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"Heavy lift: examining the requirements"



 
 
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  #21  
Old March 8th 05, 04:41 PM
Murray Anderson
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"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message
...
"Murray Anderson" wrote in message

The CG is way behind the CP at least until the SRB is close to burnout.
There isn't all that much weight up front. The specific gravity of a

Centaur
upper stage is something like .25 and the payload, including the payload
fairing, is even less dense. Even when the SRB is half burned the CG is

2
or
3 diameters behind the CP.


Is the CG really so far behind the CP - and for that long? Where do you

get
that data from? Remember 51-L? They _appeared_ neutrally stable, to me, as
they flew from 73 seconds to destruct - for some of that time flying nose
forward into Vinf. Add on an upper stage and a "20 metric ton" CEV and I'd
guess that the CG is ahead of the CP.

Might be an interesting "extra credit" problem for someone ...

Jon


The SRBs probably are dynamically stable when flying alone. They have that
skirt at the bottom to act as small tail feathers. Now suppose you put a
5-meter wide, 18 meter long upper stage on top, and a CEV under a payload
fairing on top of that (say 5 meters by 10 meters). Then if you trace the
projection onto a piece of cardboard, cut it out and balance it, you get a
rough approximation to the CP, which is way in front of the CG, even when
the SRB has burned half its propellant. The stuff up front destroys
stability if it's less dense than the stuff behind.

Murray Anderson


  #22  
Old March 8th 05, 04:55 PM
Jon S. Berndt
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Has an STS SRB ever failed (in flight or in test) "catastrophically"?
For the STS SRB, human rating _was_ designed in.

  #23  
Old March 8th 05, 05:00 PM
Jon S. Berndt
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Murray Anderson wrote:

The SRBs probably are dynamically stable when flying alone. They have


that skirt at the bottom to act as small tail feathers. Now suppose

you
put a 5-meter wide, 18 meter long upper stage on top, and a CEV under


a payload fairing on top of that (say 5 meters by 10 meters). Then if

you
trace the projection onto a piece of cardboard, cut it out and

balance it,
you get a rough approximation to the CP, which is way in front of the

CG,

I used to do this when building Estes model rockets! [BTW, I lost two
Saturn V's to rocket motor failures - Estes replaced them both]


even when the SRB has burned half its propellant. The stuff up front
destroys stability if it's less dense than the stuff behind.


Good point. I've got Missile Datcom. Might be interesting to play with
that and the SRB/CEV design - see just how bad it is. Hmm...

Jon

  #24  
Old March 8th 05, 06:10 PM
Jon S. Berndt
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Depends on how you define it. Certainly the SRB failure with
Challenger had a catastrophic result, regardless of
how "catastrophic" a failure it was.


Yes the SRB caused the 51-L accident, but if the same failure occurred
with a CEV atop it, hypothetically, it would be a survivable abort
situation. I don't recall reading about any "explosive" type of
failures of the STS SRB in testing.

Not really. More like waivered away.
Again, no one really knows what "human rating" means. I wish that
we could purge the phrase from our vocabulary.


FWIW:

"Human-Rating Requirements, JSC - 28354"
http://www.hq.nasa.gov/office/codea/...documentd.html

Jon

  #25  
Old March 8th 05, 06:14 PM
Jon S. Berndt
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Depends on how you define it. Certainly the SRB failure with
Challenger had a catastrophic result, regardless of
how "catastrophic" a failure it was.


Yes the SRB caused the 51-L accident, but if the same failure occurred
with a CEV atop it, hypothetically, it would be a survivable abort
situation. I don't recall reading about any "explosive" type of
failures of the STS SRB in testing.

Not really. More like waivered away.
Again, no one really knows what "human rating" means. I wish that
we could purge the phrase from our vocabulary.


FWIW:

"Human-Rating Requirements, JSC - 28354"
http://www.hq.nasa.gov/office/codea/...documentd.html

Jon

  #26  
Old March 8th 05, 07:38 PM
Ed Kyle
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Jon S. Berndt wrote:
Has an STS SRB ever failed (in flight or in test) "catastrophically"?
For the STS SRB, human rating _was_ designed in.


