|
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 -----
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/
<image.tiff>
Add photos to your messages with MSN 8. Get 3 months
FREE*.
|