Protecting SLS from Fire and Ice - TPS foam application proceeding at Michoud

[Chris Bergin]

https://www.nasaspaceflight.com/2017/12/protecting-sls-fire-ice-tps-foam-application-proceeding-maf/ …

Feature article by Philip Sloss.

(Everything you wanted to know about TPS foam application on big rockets but were afraid to ask!)

[whitelancer64]

Very detailed on the processes involved, that's an excellent article!

[Jason Davies]

That was really informative. You just don't get that depth with most sites covering SLS.

[Rocket Science]

Nice meaty article Philip, thank you!

[cmcqueen]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

[Rocket Science]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

The SLS uses liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer which would boil off without insulation.

[lrk]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

The SLS uses liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer which would boil off without insulation.

Not to mention, LH2 is literally cold enough to freeze air!  This would impose an even greater weight penalty than simply dealing with water ice. 

[Lars-J]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

The SLS uses liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer which would boil off without insulation.

Your point about liquid hydrogen is true, but not liquid oxygen. Many (most) other launch vehicles use LOX without jumping through all these hoops for insulating foam.

[Rocket Science]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

The SLS uses liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer which would boil off without insulation.

Your point about liquid hydrogen is true, but not liquid oxygen. Many (most) other launch vehicles use LOX without jumping through all these hoops for insulating foam.

Using the STS prop loading sequence as a analogue for SLS using "fully" cryogenic rocket engines, it will sit on the pad loaded far longer than Falcon 9 (LOX/RP-1) especially with the recent late load sub cooled LOX procedure...

[Comga]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

The article says:

This helps to maintain the propellant temperature in the required range and also keeps the outside of the tank from getting too cold, which would condense and freeze the water vapor in the air into ice; ice is a debris hazard and would add additional weight to the vehicle, reducing overall performance.  During the early stages of ascent, the foam also provides thermal protection from aerodynamic heating.

I would have thought the foam would impose a greater weight penalty than any condensed ice.

The SLS uses liquid hydrogen (LH2) fuel and the liquid oxygen (LOX) oxidizer which would boil off without insulation.

That begs the question.
The Saturn V used liquid hydrogen in its second and third stages
It used exterior and interior insulation respectively, according to online references.
SOFI was developed to overcome difficulties with those insulation methods
It would be interesting to see something about the decision making process that favored the newer methods over the old, and the trade offs between performance and cost, or rather how much it cost to make which performance improvements. This extensive article illustrates just how complex and labor and capital intensive this formed-in-place insulation is.

It appears to be the inverse of the Orion heat shield choices, where NASA went back to the Apollo methods over more efficient methods they developed subsequently. All interesting choices.


Rocker Science’s statement that the SLS will sit longer when loaded with cryogens is true, but represents another choice, not an absolute necessity. Systems engineering considers all these implications in the overall design.

[ncb1397]

I'm curious: Why does the SLS need foam insulation, while other launchers (such as SpaceX Falcon 9) manage without any such foam insulation?

Falcon 9 uses insulation. Where insulation is applied is launcher specific though. On Falcon 9, the oxygen and RP-1 tanks are separated by insulation, the fairing is insulated, and the tube providing oxygen through the RP-1 tank is insulated. On some early upper stage restart attempts, the lack of insulation on certain components caused the test to fail leading to installation of additional insulation.

[Oli]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

[JWag]

Applying foam to the interstage and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

It's interesting to speculate about. Shuttle retained intertank SOFI even after STS-107, after which they cut back on SOFI wherever possible. Perhaps they want to keep the large surface area of the skin-and-stringer intertank from absorbing and conducting heat into the LOX and LH2 tanks. Shuttle had some funny shock waves coming off the booster nose cones that caused some localized heating of the intertank on ascent, IIRC.

Not sure about the forward skirt, but it is conical and ought to have some heating of its own on ascent. The foam might provide ablative protection.

[Rocket Science]

As Chris mentions in his article the protection also extends for aerodynamic heating. The heat transfer being the greatest during the second minute of flight from Mach 1 to Mach 4.5 with test results from wind tunnel data...
https://www.nasa.gov/exploration/systems/sls/tunnel-approach-to-study-how-heat-affects-sls-rocket

[Lars-J]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

For the same reason most of SLS decisions are justified... Because that's how it was done with Shuttle.

