SpaceX Starship - IFT-3 - Starbase TX - Pre-Launch Preparations Thread

[JB47394]

I'm probably not describing my thought sufficiently.

He got it:

If using this as a way to force the gas/liquid mix out of the tank (versus separation), that works.

An alternative that we talked about was using a mechanical plunger. There are a zillion permutations of plungers that could be tried.

Googling for "flexible bladder cryogenic" gets a bunch of hits (though they seem to be focused on storing the cryogenics in the bladder). People have been looking at this since the 1960s, with the most recent paper coming out in February 2023.

Random factoid: the surface tension of water is 72 dyne/cm, of liquid oxygen is 13.2 dyne/cm, and of liquid methane is 17 dyne/cm.

 

[mongo]

I'm probably not describing my thought sufficiently.

I'm not thinking any liquid in the ballon. Just gas to expand it inside the tank, from one end. This forced the liquid inside the tank to the other.


Something like this:

View attachment 1009737

Yah, the difference is which is called inside vs outside.

An alternative that we talked about was using a mechanical plunger.

There is at least one pressure fed rocket (saw it on YouTube, maybe Tim Dodd vid?) that does that with non-cyrogenic propellants.

 

[scaesare]

He got it:


An alternative that we talked about was using a mechanical plunger. There are a zillion permutations of plungers that could be tried.

Googling for "flexible bladder cryogenic" gets a bunch of hits (though they seem to be focused on storing the cryogenics in the bladder). People have been looking at this since the 1960s, with the most recent paper coming out in February 2023.

Random factoid: the surface tension of water is 72 dyne/cm, of liquid oxygen is 13.2 dyne/cm, and of liquid methane is 17 dyne/cm.

Cool... reading... thanks!

 

[scaesare]

So, I'll read the paper you referenced @JB47394 , but thoughts on applicability for fuel transfer?

 

[scaesare]

Cool... reading... thanks!

So it looks like this is describing storing the liquid in the bladder, not in the tank outside the blader , as you suggested was the common approach:

• Bladder for fluid containment – the flexible container that holds the fluid inside the tank.

 

[mongo]

So it looks like this is describing storing the liquid in the bladder, not in the tank outside the blader , as you suggested was the common approach:

Yeah, image a ballon deflating via the opening versus inflating a ballon in a cylinder. The former makes it easier to get everything out versus the latter where pockets of fluid could get trapped between the bladder and walls.

 

[JB47394]

So, I'll read the paper you referenced @JB47394 , but thoughts on applicability for fuel transfer?

I wasn't trying to get you to read that paper in particular so much as to draw your attention to the body of existing work. There's a 1968 article titled "Cryogenic Positive Expulsion Bladders", which is exactly what you're talking about. They investigated using Mylar and Kapton as a means of moving liquid hydrogen. They never built an actual bladder, but they tested how the materials functioned in that environment.

I'd suggest googling for "flexible bladder cryogenic" for good hits. If you want to get really specific, then go for "expulsion bladder cryogenic". The latter will even get a 1968 hit titled "Metallic bladders for cryogenic fluid storage and expulsion". 1968 was a good year for this stuff, I guess.

I suspect that there is no material that actually stretches at cryogenic temperatures in the way you'd like to see. I think you're left with a thin, lightweight film that gets wadded up at the top of the tank, then gets filled with gas to expand. Just like a Mylar balloon.

 

[scaesare]

Yeah, image a ballon deflating via the opening versus inflating a ballon in a cylinder. The former makes it easier to get everything out versus the latter where pockets of fluid could get trapped between the bladder and walls.

And would seem much simpler than a diaphragm/plunger, as you'd need no spring/gas pressure mechanism... as the elasticity of the bladder could do it. Although, the tank length and cold temps might make that problematic...

 

[Pricee2]

Maybe cold gas thrusters, similar to those used for steering on the falcon nine, positioned around the perimeter of the engine bay could create enough acceleration to settle the liquids.

 

[scaesare]

Maybe cold gas thrusters, similar to those used for steering on the falcon nine, positioned around the perimeter of the engine bay could create enough acceleration to settle the liquids.

I guess the complexity is trying to do that while the ships are mated for the xfer...

 

[Ben W]

Maybe cold gas thrusters, similar to those used for steering on the falcon nine, positioned around the perimeter of the engine bay could create enough acceleration to settle the liquids.

My expectation is that they could make the two ships slowly spin around each other, and use the small centrifugal force to settle the propellants laterally. This could be done with thrusters, or with flywheels/gyroscopes; unclear if the mass of the required flywheels would outweigh (literally) the mass of the required propellant to spin up/down, but for a depot that needs to spin up/down numerous times, a flywheel probably wins. Quick math: two mated 300T ships, spun laterally around each other at 0.3rpm, would provide ~1e-3 g acceleration at the outer edge (~10m off-axis), more than enough to settle propellant after a minute or two. The propellant transfer could then be done arbitrarily slowly, since continuous thrust during the transfer would be unnecessary. Once the transfer is complete, spin down and undock.

 

[scaesare]

As the mass of ships will be significantly different at the beginning and end of the xfer, and constantly changing during, the center of mass will also be constantly changing. Seems like that would make them spinning around each other "interesting".

 

[JB47394]

Here's a wild and whacky thought. Create a hose on a robot arm that goes around slurping up the blobs of propellant in the tank.

 

[Ben W]

As the mass of ships will be significantly different at the beginning and end of the xfer, and constantly changing during, the center of mass will also be constantly changing. Seems like that would make them spinning around each other "interesting".

At a mutual spin rate of 0.3rpm (about one revolution every three minutes), and transferring the propellant very slowly (say 10kg per second), it should be very manageable. Transferring 100T of propellant at that rate would take about 3 hours, so the change in center of mass would be very gradual. The center of mass will be imbalanced anyway; after several flights you'll have a nearly empty tanker transferring fuel to a nearly full depot. The lateral spin axis is stable (see "Tennis Racket Theorem"), and flywheels could handle fine adjustments, so there shouldn't be any showstoppers with this basic approach.

 

[scaesare]

Here's a wild and whacky thought. Create a hose on a robot arm that goes around slurping up the blobs of propellant in the tank.

"Optimus: Vacuum Cleaner Edition"

 

[Grendal]

 

[ecarfan]

My summary of the info in that video: the FAA confirms that SpaceX has submitted the final mishap report for IFT-2 and a launch license for IFT-3 could come soon. Or not.

 

[JB47394]

My summary of the info in that video: the FAA confirms that SpaceX has submitted the final mishap report for IFT-2 and a launch license for IFT-3 could come soon. Or not.

It seems like they have a boatload of work in progress at the tank farm and launch site. They've cracked open everything over there except maybe the chopsticks. Surely they can't perform anything like a wet dress rehearsal for another month or so.

I'd love to see the list of problems they need to address before getting their license. They've gotta say something about how they're going to avoid blowing up the booster again, right?

 

[ecarfan]

 

[Grendal]