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

[Mike_1179]

I found this:
https://shellbuckling.com/presentations/otherTopics/pages/page_180.html

Buckling seems to happen near the neck of COPV.

This model is complicated by the fact that they were filling the tank with LOX at the time time too. If the COPV was only partially covered by cold LOX then you could get some rather interesting strains in the Al liner. That paper you reference assumes the entire exterior of the COPV is at the same temperature.

[MarekCyzio]

I found this:
https://shellbuckling.com/presentations/otherTopics/pages/page_180.html

Buckling seems to happen near the neck of COPV.

This model is complicated by the fact that they were filling the tank with LOX at the time time too. If the COPV was only partially covered by cold LOX then you could get some rather interesting strains in the Al liner. That paper you reference assumes the entire exterior of the COPV is at the same temperature.

Looks like debonding and buckling happens during autofrettage process - before COPV's are even installed. Another possibility is that COPV's did not buckle during autofrettage, but bond between composite and AL was weakened to a point where rapid change in temperature (either by submersing them in LOX or by injecting supercooled hellium) was sufficient to break the bond and cause buckling.

Edit - assuming buckling happens after COPV is submersed in LOX, it would suck LOX into the void. So my theory is that SpaceX is going to alter procedures so that thermal stress on COPV is smaller and buckling does not happen.

[DaveJes1979]

The bottles contain just shy of 20K cu inches (and no, I'm not going to do this in metric) so at  SF = 1.5 (too low in my opinion but meets the NASA spec) and a PV/W of 1E6, the weight of the current bottle is about 160 lbm.  The PV/W of a high strength aluminum is about 250K, so the difference (per bottle) is about 470 lbm, or 1880 lbm for the stage.

Not a problem for LEO as the current F9 configuration is way overpowered, but 0.85MT loss is painful for GTO missions.  Perhaps not as painful as losing another multi-hundred million dollar spacecraft, though.

I went with a spherical pressure vessel, which would give us an inner radius of ~16.8".  With 5500 psi, FS=1.5 and tensile strength of 85 ksi for 2090-TSE48 aluminum plate.  That gives us a wall thickness of 0.817", so the weight comes in at 284 lbs. for an idealized spherical design.

[HMXHMX]

The bottles contain just shy of 20K cu inches (and no, I'm not going to do this in metric) so at  SF = 1.5 (too low in my opinion but meets the NASA spec) and a PV/W of 1E6, the weight of the current bottle is about 160 lbm.  The PV/W of a high strength aluminum is about 250K, so the difference (per bottle) is about 470 lbm, or 1880 lbm for the stage.

Not a problem for LEO as the current F9 configuration is way overpowered, but 0.85MT loss is painful for GTO missions.  Perhaps not as painful as losing another multi-hundred million dollar spacecraft, though.

I went with a spherical pressure vessel, which would give us an inner radius of ~16.8".  With 5500 psi, FS=1.5 and tensile strength of 85 ksi for 2090-TSE48 aluminum plate.  That gives us a wall thickness of 0.817", so the weight comes in at 284 lbs. for an idealized spherical design.

Not sure you'd get full properties forming a hemisphere w/o a lot of post-forming processing; I've had to accept fairly serious knock-downs after spin-forming domes in previous projects, but a spherical tank is certainly an option with less weight penalty.

[Jcc]

A long term solution, even for F9, is to use autogenous pressurization for the LOX tanks. You can't do that with RP1, so still need COPVs for that, but also least those won't explode.
I don't think they will do it, but it would solve the problem, and they need to download it anyway for ITS.

[Jim]

A long term solution, even for F9, is to use autogenous pressurization for the LOX tanks.

Can't for the upper stage.  Longer duration missions require more pressure than can be provided.

[envy887]

A long term solution, even for F9, is to use autogenous pressurization for the LOX tanks. You can't do that with RP1, so still need COPVs for that, but also least those won't explode.
I don't think they will do it, but it would solve the problem, and they need to download it anyway for ITS.

What's the point of putting COPVs in the RP1 tank? It's only ~30 K cooler than ambient, so you don't gain nearly the He density improvement that is the reason for putting them in the LOX tank.

[Jim]

What's the point of putting COPVs in the RP1 tank? It's only ~30 K cooler than ambient, so you don't gain nearly the He density improvement that is the reason for putting them in the LOX tank.

It is easier to put them in a tank and make the tank a little larger to account for the lost volume than to add a structural section to the stage to house the tank. 

[envy887]

What's the point of putting COPVs in the RP1 tank? It's only ~30 K cooler than ambient, so you don't gain nearly the He density improvement that is the reason for putting them in the LOX tank.

It is easier to put them in a tank and make the tank a little larger to account for the lost volume than to add a structural section to the stage to house the tank.

I suppose that only needing to pressurize less than 1/2 the current  volume means they can take the density hit without adding more COPVs.

A long term solution, even for F9, is to use autogenous pressurization for the LOX tanks.

Can't for the upper stage.  Longer duration missions require more pressure than can be provided.

Only have to heat the LOX to ~100K for the vapor pressure to reach flight pressures. That's not feasible?

[Jim]

Only have to heat the LOX to ~100K for the vapor pressure to reach flight pressures. That's not feasible?

Where is the heat coming from?

[Johnnyhinbos]

ACES-style ICE (that's for Robotbeat's pleasure)

[Jim]

ACES-style ICE (that's for Robotbeat's pleasure)

An IFV  still might use helium on the pad.

[LouScheffer]

A long term solution, even for F9, is to use autogenous pressurization for the LOX tanks.

Can't for the upper stage.  Longer duration missions require more pressure than can be provided.

