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#1 2005-10-03 18:50:57

VTTFSH_V
Member
From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: Ion Engines as Maneuvering Thrusters

If you had an Orion-sized ship, would ion engines or clusters of ion engines work decently as maneuvering thrusters, instead of using chemical rockets?  NASA has tested ion engines as maneuvering thrusters on small satellites.


Have a nice day.  big_smile

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#2 2005-10-03 19:08:49

John Creighton
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From: Nova Scotia, Canada
Registered: 2001-09-04
Posts: 2,401
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Re: Ion Engines as Maneuvering Thrusters

More research needs to be done before ion engines can be used on a large scale like to move a space station. For instance they must work with a cheaper fuel. They also must be able to produce more thrust relative to the weight and volume of the engine. A close alternative is a VASMIR type engineer. However, I think if VASMIR engines were ready to go we would be see planetary pope missions that plan to use them in the coming decades.

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#3 2005-10-03 19:25:48

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Ion Engines as Maneuvering Thrusters

Short answer: No.

Ion engines don't provide enough thrust for maneuvering, especially not on a vehicle of such magnetude. On satelites, they are not used for maneuvering, they are used to re-boost orbit.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#4 2005-10-03 22:21:11

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
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Re: Ion Engines as Maneuvering Thrusters

I suppose it depends upon what you mean by manuvering.  If you mean simply changing the orientation of the vessle such as what the shuttles Reaction Control System (RCS) do, then no ion engines are probably not the best choice.  Changing the facing and attitude of a spacecraft, even a large one such as an Orion takes a very small Delta V,  <1m/s.  Which is insignifigant when compared to the total Delta-V requirment of most space-mission ESPECIALY those that an Orion type vessle would undertake.  Thus other qualities of the engine become more important than it's ISP.  Specificly it's specific power or thrust/weight ratio and the specific power of it's fuel.  Chemical engines far out-perform ion engines in these respects, and that is why it is what all (to my knowledge) satilites and spacecraft have used them.  Although some satilites requirments for this sort of manuvering are so low that it can be handled entirely with gyroscopes.  Perhace an ion RCS would make sense on a VERY large spacestation of some sort,.  They could be used to help spin it up and what not which could take a fair amount of energy as well as more conventional manuvers, be we are talking 2001 Space-Oddessy sized staions here.  You would want to rock such a boat to fast either.

For minor (and not so minor) corrections in orbit inclination and what not, ion engines are a good choice, although probably not for a vessle the size of Orion.  These sorts of manuvers (which are handled by the space shuttles OMS) take considerably more delta-V.  Generaly >1m/s on up to escape velocity for the planet.  Most Orion type vessles are so large that it is probably worthwhile to fire off a couple nukes to achive any major changes in it's orbit.  Other more minor changes probably should be made as it is probably more worthwhile to bring any smaller objects to it rather than the other way around.  Also even with the larger Delta-V requirments of these manuverse most satilites still don't do enough of them for an ion engine to make any sense.

But for a satilites/probe that has to make alot of manuvers (such as one exploring some of the outer-system) or for a tug (which likewise has to make lots of orbit adjustments.  An ion engine is a good choice.  The only place I could see an Orion using one would be if you had an ion-tug drag the vessle away from the planet before firing up it's engines due to enviromental concurnes.


He who refuses to do arithmetic is doomed to talk nonsense.

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#5 2005-10-04 02:59:16

VTTFSH_V
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From: Hawaii
Registered: 2005-09-13
Posts: 31

Re: Ion Engines as Maneuvering Thrusters

The only place I could see an Orion using one would be if you had an ion-tug drag the vessle away from the planet before firing up it's engines due to enviromental concurnes.

That is exactly were I was going.  Please continue to explain this.

I didn't mean maneuvering as in quick turns, but as in moving away from a planet or making a 180º rotation, slowly.  The ship could carry its own ion engines to do so, yes?

Furthurmore, what type of thruster would needed for slightly quicker turns, for, e.g., dodging a small asteroid that is detected ahead of time to be on a collision course with the ship?


Have a nice day.  big_smile

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#6 2005-10-04 05:07:45

chat
Member
From: Ontario Canada
Registered: 2003-10-23
Posts: 371

Re: Ion Engines as Maneuvering Thrusters

VTTFSH_V,

I don't see any problem with moving things with ion engines, as long as you have enough time to move them.

