SpaceX Falcon 9 - AMOS-6 - (Pad Failure) - DISCUSSION THREAD (2)

[HMXHMX]

http://m.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

(July 14, 2016) Their main product are the helium tanks used on SpaceX's Falcon 9 rocket, the one that made headlines when it landed its booster stage after launching a payload.

Link originally posted on Sept 3rd:  http://forum.nasaspaceflight.com/index.php?topic=30981.msg1577821#msg1577821

[CyndyC]

http://m.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

(July 14, 2016) Their main product are the helium tanks used on SpaceX's Falcon 9 rocket, the one that made headlines when it landed its booster stage after launching a payload.

Link originally posted on Sept 3rd:  http://forum.nasaspaceflight.com/index.php?topic=30981.msg1577821#msg1577821

I remembered your previous post and much of what you said, altho not who posted it, just that I didn't feel the need to check the references. Consequently the company name didn't stay in my mind.

One thing I remembered from your post was the main reason I alluded to the same article. You thought it was implied not all SpaceX COPV production had moved in house, whereas I thought it was implied no SpaceX COPV production is being done in house.

[HMXHMX]

http://m.waaytv.com/space_alabama/cimarron-composites-huntsville-s-lightweight-fuel-tank-experts/article_2f123dba-49e5-11e6-809e-07d4e6cc03db.html

(July 14, 2016) Their main product are the helium tanks used on SpaceX's Falcon 9 rocket, the one that made headlines when it landed its booster stage after launching a payload.

Link originally posted on Sept 3rd:  http://forum.nasaspaceflight.com/index.php?topic=30981.msg1577821#msg1577821

I remembered your previous post and much of what you said, altho not who posted it, just that I didn't feel the need to check the references. Consequently the company name didn't stay in my mind.

One thing I remembered from your post was the main reason I alluded to the same article. You thought it was implied not all SpaceX COPV production had moved in house, whereas I thought it was implied no SpaceX COPV production is being done in house.

To sum up what I know (or think I know) the liners are made by SpaceX and the wrap is done by Cimarron.  But as usual, SpaceX will take wrapping in house as soon as they can figure it out.

[Patchouli]

The gas from the COPVs is heated in a heat exchanger (on the Merlin GGs, I believe) which reduces the mass required for pressurization.

If you had to re-engineer that (Herb's input excepted), ISTM that liquid helium bottles in the engine compartment could be a feasible alternative. This would go through uprated Merlin heat exchangers to feed the same gasses to the tanks.

These would be much smaller than the gas bottles (liquid is much denser), and not have the extreme pressures, but would need more mass for insulation.

Gas pressure would be provided by GSE while on the pad, including bringing the tanks up to launch pressure.

This would be a substantial change, and they'd need to also survive reentry OK.

Cheers, Martin

An easier change would be just moving to steel or aluminum tanks and keeping them in the same location.
Though the problem may be solved just by changing some of the materials used for the COPEVs.

[StuffOfInterest]

Probably nothing new here but The Wall Street Journal has a new article regarding the accident investigation.

[pargoo]

    We saw a partial shot showing the payload fairing in hi-res.  Was a whole-vehicle hi-res pic ever released pre ka-boom? 

[biosehnsucht]

An easier change would be just moving to steel or aluminum tanks and keeping them in the same location.
Though the problem may be solved just by changing some of the materials used for the COPEVs.

There's a mass penalty in making a pure metal tank capable of the same specifications, but perhaps they can afford it after uprating the Merlins thrust...

[cuddihy]

I think darn near any metal thick enough to contain that kind of pressure without significant overwrap will be prone to brittle fracturing modes under the thermal conditions described...it's tough requirements for ANY material to stand.

[Jim]

I think darn near any metal thick enough to contain that kind of pressure without significant overwrap will be prone to brittle fracturing modes under the thermal conditions described...it's tough requirements for ANY material to stand.

