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

[ecarfan]

Ars technica article Elon Musk’s recent all-hands meeting at SpaceX was full of interesting news

The next Starship test flight will also try to reignite the spacecraft's Raptor engines in space for the first time..."Flight 3, we want to get to orbit and we want to do an in-space engine burn from the header tank and prove that we can reliably de-orbit," Musk said. "We want to do a Tipping Point header-to-main propellant transfer. This is important for the NASA Artemis program. And we also want to demonstrate the payload door for the ... Pez dispenser for delivering the Starlinks."

What does he mean by “Tipping Point”?

 

[Electroman]

In that ‘full of interesting news “ nothing about causes for booster RUD ?

 

[spacerfc]

What does he mean by “Tipping Point”?

SpaceX’s Starship wins $53M from NASA for full-scale orbital refueling test

SpaceX’s Starship program has won $53 million from NASA to perform a full-scale test of orbital propellant transfer, taking the company and space agency’s relationship on the crucial technology to the next level.

NASA revealed the results of its fifth round of “Tipping Point” solicitations on October 14th, announcing awards of more than $370 million total to 14 separate companies. This year’s investments focused on three main categories: “cryogenic fluid management, lunar surface [operations], and closed-loop [i.e. autonomous] descent and landing capability demonstrations.”

 

[ecarfan]

In that ‘full of interesting news “ nothing about causes for booster RUD ?

In the article I linked to it says:

Musk didn't discuss what happened with the Super Heavy booster on the November flight,

 

[ecarfan]

SpaceX’s Starship wins $53M from NASA for full-scale orbital refueling test: NASA revealed the results of its fifth round of “Tipping Point” solicitations on October 14th, announcing awards of more than $370 million total to 14 separate companies

Thanks, I thought it was some sort of engineering term that I was not familiar with!

 

[JB47394]

Here's the description of the 2020 Tipping Point award that SpaceX was selected for:

• SpaceX of Hawthorne, California, $53.2 million

Large-scale flight demonstration to transfer 10 metric tons of cryogenic propellant, specifically liquid oxygen, between tanks on a Starship vehicle. SpaceX will collaborate with Glenn and Marshall.​

So all NASA wants to see is some LOX being moved between tanks. I'm assuming that SpaceX will pressurize the header tanks, perform the deorbit burn and, while the header tanks are still pressurized, crack a valve to let the pressure push the propellant from the downcomer into the main tank. I'm not sure why NASA would award money for that given that they're after the transfer of propellant between vehicles. All they seem to be getting is someone blowing down a straw with soda in it.

If true, it also makes a landing burn impossible. That's consistent with the flight profile, and I wonder if they're sacrificing the landing burn attempt so they can get the $53 million.

Based on data I ran across on the web from 2020, the oxygen header tank holds 21 tons, and the downcomer holds another 3 tons. So they can use 14 tons of LOX for the deorbit burn, then drain the header tank into the main tank. I wonder how they substantiate their claim of performing the transfer.

 

[mongo]

So they can use 14 tons of LOX for the deorbit burn, then drain the header tank into the main tank

They are doing an engine test, not a full deorbit burn.

So all NASA wants to see is some LOX being moved between tanks. I'm assuming that SpaceX will pressurize the header tanks, perform the deorbit burn and, while the header tanks are still pressurized, crack a valve to let the pressure push the propellant from the downcomer into the main tank. I'm not sure why NASA would award money for that given that they're after the transfer of propellant between vehicles. All they seem to be getting is someone blowing down a straw with soda in it.

Your plan lacks a method to settle the propellant and keep the tank pressurized.
Ship to ship is 'just' tanks with disconnects...

 

[JB47394]

Your plan lacks a method to settle the propellant and keep the tank pressurized.

When will the header tanks need settling? They're full at the start, and they're settled throughout the demo burn. Then the only force acting on the ship would be a very light deceleration from the atmosphere. I don't see a problem with voids forming.

As for pressurization, whatever means they use to pressurize them for engine start would be used for the LOX transfer. If it's autogenous, then they can fire up the demo burn, settle the main tanks, resume firing on the main tanks while dumping the header LOX into the main tank. Regardless, I can't imagine a scenario where this sort of LOX movement has much to do with propellant transfer between vehicles. Then again, I may misunderstand the purpose of the exercise. Perhaps pushing 10 tons of LOX through a pipe is interesting on its own merits.

Ship to ship is 'just' tanks with disconnects...

How would you go about ensuring that contents of one tank empties into the other?

