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Running multiple HET in parallel?



 
 
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  #11  
Old February 16th 05, 02:13 PM
Paul F. Dietz
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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
  #13  
Old February 17th 05, 09:15 AM
John Schilling
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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 *

  #14  
Old February 18th 05, 03:10 AM
Allen Thomson
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Speaking of such matters, see

http://www.spaceref.com/news/viewsr.html?pid=15443

In particular see the Power Point (sorry) presentation

"Session 6: Human Mars Exploration Mission Architectures and
Technologies"

  #15  
Old February 18th 05, 10:04 AM
Malcolm Street
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Paul F. Dietz 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.

Indeed, a point that's often overlooked.

RTGs start at peak radioactivity and then decay.

A reactor can be launched inert, with sod-all radioactivity, and then sent
critical when in a safe orbit (I recall c. 1000 miles being a figure
mentioned in a debate on this here quite a while ago).

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

Yes. For electicity generation, compared to RTGs a reactor is much more
complicated, much more expensive to develop and probably much heavier and
bulkier.

There just hasn't been anything that's needed the sort of high long-term
power a reactor can put out. A manned mission to Mars, though...

Nuclear rockets (I include the type of HET array being suggested in this
definition) are another matter. So far there hasn't been anything that
hasn't been able to be done with chemical rockets. However (again) a
manned mission to Mars could well be such a mission; the problems of bone
loss and radiation exposure could prove to be such that a nuclear rocket
would be the only way to get there in a time that would keep the crew in
condition to actually do something when they got there, let alone back on
Earth. You'd have the weight of shielding to consider, and it could be a
trade-off between radiation from the engine and radiation from space. (ie
light shielding may allow sufficiently faster acceleration and hence
shorter journey times that you actually reduce overall radiation exposure).

I'm a great fan of Stephen Baxter, but his novel "Voyage" really doesn't do
the NERVA nuclear-thermal rocket program justice; it was both saner and
more successful than he makes out. For a start, in theory at least with
the hydrogen fuel radioactive emissions were limited to the 2% or so of
hydrogen that was deuterium. Of course the problem was that bits of engine
got spat out the back as well, but it was acceptable by '60's standards.
Of course you'd have to be more careful now.

--
Malcolm Street
Canberra, Australia
The nation's capital
  #16  
Old February 20th 05, 11:42 AM
Ian Stirling
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Malcolm Street wrote:
Paul F. Dietz 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.

Indeed, a point that's often overlooked.

RTGs start at peak radioactivity and then decay.


Almost true.
But, the decay chain may make more radioactivity come out of the device
as time goes on, and the output switches to hard to shield stuff.
  #17  
Old February 20th 05, 05:01 PM
Allen Thomson
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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.

  #18  
Old February 20th 05, 08:32 PM
Sander Vesik
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John Schilling wrote:

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.


RTG-s being thinkable in some scenarios does not in and of itself
make other nuclear systems so. These will have to do their own
trailblazing, the more complex and the closer to Earth they have to
operate, the more so.

--
Sander

+++ Out of cheese error +++
  #19  
Old February 22nd 05, 08:54 AM
Jan Vorbrüggen
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Current food preservation technology is not capable of
providing nutritionally viable food for the longer
mission durations under study.


I wonder...didn't some of the early Artic and Antarctic expeditions
go several years without resupply?

Jan
  #20  
Old February 22nd 05, 02:11 PM
Paul F. Dietz
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Jan Vorbrüggen wrote:

I wonder...didn't some of the early Artic and Antarctic expeditions
go several years without resupply?


Does shooting seals count as resupply?

Paul

 




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