Latest theories are for inter stellar propulsion

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  • #1
wolram
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can anyone tell me what the latest theories are for inter stellar
propulsion, and has the problem of bone loss on long space flights
been solved?
 
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  • #2
maximus
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what's propulation?
 
  • #3
Mentat
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Originally posted by maximus
what's propulation?

I think he means "propulsion".
 
  • #4
maximus
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Originally posted by Mentat
I think he means "propulsion".


ahhh! now that would make more sense!


all the stuff we send up there is still being fueled by the highly combustable rocket fuel. (i think) but most people agree that is we want to have any real possibility of long distance space travel, we're going to need to get a better fuel system. (fusion being by far the most promising!)

and i don't know about the bone loss thing. maybe the should take Medimusal-the fibre tablet! did you know that in space, astronauts grow like five inches taller because there is less spinal compresion?
 
  • #5
wolram
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exuse me i have "slight" dificulty with spelling
 
  • #6
Zantra
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I remember reading something about an "ion drive" a while back. Not sure if it ever came to fruition. Then there is of course the "vacuum energy" theory.
 
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  • #7
Originally posted by Zantra
I remember reading something about an "ion drive" a while back. Not sure if it ever came to fruition. Then there is of course the "vacuum energy" theory.

The ion drive is very much real. It is used on numerous satellites for orbit corrections and the Deep Space 1 probe used an ion drive for testing and propulsion during its comet and asteroid flybys.
 
  • #8
wolram
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what is ion drive,how much thrust does it produce?
 
  • #9
drag
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Greetings !
Originally posted by wolram
what is ion drive,how much thrust does it produce?
Ion engines are space propulsion devices that
use inert gases as their propellants. They ionise
the propellant thus providing it with an electric
charge and then use electrosatic or electromagnetic
fields to accelerate it to great exhaust speed ussualy
several times and more greater than those of
chemical rockets. Through the fields the thruster pushes
against the ions thus pushing itself in the opposite
direction according to Newton's Second Law.

The ion thrusters that have been operated in space so
far only produced up to a few hundreds of miliNewtons
of force and were ussualy powered by solar panels
at power levels of up to a few KiloWatts.

The efficiency of these systems lies in the fact that
they have such high exhaust velocities and thus can
produce far greater thrust for the same amount of fuel.

Live long and prosper.
 
  • #10
drag
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wolram, there's a NASA funded program (or was, at least)
called BPP (Breakthrough Propulsion Physics). My old
link to it doesn't work, but I think you can find it
easily through one of NASA's websites. It's about developing
new physical theories that could allow interstellar travel.
With the currently known technologies interstellar
missions with any reasonable parameters are a practical impossibility .

Live long and prosper.
 
  • #11
wolram
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cheers DRAG I am of huntimg...
 
  • #12
Janus
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One of the new promising drives is the VASIMIR. It works by heating the reaction mass up with radio waves until it reaches plasma state, containing it in a magnetic bottle, then allowing this plasma to escape out a nozzle. The VASIMIR has the advantage of the ION dirve of High exhaust velocities, but is capable of generating greater thrust.

The VASIMIR was actually developed from Controlled fusion experiments, where they were trying to find ways to create and contain the high temp Plasma needed. The containment always ended up leaking. Then someone realized that they could make use of this. If the containment is going to leak anyway, Why not just use this to our advantage in a rocket engine?
 
  • #13
LURCH
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BTW, a new propulsion system will solve the bone-loss problem automatically. If we could provide 1G of thrust, there would be no loss of bone or muscle mass, because these are effects of low-G.
 
  • #14
drag
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Greetings !

Janus, it's VASIMR - Variable Specific Impulse Magnetoplasma Rocket.
As far as I remember what I read about this the
exhaust velocity range is about 10 - 200 miles per second.
But of course, the propellant flow is reduced at higher
tempratures - exhaust velocities (due to containment and
power limmitations) and thus the total thrust is also
reduced for high exhaust velcoities.

LURCH, no such luck. Electric propulsion has high
exhaust velocities (or specific impulse) but poor
total thrust, so the acceleration is tiny.

Live long and prosper.
 
  • #15
I've found an interesting p-age about ion propulsion:http://science.nasa.gov/newhome/headlines/prop06apr99_2.htm [Broken]

BTW I've had an idea (though I've posted in again somewhere),
what if we used such powerfull electrical fields that would push the ions near the speed of light? That would increase the ions' mass a lot and because of the momentum concervation of the system it would end up to a very powerfull acceleration of the vehicle.