No, see the Saturn V

[Phillip Clark]

How is the repair of the launch pad coming along?   When is it expected to be ready of launches again?

[Herb Schaltegger]

How is the repair of the launch pad coming along?   When is it expected to be ready of launches again?

There's a thread for that ...

https://forum.nasaspaceflight.com/index.php?topic=41060.0

[cambrianera]

Which kind of masses are we talking about when talking about pressurization?
Volume to be pressurized in first stage is about 350 m3 (150 RP-1, 200 LOX);
Volume to be pressurized in second stage is about 120 m3 (47 RP-1, 73 LOX);
Pressure is about 3 bar;
Density of He is 0.18 kg/m3
Density of CH4 is 0.72 kg/m3
Density of N2 is 1.25 kg/m3
Density of O2 is 1.43 kg/m3
(all values at 1 bar/0 C°).
Masses of gas (Kg)

He CH4 N2 O2

First RP1 67 269 471 538

First LOX 96 384 672 768

Second RP1 22 86 151 173

Second LOX 34 134 235 269

Autogenous pressurization of LOX tank has small impact on second stage and very small on first.

But what about savings due to change of material of pressure vessels?
Using barlow’s formula the ratio [mass of the vessel (cylinder without head) / mass of the content] can be expressed as:
Mass ratio [Vessel/Content] = 2*(density of vessel/density of content)/(material strength/sea level pressure)
This is purely theoretical, but gives indications that, with all the most favorable assumptions, mass of vessel for He is similar to mass of gas.
The “density of content” part is normalized for pressure (1 bar), not for temperature; going from 273 K to 90 K  this value increases threefold.

Seems to me that change of material of pressure vessel to Stainless steel would imply a increase of mass comparable to the mass of He, not much more.

[HMXHMX]

Which kind of masses are we talking about when talking about pressurization?
Volume to be pressurized in first stage is about 350 m3 (150 RP-1, 200 LOX);
Volume to be pressurized in second stage is about 120 m3 (47 RP-1, 73 LOX);
Pressure is about 3 bar;
Density of He is 0.18 kg/m3
Density of CH4 is 0.72 kg/m3
Density of N2 is 1.25 kg/m3
Density of O2 is 1.43 kg/m3
(all values at 1 bar/0 C°).
Masses of gas (Kg)

He CH4 N2 O2

First RP1 67 269 471 538

First LOX 96 384 672 768

Second RP1 22 86 151 173

Second LOX 34 134 235 269

Autogenous pressurization of LOX tank has small impact on second stage and very small on first.

But what about savings due to change of material of pressure vessels?
Using barlow’s formula the ratio [mass of the vessel (cylinder without head) / mass of the content] can be expressed as:
Mass ratio [Vessel/Content] = 2*(density of vessel/density of content)/(material strength/sea level pressure)
This is purely theoretical, but gives indications that, with all the most favorable assumptions, mass of vessel for He is similar to mass of gas.
The “density of content” part is normalized for pressure (1 bar), not for temperature; going from 273 K to 90 K  this value increases threefold.

Seems to me that change of material of pressure vessel to Stainless steel would imply a increase of mass comparable to the mass of He, not much more.

You'd want to redesign the bottle into a spherical vs. cylindrical shape.  COPVs "want" to be cylindrical while monocoque metal bottles are lowest mass when spherical.

Because of an NDA (not with SpaceX) I can't show my work, but I sized a replacement bottle that has the same geometry as the current COPV, using Inconel 718, adjusting safety factors as appropriate, etc.  It ended up substantially heavier, naturally.  I conclude the inserted payload loss on F9 S2 would be on the order of a metric ton.  Using a completely new spherical design, that could be cut about in half.

No problem for LEO missions; problem for GTO.

[CyndyC]

You'd want to redesign the bottle into a spherical vs. cylindrical shape.  COPVs "want" to be cylindrical while monocoque metal bottles are lowest mass when spherical.