No matter what anyone will tell you, this kind of foam is not necessary for LH2, and has many problems. You only need to look back at Saturn V - which flew with two LH2 stages with far longer loiter times - to see that is not necessary.

[woods170]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

For the same reason most of SLS decisions are justified... Because that's how it was done with Shuttle.

No matter what anyone will tell you, this kind of foam is not necessary for LH2, and has many problems. You only need to look back at Saturn V - which flew with two LH2 stages with far longer loiter times - to see that is not necessary.

In case you had failed to notice: both LH2 tanks on Saturn V (the one on S-II and the one on S-IVB) were insulated. Boil-off was the prime reason.

S-IVB LH2 tank was insulated on the inside. S-II LH2 tank was insulated on the outside.

Read from here: https://history.nasa.gov/afj/s-ii/s-ii-insulation.html

You will also discover where spray-on-foam originated from: S-II

Although several S-II stages were produced with the original insulation concept, the results were so discouraging that North American spent considerable time and money working up an alternative. Instead of making up panels and affixing them to the tank, the company finally evolved a process for spraying insulation material directly onto the tank walls (eliminating the air pockets), letting it cure, then cutting it to the proper contour. This technique turned out to be much more economical and much lighter than the insulation panels.

[Khadgars]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

For the same reason most of SLS decisions are justified... Because that's how it was done with Shuttle.

No matter what anyone will tell you, this kind of foam is not necessary for LH2, and has many problems. You only need to look back at Saturn V - which flew with two LH2 stages with far longer loiter times - to see that is not necessary.

Why would I take your assertion as correct?  It is much more plausible that you do not fully understand the topic at-hand.  You already admitted you didn't understand the Liquid Hydrogen portion, it is equally likely you do not understand the Liquid Oxygen portion either.  For the record, neither do I.

[Rocket Science]

Chris wrote a great article a while back in 2012 stating the SLS requirements to sit fueled on the pad up to 4 hours and 13 cryo-cyles... No engineer would not add "dead mass" to their design Lars... Read more, write less... What's that line you like to use on NSF members "Better keep your day job"... .
https://www.nasaspaceflight.com/2012/04/sls-robust-face-scrubs-launch-delays-pad-stays/

[Lars-J]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

For the same reason most of SLS decisions are justified... Because that's how it was done with Shuttle.

No matter what anyone will tell you, this kind of foam is not necessary for LH2, and has many problems. You only need to look back at Saturn V - which flew with two LH2 stages with far longer loiter times - to see that is not necessary.

In case you had failed to notice: both LH2 tanks on Saturn V (the one on S-II and the one on S-IVB) were insulated. Boil-off was the prime reason.

S-IVB LH2 tank was insulated on the inside. S-II LH2 tank was insulated on the outside.

Read from here: https://history.nasa.gov/afj/s-ii/s-ii-insulation.html

You will also discover where spray-on-foam originated from: S-II

Of course insulation is needed, did I say otherwise? Read again... "this kind of foam". As in what it is and its application method.

[woods170]

Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?

For the same reason most of SLS decisions are justified... Because that's how it was done with Shuttle.

No matter what anyone will tell you, this kind of foam is not necessary for LH2, and has many problems. You only need to look back at Saturn V - which flew with two LH2 stages with far longer loiter times - to see that is not necessary.

In case you had failed to notice: both LH2 tanks on Saturn V (the one on S-II and the one on S-IVB) were insulated. Boil-off was the prime reason.

S-IVB LH2 tank was insulated on the inside. S-II LH2 tank was insulated on the outside.

Read from here: https://history.nasa.gov/afj/s-ii/s-ii-insulation.html

You will also discover where spray-on-foam originated from: S-II

Of course insulation is needed, did I say otherwise? Read again... "this kind of foam". As in what it is and its application method.

- LH2 tank on S-IVB was insulated (on the inside) with glass fiber reinforced poly-urethane.
- LH2 tank on S-II was insulated with spray-on polyurethane foam.
- Tankage on STS ET was insulated with spray-on polyurethane foam.
- Tankage on SLS is insulated with spray-on polyurethane foam.

The formulations of the polyurethane foam differs between S-II, STS and SLS, but the chemistry is basically the same.