Feel free to correct me if I'm wrong.
 
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  • #16
drag
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Greetings !
Originally posted by DrStrange
BTW I've had an idea (though I've posted in again somewhere),
what if we used such powerfull electrical fields that would push the ions near the speed of light? That would increase the ions' mass a lot and because of the momentum concervation of the system it would end up to a very powerfull acceleration of the vehicle.
Well, there's a tiny little bit of a problem there
that's called energy. Any electric propulsion system
recieves energy from a power source.

Now, the momentum that a propulsion system provides
is p = m * v with m being the propellant mass ejected
and v being the exhaust velocity. However the energy is
Ek = m * V^2 / 2 , so you can see that as the exhaust
velocity grows the energy required to accelerate the propellant
grows as a square function of it, while the momentum
only grows as a linear function.

Of course, once you're near c the relativistic mass increase
will be great while the relative velocity increase will
be poor and then primarily the mass will grow as
a linear function in each equation. However, to get that
close to c you must be able to supply the huge amount
of energy that's entailed by the square of the velocity
in the kinetic energy equation so only if you can get that
much energy will you be able to use the relativistic mass
advantage.

Further more you should consider the source of energy
itself. Even if theoreticly you were, for example, to use
something like stored anti-matter, at near c velocities
you'll have to anihilate more anti-matter than the
propellant mass you'll be ejecting due to effeciency
issues and so the whole thing turns into a mess
and results in the fact that you'll still need huge
relative amounts of anti-matter that are much greater
than the mass of the final payload to just make a single
acceleration & decceleration one-way trip.

In short, new frontiers will require new physics...

Live long and prosper.
 
  • #17
Well, drag, seems you're right. I also thought it would be impossible to find such power source (they would have already used it)
but i was too bored [zz)] to sit and analyse my idea with equations.

Anyway, this is the theory forum, right? :wink:
 
  • #18
wimms
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Originally posted by drag
Of course, once you're near c the relativistic mass increase
will be great while the relative velocity increase will be poor..
I'm confused: "once you're near c" - relative to what?? Isn't rocket with its fuel completely independent inertial frame? Then, how does it notice its own relativistic mass increase? I thought it all boils down to exhaust velocity only. Over time, Earth observer would express rocket mass' relativistic increase, but not rocket observer?
 
  • #19
drag
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Originally posted by wimms
I'm confused: "once you're near c" - relative to what?? Isn't rocket with its fuel completely independent inertial frame? Then, how does it notice its own relativistic mass increase? I thought it all boils down to exhaust velocity only. Over time, Earth observer would express rocket mass' relativistic increase, but not rocket observer?
I'm sorry if I might've phrased it in a slightly
confusing manner. I was talking about the exhaust
velocity of the propellant relative to the spacecraft - not
the velocity of the spacecraft itself.

Live long and prosper.
 
  • #20
wimms
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ok, but now I'm confused on other issue: why would we need relativistic exhaust velocities at all? All we need is ability to accelerate given mass at 1G, ejecting onboard mass from that same inertial frame. In about 1 year we'd reach 1c relative to Earth observer.
 
  • #21
Originally posted by wimms
ok, but now I'm confused on other issue: why would we need relativistic exhaust velocities at all? All we need is ability to accelerate given mass at 1G, ejecting onboard mass from that same inertial frame. In about 1 year we'd reach 1c relative to Earth observer.

We don't. But we could either accelerate at a slower rate with a given exhaust velocity, or we could accelerate faster with a faster exhaust velocity but use more energy to accelerate the exhaust. Or we could just increase fuel output and keep a lower exhaust velocity but we'd use more fuel but less energy. It's a challenge of finding the right balance of acceleration, final velocity and fuel requirements for a given mission when we finally are using plasma and ion engines as a standard.
 
  • #22
I did some quick math. If we had a capacitor of 1m length between the plates and we wanted to give to an ion with Q=e an acceleration big enough for it to have reached the speed of light in 1 meter ((1/3)*10^-8 m/s^2) we'd have a problem. The ion's mass would increase. So, we would need to keep on increasing the V of the capacitor. The math i did is giving the V needed for an ion of ten tons mass and a Q=e to get the acceleration i was talking about.
We'd need a V~=10^39 Volts.

