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| Author |
Message |
jamieaah
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long distance space travel
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Sep 8 15:02 UTC 1999 |
Will it ever be possible for man to travel to another solar system?If so what
different ways are there of getting there?Are there any realistic theories
to back up the science fiction "star gate" idea?
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| 14 responses total. |
russ
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response 1 of 14:
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Sep 9 01:56 UTC 1999 |
Possible? If we ever start making ton quantities of antimatter, sure.
And this is all with known physics. Using a matter-annihilation rocket
(whose exhaust would be pi mesons, directed by a magnetic nozzle) it
should be possible to travel to the nearer stars in just a few years
of subjective time. The problem is getting the cost of antimatter
down to something which makes a mission affordable, and given the
huge energy cost of even a gram of antiprotons and the pitiful
efficiency of our current manufacturing methods, that's a tall order.
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i
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response 2 of 14:
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Sep 9 02:33 UTC 1999 |
Are you saying that we could build the rocket, just not fill its fuel
tanks? (Given, say, a $100 billion budget.) Or is the antimatter
rocket impossible-with-vaguely-current-technology, but still far easier
than the fuel?
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russ
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response 3 of 14:
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Sep 9 05:01 UTC 1999 |
I doubt we could build the rocket without sufficient fuel to test various
engine designs. Not all engineering can be done with simulation.
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rcurl
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response 4 of 14:
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Sep 9 05:03 UTC 1999 |
...not to mention designing a gas tank to hold the antimatter.
There is something funny about space. Empty space is full of *something*,
as quarks and antiquarks spontaneously appear in empty space (empty of
both matter and energy-as-we-know-it). Something is going on in those
other 9 dimensions that we don't experience. I suspect that when we
do understand "empty space" and the other 9 dimensions, we might be able
to do some things only partly imagined in science fiction today.
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tpryan
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response 5 of 14:
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Sep 9 23:55 UTC 1999 |
Maybe the ones who will be first to travel to other stars will
fund it themselves. It may take a number of years, after getting the
dollars by doing well-paid for space things: capturing asteroids for
the metal and other ore; landing ice chunks on the moon or Mars to use
as a water supply; being the site for micro-gravity manufacturing.
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russ
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response 6 of 14:
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Sep 10 00:11 UTC 1999 |
We've already figured out how to handle small quantities of antimatter,
and we can handle things without touching them using magnetic and
electric fields. I don't think the gas tank is going to be the real
problem with antimatter rockets.
Finding ways to make wormholes or warp drives is all well and good,
but it isn't even a known possibility yet, just un-verified speculation
of physical theories yet to be tested. Antimatter has the advantage
that there isn't any new physics required, just engineering. ;-)
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i
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response 7 of 14:
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Sep 10 03:14 UTC 1999 |
What sort of reaction chamber & nozzle were we figuring on using on the
matter/antimatter rocket? It's gonna have to take quite a beating....
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russ
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response 8 of 14:
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Sep 10 05:01 UTC 1999 |
Basically, a really powerful magnet. "Beating" is an understatment,
since the product of p - pbar annihilation includes one pi-nought
meson which almost instantly decays to a pair of high-energy gamma
rays. Radiation damage is going to be a big issue to anything nearby.
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i
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response 9 of 14:
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Sep 11 02:52 UTC 1999 |
How "pure" an antimatter rocket are we looking at here? Something that's
using lots of matter as reaction mass/fuel and a touch of antimatter to
get a "hot" exhaust velocity, or a 50/50 mix aimed at getting the
ultimate in delta-v? If the latter, my impression is that most of your
thrust will come from the inertia of absorbed hard gamma, and really
nothing that we can envision can take enough of that to get meaningful
thrust and engine service life.
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russ
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response 10 of 14:
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Sep 11 13:58 UTC 1999 |
The p - pbar reaction also emits two charged pi mesons, which can be
directed by magnetic fields (they decay to muons and then to electrons,
but that process takes some microseconds). The momentum transferred
to the magnet by pushing the charged annihilation products backwards
would give the bulk of the thrust. If some method could be used to
use the gammas that would be terrific, but I question the likelihood.
The concept where I got this assumed 50/50 ratio of matter to antimatter
for best exhaust velocity. If you're just putzing around the solar
system it makes much more sense to use a much higher ratio of matter
to antimatter; you get the best energy utilization at a mass-ratio of
about 4.
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i
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response 11 of 14:
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Sep 11 16:15 UTC 1999 |
If they're giving the bulk of the thrust, aren't those two pi mesons
going to have speeds extremely close to c, thus requiring a...ah...
problematically intense magnetic field to guide them in the desired
direction? (And wouldn't they be a particle/antiparticle pair, with
opposite charges to further constrain magnet design?)
Any feel for what % of the reaction energy comes off as has-to-be-handled-
by-the-magnet-cooling-system gamma?
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russ
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response 12 of 14:
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Sep 12 03:17 UTC 1999 |
They come off at a velocity that you can probably calculate from
the mass of p and pbar, minus the masses of pi, pi-bar, and pi-nought;
the vanished rest mass becomes kinetic energy. Believe me, present-day
magnets are up to the task. At Fermilab they sling protons around at
kinetic energies of tens of billions of electron volts, and the total
energy of a p-pbar reaction is under 2 GeV. The charge/mass ratio of
a pion is considerably higher than a protons, making it easier to push
magnetically.
The amount of energy absorbed by the magnet's shielding system
depends on the geometry of the annihilation system and the nozzle.
You can run a few numbers to get the radiated gamma power for a
given thrust level, but then you need to start analyzing magnets.
My E&M is a little too stale to do this on the back of an envelope.
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i
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response 13 of 14:
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Sep 12 20:19 UTC 1999 |
Ah.....how many hundred meters of running within a few centimeters
of the magnets does it take Fermilab to deflect a fast proton through
a full radian? I don't think that either the scale or the geometry
that Fermilab uses is an option in our case.
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russ
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response 14 of 14:
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Sep 12 20:23 UTC 1999 |
Not usable, and almost certainly not necessary either. If you want to
calculate the required radius, compute the maximum energy of a pion
from the annihilation (2/3 of the vanished rest-mass, more or less)
and thus its speed. From this and its charge (1 unit) you can compute
the force from a given magnetic field, and thus the radius of its
turn. Electrons need a lot less field to bend them to a given radius
at the same speed as a proton, and pions are much lighter than protons.
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