 

[ecarfan]

I'm not sure why NASA would award money for that given that they're after the transfer of propellant between vehicles. All they seem to be getting is someone blowing down a straw with soda in it.

I had the same thought. It seems like the cost to SpaceX to perform that prop transfer test is basically zero.

If true, it also makes a landing burn impossible. That's consistent with the flight profile, and I wonder if they're sacrificing the landing burn attempt so they can get the $53 million.

Easy money. And we get to see a hell of a splash! But SpaceX can still attempt the bellyflop maneuver and get very useful data.

 

[ecarfan]

How would you go about ensuring that contents of one tank empties into the other?

Ever since SpaceX apparently abandoned the plan to dock a ship to a tanker tail-to-tail and went to a side-to-side configuration I have been wondering how they are going to push the propellants from the tanker to the ship. Will the tanker have electric pumps? Where will they be located? I have questions…

 

[mongo]

When will the header tanks need settling? They're full at the start, and they're settled throughout the demo burn. Then the only force acting on the ship would be a very light deceleration from the atmosphere. I don't see a problem with voids forming.

They need settling the entire time transfer is occurring.

As for pressurization, whatever means they use to pressurize them for engine start would be used for the LOX transfer. If it's autogenous, then they can fire up the demo burn, settle the main tanks, resume firing on the main tanks while dumping the header LOX into the main tank. Regardless, I can't imagine a scenario where this sort of LOX movement has much to do with propellant transfer between vehicles. Then again, I may misunderstand the purpose of the exercise. Perhaps pushing 10 tons of LOX through a pipe is interesting on its own merits.

It sounds like you are assuming transfer during an engine burn? My understanding is they are testing with engines off. Fluid transfer under a higher constant acceleration is a solved problem.

How would you go about ensuring that contents of one tank empties into the other?

My comment was in reference to

I'm not sure why NASA would award money for that given that they're after the transfer of propellant between vehicles. All they seem to be getting is someone blowing down a straw with soda in it.

Ship #1 tank to ship #2 tank is a variation of ship #1 tank to to ship #1 tank with different positions.

 

[JB47394]

They need settling the entire time transfer is occurring.

Let me ask this another way. Why is the LOX not settled? What is going to unsettle it?

It sounds like you are assuming transfer during an engine burn?

I'm assuming transfer while whatever provides pressurization to the header tank is operating. If they use compressed gas, then they can go at any time. If they rely on autogenous pressurization, then it would be while an engine is running.

My understanding is they are testing with engines off. Fluid transfer under a higher constant acceleration is a solved problem.

Which suggests that they have a means of pressurizing the header tanks without the engines running.

All of this is an aside to my point that this "propellant transfer" appears to be them blowing soda through a straw. At least, that's all my simple mind sees.

Ship #1 tank to ship #2 tank is a variation of ship #1 tank to to ship #1 tank with different positions.

Only if they use the same basic technique. What technique would scale from header tank on the same ship to main tanks on separate ships? In thinking about this some more, two occur to me.

1. They could blow a lot of gas into the source tank while keeping the target tank at a lower pressure. That would produce a flow of gas and liquid to the target tank, with bernoulli grabbing the blobs of liquid in the source tank and moving them to the connection point. The challenge there is keeping the two tanks at a pressure gradient, though simply pumping available gas in the target tank to the source tank should work. For a while, anyway. This could be simulated in IFT-3, though I wouldn't expect much blobbing in the confines of the small header tank.

2. They could seat the propellants in the tanks by slowly spinning the ships and then using pumps to perform a pretty standard transfer, though at lower "gravity". The challenge there is spinning roughly 1300 tons of ship. I don't know how fast they'd have to spin, and I don't know if there are any complications from two connected ships which would be of very dissimilar masses at certain times. The math is fine, but I don't know how it works out in practice (I'm thinking of odd stuff like the Dzhanibekov effect). This could be simulated by spinning Starship 26 and using a pump somewhere in the downcomer to transfer LOX to the main tank. The fact that the header tank is on the center line and the downcomer follows the skin of the ship would make that possible.

Approach 2 seems the far simpler to execute (and simulate), assuming that two connected ships can spin stably.

So if they're actually pursuing a technique that applies to inter-vehicle transfer, then it makes much more sense. I guess we wait and hope. Hope that they pull it off, and that they say something about what they did.

Edit: They vented LOX once they reached orbit. I wonder if that somehow relates to all this. Heh. Could they vent LOX to lower the main tank pressure, resulting in pulling LOX through the header downcomer? I understand that dumping LOX was needed for reentry, but were they trying to kill two birds with one stone? I'm only half serious, but it's a thought.

