Two ideas RE: Shuttle return to flight -- Do they hold up?

[Christopher P. Winter]

I thought of posting this as a followup. There are several threads where
it would fit. But then I thought it might get lost -- like my post about the
effect of atomic oxygen on RCC did, a few months back.

Anyway, I want to run these ideas past some of the professionals here, to
get some feedback on their merits.

Idea 1 -- inspecting shuttle TPS integrity. All the discussion I've seen
on this topic focuses on using some sort of camera (or in-person EVA) to
inspect the tiles, RCC panels, etc from the outside for damage. It just
occurred to me that if there are any cracks in the RCC such as were seen in
earlier foam impact tests at SWRI, they would let significant light enter the
wing structure. That is even more true for the hole produced in the latest
test.

My idea rests on the assumption that no light enters the wing if its TPS
is intact. If that is true, I think that placing some photodetectors at
certain places inside would give a reliable indication of a breach. This
should not add much weight or greatly increase the sensor data load. I leave
to those more familiar with the wing structure the questions of how many
photodetectors would be needed, and where they should be placed. What I'm
after is a go/no-go indication.

Idea 2 -- repair of an RCC breach. This one seems more dubious. Suppose
the shuttle carried a spare set of RCC panels. (They might be nested so as to
take up relatively little volume.) If a breach were found, an EVA would be
done to place a matching panel over the broken one. It could be glued or
bolted in place, or both.

Potential problems with this idea are whether the attachment methods
would hold well enough, and the likelihood of step-height changes at the
edges of the replacement panel causing a premature airflow transition.

OK, those are my ideas. Have at them now. <g>

Chris W.

[Jorge R. Frank]

Christopher P. Winter > wrote in
:

> My idea rests on the assumption that no light enters the wing if
> its TPS is intact.

Unfortunately, it's not. The critical damage threshold for the wing
leading edge RCC is 0.25 in, not full penetration.

> Idea 2 -- repair of an RCC breach. This one seems more dubious.
> Suppose
> the shuttle carried a spare set of RCC panels. (They might be nested
> so as to take up relatively little volume.)

I'm not sure you can nest them due to the very gradual size changes from
panel to panel. In either case, the mass penalty would be prohibitive.

> Potential problems with this idea are whether the attachment
> methods
> would hold well enough, and the likelihood of step-height changes at
> the edges of the replacement panel causing a premature airflow
> transition.

The step-height tolerance is around 0.1 inches for the RCC. Pretty tight.

> OK, those are my ideas. Have at them now. <g>

Good thinking, though. Keep 'em coming!

--
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[JazzMan]

Christopher P. Winter wrote:
>

>
> I can accept the mass-penalty objection. Of course, it probably would not
> be necessary to carry a complete set of replacement panels. Maybe just a few
> flat patches, and some with various curvatures. Is RCC at all flexible? If
> so, it might be possible to force a patch to conform to a curvature mismatch
> without inducing too much stress.
>

A question: Once the orbiter got out of the high temperature phase
of re-entry, how critical is the integrity of the leading edge for
maintaining flight control ability? Assuming you had some way of
applying a patch that would last through just one re-entry and
it was very poorly shaped, could the shuttle still fly and land?

It seems to me that the biggest problem with re-entry is the
high-temperature plasma getting into the aluminum structure and
burning it away. If you could devise some way to keep the plasma
out of the wing just long enough to get past that part of
re-entry, you'd go a long way to getting the orbiter back in
one piece.

JazzMan

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[Jorge R. Frank]

Christopher P. Winter > wrote in
:

> On 11 Jul 2003 00:38:51 GMT, "Jorge R. Frank" >
> wrote:
>
>>Christopher P. Winter > wrote in
:
>>
>>> My idea rests on the assumption that no light enters the wing if
>>> its TPS is intact.
>>
>>Unfortunately, it's not. The critical damage threshold for the wing
>>leading edge RCC is 0.25 in, not full penetration.
>
> I needed some time to think about this. If I understand you
> correctly,
> the photodetector solution fails because a) a normal wing is not
> light-tight, and b) an RCC panel could be critically damaged and still
> not admit sunlight.

I'm not 100% sure about a), but it sounds reasonable. b) is definitely
true; RCC panels are around a third of an inch think.

