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

[mongo]

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

Cool link!
Steel scuba tanks of 0.234 inch thickness have been tested to 5,000 psi, burst above 8k. Guess it depends what one means by thin. Basically, the COPVs combined need to hold the entire tank volume at 2 ? PSI. So they could trade tank volume for pressure if need be, with subsequent loss of LOX capacity.

Do thermal cycles cause work hardening?

 

[jbcarioca]

I'm involved in a construction project that required ultra high strength bolts for a marine enviornment and the engineers eventually settled on Inconel as the fabrication material. They are custom manufactured parts, but Inconel was very difficult to source since Tesla is buying so much of the supply for vehicle manufacturing. Evidently Inconel is used in some of the high voltage systems in a Tesla.

Inconel is used in the high temperature fuses on current S and X batteries, I do not know whether 3 batteries do or not. Originally Inconel fuses were developed as part of a longevity extension study, according to Elon, who said that when the P85D Ludicrous upgrade was announced. At that time Inconel was used in the fuse because it allowed for much more precise temperature control than prior fuses, thus allowing higher discharge rates. Subsequently the same fuses were used for all S and X batteries.

I probably could look all this up again. I remember it clearly because it made me decide to buy the upgrade even though I probably would very rarely ever use the extra acceleration. I don’t since I’m mostly in “Chill’ mode.

 

[Grendal]

As I mentioned in my much earlier post, it really depends on what NASA chooses to focus on for safety. The reality is that supercooling may increase the possibility of an incident, however, SpaceX likely has a much safer and much better system for an abort should an incident happen. That system improves the chance of protecting astronauts in a catastrophic event. So what do you choose to focus on?

 

[Bobfitz1]

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.

There seems to be confusion about what using inconel would actually mean. I thought the idea was to replace both aluminum inner tank and the CF outerwrap which serves to greatly increase the strength (therefore how much pressure) of the aluminum tank.

But inconel is much stronger than aluminum, so the CF would be eliminated as would risk of LOX or even SOX being ignited.

It's not clear how thick the inconel tank would need to be to handle the necessary pressure. There are quite a few COPVs distributed through the LOX volume. Does anyone know how small or large they range? How much heavier the inconel would be compared to the
aluminum + CF depends on what thickness is required. It may not be as large a weight increase as people are assuming. Block 5 improvements might render that scale of weight increase not significant as to performance specs, including return for landing.

 

[jbcarioca]

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.

I think you’re correct. SpaceX has several,proprietary Inconel alloys now and has also developed the alloy used in Tesla battery high temperature fuses. One very probable possibility is that Space X thinks they can make a small quantity of Inconel provide the protection that has previously required large quantities.

That is no great insight on my part. Smaller and smaller quantities of heavier materials are constantly being developed as nanotechnologies advance very rapidly. Why would that not be an active consideration for BFR and, later, SMS.

This looks to be a very cheap research project that potentially will allow safer, lighter, fuel storage. Why not? That sounds smart to me. If it works gloriously it might even be retrofitted to Falcon Heavy and F9.

 

[Bobfitz1]

As I mentioned in my much earlier post, it really depends on what NASA chooses to focus on for safety. The reality is that supercooling may increase the possibility of an incident, however, SpaceX likely has a much safer and much better system for an abort should an incident happen. That system improves the chance of protecting astronauts in a catastrophic event. So what do you choose to focus on?

Great point. Watching video of the Dragon abort test two or three years ago makes me believe it could save a crew in almost any in flight RUD scenario. NASA should take that into account when evaluating risks of a booster failure.

 

[mongo]

Inconel is used in the high temperature fuses on current S and X batteries, I do not know whether 3 batteries do or not. Originally Inconel fuses were developed as part of a longevity extension study, according to Elon, who said that when the P85D Ludicrous upgrade was announced. At that time Inconel was used in the fuse because it allowed for much more precise temperature control than prior fuses, thus allowing higher discharge rates. Subsequently the same fuses were used for all S and X batteries.

I probably could look all this up again. I remember it clearly because it made me decide to buy the upgrade even though I probably would very rarely ever use the extra acceleration. I don’t since I’m mostly in “Chill’ mode.

Tesla switched the contactor to Inconel. The fuse changed from a standard thermal type to an active pyro version powered by its own battery. That allowed them to dial up the inverter/motor current since the fuse was so stable vs a standard one which had a trip point that varied based on manufacturing, temperature, and self heating load profile. The thermal fuse was also a hot spot and source of loss at higher currents. So the fuse rating was less than the system could handle, but the new fuse could pass 1,500 but blow instantly at say 1,600 (some level the DUs would never pull normally)

The contactor material change was needed due to the amount of heat generated at the contacts by the now ~1,500 amp draw.