pressure than the compressed propellant.

and you could use nitrogen , its safer you could actually breath it and its innert. so non flamable.
_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

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#34662 - 05/31/10 07:56 PM Re: Orion, Mission to Alpha Centauri [Re: paul]
ImagingGeek Offline
Senior Member

Registered: 05/19/10
Posts: 410
Loc: Canada
Originally Posted By: paul
why do you need to throw something outside the ship?
why not just throw it out inside the ship.

the same reaction would occur.

and you still have your propellant.


Doesn't work that way - material thrown within the ship will encounter resistance with the air, hull, etc. This will generate a force equal to the force of the propellant, thus neutralizing the thrust of the propellant. Its the ol' opposite and equal reaction thingie - the movement of the propellant will "push" on the ship, but the interaction of the propellant with the ship will push back equally. Net effect - zero thrust.

These kinds of internal energy transfer system only work in places where there is friction to counter the unwanted "return" energy of the propellant. Basically, you can thrust in one direction using a lot of force quickly, pushing the object forward. You then recover your propellant slowly, so the force of the propellant moving in the "wrong" direction doesn't exceed the static friction holding you in place.

That doesn't work in space - no friction.

Originally Posted By: paul
you would only need a compressor and a nozzle that vectors
inside a compartment that has a lower pressure than the compressed propellant.


Doesn't work that way, for the reasons mentioned above. In space, the net thrust of this kind of system is zero. And even in places where it is possible, the ISP would suck.

Originally Posted By: paul
and you could use nitrogen , its safer you could actually breath it and its innert. so non flamable.


The propellant used is dictated by the engine driving the spacecraft. Nobel gases are preferred for ion-based engines, due to the relative ease of ionizing them and the lack of intermolecular bonds. If using chemical engines, you need something that burns. If using nuclear, you need a fissile/fussile fuel, etc, etc, etc.

Bryan
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#34663 - 05/31/10 08:52 PM Re: Orion, Mission to Alpha Centauri [Re: ImagingGeek]
paul Offline
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Registered: 03/21/06
Posts: 4122
I think thats a load !!!

if I have a nozzle at one end of a long pipe and the entire pipe
is at 14.7 psi.

lets say the pipe is 60 inch diameter and 500 ft long.
and its inside your space ship.

and I have a compressor at the other end of the pipe that compresses air to 100 psi.

if I release the compressed air through the nozzle the reaction of the thrust will be felt by the pipe until the pressure in the pipe reaches 100 psi.

and if the compressor can maintain the 14.7 psi then
this can be continuous.

not only that but the friction between the pipe and the compressed air in the pipes that carries the compresed air back
to the nozzle will also be a force in the direction of movement.

according to your way of thinking if there was a hose attached to the place where the nozzle is attached instead of a nozzle and the hose was just laying there on the floor and someone turned on the air valve so that air could come out , the hose would just sit there , and it wouldnt move because you were taught that , and you could just walk up to it and pick it up.

me , I would want the air pressure to be turned off first.
so the hose wouldnt slap me in the head as I approached it.

so if the hose will move then if I held the hose , the ship would move.

the problem here is that when you are driving down
"think street"
and you see a "do not enter" sign you do not enter , instead you turn onto "do not think street" , I dont see any "do not enter" signs.

so I stay on "think street"




_________________________
3/4 inch of dust build up on the moon in 4.527 billion years,LOL and QM is fantasy science.

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#34667 - 06/01/10 09:20 AM Re: Orion, Mission to Alpha Centauri [Re: paul]
kallog Offline
Megastar

Registered: 03/17/10
Posts: 1100
Watch out Paul, here I come into this thread too! :P

Originally Posted By: paul

so I stay on "think street"


I'm all in favour of thinking too, that's why I like this forum so much.

Just because somebody didn't explain all their reasoning about everything doesn't mean they didn't think it, either right then or way back in the past.

I remember when I was a physics student, a fellow student was spinning on his chair without touching anything else. As we've probably all done, twist your body quickly, then slowly back the other way. You get a net rotation in little fits and starts. He was doing that and said "Hey shouldn't this be impossible?". But then we figured out that the friction is different for different speeds so it does allow angular momentum to not be conserved locally.


The flailing hose example is irellivant because it's obviously losing material, air, that isn't recovered.

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