Well, you can't use the engine as the heat source for autogenous pressurization.  But you've got lots of LOX and kerosene, so there is no reason you could not burn some to heat and pressurize the LOX.  You need some extra hardware, but it's not too big or heavy.  That's what ACES does, I believe.

[Jim]

Well, you can't use the engine as the heat source for autogenous pressurization.  But you've got lots of LOX and kerosene, so there is no reason you could not burn some to heat and pressurize the LOX.  You need some extra hardware, but it's not too big or heavy.  That's what ACES does, I believe.

No,  more than heat is needed.  The IFV ICE waste heat is used to heat the propellants to provide the pressurant gases. The ICE powers pumps to increase the pressure of the gases.  The ICE exhaust is used for settling thrust.

For rocket engine autogenous pressurization, the engine operation provides a high pressure source, either a portion of the turbo pump propellant output is heated into gas or the turbo pump exhaust is cooled

[matthewkantar]

IFV or IVF? Just asking.

Matthew

[envy887]

Are tanks depressed during coast period? If so, just for the ~10 hr coast to GEO insertion, or also for the ~20 min coast to GTO insertion?

[bstrong]

There is a list of references on COPVs submerged in cryogenic liquids in the technology overview Firefly just posted (looks like they were planning to put COPVs inside COPVs).

Materials – Cryogenic Application (Resins): The structures team at Firefly knew that their first hurdle was going to be identifying the correct resin formulation which would work for the cryogenic application required on the Firefly vehicle. The engineers at Firefly were familiar with the cutting edge work which had been on going at NASA’s Marshall Space Flight Center and a small company in Huntsville named Cimarron Composites. This work was thorough and provided the basis for the Firefly designers. There were several key papers written covering this work. The first entitled, “A Systematic Approach to Cryogenic COPV Design” [57]. This work largely covers the technical approach to the testing of polymer matrices at low temperatures. The next work which has a bearing on the Firefly effort is DeLay, Patterson, Noorda and Schneider’s “Development of Cryogenic Composite Overwrapped Pressure Vessels (COPVs)” [58]. This work examines the use of high pressure COPVs emerged in cryogenic liquids and the material effects. This work was augmented by Schneider, Gargis and DeLay’s work “Apparent Hoop Tensile Strength of Fiber Reinforced Composites and LN2 Temperatures” [59]. This work specifically probes COPV rings at ambient and LN2 temperatures. The team also made use of Ray, Greene, Revilock and Sneddon’s work “High Pressure Composite Overwrapped (COPV) Development Tests at Cryogenic Temperatures”. [60] This work also focused on testing high pressure composites submerged in Cryogenic liquids. The Firefly team used this strong depth of work as the basis for their approach to the Alpha vehicle tankage.

The issues of microcracking is of great concern in the use of composites at cryogenic temperatures. Two additional works focusing on this area were used by the Firefly engineers as checks. The first is John A Nairn’s “Matrix Microcracking in Composites” [61] and the second is Olofsson, Langstrom, Mattsson and Ohlsson’s work “Manufacture with Spread Tow Fiber Materials, For Reduced Micro-Cracking” [62].

57. Dyess, Mark and Hastings, Chad and Schneider, Judy and DeLay, Tom, A Systematic Approach to Cryogenic Copv Design, 48th AIAA/ASME Structures Structural Dynamics and Materials Conference, April 1, 2007.

58. DeLay, Tom and Patterson, James and Noorda, Jared and Schneider, Judy, Development of Cryogenic Composite Over-Wrapped Pressure Vessels (COPVS), 52nd International Sampe Symposium, June 3-7, 2007.

59. Schneider, Judy and Gargis, Matt and DeLay, Tom, Apparent Hoop Tensile Strength of Fiber Reinforced Composites at LN2 Temperatures, 52nd International Sampe Symposium, June 3-7, 2007.

60. Ray, David M., P.E. and Greene, Nathanael J. and Revilock Duane and Sneddon, Kirk and Anselmo, Estelle, High Pressure Composite Overwrapped Pressure Vessel (COPV) Development Tests at Cryogenic Temperatures, 49th AIAA/ASME/ASCE/AHS Structures, Structural Dynamics, and Materials Conference, Schaumberg, IL., April 7-10, 2008.

61. Nairn, John A., 2.13 Matrix Microcracking in Composites, Comprehensive Composite Materials, Elsevier Science, 2000.

62. Olofsson, K. and Langstrom, R. and Mattsson, D. and Ohlsson, F., Manufacture with Spread Tow Fiber Materials, for Reduced Micro-Cracking, 20th International Conference on Composite Materials Copenhagen, July 19-24, 2015.

[Jim]

Are tanks depressed during coast period? If so, just for the ~10 hr coast to GEO insertion, or also for the ~20 min coast to GTO insertion?

Depends on the coast length

[envy887]

Are tanks depressed during coast period? If so, just for the ~10 hr coast to GEO insertion, or also for the ~20 min coast to GTO insertion?

Depends on the coast length

Depending on coast length, solar thermal management and collecting boiloff might be sufficient. The LOX tank gets ~100 MJ/hr once out of LEO, which if absorbed and turned into boiloff would get it to ~3 bar in something like 2 hours. All it needs is some black paint

The ICE might be a lot easier to control. Or perhaps leave it pressed, what's the reason for depressing on coasts?

[Johnnyhinbos]

Are tanks depressed during coast period? If so, just for the ~10 hr coast to GEO insertion, or also for the ~20 min coast to GTO insertion?

Depends - are they on a reusable stage? If not, then they probably are depressed...