Because of an NDA (not with SpaceX) I can't show my work, but I sized a replacement bottle that has the same geometry as the current COPV, using Inconel 718, adjusting safety factors as appropriate, etc.  It ended up substantially heavier, naturally.  I conclude the inserted payload loss on F9 S2 would be on the order of a metric ton.  Using a completely new spherical design, that could be cut about in half.

No problem for LEO missions; problem for GTO.

Spherical sounds like a better way to go no matter what else, not only for the lower mass, but also for a flow of geysering LOX and thermal gradients that would be less restricted around a sphere than around a cylinder.

Something else stood out to me while re-reading the COPV essay in SpaceNews. I won't be surprised if this or something similar has been brought up earlier, but I've only seen posts about metallic liner options, and suggestions for external COPV insulation. In NASA ground & flight experiments with composite tanks using internal insulation, not metallic liners, and using cryogenic liquid hydrogen, which is colder than cryogenic liquid oxygen, the tanks survived 50 fill and drain cycles. NASA also tried external insulation, but those results apparently weren't as successful, enough to be included in this interview. Does anyone know what insulation material was used in these experiments?

NASA didn't translate that success into operational flight, but it might be a way SpaceX could go, and avoid a larger redesign necessary to cease submersion in the cryogenic cycling environment.

And now I really must get back to my library book for awhile before it comes due, Headstrong: 52 Women Who Changed Science and the World.

Weren’t composite tanks with cryogenic fluids used for some experimental vehicles?
NASA has had experience with ground test composite tanks and cryogenic fluids, as well as flight tests of composite tanks with liquid hydrogen. I should point out that liquid hydrogen is colder than liquid oxygen.
The DC-XA vehicle’s composite liquid hydrogen tank used internal insulation bonded to the composite tank inner wall. This tank survived approximately 50 fill and drain cycles. The X-33 composite liquid hydrogen tank did not have internal insulation. The insulation was bonded to the exterior wall. Analysis of the DC-XA design indicated that the internal insulation reduced the thermal gradient across the tank walls because gaseous hydrogen interacted with the composite matrix behind the insulation, rather than the cryogenic liquid hydrogen.
These experiments were not followed by use on operational launchers.

[Jet Black]

An easier change would be just moving to steel or aluminum tanks and keeping them in the same location.
Though the problem may be solved just by changing some of the materials used for the COPEVs.

There's a mass penalty in making a pure metal tank capable of the same specifications, but perhaps they can afford it after uprating the Merlins thrust...

Might have a hit on their landing capability - remember they have to slow down the extra weight as well as lift it.

[hans_ober]

Shouldn't have much on an effect on the first stage. Very important for the second stage though. It eats directly into mass capability.

[matthewkantar]

I think darn near any metal thick enough to contain that kind of pressure without significant overwrap will be prone to brittle fracturing modes under the thermal conditions described...it's tough requirements for ANY material to stand.

No, see the Saturn V

Saturn did not subcool LOX, so similar, not the same.

Matthew

[Jim]

I think darn near any metal thick enough to contain that kind of pressure without significant overwrap will be prone to brittle fracturing modes under the thermal conditions described...it's tough requirements for ANY material to stand.

No, see the Saturn V

Saturn did not subcool LOX, so similar, not the same.

Matthew

Not relevant for this.

[docmordrid]

We may get answers at todays r/SpaceX Musk AMA at 2200 UT.

https://www.reddit.com/r/spacex/comments/58yc14/elon_musk_will_be_doing_an_ama_on_rspacex_at_3pm/

[OnWithTheShow]

I think darn near any metal thick enough to contain that kind of pressure without significant overwrap will be prone to brittle fracturing modes under the thermal conditions described...it's tough requirements for ANY material to stand.

No, see the Saturn V

So what were the helium tanks in Saturn V made of? What was the thickness/weight. I cant find it.