> Daryl wrote:
Heh, heh. Welcome aboard.:)
> So I'm not sure what it's possible to have a system that follows are
I think the previous post was for minimum fuel useage, not zero fuel useage.
> In particular, I seem to remember reading about a system that used
Haven't heard of this one yet. AFAIK the natural decay of any radioactive
element on earth would be highly unlikely to provide the actual thrust for a
spacecraft on it own. The only use for such a device I have seen is the RTGs
used aboard probes and satellites. Its primary purpose is to generate
electricity for onboard systems.
> Also, something to think about, the net kinetic energy stays the same
Mass driver type drives have also been discussed in cases where a ship might
latch onto a large body of rock/dirt, mine its contents, and expend the
smaller mass portions for thrust.
> Actually, thinking about it, a perfectly efficient
I remember some scientists discussing a laser powered craft some time ago,
not to mention in sci-fi novels. I always wondered what might happen if
something strayed in its path. Many authors only described it for use in
initial acceleration, due to beam convergence problems and enormous energy
requirements for the laser.
This is my first post to this list ... so be kind :-).
> > > Nuclear power is great for generating
THRUST
> Very true, but then you still have an expendable fuel: water! When you
Doesn't one of Newton's Laws state that the net kinetic velocities must remain
constant in a system.
So I'm not sure what it's possible to have a system that follows are current
day view on how physics works and still not consume any fuel.
With that said, I think it might be possible to create a system that doesn't
use much fuel.
In particular, I seem to remember reading about a system that used radioactive
decay for it's thrust. You took a chunk of radioactive material and surrounded
it on three sides by shielding and just let it decay... the particles thrown
off during it's "decay" resulted in a miniscule amount of thrust which would
last a long long time.
Also, something to think about, the net kinetic energy stays the same in a
system... so if you could throw a miniscule amount of mass out at close to the
velocity of light you could probably keep a sizable amount of thrust up for a
pretty good period of time before you ran
out of fuel (sorta a particle accelerator/rail gun down the center
of your ship). Actually, thinking about it, a perfectly efficient laser
(converting mass directly to light) would probably be the most efficient
thrust mechanism (but that's entering the realm of speculation).
I suddenly have the urge to the do the math on this. Constants:
C=300,000,000 m/s or 3x10^8 (or thereabouts)
1G=9.8 m/s^2 (round to 10 m/s^2)
The formulas used:
force = mass * velocity (therefore velocity = force / mass)
(average) acceleration = velocity / time
So for our starship we've got (average) acceleration =
([force of ejected material] / [mass of starship]) / time
== (FoEM / (MoS * time))
Now if we assume the force of the ejected material is being pushed out at C or
thereabouts so FoEM = Mass of Ejected Material * C We have
(average) acc = ((MoEM * C) / (MoS * time))
So our variable here is MoEM (we can always throw more out the back)... time
would be a second (to calculate average acceleration over a longer period of
time... it would just increase the MoEM linearly)).
So let's assume we have a 1x10^6 kg ship which we want to accelerate
at 1 G (10 m/s^2), and we have a really cool rail gun mechanism that
can accelerate things to close to the speed of light (3x10^8)... it would
require us to throw out per second:
10 = ((MoEM * 3x10^8) / 1x10^6)
10 / 3x10^2 = MoEM
MoEM = 0.0333... kg (or roughly 33.3 grams per second).
(which would give you 30 million seconds of fuel before you completely
expended your ship (almost a year) :-) (of course the ships weight
would decrease as you traveled :-). (Note: This 30 million seconds is
a constant for all masses of ships accelerating at 1G).
If you have a less efficient drive (ie unable to throw things out the back at
light speed) your mass of emitted material goes up proportionally. (So if you
could only accelerate things
to 1/3 light speed you'd have to throw out 0.1 kg per second).
Hope I'm not wrong on the above (since it's been about 5 years since my last
physics class and I'm working on memory)... feel free to correct me if I am.
> Daryl Lonnon writes:
@:) This is my first post to this list ... so be kind :-).
@:)
@:) So I'm not sure what it's possible to have a system that follows @:) are
current day view on how physics works and still not consume @:) any fuel.