The foam is needed and no, it does not have many problems (contrary to what you suggested in your earlier post).
The other ways of insulating (LH2) tankage had much bigger problems:
- Honeycomb insulation panels for S-II had bonding difficulties and required a complicated, and never fully successful helium purge during tanking to prevent debonding issues.
- Internal insulation on S-IVB had bonding problems as well as being very labour-intensive. Individually numbered tiles were hand-fitted into place inside the tankage.

There are clear reasons why spray-foam is the way to go:
- Simple
- Fast
- Efficient insulation properties
- Less labour intensive than other methods (= cheaper)
- Less bonding problems than other methods

[MaxTeranous]

I do get that the spray foam insulation is needed for SLS in it's current guise, it just this (excellent) article makes it feel like it takes a lot of time and effort (and thus money) due to design decisions and requirements when compared to other rockets. Falcon was used as a comparison earlier in the thread, and as stated that has insulation too, but LH2 (rather than RP-1) requires way more insulation, and the need to sit fully fueled for 4 hours (rather than "easy" and quick RP-1 tanking and detanking) as a requirement that also leads to even more insulation. Add them together and the $$$$ looks to skyrocket in comparison. Is the cost breakdown of all the insulation for each SLS rocket known?

[envy887]

I do get that the spray foam insulation is needed for SLS in it's current guise, it just this (excellent) article makes it feel like it takes a lot of time and effort (and thus money) due to design decisions and requirements when compared to other rockets. Falcon was used as a comparison earlier in the thread, and as stated that has insulation too, but LH2 (rather than RP-1) requires way more insulation, and the need to sit fully fueled for 4 hours (rather than "easy" and quick RP-1 tanking and detanking) as a requirement that also leads to even more insulation. Add them together and the $$$$ looks to skyrocket in comparison. Is the cost breakdown of all the insulation for each SLS rocket known?

Sitting for 4 hours isn't the issue. They have to top the tanks anyway, and could easily just pour more fuel in. LH2 tanks need insulation because they otherwise will condense liquid air, which is a massive heat sink into the tank, and also a fire hazard due to the high LOX content.

I would be interested in a detailed explanation of why some vehicles use external insulation on LOX tanks and non-tank surfaces, while others do not.

[Steven Pietrobon]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

[eeergo]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

[DaveS]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

Ariane V doesn't have any debris concerns with the insulation as it doesn't have an orbiter hanging off it that has a fragile TPS. So that was something unique to the shuttle.

[woods170]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Yes, and ESA and it's contractors are slowly moving away from it. For Ariane 6 they are shifting to spray-on PU foam for the upper stage. If and when proven successful the plan is to implement spray-on foam on the main stage of A6 as well. But the initial vehicles will still fly with insulation tiles similar to the ones used on A5.

The expanded PU tiles on A5 are a carry-over from the tiles used on the H8 and H10 stages of Ariane 1, 2, 3 and 4.

[eeergo]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

Ariane V doesn't have any debris concerns with the insulation as it doesn't have an orbiter hanging off it that has a fragile TPS. So that was something unique to the shuttle.

Obviously But there must exist some level of knowledge, if perhaps not as detailed as STS with its cameras and cryopumping studies. Large TPS shedding might be damaging to other LV parts as well (see STS-112)

[Lars-J]

If you are listing alternatives insulation strategies, why not use the most successful hydrogen stage of all time? (I believe) - Centaur.

[woods170]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

Ariane V doesn't have any debris concerns with the insulation as it doesn't have an orbiter hanging off it that has a fragile TPS. So that was something unique to the shuttle.

Obviously But there must exist some level of knowledge, if perhaps not as detailed as STS with its cameras and cryopumping studies. Large TPS shedding might be damaging to other LV parts as well (see STS-112)

Ariane has not experienced any significant loss of insulation tiles since they started using them on the H8 upper stage on Ariane 1.

[eeergo]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

Ariane V doesn't have any debris concerns with the insulation as it doesn't have an orbiter hanging off it that has a fragile TPS. So that was something unique to the shuttle.

Obviously But there must exist some level of knowledge, if perhaps not as detailed as STS with its cameras and cryopumping studies. Large TPS shedding might be damaging to other LV parts as well (see STS-112)

Ariane has not experienced any significant loss of insulation tiles since they started using them on the H8 upper stage on Ariane 1.

This begs the question: was the panel solution studied for STS?

