NASA orders SpaceX to examine changing to Inconel tanks from carbon fiber

[mongo]

Liquid or solid O2 in contact with carbon is not in itself a problem. The issue was that solid oxygen formed inside the carbon fibre matrix due to the liquid O2 being further cooled by the helium. That either caused heating due to the pressure increase or heat due to breaking of carbon fibers. The heat then instantiated combustion or further rupture of the high pressure vessel containment .

 

[Cosmacelf]

Well, if successful, an Inconel tank would seem to be much safer. Frankly, relying on a specific way of filling helium and LOX at just the right temperature and speed to prevent an explosion struck me as a bit dodgy.

 

[Cosmacelf]

It would be a good armchair assumption, though, to say that an Inconel tank would weigh more than their existing tanks, so maybe this would result in less margin for booster recovery, which is why SpaceX didn’t do this in the first place.

 

[mongo]

Well, if successful, an Inconel tank would seem to be much safer. Frankly, relying on a specific way of filling helium and LOX at just the right temperature and speed to prevent an explosion struck me as a bit dodgy.

Loading the Helium at an effective temperature (valves and pipes may act as orifi) above the freezing point of oxygen prevents the issue. That sounds more like a design constraint than something dodgy. Also concider that there hasn't been an issue before or after.

An Inconel tank would not have made a difference unless the new tank has no overwrap at all. Aditionally, carbon fiber has a slightly negative CTE vs positive CTEs for Inconel and Aluminum, so both will form gaps.

 

[Cosmacelf]

Loading the Helium at an effective temperature (valves and pipes may act as orifi) above the freezing point of oxygen prevents the issue. That sounds more like a design constraint than something dodgy. Also concider that there hasn't been an issue before or after.

An Inconel tank would not have made a difference unless the new tank has no overwrap at all. Aditionally, carbon fiber has a slightly negative CTE vs positive CTEs for Inconel and Aluminum, so both will form gaps.

I’m not sure I understand your point about gaps, but wouldnt an Inconel tank be pure Inconel and not an Inconel wrap around aluminum?

 

[jkn]

I’m not sure I understand your point about gaps, but wouldnt an Inconel tank be pure Inconel and not an Inconel wrap around aluminum?

Inconel tank without carbon fiber over wrap would be too heavy. There is no need to replace aluminum, which is not touching O2.

 

[mongo]

I’m not sure I understand your point about gaps, but wouldnt an Inconel tank be pure Inconel and not an Inconel wrap around aluminum?

I was thinking of Inconel vs Aluminum in a COPV. A pure Inconel tank would much heavier (and more difficult to manufacture).

@jkn The O2 does permeate the wrap to the Al, but that's not an issue.

Each stage of Falcon 9 uses COPVs to store cold helium which is used to maintain tank pressure, and each COPV consists of an aluminum inner liner with a carbon overwrap. The recovered COPVs showed buckles in their liners. Although buckles were not shown to burst a COPV on their own, investigators concluded that super chilled LOX can pool in these buckles under the overwrap. When pressurized, oxygen pooled in this buckle can become trapped; in turn, breaking fibers or friction can ignite the oxygen in the overwrap, causing the COPV to fail. In addition, investigators determined that the loading temperature of the helium was cold enough to create solid oxygen (SOX), which exacerbates the possibility of oxygen becoming trapped as well as the likelihood of friction ignition.

 

[LargeHamCollider]

from SpaceX:


OrbitalATK links to a paper (AIAA 2002-4349) discussing testing of titanium COPVs.

Hmmm, was sure SpX COPVs had a Ti liner, not sure where I got that from.

 

[jkn]

I was thinking of Inconel vs Aluminum in a COPV. A pure Inconel tank would much heavier (and more difficult to manufacture).

@jkn The O2 does permeate the wrap to the Al, but that's not an issue.

But LOX going through carbon fiber mean that LOX and carbon mix. That is a problem. If He tanks needs inconel, it must be outside separating O2 and C.

 

[mongo]

But LOX going through carbon fiber mean that LOX and carbon mix. That is a problem. If He tanks needs inconel, it must be outside separating O2 and C.

