Prudence Lost

Agreed, the MMT leader comes off very well in the news conference talking
about a subject he probably knows very little about, only having a crash
course on the subject over the last week. You have to remember, in reality
he is most likely a manager who has been away from any technical work for
quite some time and is just parroting what he recently learned.
Intelligent, but still just parroting others, while at the same time
leading the direction of the investigation to a conclusion, which seemed to
be the one he favored. Do nothing, don't do the Prudent thing. Which would
have been to fix and study the repair. All their time was spent justifying
the imprudent course of action.

Shades of Columbia

To me, I see some shades of Columbia in the path the MMT went down. Well
only because I followed the Columbia investigation very closely.

First, one of the major contributing factors to the Columbia Disaster is
still present. That there must be proof positive that there is a "major"
problem before they will consider doing something. In Columbia's case this
was to "prove" that there was major damage to the wing "tiles" before
further action is taken, obtaining pictures. In this case, prove something
is majorly wrong before a repair will be considered. Instead of just fixing
the problem and coming home with the vehicle in the "best" shape possible.

Second, the analysis ended when unexpected results were reached. In
Columbia's case, the results indicated that the RCC would be fully
penetrated by the impact. This result was then quickly explained away with
words about modeling inaccuracies of the crater program that was many
orders of magnitude outside it's database. They didn't believe the results
and used a few thoughts and word to go from the RCC being fully penetrated
to zero damage. The Columbia MMT just dropped the RCC analysis at that
point and concentrated on "tile" damage.

On this flight, the unexpected results are with respect to all the entry
damage aft of the ding that occurred in the arc jet. I really know nothing
about inaccuracies of the arc jet facility, who knows maybe they get the
type of "entry" tunneling damage all the time. And, having been seen many
times before in the arc jet facility, is well understood. I don't know,
maybe this is the case. If not, then it truely is an unexpected result of
the test that was explained away with words, and the analysis ending
without a real understanding of the "new" phenomena that occurred during
the test. The explanation, that it is turbulent flow, the boundary layer is
very thin, shock waves from the arc jet itself. Was it simply explained
away with words or is it something that is well understood?

Third, incorrect models used. In Columbia's case, the "crater" program was
created and used to assess damage to the RCC coating, small impact to what
is a rigid surface with no flexing. Like scuffing of a little coating on a
rigid thing. The actual impact was much larger, affecting much more than
the coating, actually flexing the graphite/carbon composite matrix. Which
really doesn't flex well, it's brittle and fractures.

On this flight, it seemed to me that the CFD study concentrated on the hole,
didn't assess any entry damage at all like that seen in the arc jet. I sure
hope this tunneling is a common test artifact and not something new, that
it is well understood and has been studied many times before. So that is
was appropriate to leave it out of the CFD study. I don't expect to see any
reporters coming up with the right questions for the MMT Mission Status
Briefing and News Conference. So, here are the question that I missed the
answers to, "How many times has tunneling damage been seen in the arc jet
facility", "How well is this tunneling phenomena understood?", "When was
this phenomena studied, how many times was it studied?". Maybe they were
already asked and answers, and I missed that part of the news conference.

On the risk of a space walk, the risk is to one astronaut. The risk of
flying a damaged vehicle on entry is to all seven astronauts, therefore
seven times as great. Is, 7 X SpaceWalkRisk EntryDamageRisk? All the risk
discussion is just a bunch of value judgments, and of minimal value, no one
really knows the risk. That being said, I'd put they're risk of flying this
damaged vehicle on entry at greater than 2%. Two percent is the risk they
started with on the ground.

Prudence Lost

In an earlier MMT meeting he said something about running a repaired ding
case in the arc jet. This never happened. Along the path to the decision,
Prudence got lost. The dissenting voice seems to have been the JSC
Engineering Group who wanted to look at the benefits of a repair. The final
words of the JSC Engineering Group was that it was the prudent thing to do.
In other words NASA is doing the imprudent thing in not really considering
the repair option to it's fullest. Any repair would eliminate the vertical
face in the hole, which NASA seems to realize is causing the unexplained,
or explained away, or is it well understood, arc jet entry damage aft of
the launch damage.

The Prudent thing to do, is to have the vehicle in the best shape possible
before entry. The Prudent thing to do, is to repair the damage, then study
the repair to see if it needs an additional adjustment.

It's not too late, until the deorbit burn. Hopefully NASA will change it's
collective mind and do the Prudent thing.
--
Craig Fink
Courtesy E-Mail Welcome @
--

MichaelJP wrote:


"Jim in Houston" wrote in message
...
Very well thought out. Tested thoroughly. Discussed endlessly.
John Shannon along with the rest of the MMT are extremely qualified to
sort through the data and make the decision.
I agree with the decision, but I am a bit disappointed, I would have
liked to have seen how the repair would hold up to real conditions.
Having said that however, the rationale to not do the repair is sound,
and I agree.

Agreed - though I too am a little disappointed. However it will still be
interesting to see how both the fluid dynamics analysis and arc jet tests
compare with the post-re-entry TPS condition.