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Your with the THEMIS team. You must know Noel
Gorelick, aka "Bamf". Say hi to him for me. He knows who I am. :)
RFB
----- Original Message -----
Sent: Saturday, December 21, 2002 11:26
AM
Subject: Re: Last point
Hi Dave -
I think you need to understand that nuclear
fission-powered drives and ion propulsion are very different types of
propulsion. In a nuclear fission drive, radiation from a solid-core uranium
plant produces thermal energy which heats up a propellant gas, like hydrogen
or ammonia. It is this gas that produces the acceleration for the ship. You
should think of a nuclear fusion drive as a cold-gas thruster that you can
heat up to high exit velocities -- there is no combustion as occurs in
chemical rockets. If I interpret what you're saying below correctly, I think
you've got that right. For your reference, a typical nuclear fission-heated
gas drive can produce about 300-450 kN of thrust. Compare to the space shuttle
main engines which produce 1700 kN of thrust each and the shuttle solid rocket
boosters that produce 11,800 kN of thrust each. Fission-powered rockets don't
produce anywhere near that much thrust, but because they can burn
-significantly- longer (with Isp's in the 1000 sec range), they are a superior
drive system. Just keep in mind the trade-offs -- the thrust is far lower than
with chemical rockets.
But, I must point out that I think you are
still a little confused about ion drives. They are -nothing- like
fission-power drives. It is a completely different process. Ion drives are
totally electric. Could you maybe be thinking of an arcjet or resistojet, in
which an electric arc heats up a propellant and accelerates it out? This is
indeed somewhat similar (from a conceptual standpoint -- not an engineering
standpoint!) to a nuclear-powered drive. The typical Isp for these drives is
also around 1000s, so they are about as fuel-efficient, but they do not have
anywhere near the thrust of a nuclear drive, as you point out. Of course, you
don't have to add all the mass of the reactor shielding either, so there are
trade-offs even here.
An ion drive, however, is a completely different
beast. With an ion drive, you are accelerating charged particles directly,
there is no heating of an additional gas or anything. The amount of thrust, as
I indicated earlier, is very, very small, about a Newton (0.001 kN). But the
efficiency can be literally ten times that of a nuclear-powered drive, so
that's not to be sneered at. A plasma drive, btw, is -not- a nuclear fission
drive. A plasma drive is also a kind of electric propulsion, but instead of
just emitting charged particles (and by the way, a "plasma" is nothing more
than a stream of charged particles), we accelerate those particles using a
magnetic field. Plasma drives are just one type of what we call
electromagnetic propulsion, whereas ion drive are one type of what we call
electrostatic propulsion. But please understand that neither of these drives
is anything like a nuclear-fission powered drive. Both of these thrusters, the
plasma and the ion drives, produce very small thrusts at very high Isp's. You
would only want to consider electric propulsion for a very small subset of
space missions, basically very long-duration, long-distance missions.
I really think what you are wanting is a nuclear fission drive, as I
outlined above. I think the confusion is probably nothing more than your using
one term when you mean another. NERVA (an expendable drive) is the only
prototype nuclear-fission drive that has ever been built. A concept called
CERMET (an advanced reusable NERVA) has been proposed, but to my knowledge has
never built. Deep Space 1, as you correctly pointed out, uses electric
propulsion, but I don't think that is what you really want to use for the
missions you have in mind. If you have an engineering background, I'd be happy
to refer you to some papers that might help you design your nuclear fission
drive in Orbiter, just let me know!
Hope this helps,
Kilo
On
Saturday, December 21, 2002, at 09:41 AM, DarkDAVE wrote:
plasma drives on the other
hand also use ionized gas as propelant but have higher thrust, especialy if
it has a nuclear fission plant as it's core. only reason current why ion
drives have low thrust is because their eletrical power comes from solar
radiation. plasma drives are like an ion drive connected to a high heat
source rather than a low eletrical power
source.
----- Original Message
-----
From: Keith
Watt
To:
orbiter@firedrake.org
Sent:
Saturday, December 21, 2002 11:58 PM
Subject: Re: Last
point
Hello all -
I've hesitated to jump in here, but I think
there is a misconception that needs correcting. I get the impression that
some people on this list feel that ion drives are very fast, high-propulsion
drives. Nothing could be further from the truth. What is wonderful about ion
drives is that they are extremely -efficient- drive, having Isp's in the
2000-10000 secs range, but the thrust is at best on the order of 1 Newton
(see Humble, Henry, and Larson, _Space Propulsion Analysis and Design_ for
data -- I highly recommend this book if you have an engineering background).
For comparison, just the maneuvering thrusters on the spacecraft I work
with, 2001 Mars Odyssey, are 22 Newton thrusters. Ion drives produce a tiny,
tiny, amount of force. You may have read that the exhaust velocities can
reach 10,000 m/s, and that's certainly true. But remember that momentum is
velocity * mass. The mass of these particles being ejected is beyond tiny,
so the actual force produced is very, very small. You need to think of ion
drives as being in the same category as solar sails, because that's what
their orbits look like -- non-Keplerian spirals.
