Directing rocket exhausts?

Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?


Christopher
+++++++++++++++++++++++++
"Kites rise highest against
the wind - not with it."
Winston Churchill

(Christopher) writes:

Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?


Existing plasma thrusters use mechanical gimbals, because they get the
job done in a very well understood manner. Magnetic thrust vectoring
is not out of the question, and is appealing on several grounds - not
the least of which is that anything that gets rid of unnecessary moving
parts is a Good Thing.

However, plasma dynamics is a Wierd Science, and it's hard to predict
exactly how a plasma exhaust will respond to some arbitrary, asymmetric
magnetic field. Also hard to test on the ground, because the walls of
your test chamber interfere with both the plasma exhaust and the applied
magnetic field.

So this is a long-term thing, for people with a lot of experience operating
plasma thrusters in space and trying to optimize Nth-generation designs.
The Russians have been flying plasma thrusters for thirty years, and are
still using mechanical gimbals.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
* for success" *
*661-951-9107 or 661-275-6795 * -58th Rule of Acquisition *

In article ,
Christopher wrote:
Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Many of them do. Other methods of thrust vectoring are sometimes used,
e.g. fluid injection into the side of the nozzle.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force...

As John has already noted, this is feasible in principle but hasn't yet
been used in practice. Similarly, you can vector the thrust of an ion
engine by shifting the grids in relation to each other -- this was
demonstrated nearly forty years ago -- but operational ion-thruster
systems still do vectoring with mechanical gimbals.

Non-mechanical thrust vectoring is the sort of sophisticated refinement
that would start showing up if these systems were being aggressively
developed and improved. By and large, they aren't.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

(Christopher) wrote in message ...
Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?

I didn't see any mention of this on the VASIMR site. It's a neat idea,
but I'm sure a mechanical method would win because:
1. It would be cheaper, given the low thrusts involved
2. There would be no cosine losses

Though thinking about it, you'd probably just turn the whole ship.
That would work at the low forces and accelerations typical of
electric propulsion.

John Schilling wrote:

(Christopher) writes:

Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?

Existing plasma thrusters use mechanical gimbals, because they get the
job done in a very well understood manner. Magnetic thrust vectoring
is not out of the question, and is appealing on several grounds - not
the least of which is that anything that gets rid of unnecessary moving
parts is a Good Thing.

However, plasma dynamics is a Wierd Science, and it's hard to predict
exactly how a plasma exhaust will respond to some arbitrary, asymmetric
magnetic field. Also hard to test on the ground, because the walls of
your test chamber interfere with both the plasma exhaust and the applied
magnetic field.

So this is a long-term thing, for people with a lot of experience operating
plasma thrusters in space and trying to optimize Nth-generation designs.
The Russians have been flying plasma thrusters for thirty years, and are
still using mechanical gimbals.

Yet another reason for a strong presence in Earth orbit (and the
Moon), the ability to test novel propulsion systems (espically where the
word 'nuclear' is involved) in a closer approxamation of operational
conditions.


--

You know what to remove, to reply....

On 24 Nov 2003 12:02:35 -0800, (John Schilling)
wrote:

(Christopher) writes:

Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?


Existing plasma thrusters use mechanical gimbals, because they get the
job done in a very well understood manner. Magnetic thrust vectoring
is not out of the question, and is appealing on several grounds - not
the least of which is that anything that gets rid of unnecessary moving
parts is a Good Thing.

However, plasma dynamics is a Wierd Science, and it's hard to predict
exactly how a plasma exhaust will respond to some arbitrary, asymmetric
magnetic field. Also hard to test on the ground, because the walls of
your test chamber interfere with both the plasma exhaust and the applied
magnetic field.

So this is a long-term thing, for people with a lot of experience operating
plasma thrusters in space and trying to optimize Nth-generation designs.
The Russians have been flying plasma thrusters for thirty years, and are
still using mechanical gimbals.

Thanks for that, and the other replys. Nice to know my idea was on
the right track for directional ability with a plasma rocket engine(s)
in space-and in an atmosphere if the plasma engine is as powerful as a
jet engine is today.



Christopher
+++++++++++++++++++++++++
"Kites rise highest against
the wind - not with it."
Winston Churchill

On 24 Nov 2003 12:02:35 -0800, (John Schilling)
wrote:

(Christopher) writes:

Liquid propellant rocket engines have the engine on a gimbals frame so
servo motors can move the exhaust a few degrees in the X and Y axis so
the rocket can be steered.

Would a plasma rocket engine have a similar mechanical frame work, or
as the plasma is electrically conductive and is afected by magnetic
fields would you have the enging in a ridgid frame work and have a
circular ring of electromagnetic nozzle elements or a ring of magnetic
panels so you can pitch and yaw the plasma stream for a turning force
for direction like the gimbals on a liquid propelled rocket does?


Existing plasma thrusters use mechanical gimbals, because they get the
job done in a very well understood manner. Magnetic thrust vectoring
is not out of the question, and is appealing on several grounds - not
the least of which is that anything that gets rid of unnecessary moving
parts is a Good Thing.

However, plasma dynamics is a Wierd Science, and it's hard to predict
exactly how a plasma exhaust will respond to some arbitrary, asymmetric
magnetic field. Also hard to test on the ground, because the walls of
your test chamber interfere with both the plasma exhaust and the applied
magnetic field.

So this is a long-term thing, for people with a lot of experience operating
plasma thrusters in space and trying to optimize Nth-generation designs.
The Russians have been flying plasma thrusters for thirty years, and are
still using mechanical gimbals.

Thanks for that, and the other replys. Nice to know my idea was on
the right track for directional ability with a plasma rocket engine(s)
in space-and in an atmosphere if the plasma engine is as powerful as a
jet engine is today.



Christopher
+++++++++++++++++++++++++
"Kites rise highest against
the wind - not with it."
Winston Churchill