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Running multiple HET in parallel?



 
 
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  #1  
Old February 9th 05, 08:46 AM
Sander Vesik
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Default Running multiple HET in parallel?

Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased
performance? Is it being already used somewhere?

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  #2  
Old February 9th 05, 08:27 PM
Ian Stirling
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Sander Vesik wrote:
Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased
performance? Is it being already used somewhere?


As long as you seperate them enough, sure.
  #3  
Old February 10th 05, 12:30 PM
Michael Smith
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On Wed, 9 Feb 2005 07:46:49 +0000 (UTC)
Sander Vesik wrote:

Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased
performance? Is it being already used somewhere?


Just the energy cost, I think.

It would be interesting to work out how much of a spacecraft you would have with a couple of submarine style fission reactors and as many ion or hall thrusters as you had power for.

Given the lack of enthusiasm for this approach I can only assume that it doesn't deliver transit times short enough to be safe for humans.
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  #4  
Old February 10th 05, 03:08 PM
Earl Colby Pottinger
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Sander Vesik :

Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased
performance? Is it being already used somewhere?


More thrusters, more power needed.

E.C.P.

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  #5  
Old February 12th 05, 06:48 AM
John Schilling
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Sander Vesik wrote:
Are there any known issues with running multiple HET
(Hall Effect Thruster) in parallel to get increased
performance? Is it being already used somewhere?



I've seen it done, and it seems to work just fine. Ground tests
only, so far. And I happen to have the paper on my desk.

"The Air Force Clustered Hall Thruster Program", W.A. Hargus Jr and
G. Reed, AIAA-2002-3678, 38th AIAA Joint Propulsion Conference, 2002


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  #6  
Old February 13th 05, 11:38 PM
Allen Thomson
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Michael Smith wrote:

It would be interesting to work out how much of a
spacecraft you would have with a couple of submarine
style fission reactors and as many ion or hall thrusters
as you had power for.


Given the lack of enthusiasm for this approach I can
only assume that it doesn't deliver transit times short
enough to be safe for humans.


It would be interesting to know if there is currently
any propulsion approach available that would allow
significantly faster than Hohmann trips for humans
to other planets/moons/major asteroids. (Our moon
excepted, of course.) "Currently available" can be
interpreted to mean "available by 2025 at a development
+ procurement cost of no more than $10G in 2004 dollars
per year between now and then."

Equally intresting would be to know about the technology
for life support systems that would reasonably reliably
sustain a half-dozen people for two or more years in
space without help from Earth.

  #7  
Old February 14th 05, 06:18 AM
Henry Spencer
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In article .com,
Allen Thomson wrote:
It would be interesting to know if there is currently
any propulsion approach available that would allow
significantly faster than Hohmann trips for humans
to other planets/moons/major asteroids... "Currently available"
can be interpreted to mean "available by 2025 at a development
+ procurement cost of no more than $10G in 2004 dollars
per year between now and then."


Yes: orbital assembly/fueling will let you do faster-than-Hohmann trips
for small expeditions with chemical propulsion. You need an orbital fuel
depot, and lots of fuel launches, but the former is fairly straightforward
if you don't insist on using LH2, and the latter provides high flight
rates for RLVs and a large competitive market for launchers of all sorts.

Double yes: if you're willing to spend a bunch on R&D to reduce launch
rates -- which is probably a bad deal, but is undeniably attractive to
organizations that specialize in R&D -- solid-core nuclear rockets can
considerably improve the picture, speeding things up further or permitting
larger expeditions or both. Rover/NERVA solved most of the major
technical problems of a first-cut version in the 60s, and demonstrated
that a fast-paced program could improve the state of the art remarkably
quickly in this area. You can start with NERVA derivatives, and pursue
more ambitious designs in parallel with the first expeditions. The one
big hassle is low-emissions test facilities, and it's one that should
yield quickly to substantial amounts of money -- no breakthroughs are
required.

Liquid-core or nuclear-lightbulb is substantially better, and gas-core
is much better, although they are longer-term options with significant
development issues.

Equally intresting would be to know about the technology
for life support systems that would reasonably reliably
sustain a half-dozen people for two or more years in
space without help from Earth.


Adequate water recycling -- the big issue -- has been demonstrated, on
a modest scale. (Air is a minor side issue by comparison.) The simplest
way to address the food loop is not to try, given that freeze-dried food
weighs less than half a ton per man-year. Generally, much the simplest
and most reliable way to tackle a lot of the smaller recycling/repair
issues is brute force: more mass, and more fuel to push it, is cheaper
than major engineering R&D.

Of course, trying to sell that approach to R&D-oriented organizations is a
bit of a challenge. "Anything which they do not wish to do is always
lacking in technology. Whether single stage to orbit or Mars missions,
the technology is never quite ready..." (Jim French)

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  #8  
Old February 14th 05, 06:23 AM
D Schneider
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Allen Thomson wrote:

[...]
Equally intresting would be to know about the technology
for life support systems that would reasonably reliably
sustain a half-dozen people for two or more years in
space without help from Earth.


Which leads me down the path to wondering about life support in large
"cycler hotels"; it is easy to imagine that such a venue would have more
repair resources than a small station (ISS, for example). More tools, a
machine shop (wonder what a 0g machine shop would look like!), spare
parts, etc.

But on the flip side, it isn't clear yet that all the ELCS could be scaled
up for a larger venue; would you need to have 15 Elektron units for a 50
person hotel? Or could you do it with 2 or 3 units (enough overcapacity
that if one unit is offline, the other could cover for a reasonable repair
period)?

/dps

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  #9  
Old February 14th 05, 03:57 PM
Richard Hofer
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In recent years, Hall thruster clusters (i.e., running in parallel)
have been investigated by the Air Force and the University of Michigan.
As a first stab, there have been no show stoppers identified with
operating Hall thrusters together. Brian Beal's Ph.D. dissertation was
concerned with a cluster of four 200 W thrusters and Mitch Walker also
devoted portions of his dissertation on a pair of 5kW thrusters. You
can find both of these at:
http://www.engin.umich.edu/dept/aero...ertations.html

For a while now, the Air Force has been focussed on clusters as a means
to achieve high-power operation, while NASA has continued with
monolithic thrusters. This was for a variety of reasons, not the least
of which is that NASA is looking at using Hall thrusters at several
hundred kilowatts, while the Air Force will probably stay below 100 kW
for quite a while. As NASA continues to push to higher powers, there
will be a logical point where Hall thruster clusters become necessary.
This is for a variety of reasons, not the least of which are thrust
density, limitations on the magnetic circuits, vacuum facility
limitations, and redundancy. One concept for using Hall thrusters in
the Moon/Mars initiative is to attach them to cargo tugs that go back
and forth from LEO to some higher orbit, or even all the way to the
destination. The crew shows up much later after making a "quick" trip
on a chemical rocket. These types of missions require, at least,
several hundred kilowatts.

 




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