Thanks very much for the reply. But are there really enough illegal
space launches to significantly affect the statistics? If the illegal
launches have the same statistical properties as those publicly
declared, then they won't affect the statistics much unless they
outnumber publicly-declared launches. If they have dissimilar
characteristics, then they might not be very relevant. For example, if
the clandestine launches represent secret, cost-is-no-object military
operations, then they might not be very relevant for
commercially-oriented purposes.
In posing my question, I was hoping that there were additional public
studies that I was not aware of. Otherwise, I'm influenced by Futron's
study of US space-launch vehicles over the 20 years from October 1984
through September 2004 (it seems no longer to be on the web, but I can
provide a copy). The sample included 1255 liquid stages suffering 6
propulsion failures and 1831 solid stages suffering 4 failures. On the
face of it, the liquid failure rate (0.48%) looks distinctly higher than
the solid rate (0.22%). But the solids are comprised of two very
different beasts, namely small Delta II-like solids without TVC, and
large Titan SRM-like solids with TVC. The small solids undeniably have
a great track record, with just one failure (the Delta 7925-10 in 1997)
in 1260, i.e., 0.08%. Large solids, though, fare no better than
liquids, with 3 failures in 571, i.e., 0.53%.
Or consider propulsion-related failures of the heavy Titans.
Conveniently, each had two SRMs and two liquid core stages. In 123
launches, SRMs failed twice (34D-9 in 1986 and K-11 in 1993) and core
stages failed twice (2nd stage of 23C-17 in 1978 and 1st stage of 34D-7
in 1985).
Consider the Shuttle. One out of 270 SRBs failed against five or so
SSME anomalies. But which would you prefer to have avoided: the one SRB
failure or all of the SSME anomalies combined?
About half of the above liquid anomalies were manifest at ignition. In
the Shuttle's case, thanks to hold-down, the consequence was merely a
delay. That's not an option for a solid.
I've considered only a fraction of the publicly-available data, but that
fraction is nonetheless rather voluminous. It indicates that small
solids without TVC are indeed very reliable. But larger solids don't
appear to be any more reliable than liquids, especially for ground-lit
stages (which, ironically, is just where the rocket equation would tell
you that solids are most appropriate). And solids' failures tend to be
both less predictable and quite a bit nastier.
On 11/07/2015 09:54 PM, Anthony Cesaroni wrote:
Forwarded message below at Bill’s request.
---------- Forwarded message ----------
From: *William Claybaugh* <wclaybaugh2@xxxxxxxxx
<javascript:_e(%7B%7D,'cvml','wclaybaugh2@xxxxxxxxx');>>
Date: Friday, November 6, 2015
My regular email server is under DDOS attack and so I have neither
been receiving or replying to arocket posts.
A review of the archive showed that Nels had asked for the data
backing up the assertion that the 1980 - 2010 space launch data set
shows a liquid failure rate double the solid motor failure rate; I'd
like to try and reply to that request:
The organizations for which I--twice--developed this data set paid a
very great deal of money to get it done; naturally, I did not take a
copy when I left each of those organizations.
Building a accurate data set required access to the private data of
three space insurance companies; after reconciling those, it was
necessary to further reconcile that "master" data set against a
classified data set. This is because, 1) despite treaty obligations,
not all launches to earth orbit are registered with the UN, and, 2)
failed attempts are sometimes not announced--particularly during the
first decade of this timeframe. Further, the binning of failure modes
into GN&C, liquid, or solid caused often requires access to classified
analysis for certain foreign systems.
Obviously, it is not possible to reconstruct this data set for public
release; further, any data set based only on publicly available
information is certain to underrepresent the overall failure rate and,
particularly, the cause of failures.
That said, there are certain conclusions that have been publicly drawn
from the comprehensive data: that overall, the failure rate is just
under 10%, that after GN&C failures liquid rocket bits account for
about 2/3 of the remainder and solid motors for 1/3; it is also public
knowledge that half of all failures occur in the first 14 launches of
new vehicles--the long run failure rate is less than 5%. This last
observation is the technical basis for NASA requiring 14 consecutive
successful launches before it will contract to fly it's most valuable
payloads on a new vehicle.
We might also note the Aerospace Corporation observation that launch
failures are initially design or manufacturing failures but after
about a dozen launches failures tend to be process failures.