So i sat down trying to find a way to create such V. I came up with something. In order to create such V from a phnio we need a really big magnetic field. In order to create such fields we need another phnio through which passes a lot of reuma. The answer for this is superconductivity. The law of Ohm says that I= V/R. Superconductivity is when you force a materials electric resistance to drop to zero. This is achieved by cooling some materials near 0 degrees K. This is already used in particle accelerators such as Fermilab, CERN etc. So, with the law of Ohm, if R drops to zero then with little V you get unlimited I(okay, there are some restrictions but you get enough for what we want here). And with great I comes great magnetic field and with this comes the V you need. And all the energy you need is in order to achieve superconductivity. And that amount of energy is not really huge.

If I've made a mistake anywhere, please correct me. All these are thoughts i haven't yet discussed with others. Also if you have any difficulty getting something because I've not explained it yet just tell me. :wink:
 
  • #23
WHOOPS!

WHOOPS! English is not my natural language so i had to write some words whose translation in English i didn't know in latin characters but in another language. Anyway, it seems that i posted my reply without replacing those words. (feels stupid)


So, replace the word phnio with coil and reuma with current(I). Everything should work out now, right?


Sorry for this, Eh? (bigger stupidity feeling)
 
  • #24
LURCH
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Originally posted by drag
Greetings !

Janus, it's VASIMR - Variable Specific Impulse Magnetoplasma Rocket.
As far as I remember what I read about this the
exhaust velocity range is about 10 - 200 miles per second.
But of course, the propellant flow is reduced at higher
tempratures - exhaust velocities (due to containment and
power limmitations) and thus the total thrust is also
reduced for high exhaust velcoities.

LURCH, no such luck. Electric propulsion has high
exhaust velocities (or specific impulse) but poor
total thrust, so the acceleration is tiny.

Live long and prosper.

I agree; electric, plasma, or laser drives would not accomplish this, but a nuke drive (a la the Orion Project) easily could.
 
  • #25
Janus
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Originally posted by wimms
ok, but now I'm confused on other issue: why would we need relativistic exhaust velocities at all? All we need is ability to accelerate given mass at 1G, ejecting onboard mass from that same inertial frame. In about 1 year we'd reach 1c relative to Earth observer.

The higher the exhaust velocity, the greater the efficiency of the rocket.

The formula for finding the final velocity of a rocket (taking relativity into account) is

v= c*tanh(Ve/c * ln(MR))

where Ve is the exhaust velocity and MR is the mass ratio: (Ship mass + fuel mass)/ ship mass

Thus for any v,the MR needed is

MR = e^( tanh^-1(v/c) *c/Ve)

So to reach, say, .95c with an exhaust speed of .1c would take a mass ratio of 90224199 to 1 (about 90 million kg of fuel for every kg of payload)

At .05c exhaust velocity, this jumps up to 8.14 * 10^15 kg of fuel (about 8 time the mass of the martin moon Deimos) for every kg of payload.

Bouncing our final velocity up to .99c gives MRs of

3.12 x 10^11 to 1

and

9.74 x 10^22 to 1

respectively, for our two exhaust velocities.

This means that it would take 3 times the mass of Deimos to get 10,000 kg up to .99c with a .1c exhaust velocity,

And about 1 1/2 Earth masses to get 1000 kg up to the same speed with an exhaust velocity of .05c

It clearly pays to get our exhaust velocity as high as we can.
 
  • #26
drag
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Greetings !
Originally posted by Janus
It clearly pays to get our exhaust velocity as high as we can.
Of course, balancing that with the power source's maximum
output and its fuel consumption.

(btw, the non relativistic rocket thrust formula:
Vfinal / Vexhaust = ln ( Menitial / Mfinal )

Lurch, the nuclear drive is indeed very promissing for
high mass (manned for example) interplanetary missions.
However, there are difficulties to overcome - the whole
safety issue of surface to orbit transfer and the radiation
for manned missions as well as the specific design
of the engine. Also, the exhaust velocity is still about
twice higher then the best chemical rockets (about 5.5 miles/sec
or 9 km/sec) which is still a bit slow for a manned Mars
mission for example, which needs about 20 km/sec or 12 miles/sec.
Disregarding other factors this means, according to the
rocket thrust formula, an enitial mass that is over 9 times
higher than the final Mars arrival mass, and don't forget that
some part of the ship has to return with the astronauts.
Of course, this is a great improvement compared to chemical
propulsion for this mission and the costs is reduced to
relativly acceptable levels.

Live long and prosper.
 