It isn't. On the other hand, it is possible either to carry a large amount of
fuel (by using dense fuels like nuclear materials or antimatter) or to pick it
up on the way. Probably the best way to do the latter, within a solar system,
is to use solar power. Maybe a solar powered laser system?
Again, you're highly unlikely to get Kra'Vak manouvering by hotwiring your
solar calculator to the sight from your.45 but who knows what the future
holds?
> Mike Miserendino writes:
@:)
@:) I remember some scientists discussing a laser powered craft some
@:) time ago, not to mention in sci-fi novels. Many authors only
@:) described it for use in initial acceleration, due to beam @:) convergence
problems and enormous energy requirements for the
@:) laser.
Yeah, the general theory on lasers is that only a ground-based
installation is worthwhile. You can't get enough power from batteries or solar
panels on the spacecraft, and if you install a reactor, well, that's that much
more weight you have to haul into space. The only plausible way to do this
today is to build a ground station with a very large laser and an extremely
large power plant and just blast stuff up into orbit. Or out of orbit,
whatever.
> In message <199608272223.SAA11968@cliff.cris.com> Mike wrote:
> Daryl wrote:
It's a trade off between energy efficiency and mass efficiency. To get twice
the exhaust velocity (and hence twice the thrust) you need
four times the energy. So high-mass efficiency drives either need
very large energy sources (matter/anti-matter?) or keep to low
thrust (but high efficiency).
> I remember some scientists discussing a laser powered craft some time
If it's powerful enough to accelerate a massive craft at decent velocities, I
think we can assume that you don't want to get in
its way. Much like other high-energy drives.
> initial acceleration, due to beam convergence problems and enormous
Depends on the size of the lasers. The Moties in _Mote in Gods Eye_
had one going for a long time if I remember to power their scout across
several light years.
> On Wed, 28 Aug 1996, Joachim Heck - SunSoft wrote:
> It isn't. On the other hand, it is possible either to carry a large
> -joachim
You could always try the ram-scoop method - giant magnetic fields that
sweep matter into your ship. The faster you go, the more matter you can
scoop up. Interstellar space may not be particularly thick, but if you're
going a significant fraction of light and have ram scoops a couple of
kilometers wide you should be able to pick up a bunch of matter, mostly
hydrogen.
--Binhan
> Sam wrote:
Except most other drives do not have continuous output covering vast distances
of space, or require constant attention and delicate adjustments. If debris
passed through the laser's path, its interference might disrupt the flight
path as only a portion of the beam strikes its intended target's surface area.
This could send the ship off course as well as make it difficult for the laser
to home in on the target area again.
> Depends on the size of the lasers. The Moties in _Mote in Gods Eye_
Well if we're talking sci-fi, they could probably find a way to push a
black
hole. ;)
> Binhan wrote:
Ah, the Bussard ram scoop idea, sorta like a giant spider web. Such a ship
always seems so frail and subject to damage. With scoops a few kms wide you go
fishing for Kra'Vak! I knew someone would find a way to deal with those little
buggers.;)
> joachim wrote:
Highly unlikely. To draw sufficient solar power requires quite a bit of space
in the way of collectors(Not a hot item aboard a military ship). This might
work well from a planetary body, but a spacecraft will unlikely find
sufficient energy outside of 3 AUs.
> Ah, the Bussard ram scoop idea, sorta like a giant spider web. Such a
But as it's sci-fi, the scoop field needn't be composed of
matter. On this topic, I have a (very) vague recollection that the density of
matter in space is on the order of 1 Hydrogen atom per millilitre "locally"
(ie fairly near the sun) and drops to about 1 per litre "out there". Does
anyone know if those figures are anything like right?
> Well if we're talking sci-fi, they could probably find a way to push a
I remember a Jerry Pournelle article in which he suggested dropping
same-charged particles into a black hole to build up a charge, then
moving it around electrostatically!
> >Well if we're talking sci-fi, they could probably find a way to push
It'd have to be a bloody big charge to overcome the gravity. Actually, that
reminds me of my favourite 'star drive' theory. This requires the idea that
you can control and generate gravity. What you do is create a 'virtual mass'
in front of your ship, and the body of the ship accelerates towards it down
the gravity well. But of course, the point of mass is a fixed distance in
front of the ship, so now that's moved. Basically, you can keep on going as
far as you like with this, and it doesn't have any of the problems of buzzard
ramjets or nuclear explosive pulses or riding laser beams etc...