> OK, how about this: Consider an RCC panel with 0.25 inch removed
> at one
> spot. Would that spot have significantly different thermal
> characteristics than the rest of the panel? If exposed to direct
> sunlight in space (1350W/sq. meter), would the panel behind the spot
> warm up more than elsewhere? Would the difference be detected with a
> simple (i.e. short-wave, non-cooled) IR sensor?

I have no idea.

> I can accept the mass-penalty objection. Of course, it probably
> would not
> be necessary to carry a complete set of replacement panels. Maybe just
> a few flat patches, and some with various curvatures. Is RCC at all
> flexible? If so, it might be possible to force a patch to conform to a
> curvature mismatch without inducing too much stress.

RCC is not terribly flexible.

> As for the 0.1-inch step-height problem, I imagine the edges of
> the
> replacements could be beveled.

The current thinking is to open an "umbrella"-like support behind the hole.
You'd put a flat patch over that, and a spray-on ablator to fill the gaps.
Finally, trowel the ablator to smooth out the step-height. But RCC repair
capability is very much a work-in-progress; there are a lot of different
ideas being considered.

The *hope* is that the ET bipod ramp fix (along with a couple of other ET
foam fixes) will mitigate the risk of *large* pieces of foam to the extent
that you no longer have to worry about large holes in the RCC, just small
holes and divots.

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[Jorge R. Frank]

Rusty Barton > wrote in
:

> Would it be possible to fit some type of boost protective covers over
> the RCC areas of the Shuttle? These could possibly be ejected after
> the External Tank is jettisoned to prevent the covers from following
> the Shuttle into orbit. This might preclude the need for on orbit
> inspection of the RCC areas after each launch.

Generally I'm not in favor of adding a cover that would require active
ejection. That's one more crit-1 failure mode, and should be avoided if
possible. However, an ET aerodynamic fairing could accomplish the same
purpose and would be passively separated with the ET. It would add weight
to the ET, but it would "pay for itself" because the reduction in drag
would result in zero net performance loss. See p. 189 of Jenkins, 3rd ed,
for some illustrations of ET aerodynamic fairing concepts that were
considered during early shuttle development.

I do not think such a concept could be, or should be, a return-to-flight
constraint, but it should be considered for extended shuttle service life.

> Gemini and Apollo each used some type of boost covers during launch.

You sure about Gemini? I know Apollo did, and it was jettisoned with the
escape tower, but Gemini had no escape tower.


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JRF

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[Rusty Barton]

On 13 Jul 2003 03:11:53 GMT, "Jorge R. Frank" >
wrote:


>> Gemini and Apollo each used some type of boost covers during launch.
>

>You sure about Gemini? I know Apollo did, and it was jettisoned with the
>escape tower, but Gemini had no escape tower.

I believe that Gemini had a white fiberglass? cover over the end of
the nose of the spacecraft during launch. It protected the spacecraft
rendezvous radar hardware during ascent. Here are several pictures
showing Gemini with and without it.

Gemini with nose fairing before or during launch:

http://images.jsc.nasa.gov/iams/images/pao/GT10/10074429.htm

http://images.jsc.nasa.gov/iams/images/pao/GT10/10074429.jpg


http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-000612.html

http://grin.hq.nasa.gov/IMAGES/LARGE/GPN-2000-000612.jpg



Gemini without nose fairing after reaching orbit:

http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001495.html

http://grin.hq.nasa.gov/IMAGES/MEDIUM/GPN-2000-001495.jpg


http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001049.html

http://grin.hq.nasa.gov/IMAGES/MEDIUM/GPN-2000-001049.jpg



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Visit my Titan I ICBM website at: | body to science fiction."
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[Jorge R. Frank]

Rusty Barton > wrote in
:

> On 13 Jul 2003 03:11:53 GMT, "Jorge R. Frank" >
> wrote:
>
>
>>> Gemini and Apollo each used some type of boost covers during launch.
>>
>
>>You sure about Gemini? I know Apollo did, and it was jettisoned with
>>the escape tower, but Gemini had no escape tower.
>
> I believe that Gemini had a white fiberglass? cover over the end of
> the nose of the spacecraft during launch. It protected the spacecraft
> rendezvous radar hardware during ascent. Here are several pictures
> showing Gemini with and without it.