[DaveS]

On Ariane V, they use 2 cm thick insulating tiles made from expanded polyurethane.

http://www.sciencephoto.com/media/87848/view

Thank you for that, I had long searched for a good explanation or picture of what Ariane 5 used for TPS (especially how it compared to the Shuttle's ET, when particle release was a concern for STS - I still wonder how it compares).

Ariane V doesn't have any debris concerns with the insulation as it doesn't have an orbiter hanging off it that has a fragile TPS. So that was something unique to the shuttle.

Obviously But there must exist some level of knowledge, if perhaps not as detailed as STS with its cameras and cryopumping studies. Large TPS shedding might be damaging to other LV parts as well (see STS-112)

Ariane has not experienced any significant loss of insulation tiles since they started using them on the H8 upper stage on Ariane 1.

This begs the question: was the panel solution studied for STS?

AFAIK, no. They really did not care about foam loss from the ET until after STS-107. And it wouldn't have done much good any way. The critical foam loss areas were the protuberances(bipod spindles, pressurization line brackets etc), not the acreage foam on the actual tanks.

[Wayne Hale]

I'm no expert on SLS or the insulation trades that have been made there. However, I can help a little with the shuttle history which may be of interest in this discussion.  During early shuttle design, and again after STS-107 there was considerable effort made to look at putting the insulation on the inside of the tank rather than the outside.  The conclusion at both times was that there was considerable risk that foam could come off and be ingested into the engine turbopumps with catastrophic results.  So the foam remained outside.

Foam loss was a significant issue for the shuttle program even before STS-107 and efforts were made to reduce foam shedding during ascent in several areas . . . but as we later learned, not enough effort was made to eliminate the losses.  Prior to STS-107, as we all infamously know now, foam loss during ascent was considered a nuisance problem that resulted in minor orbiter tile damage increasing turnaround time between flights.

Losses of the robotically sprayed 'acreage' foam were minimal, most of the foam losses occurred in the hand crafted specialty areas like the ice/frost ramps, PAL ramp, and of course the bipod ramp.  After much investigation these foam on foam areas were subject to differential thermal expansion which caused loss of significantly sized foam.

Foam insulation was necessary for the shuttle to maintain propellant 'quality' - temperature and density.  Boiloff would have been high, but the loss of density of the LOX and LH2 would have made significant ascent performance losses if the foam had not been there.  And ice formation was always a concern.  Much of the foam was sized to ensure the outer tank surface stayed at or above 32 deg F under most conditions.  The Final Inspection Team ensured that there were no areas of ice formation where there were imperfections in the insulation, etc.

Intertank insulation was required for ascent heating primarily although it did help with the prelaunch time while tanked on the launch pad.  It not only prevented heat transfer into the propellant tanks but preserved the material strength of the aluminum skin of the intertank during the aeroheating of ascent.

That is a quick summary.  I expect the SLS team - which has a lot of shuttle veterans - are making engineering trades for all of this, not simply doing it 'because the shuttle did it'.  In fact, I would go further to state that there is a conscious mind set to do things differently than shuttle with most of the SLS team, as far as I have interacted with them.

[mike robel]

Wayne,

Thanks for your perspective.  It is very illuminating for me.  However, I note the Saturn SIVB had internal insulation and proved to be a very reliable booster, as discussed in https://history.nasa.gov/SP-4206/ch6.htm.  There was no mention of engine ingestion in the cited work.

The S-II had external insulation, at first in premolded pieces (which had a lot of problems), and later it was sprayed on.

I wonder if the external insulation was selected because the shuttle tank was not constructed by McDonnel-Douglas, but by Martin (if I recall correctly) and then by North American Rockwell (I think) and still later Boeing?

Mike

[Markstark]

This may be relevant to the discussion

[mike robel]

Thanks. 

[DaveS]

Wayne,

Thanks for your perspective.  It is very illuminating for me.  However, I note the Saturn SIVB had internal insulation and proved to be a very reliable booster, as discussed in https://history.nasa.gov/SP-4206/ch6.htm.  There was no mention of engine ingestion in the cited work.

The S-II had external insulation, at first in premolded pieces (which had a lot of problems), and later it was sprayed on.

I wonder if the external insulation was selected because the shuttle tank was not constructed by McDonnel-Douglas, but by Martin (if I recall correctly) and then by North American Rockwell (I think) and still later Boeing?

Mike

NAR was the orbiter vehicle only. NAR subsequently became Rockwell Intl and was bought by Boeing. Martin-Marietta was bought up by Lockheed creating Lockheed Martin.

[envy887]

...
Intertank insulation was required for ascent heating primarily although it did help with the prelaunch time while tanked on the launch pad.  It not only prevented heat transfer into the propellant tanks but preserved the material strength of the aluminum skin of the intertank during the aeroheating of ascent.
...

Is this due to the booster nose cone shockwaves impinging on the intertank? I don't know of any other multicore vehicle that insulates the intertank or interstage with SOFI, though DIVH and FH do both appear to have insulation there.

[JohnF]

Very very basic question, common sense wise, why get away from the Saturn V design for a rocket going to the moon ?, the blueprints for man's greatest machine surely still exist. The shuttle design booster seems to troublesome, from foam to O rings etc. I suppose I will answer my own question, tooling perhaps ?

[DaveS]

Very very basic question, common sense wise, why get away from the Saturn V design for a rocket going to the moon ?, the blueprints for man's greatest machine surely still exist. The shuttle design booster seems to troublesome, from foam to O rings etc. I suppose I will answer my own question, tooling perhaps ?

The o-rings are since long fixed and the foam is of no concern to an inline vehicle really. The tooling and engineering knowledge that went into the Saturns are since long gone. Recreating it would essentially be creating it anew.

[Hog]

Very very basic question, common sense wise, why get away from the Saturn V design for a rocket going to the moon ?, the blueprints for man's greatest machine surely still exist. The shuttle design booster seems to troublesome, from foam to O rings etc. I suppose I will answer my own question, tooling perhaps ?

There are no issues related to SOFI or SRB O-rings as related to SLS.  Any shed foam wont hit the vehicle like the sidemounted Orbiter Vehicles, remember all that ice that fell when the F-1s came to life?
O-rings were redesigned for the 1st RTF back almost 30 years ago now.

We were lucky IMO to get away from the Apollo program without a LVLC.  Saturn-V as mans greatest machine, interesting view.

I'm sure there are budgetary concerns as well.  There was also a big push to use Shuttle derived technologies.

[rayleighscatter]

Very very basic question, common sense wise, why get away from the Saturn V design for a rocket going to the moon ?, the blueprints for man's greatest machine surely still exist. The shuttle design booster seems to troublesome, from foam to O rings etc. I suppose I will answer my own question, tooling perhaps ?

Saturn V had a lot of issues and to iron them all out would require an update, essentially, of every piece. And we have a case study on that with J2-X.

[penguin44]

Also, weren't the blueprints for it lost in the 70s?

[ncb1397]

Very very basic question, common sense wise, why get away from the Saturn V design for a rocket going to the moon ?, the blueprints for man's greatest machine surely still exist. The shuttle design booster seems to troublesome, from foam to O rings etc. I suppose I will answer my own question, tooling perhaps ?

Saturn V had a lot of issues and to iron them all out would require an update, essentially, of every piece. And we have a case study on that with J2-X.

J-2x had so many changes in part because of the different architecture. For instance,throttling requirements were set so as not to impart too much force on the docking adapter between Orion and Altair in the "1.5 launch" Constellation architecture. If all you wanted to do was build another Saturn V, you wouldn't need to make such changes. You wouldn't need higher isp, nozzle extensions or anything like that.

[Steven Pietrobon]

Also, weren't the blueprints for it lost in the 70s?

No. NASA still has them. You can buy some of them here:

http://www.aerospaceprojectsreview.com/catalog/drawndoc.htm

[MaxTeranous]

It's a many order problem. NASA may have the blueprints, but not the tooling, processes, and skills. To make the tooling may in turn need other tooling that don't exist. That may have been made by a subcontractor that doesn't exist, so any documentation is gone. Using skills that are no longer used in modern manufacturing, so largely don't exist. And you have to do that for all ~3 million parts....

[the_other_Doug]

AIUI, tooling for large projects is usually stored for a certain period of time, and then scrapped when the decision is made that the product will never again be produced.

It's mainly a matter of paying for properly environmentally-controlled storage space.  There is nothing to stop NASA or a contractor from storing the tooling for a major rocket or spacecraft system indefinitely, except for the expense.

As for blueprints, same thing applies.  And storage for the blueprints is rather less of an expense.  I don't imagine any of the blueprints from the Apollo era and on, for launch vehicles or spacecraft, have been lost.  They are useful for historical reasons, if nothing else.