Of course, generating gravity is a but, um, 'nontrivial' :-).
> Rob Paul
> Mike Miserendino writes:
@:) Ah, the Bussard ram scoop idea, sorta like a giant spider web. @:) Such a
ship always seems so frail and subject to damage. With @:) scoops a few kms
wide you go fishing for Kra'Vak! I knew someone @:) would find a way to deal
with those little buggers.;)
That's it! The ultimate fuel source in space - other people's space
ships! Call it the Predator Drive or the Food Chain Drive - you put a
big scoop on the front of your ship, which feeds into a big furnace. Every few
light years or so, you suck down a passing alien spaceship which blows up in
the furnace, providing you with valuable forward momentum! The best part of it
is, these aliens have spent years putting energy into their ships with
chemical fuels, electric engines,
laser beams, solar sails, nuclear reactors and what have you - and now
you get to reap what _they_ have sown! Perfect!
PS The NASA ion engine project is called NSTAR (see also Solar Electric
Propulsion) and is supposed to fly on (well, propel, actually)
the first New Millenium mission, DS-1, a comet flyby scheduled to
launch in 1998.
> Absolutely Barking Stars writes:
@:) Actually, that reminds me of my favourite 'star drive' @:) theory. This
requires the idea that you can control and generate @:) gravity. What you do
is create a 'virtual mass' in front of your @:) ship, and the body of the ship
accelerates towards it down the @:) gravity well. But of course, the point of
mass is a fixed distance @:) in front of the ship, so now that's moved.
Basically, you can keep @:) on going as far as you like with this, and it
doesn't have any of @:) the problems of buzzard ramjets or nuclear explosive
pulses or @:) riding laser beams etc...
@:)
@:) Of course, generating gravity is a but, um, 'nontrivial' :-).
I read a story a long time ago - I think by Fred Pohl - about a
spaceship with the most amazing engines ever. They had developed these engines
that could provide hundreds or thousands of gs of thrust. Problem was, the
pilots tended to get squished. So they built a spaceship with the engines and
cockpit at one end (the back), a looooooooooooong stick, and this enormous
weight at the other end. Boy was that stick ever long, and that weight big. So
anyway, the pilot would turn the engines on, they would crank the weight real
close and the gravity of the weight would pull the pilot forward and cancel
out his inertia. So the test pilot jumps in and takes off. A few hours later,
he's moving at.9 c and doing loops around the solar system every few hours.
Problem is, he doesn't come back. Turns out the winch that pulled the weight
around has broken, so if he tries to slow down, the gravity from the weight
will crush him! Very cute. The physics worked, but the numbers were
unreasonably huge.
> In message <199608281226.IAA21760@sparczilla.East.Sun.COM> you wrote:
> Daryl Lonnon writes:
Density of propellant doesn't matter a great deal, since it's the actual mass
of the stuff which slows you down. Carrying around
a great big asteroid of water-ice may seem impractical, but just
think of the armour it gives you!:)
In message <Pine.ULT.3.91.960828164053.21981B-100000@essex.UCHSC.edu>
> you wrote:
> You could always try the ram-scoop method - giant magnetic fields that
> sweep matter into your ship. The faster you go, the more matter you
Such a shame that the Bussard ram drive acts as such a good brake! Ignoring
the friction caused by them, you'd still need scoop diameters in the tens of
thousands of kilometres for them to be effective.
You could get around it by 'seeding' the space ahead of the ship with dense
packets of hydrogen (or similar fuel). Of course, you'd need to
know _exactly_ which course your ship is going to be taking probably
several years in advance for this to be effective.
> Rob Paul wrote:
Cool. Think they could drop it over the employer of my previous job?
> Sam wrote:
Sheesh. I thought repaving roads was bad!;)
> At 04:42 PM 8/30/96 -0400, you wrote:
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> HELP! How can I unsubscribe from this list serve? I keep getting
Send an email to:
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Mk
> At 07:24 AM 8/31/96 -0500, you wrote:
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