Thanks, Rusty!
--
JRF

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[Doug...]

OK -- it's been suggested to provide boost protective covers for the wing
leading edges and possibly the nose cap. It occurs to me that you'd have
to have a pretty robust BPC, since RCC supposedly has pretty decent
tensile strength and it failed pretty obviously when a briefcase-sized
chunk of foam hit it.

What's more, if a BPC is designed to allow the orbiter to survive an
impact of the force with which Columbia's wing was struck, it would have
to be able to absorb and transmit a good deal of kinetic energy into the
orbiter structure without damaging or compromising its own mountings and
without damaging the more fragile RCC below it. And without damaging any
other portion of the vehicle.

Finally, it would have to be jettisonable in such a way as to leave an
aerodynamically smooth surface at the separation planes. And cannot
allow any recontact between the BPC segments and the vehicle.

When you consider all the factors, it doesn't sound like the simple fix
you might think it is...

--

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it's the sudden stop at the end... |

[GCGassaway]

Doug Van Dorn wrote:

>>>>>>>
OK -- it's been suggested to provide boost protective covers for the wing
leading edges and possibly the nose cap. It occurs to me that you'd have to
have a pretty robust BPC, since RCC supposedly has pretty decent tensile
strength and it failed pretty obviously when a briefcase-sized chunk of foam
hit it.

What's more, if a BPC is designed to allow the orbiter to survive an impact of
the force with which Columbia's wing was struck, it would have to be able to
absorb and transmit a good deal of kinetic energy into the orbiter structure
without damaging or compromising its own mountings and without damaging the
more fragile RCC below it. And without damaging any other portion of the
vehicle.

Finally, it would have to be jettisonable in such a way as to leave an
aerodynamically smooth surface at the separation planes. And cannot allow any
recontact between the BPC segments and the vehicle.

When you consider all the factors, it doesn't sound like the simple fix you
might think it is...
<<<<<<<


I do not see the practicality of it either. First, let's compare with Apollo
CM BPC’s. Those were not all THAT protective, not like a shuttle would need.
The forward half of the Apollo BPC was called the hard BPC, it was a relatively
strong and hard conical assembly from the top down to just a bit below the LES
tower legs. The remaining lower half was called the “soft” BPC. It was made out
of multiple segments of fiberglass spliced together radially in 7 places. It
didn’t seem to give that much protection other than to keep the highly
reflective mylar (?) surface of the CM clean while on the pad and for the early
launch phase, till the LES was jettisoned. IIRC, when the tower jettisoned, the
lower BPC collapsed inwards on itself since it had no real strength, there was
enough dynamic pressure on it to collapse it. The forward “hard” BPC might be
considered armor, but in relative terms the lower “soft” BPC was more like a
raincoat than armor.

Now, a shuttle type BPC for the leading edges would have to be “hard” for its
full length, and hard means not only strong (armor), but heavy. Since it would
need to avoid hitting the orbiter when it was released, it probably would have
to ride a long way till the atmosphere was virtually non-existent. Given the
strength it would need by itself, the technical problems of attaching it, and
the technical problems of separating it, I would think it would be more
practical to introduce the...

RRCC: Reinforced-Reinforced Carbon-Carbon

Yes, it would add more weight, but the weight penalty would probably not be as
bad as carrying a BPC that weighed twice as much (or more) and introduced all
the complicated other problems.

How much reinforcement and how? I do not know. It would be great if Kevlar
could be added to the fabrication of the RCC, but I have a gut feeling that
Kevlar is incompatible due to the extreme heat.

If the RCC panels could have some sort of lightweight “filler” material inside
of portions of them to help give some internal stiffness, rather than being as
thin-walled hollow as they are now? If this was a composite aircraft, the
answer might be as simple as filling the cavity with foam....(ironic to say
that), but I can’t think of any foam that could take the heat. Possibly, just
possibly, using silica tile type material, cut to match the inside contour of
the RCC segments. Although that still might not be robust enough to support the
RCC from cracking/fracturing. And I know it might not be practical to do that
and still have the internal access needed to actually attach and service the
RCC segments.

So, any practical solution to trying to improve ability to withstand impact
probably would be more along the lines of just making the panels thicker, plus
making the attachment brackets stronger as well, since IIRC last week’s test
also did a number on at least one bracket assembly.

