Starship On-orbit refueling - Options and Discussion

[Narnianknight]

I have seen a theory of allowing it to be androgynous by making the ship plumbing capable of switching the main fill lines between CH₄ and LOX. The unsymmetrical parts would only be used ground-side. I don't know whether it's a reasonable theory or not.

[Narnianknight]

The photos show a two-ring segment.  Maybe it's a truncated forward barrel, and the regular QD is still present in the tail skirt assembly?  But if that's true, what's this going to connect to?  And why aren't they trying to make the QD do double duty for both GSE and refueling?  Is every client Starship going to have to have two QDs?

They can't do a docking QD in the forward, because they would need to put a LOX transfer tube through the methane tank and do the settling burn in the opposite direction. Also, the forward barrel is inside the methane tank (where the stringers are not that dense), and if you meant above the forward dome, they wouldn't waste mass with two rings between the forward dome and the nose cone.

[ShadowAndFlame]

I have seen a theory of allowing it to be androgynous by making the ship plumbing capable of switching the main fill lines between CH₄ and LOX. The unsymmetrical parts would only be used ground-side. I don't know whether it's a reasonable theory or not.

How hazardous is residual LOX in the LNG tank and vice versa? Are there "LEL" and "UEL" explosion limits for cryogenics?

[Narnianknight]

I have seen a theory of allowing it to be androgynous by making the ship plumbing capable of switching the main fill lines between CH₄ and LOX. The unsymmetrical parts would only be used ground-side. I don't know whether it's a reasonable theory or not.

How hazardous is residual LOX in the LNG tank and vice versa? Are there "LEL" and "UEL" explosion limits for cryogenics?

I assume such a scheme would use redundant seals and CO₂/nitrogen/helium (not sure which) purges for the relevant plumbing between launch and docking to eliminate that concern.

[TheRadicalModerate]

I have seen a theory of allowing it to be androgynous by making the ship plumbing capable of switching the main fill lines between CH₄ and LOX. The unsymmetrical parts would only be used ground-side. I don't know whether it's a reasonable theory or not.

How hazardous is residual LOX in the LNG tank and vice versa? Are there "LEL" and "UEL" explosion limits for cryogenics?

Having the two lines interchangeable sounded terrifying to me, but it's likely that everything downstream of the necessary valves would be exposed to vacuum, which will dry them thoroughly.  And only the depot would need to be able to do the switcheroo.  Then the better question is whether you can engineer a set of fail-safe valving that makes leaks very, very unlikely.

The photos show a two-ring segment.  Maybe it's a truncated forward barrel, and the regular QD is still present in the tail skirt assembly?  But if that's true, what's this going to connect to?  And why aren't they trying to make the QD do double duty for both GSE and refueling?  Is every client Starship going to have to have two QDs?

They can't do a docking QD in the forward, because they would need to put a LOX transfer tube through the methane tank and do the settling burn in the opposite direction. Also, the forward barrel is inside the methane tank (where the stringers are not that dense), and if you meant above the forward dome, they wouldn't waste mass with two rings between the forward dome and the nose cone.

I was just trying to make sense of where a two-ring segment might go.  If you pushed the forward and common domes forward to make a higher-capacity depot, two segments to get you over the forward dome is about right.

But I agree that forward-placed refueling QDs are pretty much a terrible idea.  The interchangeable fill and pressurant lines make a certain amount of sense, and the two-ring segment could just be for proving out the concept.  It was going to scrap, after all.

[Narnianknight]

I have seen a theory of allowing it to be androgynous by making the ship plumbing capable of switching the main fill lines between CH₄ and LOX. The unsymmetrical parts would only be used ground-side. I don't know whether it's a reasonable theory or not.

How hazardous is residual LOX in the LNG tank and vice versa? Are there "LEL" and "UEL" explosion limits for cryogenics?

Having the two lines interchangeable sounded terrifying to me, but it's likely that everything downstream of the necessary valves would be exposed to vacuum, which will dry them thoroughly.  And only the depot would need to be able to do the switcheroo.  Then the better question is whether you can engineer a set of fail-safe valving that makes leaks very, very unlikely.

I still prefer the ground-side gender bender serving depot launches for a number of reasons, but I can't come up with anything rendering the switcheroo impossible. Perhaps we'll see more hardware soon to give us more ideas.

[InterestedEngineer]

Electro Luminescent cooling.

They continue to push LH2 or bust in the article, but they mention LOX, which means it'd work or LCH4 as well

https://www.nasa.gov/directorates/stmd/niac/niac-studies/mars-roundtrip-success-enabled-by-integrated-cooling-through-inductively-coupled-led-emission-mars-icicle/

[catdlr]

Prop transfer.

https://twitter.com/NASASpaceflight/status/1928195079748943979

[TheRadicalModerate]

A couple of screenshots from the preso attached below.  Three things:

1) Still looks like the docking / berthing / stabilization mechanism is the four struts, slotted into four receptacles.  Compare that to the shots narianknight posted here, here, and here, which I presume are an early attempt at implementing the receptacles.

2) In the first screenshot below, it looks kinda like the two Ships (both depot and target) are vertically aligned.

3) In the second screenshot, it looks like they're significantly offset from one another.  This could be a perspective problem, or it could be evidence that the depot's presumably male QD is separate from the female QD used with the GSE.  It also could be an indicator that the depot is longer than the target, but then you'd expect the rear flaps to be more-or-less aligned.

[Oersted]

Don't over-interpret your second screenie. As far as I remember it, the clip didn't show the two ships attached to each other at that stage. Also, the graphics artist had to show that there were two ships. Can't do that if they're perfectly superposed.

The first screenie, with the four attachment points, is much more informative. 

[catdlr]

A couple of screenshots from the preso attached below.  Three things:

1) Still looks like the docking / berthing / stabilization mechanism is the four struts, slotted into four receptacles.  Compare that to the shots narianknight posted here, here, and here, which I presume are an early attempt at implementing the receptacles.

Four attachment points are provided, with the forward two serving for alignment. The lower two, located near the aft section on both sides of the SGD, as shown in the pictures that you linked, will house the fuel transfer lines.

[Twark_Main]

Don't over-interpret your second screenie. As far as I remember it, the clip didn't show the two ships attached to each other at that stage. Also, the graphics artist had to show that there were two ships. Can't do that if they're perfectly superposed.

They're docked at that point.  The CGI artist just located the "camera" so the ships are being viewed at an angle.

You can tell it's viewed at an angle by comparing the Y distance (in pixels) between the tip of the nose and the fins.  The fins should be latched in the same position (fully down) because at this stage in proximity operations you want as much clearance as you can get (confirmed in the first screenshot). But in the closer ship the fins and nose are noticeably "squashed together" vertically.  This is because the fins are no longer located on the vehicle centerline.

[OTV Booster]

A couple of screenshots from the preso attached below.  Three things:

1) Still looks like the docking / berthing / stabilization mechanism is the four struts, slotted into four receptacles.  Compare that to the shots narianknight posted here, here, and here, which I presume are an early attempt at implementing the receptacles.

Four attachment points are provided, with the forward two serving for alignment. The lower two, located near the aft section on both sides of the SGD, as shown in the pictures that you linked, will house the fuel transfer lines.

Do we know the aft struts will house transfer lines or is that conjecture?


Edit to add: Hadn't seen Elon's update when this was posted. This is the plan du jour.