You lost me. The carbon fiber is the outside of the tank and submered in LOX so they are always in contact. LOX or O2 gas permeating the CF matrix is also not an issue. LOX turning to SOX which is constrained in the matrix is a big problem.

Interesting idea of adding an impermeable outer layer to prevent LOX infiltration.

 

[jkn]

You lost me. The carbon fiber is the outside of the tank and submered in LOX so they are always in contact. LOX or O2 gas permeating the CF matrix is also not an issue. LOX turning to SOX which is constrained in the matrix is a big problem.

Interesting idea of adding an impermeable outer layer to prevent LOX infiltration.

LOX mixed with carbon is certainly a problem. That mixture has been used as an explosive in mines! It is several times more energetic than dynamite.

 

[mongo]

LOX mixed with carbon is certainly a problem. That mixture has been used as an explosive in mines! It is several times more energetic than dynamite.

How about: not a problem in the absence of an ignition source? The environment in the tank is less conducive to ignition than when Oxyliquit is used in mines. Also surface area if carbon is less, and should be mostly shielded by the epoxy. The volatility helps explain the Atmos issue.

Very interesting about spilling O2 on a runway.

 

[miimura]

How about an Inconel shell around the COPV to separate the LOX from the COPV? You don't want the LOX to get into the COPV layers, so put a barrier around it. Of course structural support and thermal expansion are obvious issues that need to be overcome.

 

[jkn]

How about: not a problem in the absence of an ignition source? The environment in the tank is less conducive to ignition than when Oxyliquit is used in mines. Also surface area if carbon is less, and should be mostly shielded by the epoxy. The volatility helps explain the Atmos issue.

Very interesting about spilling O2 on a runway.

SpaceX can use carbon fiber in contact with LOX, because there almost never is an ignition source. I think NASA is not happy with 'almost never'. Of course epoxy decreases surface area, reducing explosion power and risk of ignition.

I understood that normally carbon fiber used by SpaceX was solid enough to prevent O2 permeating it. In Amos case there were manufacturing error (not enough epoxy).

 

[mongo]

SpaceX can use carbon fiber in contact with LOX, because there almost never is an ignition source. I think NASA is not happy with 'almost never'. Of course epoxy decreases surface area, reducing explosion power and risk of ignition.

I understood that normally carbon fiber used by SpaceX was solid enough to prevent O2 permeating it. In Amos case there were manufacturing error (not enough epoxy).

Yeah, almost never and fuel tanks have a history of sometimes....

Only thing I've found related to that (manufactuing error) is an unconfirmed Reddit post.

 

[hacer]

Task Order from NASA to SpaceX for an “Inconel tank feasibility study..

Has it been confirmed this is a genuine Task Order from NASA? The idea of substituting inconel for carbon fiber in the largest structures in F9 seems ludicrous. Inconel's density is 8.5 g/cc, Different CF composites have slightly different densities, ranging from 1.4 - 2 g/cc.
So inconel is 4 to 5 times as dense as CF. But wait... has inconel EVER been used to construct a rocket fuel tank?

Given it's physical properties, strength, hardness, etc. could huge sheets of it (which aren't made to my knowledge) be formed into tanks with current means?

IMO, if this order is for real, someone in NASA has lost their mind and no one sane is supervising what they are doing.

I once worked with a huge pressure test chamber used for testing undersea things that was made out of inconel. I assume they used inconel for its corrosion resistance since it held saltwater and for its low thermal expansion coefficient since it could cycle temperature as well as pressure. The thing was massive, so it means that you can make huge tanks out of inconel, but this chamber had like 4" thick walls so there is no way you would suffer that kind of weight for a space application. I don't have any idea if you could make a thin-walled tank out of inconel.

 

[Xenoilphobe]

This was posted yesterday on forum.nasaspaceflight.com by user @gongora, claimed to be a (see below) Task Order from NASA to SpaceX for an “Inconel tank feasibility study...regarding full transition to Inconel tanks for crewed vehicles”. If you don’t know what Inconel is, see Inconel - Wikipedia .

