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?

--
Sander

+++ Out of cheese error +++

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.

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.
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

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.

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)

--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

On Mon, 14 Feb 2005 05:18:28 GMT
(Henry Spencer) wrote:

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.

Correct me if I am wrong, but I can't see anybody supporting the
development of nuclear rocket engines, given the political problems
associated with simple RTGs.

A nuclear-electric thruster system, while inefficent, can at least be
built from well understood components.

I know the USSR had spacecraft with reactors. Did the USA use them early
on as well?
--
Michael Smith
Network Applications
www.netapps.com.au | +61 (0) 416 062 898
Web Hosting | Internet Services

Michael Smith wrote:

Correct me if I am wrong, but I can't see anybody supporting the
development of nuclear rocket engines, given the political problems
associated with simple RTGs.

Why should this follow? RTGs are much more radioactive at launch
than are reactors.

The bigger problem with space reactors is development cost and
lack of application.

Paul

Michael Smith wrote:
On Mon, 14 Feb 2005 05:18:28 GMT
(Henry Spencer) wrote:

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.

Correct me if I am wrong, but I can't see anybody supporting the
development of nuclear rocket engines, given the political problems
associated with simple RTGs.

Well, I support it.

Michael Smith writes:

On Mon, 14 Feb 2005 05:18:28 GMT
(Henry Spencer) wrote:

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.

Correct me if I am wrong, but I can't see anybody supporting the
development of nuclear rocket engines, given the political problems
associated with simple RTGs.

A nuclear-electric thruster system, while inefficent, can at least be
built from well understood components.


I'm not following your logic. The "political problems associated with
simple RTGs", were entirely due to A: some minor but non-negligible
safety issues pertaining *only* to RTGs and not to any other space
nuclear power system, and B: the fact that they used the N word.

"Nuclear rocket" and "nuclear electric thruster system", both use
the N word. If the political problems associated with simple RTGs
will suffice to kill the one, they will just as surely suffice to
kill the other.

In fact, the political problems associated with simple RTGs, were
overcome, and the RTGs flew. With that trail now blazed, I don't
think nuclear systems are unthinkable. But if they are, they are
*all* unthinkable.


--
*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" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

Henry Spencer wrote:

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)


I don't know enough about long-term nutrition and related
matters to have an opinion, but note that the manned-Mars
presentation at the recent Mars roadmap meeting contains
the following assertions at slide 21:

http://www.hq.nasa.gov/office/apio/p...an_studies.ppt

Closing the life-support air and water loops with low
expendables is a key leveraging technology for long
duration human exploration missions

Current food preservation technology is not capable of
providing nutritionally viable food for the longer
mission durations under study. Food production
technologies under the environmental conditions of these
missions is not developed to the point of being the
primary source of food.

Power requirements for both closed loop life support and
food production can be significant, indicating that
advanced life support and advanced power systems are
closely coupled.


[Boxed summary]

Closing the air and water loops is essential to reduce the
total mass of long duration missions to a reasonable level.

Improvements in food storage technology or production
technology are also needed to reduce overall mass and ensure
crew health.