If you are willing to wait then ion engines will do the job on any structure in space, and most jobs.
If you need a quick turn then the number of ion engines and cost of the engines to do that, will outweigh the usefulness of the engines themselves.


The universe isn't being pushed apart faster.
It is being pulled faster towards the clumpy edge.

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#7 2005-10-04 09:42:38

GCNRevenger
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From: Earth
Registered: 2003-10-14
Posts: 6,056

Re: Ion Engines as Maneuvering Thrusters

The trouble with using an ion drive on such a large vessel is that its sheer mass is so big that the ion engine would have to produce relativly large amounts of thrust.

Now, specific impulse and thrust are inversely proportional for a given amount of electrical power in ion engines, so if you set a high thrust setting then you lose the specific impulse advantage of the engine in the first place.

If you want both high thrust and high Isp, you then need a very large power plant (heavy duty nuclear reactor), which will also weigh down your ship and likewise defeat the purpose.


"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw

The glass is at 50% of capacity

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#8 2005-10-04 10:32:10

Austin Stanley
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From: Texarkana, TX
Registered: 2002-03-18
Posts: 519
Website

Re: Ion Engines as Maneuvering Thrusters

The only place I could see an Orion using one would be if you had an ion-tug drag the vessle away from the planet before firing up it's engines due to enviromental concurnes.

That is exactly were I was going.  Please continue to explain this.

Well fireing of a nuke could potentialy cause problems for any nearby satilite and certianly trouble for the construction station.  So it make sense to move the thing away before firing.  This is where an ion engine might come in.  But it wouldn't make sense to incoporate it into the ship, as it wouldn't be needed for most of the rest of the journey.  It would be a first stage of sorts.  And since moving stuff around in orbit is something we are going to want to do eventualy, it makes sense to have a dedicated tug to do this with, eventualy.  Of course all this assumes the Orion was built in space, if you launched it from the ground, throw all this out the window.

I didn't mean maneuvering as in quick turns, but as in moving away from a planet or making a 180º rotation, slowly.  The ship could carry its own ion engines to do so, yes?

Well you see those two are really VERY diffrent kinds of manuvers.  A quick (or slow) rotation takes drasticly less Delta-V than changing the orbit does.  This is why the spaceshuttle carries two diffrent sorts of engines to acomplish these manuvers.  As I said before, ion engines have to little power/thrust and/or specific power to make them worth using as a RCS, and an Orion is to big to consider using them as a OMS.

Furthurmore, what type of thruster would needed for slightly quicker turns, for, e.g., dodging a small asteroid that is detected ahead of time to be on a collision course with the ship?

The only diffrence bettwen a quick and a slow rotation is the rate the energy is applied, ie. thrust.  The delta-V is exactly the same.  This amount of energy is so small in comparision to the ships mass, that it generaly doesn't make any sense to go with efficent but slow engines like an ion engine.

In terms of dodging asteriods, frankly you wont do it.  Space is BIG, and EMPTY.  So any asteriods that cross your orbit you are going to see coming a LONG way away.  In fact unless you specificly decied to pass by an asteriod, there is realy no chance that you are going to come into contact with one.

The only time this wouldn't be true is when traveling at fraction of C in bettwen solar systems.  Stuff IS probably out their (although we have no idea where and how much), and hitting it would be a bad idea even at some small fraction of C.  However at those speeds (and with a vessle the size of any interplantery spacecraft ie. >1000MT) doging is impracticle, and most studies have looked at protection and/or deflection/destruction of incoming particles.


He who refuses to do arithmetic is doomed to talk nonsense.

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#9 2005-10-05 12:18:25

ftlwright
Member
Registered: 2004-11-17
Posts: 61

Re: Ion Engines as Maneuvering Thrusters

You *might* be able to get by with an arcjet in this case, as they can be used as swapout replacements for monoprop methane thruster used in most satellites.

There's really nothing preventing you from using an ion, hall or MDT as a maneuvering thruster; there just isn't much reason to do so.  It has already been pointed out, but using an ion thruster for attitude control is a non-optimal operating regime for this type of device.

To be honest, the best strategy for an Orion sized spacecraft would be to "Damn, the torpedoes, full speed ahead!"

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