My interpretation of this NASA directive is that NASA does not believe that carbon fiber tanks are sufficiently reliable for vehicles that transport humans. Recall that the AMOS-6 mission failed when the F9 exploded on the pad during fueling prior to a planned static fire because one of the second stage COPVs (carbon-fiber overwrapped pressure vessel) that hold helium failed (details at Amos-6 - Wikipedia ).

I hope I am interpreting this wrong and this does not mean what I think it means. If SpaceX has to redesign the F9 to use only Iconel tanks for NASA crewed missions (taking astronauts to the ISS) that will take years.

I am waiting for industry experts on sites like Spaceflight Now – The leading source for online space news to weigh in on this news so I can better understand it.

———————————————————————-

• 80KSC018F0039
  Effective Date 12/15/2017, Completion Date 04/16/2018 $10,134,469.00
  
  Performance of this Task Order is in accordance with the terms&conditions of the base contract NNK14MA74C. The purpose of the Commercial Crew Program (CCP) is to facilitate the development of a U.S. commercial crew space transportation capability with the goal of achieving safe, reliable and cost effective access to and from low Earth orbit (LEO) including the International Space Station.
  
  In accordance with the Commercial Crew Transportation Capability (CCtCap) contract NNK14MA74C, the Contractor shall complete the design, development, test, evaluation, and certification of an integrated CTS capable of transporting NASA crew to and from the ISS, in accordance with the design reference missions and the certification standards and requirements specified in this contract.
  
  In accordance with Attachment J-03, Contract Performance Work Statement (PWS), the task ordering procedures and other terms and conditions in the contract, the Contractor shall perform special studies, test and analyses, as initiated by written direction from the Contracting Officer. IDIQ tasks may include performing technical, cost, schedule and risk assessments for potential new or changes to existing requirements, as identified by the Government, for their impact on the Contractor's design, schedule and cost/price as it relates to CCtCap or life cycle activities; performing additional analyses, modeling, and/or tests of hardware or software to provide further confidence and understanding of robustness of design and advance planning, feasibility or trade studies for development or certification activities.
  
  In accordance with this task order statement of work, the Contractor shall perform an Inconel tank feasibility study and submit a cost proposal to implement follow-on Inconel development and initial cost information regarding full transition to Inconel tanks for crewed vehicles. The feasibility report includes manufacturing R&D activities performed, results; and detailed information regarding the Spin-forming Process.
  
  The task order also includes Solid Oxygen (SOx) test stand development and build; ground fluid system and supporting infrastructure development in order to collect information regarding the pressurized tanks used in the CTS.

Cool, same stuff used in submachine gun suppressors (the baffles), the high heat and the rapid cycling wears out pretty much everything else.

 

[mongo]

I once worked with a huge pressure test chamber used for testing undersea things that was made out of inconel. I assume they used inconel for its corrosion resistance since it held saltwater and for its low thermal expansion coefficient since it could cycle temperature as well as pressure. The thing was massive, so it means that you can make huge tanks out of inconel, but this chamber had like 4" thick walls so there is no way you would suffer that kind of weight for a space application. I don't have any idea if you could make a thin-walled tank out of inconel.

Well, you could make a thin tank, but not for SpaceX's needs. Pressure is >5,500 psi (marine depth of 12,000 ft).

Other factoids:
Safety report that likely led to this order
The Shuttle used Titanium over wraped with Kevlar
Deepest point in ocean is slightly over 36k
Inconel is great for combustion heat exchangers

 

[RCOST]

You can definitely make a thin Inconel tank for that type of service and pressure. The Navy MK15 Rebreather used Inconel spheres for a long time since it wasn't magnetic. Not sure how big the tanks are there though. Biomarine MK15

 

[Cosmacelf]

Regardless, the request to investigate Inconel didn’t come out of nowhere. Considering that NASA used a different construction for the space shuttle, presumably the thought to investigate Inconel came from SpaceX. Ie. NASA said they wanted something more reliable, so SpaceX said they would investigate Inconel for $10M.