I won’t be surprised if nothing is done, and the attention goes towards
preventing Bipod foam from ever coming off again (IIRC there won’t be any more
bipod ramps, period). Which is great unless some other significant piece of
foam or something else comes off the ET (or SRB).

- George Gassaway

[Christopher P. Winter]

On Sun, 13 Jul 2003 12:22:15 -0400, "Terrell Miller" >
wrote:

>"Christopher P. Winter" > wrote in message
...
>
>> Anyway, I want to run these ideas past some of the professionals here,
>to
>> get some feedback on their merits.
>
>> My idea rests on the assumption that no light enters the wing if its
>TPS
>> is intact. If that is true, I think that placing some photodetectors at
>> certain places inside would give a reliable indication of a breach. This
>> should not add much weight or greatly increase the sensor data load. I
>leave
>> to those more familiar with the wing structure the questions of how many
>> photodetectors would be needed, and where they should be placed. What I'm
>> after is a go/no-go indication.
>
>IOW, you want credit for the idea, but you have no intention of doing the
>research to determine whether your idea would actually work, and you're not
>gonna lift a finger to do any of the actual gruntwork if it does.
>
>You are the Pointy Haired Boss and I claim my $5 :)

Interesting analysis. I wrote a sarcastic reply. Then I discarded it,
because I want to keep this conversation serious.

Yes, I would love to get credit for the idea. I'd also be happy to do the
research to fix any problems it has (which, as JRF pointed out, are many) and
the "gruntwork", as you call it, to implement a real solution. Would that I
were in a position to do so.

As things stand, I could have either put the idea(s) out for discussion
here, sent them to the CAIB in a letter, or sat on them. I chose the former
because it seemed the quickest way to get something going.

If I had sent them to the CAIB, it would have been weeks before anyone
saw the letter, and who knows how long before those ideas were evaluated (if
they ever were). However, I'll also note that this would be a better route to
keeping whatever credit my ideas might earn for myself alone.

If I had sat on them... But you can figure that one out.

Chris W.

[Christopher P. Winter]

On 13 Jul 2003 02:23:07 GMT, "Jorge R. Frank" > wrote (in
part):

>Christopher P. Winter > wrote in
(in part):
>
>
>> OK, how about this: Consider an RCC panel with 0.25 inch removed
>> at one
>> spot. Would that spot have significantly different thermal
>> characteristics than the rest of the panel? If exposed to direct
>> sunlight in space (1350W/sq. meter), would the panel behind the spot
>> warm up more than elsewhere? Would the difference be detected with a
>> simple (i.e. short-wave, non-cooled) IR sensor?
>
>I have no idea.
>

Of course, even if such hot spots developed, seeing them probably means
putting an imaging sensor behind each panel, and a bunch of extra electronics
and other hardware somewhere -- another over-massive "solution".

>
>The *hope* is that the ET bipod ramp fix (along with a couple of other ET
>foam fixes) will mitigate the risk of *large* pieces of foam to the extent
>that you no longer have to worry about large holes in the RCC, just small
>holes and divots.

I agree that this deserves higher priority. Ben Franklin's homily about
an ounce of prevention was never truer.

Chris W.

[Jorge R. Frank]

(GCGassaway) wrote in
:

> Doug Van Dorn wrote:
>
>>>>>>>>
> OK -- it's been suggested to provide boost protective covers for the
> wing leading edges and possibly the nose cap. It occurs to me that
> you'd have to have a pretty robust BPC, since RCC supposedly has
> pretty decent tensile strength and it failed pretty obviously when a
> briefcase-sized chunk of foam hit it.

> Finally, it would have to be jettisonable in such a way as to leave an
> aerodynamically smooth surface at the separation planes. And cannot
> allow any recontact between the BPC segments and the vehicle.
>
> When you consider all the factors, it doesn't sound like the simple
> fix you might think it is...
><<<<<<<

> I do not see the practicality of it either.