So why use ion
engines at all, you might ask? Because, as I said, their high Isp makes them
phenomenally fuel efficient. That means that you can accelerate almost
continuously. It takes years to get up to a decent velocity, but you can
reach velocities chemical rockets can't, simply because they will run out of
fuel first. You would never want to use an ion drive, for example, to escape
Earth orbit or to travel to the Moon. It would take nearly a year to get
there. Even Mars is a bit too close to really see a benefit, though you
might could make a case for it. Basically, if you want to go a very long
distance, electric (ion) propulsion is your best bet; if you want high
accelerations, you'll never beat a chemical rocket. Also, if you are using
ion propulsion, you'd better be extremely accurate in your piloting, because
changing course is very, very difficult once you've built up some velocity
over a couple of years...
If you have any questions about it, I'll do
my best to answer them. I am currently on the Mars Odyssey THEMIS Camera
team, but before that I was a spacecraft design and mission analysis
engineer at NASA/Marshall Space Flight
Center.
Regards,
Kilo
-----------------------------
Keith
Watt, M.A., M.S.
2001 Mars Odyssey THEMIS Camera
Team
K.Watt@asu.edu
On Saturday, December 21, 2002, at 02:35
AM, Dark DAVE wrote:
Ever heard of Deep Space 1? that's a retired ion
drive satelite. It's the 2nd of it's kind and is now has been manualy shut
down in space. It also took photos of a comet, and then an
asteroid.
A plasma drive prototype already exist, i think it belongs
to JPL, not sure, but it is working on the ground quite well... it's only a
matter of time before they build one in a space craft. A plasma drive works
almost the same as an ion drive, but it uses heat to propel the ionized
propelant.
do a search on google.com for Deep Space
1.
David
>From: "Technician"
>Reply-To:
orbiter@firedrake.org
>To:
>Subject: Re: Last
point
>Date: Fri, 20 Dec 2002 13:23:20
-0600
>
>Well, what I meant by not being realistic is
that, as far as we know, there
>is no working ion drive spacecraft
prototype in NASA's inventory.
>:)
>-----Original
Message-----
>From: DarkDAVE
>To:
orbiter@firedrake.org
>Date: Thursday, December 19, 2002 11:03
PM
>Subject: Re: Last point
>
>
>
>Sounds interesting! I'll have to read up on the centurion manual. So
you
>say
> >it's not realistic? I am only interested
in realistic models, even if it's
> >hypothetical it can still
be realistic if the manual indicate where all
>that
>
>thrust and fuel come from and how it's produced in real life using
real
> >physics maths and models.
> >
>
>I fully intend to make my own nuclear powered plasma drive ship my
self
> >(plasna druve us an ion drive that heats up the ions).
And ill back up all
> >the performance specs with a technical
manual to indicate how it can work
>in
> >real life.
I might have to use some of NASA's current designs for going to
>
>Mars.
> >
> >Just out of interest has anybody
modeled the X-33 or the X-43A? The X-33
> >program failed, but
the X-43A as i recall is a scramjet/rocket hybird ship.
>
>
> >Not sure if i can answer your question tho, ill leave
it to some one else
>to
> >do so.
>
>
> >David Ong
> >
> >
>
>> The Centurion 2069 ship I imported into Orbiter is set up for 'ion
drive'
> >> engines. Capable of velocities well over 250Kps.
Atmospheric flight is
> >> obtained by conventional airfoil
wings, control surfaces and rudders.
> >> However, I have to
mount much smaller engines for slower flight speeds,
> >>
since the primary engines put out way too much thrust to control
landings
> >> very well, even in Earth's gravity and
atmosphere, extremely difficult to
> >> control when landing
on the Moon or other low gravity/atmosphere
> >>
planet/moon.
> >>
> >> In this
configuration, going to Brighton Beach Moon base from Cape
>
>Canaveral
> >> takes about an hour or so at 120Kps.
Slowing down is not a problem, OI is
> >> not a problem.
Next test is to fly from Brighton Beach to Olympus, Mars,
>
>at
> >> a test speed of 200Kps.
>
>>
> >> Ok, so it isnt following real world scenarios.
But, all things advance.
> >NASA
> >> has
re-opened the space nuclear power research and soon we could see
>
>either
> >> the shuttles or shuttle replacements powered
by nuclear reactors, which
>in
> >> turn provides
plenty of juice for HV ion drive engines.
> >>
>
>> I do have one inquery. Is there a way to have such a high velocity
ship
> >have
> >> retro thrusters that
automatically adjust their density output based on
> >>
velocity, and adjust themselves as the velocity changes? Can this
be
> >applied
> >> to the retro, pitch, bank
and yaw thrusters as well? Will the engine in
>
>the
> >> sim run such engines in this
manner?
> >>
> >> RFB
>
>
> >
> >--
> >Orbiter discussion
list:
> >- mail orbiter-request@firedrake.org with subject
"unsubscribe" to leave
> > or ask the listmaster
(@firedrake.org)
> >- archives at
http://lists.firedrake.org/orbiter/
>
>
>
>
>--
>Orbiter discussion
list:
>- mail orbiter-request@firedrake.org with subject
"unsubscribe" to leave
> or ask the listmaster
(@firedrake.org)
>- archives at
http://lists.firedrake.org/orbiter/
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