For that matter, venting the LOX is somewhat like the first technique that I describe above - using a pressure differential to transfer propellant. Venting to space is a pretty good pressure differential. Again, just a thought.

 

[mongo]

Let me ask this another way. Why is the LOX not settled? What is going to unsettle it?

The universe in general? LOX is going to boil at the edges, react to cohesive forces, and slosh due to any structure movement. Drawing fluid from one section will tend to stress it also.

My guess for real setup:
Orient ships for max heating of tanker
Vent at an angle from the tanker on the mating side (no heat shield) for micro acceleration
Let piping do the work, or boost with solar powered pumps

A bespoke depot that never re-enters offers other benefits.

 

[adiggs]

Maybe this is as simple as the theory of how to do this is straightforward from NASA and SpaceX's point of view, but it hasn't been done at this scale so its time to test (has it been done at any scale?). Space and vacuum not necessarily behaving the same way as the Earth surface and 1g and all, and even behaving in unexpected ways.

Plenty of theories work out on paper, but don't prove out when the experiment is conducted. Doing the transfer within the 1 vehicle sounds like a baby step towards the desired end result - sort of like landing the first Falcon 9s on the water to prove that they really could put stage 1 where they say they could.

 

[JB47394]

(has it been done at any scale?)

The only thing I could find was a 2022 Purdue experiment that flew on a zero g aircraft to understand how cryogenics flow through pipes. They were specifically interested in how the cryogenics went through phase transitions, but they had future propellant transfer systems in mind. Baby steps.

 

[scaesare]

(been following y'alls interesting conversation)

So, naive "I've not yet looked this up myself" kind of question:

While settling & pressurizing liquids in tanks using traditional methods has worked for typical flight regimes thus far, we are entering a new era of things not attempted in 0G. Witness IFT-2's booster RUD, which there's a good chance was due to 0G tanked liquid issues during booster separation/flip...

Now while the booster issue ir probably solvable with separation/flip profile changes. the challenges for transfer are a bit unique...

Finally, the question- While not necessary up to this point, is it possible that some sort of diaphragm or expanding bladder inside the tank to both force the liquid against the end with intakes as well as provide pressure be worth exploring?

It wouldn't seem to take much pressure in 0G... even 1 PSI would push a free-floating liquid... it could even be whatever supplies ullage gas on the other side of the diaphragm or inflating the bladder.

I'm sure there are many issues... especially given the size and temps involved. I can think of several: sealing a diaphragm against the tank walls, how to mount the diaphragm to allow it to slide, bladder expansion at that scale, making any of that work at cryo-temps, etc...

Are these insurmountable you suppose, and if so, are they just too overly complicated?

 

[mongo]

Finally, the question- While not necessary up to this point, is it possible that some sort of diaphragm or expanding bladder inside the tank to both force the liquid against the end with intakes as well as provide pressure be worth exploring?

You still get boiling inside the bladder.
If you had a gas permeable, but not liquid permeable, membrane, that might work.

Also still need ullage gas.
[Edit: was covered in post]

 

[scaesare]

You still get boiling inside the bladder.
If you had a gas permeable, but not liquid permeable, membrane, that might work.

So I was thinking the bladder is expanded from one end with gas, and it pushes against the liquid inside the tanks. A "balloon" if you will...

Also still need ullage gas.

So, I wrote: "it could even be whatever supplies ullage gas on the other side of the diaphragm or inflating the bladder" meaning that I assumed a source of such would still be needed, it could just act against the bladder/diaphragm to provide the pressure to force the liquid... do you see any issues with that?

 

[mongo]

So I was thinking the bladder is expanded from one end with gas, and it pushes against the liquid inside the tanks. A "balloon" if you will...

Right, but the liquid in the ballon is also evaporating and that gas gives the same issue as we had to start. If using this as a way to force the gas/liquid mix out of the tank (versus separation), that works.

So, I wrote: "it could even be whatever supplies ullage gas on the other side of the diaphragm or inflating the bladder" meaning that I assumed a source of such would still be needed, it could just act against the bladder/diaphragm to provide the pressure to force the liquid... do you see any issues with that?

Yeah, my bad. I somehow only quoted part of your post and then went back and added that line. I've since gone back and crossed it out.

 

[scaesare]

Right, but the liquid in the ballon is also evaporating and that gas gives the same issue as we had to start. If using this as a way to force the gas/liquid mix out of the tank (versus separation), that works.


Yeah, my bad. I somehow only quoted part of your post and then went back and added that line. I've since gone back and crossed it out.

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: