Single vs. Multiple Engines: Cost (WAS 10 meter diameter CaLV)

John Stoffel wrote:
"Proponent" == Proponent writes:

Proponent Henry Spencer wrote:
If the engines are reasonably
reliable in the first place, and the failures are benign (almost always
true for well-debugged liquid-fuel engines), then for modest numbers of
engines, engine-out capability makes for a *much* more reliable vehicle
overall.

Proponent I'm all for five or more engines from a reliability
Proponent standpoint, but what about cost? Arguments in favor of
Proponent many engines are

Proponent 1. Increased reliability means fewer failures, and
Proponent failures, at least catastrophic ones, are very costly.

This should really be stated more as "increased redundancy leads to
overall system reliability increases." Having more engines means that
when one fails, you can keep going, or at least abort with the vehicle
and cargo intact.

Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible. Are specific engines analyzed for the probablity of each
type of failure?

In article .com,
wrote:
Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible.

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Are specific engines analyzed for the probablity of each type of failure?

It would be difficult to get a meaningful number for probability of
catastrophic failure, since it's quite rare and the experience base
for most engines isn't all that large.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

Henry Spencer wrote:
In article .com,
wrote:
Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible.

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Are specific engines analyzed for the probablity of each type of failure?

It would be difficult to get a meaningful number for probability of
catastrophic failure, since it's quite rare and the experience base
for most engines isn't all that large.

And you need to distinguish between catastrophic, but stopped by a
Kevlar shield, and CATASTROPHIC, which goes through the shield.

Henry Spencer wrote:

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Are specific engines analyzed for the probablity of each type of failure?

It would be difficult to get a meaningful number for probability of
catastrophic failure, since it's quite rare and the experience base
for most engines isn't all that large.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |


According to Ed Kyle's launch log, Soyuz-U has failed twenty times,
with no more than 18 of those propulsion related. At least two of those
were conspicuously catastrophic.

I can't find information on a number of the failures beyond the fact
that they happened. If any were either non-propulsion failures or
catastrophic, that would make the ratio less favorable.

Will McLean

On 17 May 2006 23:06:03 -0700, wrote:


Henry Spencer wrote:
In article .com,
wrote:
Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible.

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Hmmm, a bit off-topic perhaps, but do solids actually explode? Or is it
a case of hot gases cutting through the liquid propellant tanks?


Solid rocket motors have many failure modes, including but not limited
to actual explosions. Internal detonations of the propellant load, case
rupture and rapid deflagration, the works. And, as you note, sometimes
they "just" experience burm-through. Which still means you lose the
vehicle, even if you've got other, previously undamaged, motors or
engines.

Engine-out capability, even if it's just intact-abort capability, pushes
one very strongly in the direction of liquid engines.


--
*John Schilling * "Anything worth doing, *
*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
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Henry Spencer wrote:
In article .com,
wrote:
Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible.

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Hmmm, a bit off-topic perhaps, but do solids actually explode? Or is it
a case of hot gases cutting through the liquid propellant tanks?




Are specific engines analyzed for the probablity of each type of failure?

It would be difficult to get a meaningful number for probability of
catastrophic failure, since it's quite rare and the experience base
for most engines isn't all that large.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

In article .com,
wrote:

Henry Spencer wrote:
In article .com,
wrote:
Isn't the risk analysis for best number of engines dependent on _how_
the engine fails (benignly or catastrophically)? Catastrophic mode,
where _any_ engine failing will destroy the vehicle, drives one to have
fewer engines. Benign failure, where you might be able to land with a
certain fraction of engines out, drives one to have as many engines as
possible.

Correct. The interesting thing is that liquid-fuel rocket engines, once
reasonably well debugged -- that is, past teething troubles like marginal
ignition systems -- seem to very rarely fail catastrophically.

Hmmm, a bit off-topic perhaps, but do solids actually explode? Or is it
a case of hot gases cutting through the liquid propellant tanks?

Yes, solids DO explode! They are finicky about storage temperatures,
propellant slump, cracks in the grain, method of pouring, age, etc.

I used to work on the Trident SLBM program and did a lot of analysis on
flights (both successful and the failures).

Are specific engines analyzed for the probablity of each type of failure?

Yes.

It would be difficult to get a meaningful number for probability of
catastrophic failure, since it's quite rare and the experience base
for most engines isn't all that large.


A lot of the data are empirical -- you have to fly a lot of them in
order to get a probability. It is the unknowns that get you, not the
knowns. Solids are really dicey for manned programs.

"Orval Fairbairn" wrote in message
news
Yes, solids DO explode! They are finicky about storage temperatures,
propellant slump, cracks in the grain, method of pouring, age, etc.

I used to work on the Trident SLBM program and did a lot of analysis on
flights (both successful and the failures).

snip

A lot of the data are empirical -- you have to fly a lot of them in
order to get a probability. It is the unknowns that get you, not the
knowns. Solids are really dicey for manned programs.

So, what are your thoughts on NASA's plans to add a segment to the RSRM and
change the thrust profile (grain cross section) and use it on the CLV and
CaLV? In your opinion, can you really say you're using "proven shuttle
hardware" when you make these sorts of changes to a large, segmented, rocket
booster?

Jeff
--
"They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor
safety"
- B. Franklin, Bartlett's Familiar Quotations (1919)

In article .com,
wrote:
Hmmm, a bit off-topic perhaps, but do solids actually explode? Or is it
a case of hot gases cutting through the liquid propellant tanks?

Yes. :-)

Sometimes solids just leak hot gas, which then causes other problems. For
example, the spectacular Delta II explosion over the Cape about ten years
ago was the result of a hot-gas leak reaching one of the detonating cords
connecting the charges of the destruct system.

On the other hand, yes, sometimes solids really do explode, as witness the
first ground test of the Titan IVB SRB: no liquid fuels or destruct
system present, but still KABOOM!! Similarly, if memory serves, the 1986
Titan 34D loss was an outright explosion of an SRB.

The boundary between the two is somewhat vague. In particular, you can
argue about cases like the Delta II -- part of the reason why the destruct
system is there is because an orderly shutdown of a solid is difficult, so
some of the destruct-system-triggered cases can arguably be considered
catastrophic failures of the overall solid-fuel system.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

(Henry Spencer) wrote:
On the other hand, yes, sometimes solids really do explode, as witness the
first ground test of the Titan IVB SRB: no liquid fuels or destruct
system present, but still KABOOM!!

Sometimes that can be caused by the plugging of the nozzle - other
times the propellant undergoes what is known as a 'deflagration to
detonation transition'.

I encountered that phrase in a book about the development of the
Trident-I, where they did indeed encounter that problem. I've always
thought it a lovely bit of delicate phraseology.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL