Author Topic: Protecting SLS from Fire and Ice - TPS foam application proceeding at Michoud  (Read 5079 times)


Offline whitelancer64

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

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

Offline Rocket Science

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Nice meaty article Philip, thank you! :)
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Offline cmcqueen

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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:

Quote
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.
« Last Edit: 12/11/2017 12:22 AM by cmcqueen »

Offline Rocket Science

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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:

Quote
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.
"The laws of physics are unforgiving"
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Offline lrk

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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:

Quote
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. 

Offline Lars-J

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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:

Quote
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.

Offline Rocket Science

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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:

Quote
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...
« Last Edit: 12/11/2017 04:11 PM by Rocket Science »
"The laws of physics are unforgiving"
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Offline Comga

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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:

Quote
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.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline ncb1397

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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.
« Last Edit: 12/11/2017 06:53 PM by ncb1397 »

Offline Oli

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Applying foam to the intertank and the forward skirt seems a bit much. Any particular reason why it's being done with SLS?
« Last Edit: 12/11/2017 10:19 PM by Oli »

Offline JWag

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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.

Offline Rocket Science

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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
« Last Edit: 12/12/2017 01:09 PM by Rocket Science »
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Offline Lars-J

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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.
« Last Edit: 12/12/2017 03:49 AM by Lars-J »

Offline woods170

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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

Quote from: NASA
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.
« Last Edit: 12/12/2017 09:35 AM by woods170 »

Offline Khadgars

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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.

Offline Rocket Science

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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/
« Last Edit: 12/12/2017 04:39 PM by Rocket Science »
"The laws of physics are unforgiving"
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Offline Lars-J

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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.

Offline woods170

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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

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