There have been three failures of large segmented
solid rocket boosters since 1986, inclusive. They
we

1/28/1986 STS-51L (We know all about that one)

4/18/1986 Titan 34D-9, Vandenberg SLC-4E, SRM case
insulation and case burn through. Catastrophic
explosion over pad 8.5 seconds after liftoff.
Believed to have been caused by insulation
debonding from the internal surface of the motor
case.

8/2/1993 Titan 403-K11, Vandenberg SLC-4E, Vehicle
exploded 101 sec. after liftoff. The cause was a
case burn through of solid rocket motor 1, case
segment 3. The failure was traced to a faulty
repair of a "restrictor" that involved cuts into
the propellant grain that were improperly potted.

Two of these three were instantaneous solid booster
case failures. In addition, no one noticed the
51-L joint burn-through until examining tracking
film after the incident. The vehicle disintegration
itself was all but instantaneous.

NASA upgraded its nondestructive test methods after
the 51-L and 34D-9 failures, but no test can
absolutely preclude the possibility of an
instantaneous case failure, even on shuttle SRBs.
The K-11 failure is instructive in this regard,
because all of the post-34D-9 NDT methods were in
use during its prelaunch checkout.

- Ed Kyle

  #27  
Old March 8th 05, 07:51 PM
Jeff Findley
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"Jon S. Berndt" jsb.at.hal-pc-dot.org wrote in message
...
From what I've read, it takes a whole lot to ignite the SRB propellant. Is
this really a concern?


Of more concern would be the occasional explosion/fire at an ammonium
perchlorate plant (I believe this is the oxidizer used in the SRB fuel).
Just search for "ammonium perchlorate factory explosion" in Google and
you'll see what I mean. Once it's mixed with fuel and cast into an SRB (or
segments), it is far harder to ignite.

Jeff
--
Remove icky phrase from email address to get a valid address.



  #28  
Old March 8th 05, 07:52 PM
Ed Kyle
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Jon S. Berndt wrote:
"Ed Kyle" wrote in message
The presence of
"live" SRBs in the VAB has added cost to the shuttle
program due to safety limitations, for example. A
worst-case fear has long been the unlikely-but-not-
impossible case of an SRB lighting up within the
VAB during processing.


From what I've read, it takes a whole lot to ignite the SRB

propellant. Is
this really a concern?


Yes. During Apollo, contractors offices were actually
in the VAB, in the upper reaches of the "tower" portions
of the building between the high bay areas. The workers
were just steps away from the launch vehicle hardware
they were responsible for.

For shuttle, NASA had to vacate the VAB of all but
essential personnel who have been briefed about the
risks involved. Those offices - the equivalent
of a skyscraper's worth of work space - are mostly
vacant today. (Some are used to store Columbia
remains.) An entirely new set of office buildings
had to be constructed to house shuttle processing
contractors outside the VAB - after they had labored
in trailers for several years.

- Ed Kyle

  #29  
Old March 8th 05, 08:03 PM
Rand Simberg
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On 8 Mar 2005 07:55:45 -0800, in a place far, far away, "Jon S.
Berndt" made the phosphor on my monitor glow in such
a way as to indicate that:

Has an STS SRB ever failed (in flight or in test) "catastrophically"?


Depends on how you define it. Certainly the SRB failure with
Challenger had a catastrophic result, regardless of how "catastrophic"
a failure it was.

For the STS SRB, human rating _was_ designed in.


Not really. More like waivered away.

Again, no one really knows what "human rating" means. I wish that we
could purge the phrase from our vocabulary.
  #30  
Old March 8th 05, 08:07 PM
Jon S. Berndt
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Ed wrote:

NASA upgraded its nondestructive test methods after
the 51-L and 34D-9 failures, but no test can
absolutely preclude the possibility of an
instantaneous case failure, even on shuttle SRBs.


[thanks for the thorough and informative post]

Do you know offhand how many of the Titan 34D solid boosters have
flown? I can appreciate the concern about SRBs in general. However, I
still feel that the STS SRB history _specifically_, with 225 out of 226
mission firings that performed satisfactorily (a 99.56% success rate) -
with the lone failure having been addressed and even then potentially
survivable in a CEV launcher application - I feel that that at least
warrants consideration as suggested in Jeff Foust's article in The
Space Review.

There are probably other considerations, too. For one, is the SRB too
rough a ride for anything placed atop it?

Jon

 




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