  • #27
LURCH
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Originally posted by drag
Greetings !

Of course, balancing that with the power source's maximum
output and its fuel consumption.

(btw, the non relativistic rocket thrust formula:
Vfinal / Vexhaust = ln ( Menitial / Mfinal )

Lurch, the nuclear drive is indeed very promissing for
high mass (manned for example) interplanetary missions.
However, there are difficulties to overcome - the whole
safety issue of surface to orbit transfer and the radiation
for manned missions as well as the specific design
of the engine.


Yes, the problems of surface-to orbit transfer and radiation safety are two of the reasons I advocate the construction of a Lunar launch facility. Feul components could be shipped their and enriched in an on-site facility for the vehicles. An accident in such a facility will sicken or kill only those in the facility. Still trajic, but not catastrofphic.


Also, the exhaust velocity is still about
twice higher then the best chemical rockets (about 5.5 miles/sec
or 9 km/sec) which is still a bit slow for a manned Mars
mission for example, which needs about 20 km/sec or 12 miles/sec.
Disregarding other factors this means, according to the
rocket thrust formula, an enitial mass that is over 9 times
higher than the final Mars arrival mass, and don't forget that
some part of the ship has to return with the astronauts.
Of course, this is a great improvement compared to chemical
propulsion for this mission and the costs is reduced to
relativly acceptable levels.

Live long and prosper.

I think you're talking about nuclear-thermal drive, yes? I was thinking more along the lines of the pulse detonation drive of Project Orion. Mars would be a couple of weeks away and, if Hydrogen could be harvested on-site, the moons of Jupiter could be reached in a few months. Had the Project not been canceled in the '60s, these destinations would already be in our past.

Thsi drive system also solves the problem of crew exposure to radiation.
 
  • #28
drag
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Greetings !
Originally posted by LURCH
Yes, the problems of surface-to orbit transfer and radiation safety are two of the reasons I advocate the construction of a Lunar launch facility. Feul components could be shipped their and enriched in an on-site facility for the vehicles. An accident in such a facility will sicken or kill only those in the facility. Still trajic, but not catastrofphic.
Well, I'm totally for a Moon base whether it's that reason
or any other.(Hey ! I got land there so I could really use
some rent profits ! )

As for the nuclear stuff orbital launches,
I personally think that the problem is more of a political
nature both on the US national and the international
different fronts. My technical knowledge on the subject
is limmited but I do believe that very high and fully
adequate safety can be provided by even some modern rocket
launch vehicles as well as additional transfer safety
equipement.
Originally posted by LURCH
I think you're talking about nuclear-thermal drive, yes?
Indeed.
Originally posted by LURCH
I was thinking more along the lines of the pulse detonation drive of Project Orion. Mars would be a couple of weeks away and, if Hydrogen could be harvested on-site, the moons of Jupiter could be reached in a few months. Had the Project not been canceled in the '60s, these destinations would already be in our past.

Thsi drive system also solves the problem of crew exposure to radiation.
Well, abviously it's inadequate for use within the atmosphere
or even in orbit or even some distance farther. I mean, first
you have environmental damages and then you have settelite communication disruptions as well as possibly more direct
influences like course changes, radiation damage to the
electronics and charging during plasma interactions(though those
may be insignificant for a relativly small ship - I don't know,
you probably have to do all the huge mathematics to find out).

Anyway, as for use in just interplanetary space, I do not
believe that a viable technical design for that system
actually exists, but I could be mistaken. By viable I also
mean reasonable in terms of the general resulting mission
effeciency parameters as compared to missions using other
types of primary propulsion systems.

BTW, another possibility is to use a nuclear power source
to power an electric propulsion system. However, I do not
believe that such combined designs can currenly compete with
the "direct" use of the nuclear-thermal propulsion in most
efficiency terms.

Live long and prosper.
 
  • #29
LURCH
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Originally posted by drag


BTW, another possibility is to use a nuclear power source
to power an electric propulsion system. However, I do not
believe that such combined designs can currenly compete with
the "direct" use of the nuclear-thermal propulsion in most
efficiency terms.

Live long and prosper.

Yea, nuclear-thermal is way ahead of nuclear-electric ATM. But I don't think even those forms of propulsion will be accepted by the general public for surface-to-orbit. Remember the protests over the launch of Cassini?
 
  • #30
drag
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It's just stupid. I wonder what they'll say when anti-matter
banks are launched into orbit...
 

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