Since this is coming a couple of posts downstream from a reply to me, I
feel compelled to restore context here, since I was most definitely *not*
suggesting a jettisonable boost protective cover:

<quote>
Generally I'm not in favor of adding a cover that would require active
ejection. That's one more crit-1 failure mode, and should be avoided if
possible. However, an ET aerodynamic fairing could accomplish the same
purpose and would be passively separated with the ET. It would add weight
to the ET, but it would "pay for itself" because the reduction in drag
would result in zero net performance loss. See p. 189 of Jenkins, 3rd ed,
for some illustrations of ET aerodynamic fairing concepts that were
considered during early shuttle development.

I do not think such a concept could be, or should be, a return-to-flight
constraint, but it should be considered for extended shuttle service life.
</quote>

> Now, a shuttle type BPC for the leading edges would have to be “hard”
> for its full length, and hard means not only strong (armor), but
> heavy. Since it would need to avoid hitting the orbiter when it was
> released, it probably would have to ride a long way till the
> atmosphere was virtually non-existent. Given the strength it would
> need by itself, the technical problems of attaching it, and the
> technical problems of separating it, I would think it would be more
> practical to introduce the...
>
> RRCC: Reinforced-Reinforced Carbon-Carbon
>
> Yes, it would add more weight, but the weight penalty would probably
> not be as bad as carrying a BPC that weighed twice as much (or more)
> and introduced all the complicated other problems.

OK, here's the tradeoffs. An aerodynamic fairing on the ET would add
weight to the ET, but it would not affect overall performance because it
would also reduce drag during low-speed flight. Reinforcing the RCC would
add weight to the orbiter without reducing drag, causing a net performance
loss.

> I won’t be surprised if nothing is done, and the attention goes
> towards preventing Bipod foam from ever coming off again (IIRC there
> won’t be any more bipod ramps, period).

That's correct. There is some attention being paid to orbiter hardening,
but that is not considered a return-to-flight constraint at this time.

> Which is great unless some
> other significant piece of foam or something else comes off the ET (or
> SRB).

NASA is looking at all potential sources of debris, not just the bipod
ramp. There is a lot of attention being paid to the intertank flanges since
those areas have seen a lot of foam shedding in the past.


--
JRF

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[Doug...]

In article >,
says...
> Paddler wrote:
>
> >>>>>
> On the issue of detecting damaged RCC...If the structure behind the RCC was
> painted a bright colour(flourescent orange) could this make any damage a lot
> easier to see by remote cameras(satellites etc)? This may be less costly than
> sensors...
> <<<<<
>
> Here's an idea.... have the RCC painted gray, so if anything abnormal happens
> to it, like a hole, you will see darkness inside if it.
>
> Oh.... it's already like that.... so no need to do anything new for that
> particular reason. With gray RCC, anything that is lighter or darker than the
> RCC means something’s wrong.
>
> Now, I have wondered if some sort of sensing might be possible, without being
> too complex to retrofit. The basic idea being that if there is any sort of
> breach in the RCC, that sunlight would be able to come in. So, have an orbiter
> point at the sun for a brief time. Use some sensing method inside the hollow
> RCC to look for any signs of sunlight coming in. That might give some incentive
> to actually have the aluminum leading edge box covered with a white material
> that would reflect the light. Maybe something as simple as a few light
> detectors. Maybe something a bit more adventurous, like some fiber-optic cables
> and a TV camera in each wing. A main fiber optic cable would look along the
> main straight swept part of the wing. Another for the “glove” straight section.
> And one or two to handle the curved sections. Rigged to a TV camera in a way so
> as to see 4 fiber optic cables at once. Would cut the resolution in half, but
> if that camera saw anything but all black, it’s time to suit up and see what
> might be wrong.
>
> There would no doubt be many other ways to do the same sort of thing.
> Unfortunately it would only show a hole or just maybe a Tee seal that would be
> dislodged enough. It would not show cracks, and would only be relevant for RCC.

Exactly -- remember that, especially along the leading edge of the wing,
many cracks would only admit sunlight if pointed exactly right. If an
RCC panel or a T-seal were slightly dislodged, leaving a crack between
panel and T-seal of, say, a quarter-inch width running 30 inches along
the seal, you'd only see light through the crack if the sun were pointed
directly into the crack. There is no light scattered by atmospheric
effects on orbit, and along the leading edge there would be very little
reflected light from the orbiter body itself (though perhaps some would
be reflected by the open payload bay doors).

--

It's not the pace of life I mind; | Doug Van Dorn
it's the sudden stop at the end... |