Starship On-orbit refueling - Options and Discussion

[Twark_Main]

What cryocooler model are you seeing where the second-to-last stage is also capable of reaching cryogenic temperatures?

...

Note that I'm excluding ultra-cryogenic coolers

What do you mean by "cryogenic temperatures"?

LOX temperatures, as opposed to LH2 temperatures.

That's a pretty big range.  At 6bar, boiling is 111K.  At 0.5bar, it's 83K.  You could also wind up with superheated ullage gas from the autogenous system and a tanker, depending on how rendezvous and prox ops are done.  So you may need to cool gas from ~130K all the way down to 83K.  And there are different pressure ranges to accompany that temperature range.

Yup. That's what I (and most other people) mean by "cryogenic temperatures," which was the question. 

Anyway, for these 'normal' cryogens you typically see only two stages, one compressor stage and one cryo (pulse tube or sterling) stage. Shutting off one of the stages in series isn't really a thing.

[StraumliBlight]

TechPort: Alternative Cryocooler Development [Updated Dec 18]

The goal of this activity is to broaden industry base and develop 20K and 90K Cryocooler alternatives - both various cycle and vendor alternatives - that can be infused into Moon2Mars campaign. The activity will develop technology alternatives to existing Reverse Turbo-Brayton cycle 20K & 90K cryocooler systems, assess alternate concepts / supplier for components, and provide investment to continue the development of 90K and 20K cryocooler systems to a flight ready status of TRL 6.

In-house Government design of Cryocooler system concepts capable of:
 • 15-25 Watts Lift at 20K temperature
 • 30-150 Watts Lift at 90K temperature
 • Operation within in-space environments

Cryocooler system demonstration to TRL-6 through conducting ground tests in thermal-vacuum and vibration at representative flight system environments

[DanClemmensen]

TechPort: Alternative Cryocooler Development [Updated Dec 18]

The goal of this activity is to broaden industry base and develop 20K and 90K Cryocooler alternatives - both various cycle and vendor alternatives - that can be infused into Moon2Mars campaign. The activity will develop technology alternatives to existing Reverse Turbo-Brayton cycle 20K & 90K cryocooler systems, assess alternate concepts / supplier for components, and provide investment to continue the development of 90K and 20K cryocooler systems to a flight ready status of TRL 6.

In-house Government design of Cryocooler system concepts capable of:
 • 15-25 Watts Lift at 20K temperature
 • 30-150 Watts Lift at 90K temperature
 • Operation within in-space environments

Cryocooler system demonstration to TRL-6 through conducting ground tests in thermal-vacuum and vibration at representative flight system environments

I'm in favor of NASA funding and/or conducting leading-edge engineering research, but cryocoolers seem to be be something that private industry would develop anyway without direct NASA funding. How are these decisions made?

[Twark_Main]

TechPort: Alternative Cryocooler Development [Updated Dec 18]

The goal of this activity is to broaden industry base and develop 20K and 90K Cryocooler alternatives - both various cycle and vendor alternatives - that can be infused into Moon2Mars campaign. The activity will develop technology alternatives to existing Reverse Turbo-Brayton cycle 20K & 90K cryocooler systems, assess alternate concepts / supplier for components, and provide investment to continue the development of 90K and 20K cryocooler systems to a flight ready status of TRL 6.

In-house Government design of Cryocooler system concepts capable of:
 • 15-25 Watts Lift at 20K temperature
 • 30-150 Watts Lift at 90K temperature
 • Operation within in-space environments

Cryocooler system demonstration to TRL-6 through conducting ground tests in thermal-vacuum and vibration at representative flight system environments

I'm in favor of NASA funding and/or conducting leading-edge engineering research, but cryocoolers seem to be be something that private industry would develop anyway without direct NASA funding. How are these decisions made?

"TRL-6" and "tests in thermal-vacuum and vibration at representative flight system environments" aren't something private industry would develop anyway.

This is just (as you'd hope, for efficiency) NASA doing the minimum R&D work necessary to adapt the latest in commercial technology.

[mikelepage]

To refresh my memory of the thread, I went to print view and did a search on "androgynous", which I wouldn't necessarily recommend if only because a lot of us still get squeamish around using the appropriate sexual metaphors inherent to this thread (Musk included). The distinction between androgynous (one pipe/connector for each of methane/oxygen, through which prop can go both ways) and hemaphroditic connectors (having separate male and female connectors on both ships) is a pretty useful one imo. Specifically, if people could stop saying androgynous when you mean hemaphroditic, that would increase clarity.

Also, at some point it will probably be useful to dock two starships together in a "69" position - for example if we need a cargo starship to install/service anything at the aft end of the other starship, or a crew starship needs to do in-space inspection of the raptors. It's useful nomenclature because everyone instantly knows exactly what I mean. Might I suggest we get our snort-laughs out of the way now? 

In any case, I was trying to recall whether we reached any consensus about whether we thought the 4-points-of-contact shown in the attached video (credit: SpaceX website) contained any kind of plumbing for prop transfer? And I see we have two camps for and against.

For a while I have been thinking that the 4 probe-drogue setup is purely a mechanical linkage such that the two ships' QD interfaces can be brought together for prop transfer, but in looking at this screen capture of what's on the SpaceX website currently, it's evident that there are two components to each of the 4 points. I could easily believe that the bulky longer one with the probe is there to handle the physical loads, and - once the ships are firmly linked - the narrow one adjacent in each set can extend for prop transfer.

[CMac]

So standard orientation is missionary?

[Twark_Main]

The distinction between androgynous (one pipe/connector for each of methane/oxygen, through which prop can go both ways) and hemaphroditic connectors (having separate male and female connectors on both ships) is a pretty useful one imo. Specifically, if people could stop saying androgynous when you mean hemaphroditic, that would increase clarity.

Ironically, those definitions are pretty unclear. 

It's possible to have all three of "one pipe and connector each for methane and oxygen, and "prop can go both ways," and "have separate male and female connectors on both ships." For example it can have a male connector for LOX and a female connector for CH4 (and vice versa on the depot). Is that androgynous or hermaphroditic or both or neither?

There's nothing I can find in those definitions to help us decide, so I expect something is missing (or else the two aren't mutually exclusive, which probably isn't what you meant).

Also, at some point it will probably be useful to dock two starships together in a "69" position - for example if we need a cargo starship to install/service anything at the aft end of the other starship, or a crew starship needs to do in-space inspection of the raptors.

Inspections would probably be done with small N2 drones.

In-space assembly and service will require a lot more infrastructure (handholds everywhere, grapple fixtures on everything, Canadarm-like manipulator, etc). This is more "space station" instead of "two cars in the middle of nowhere."

It's like if your mechanic drove a special car that transformed into a lift right at the scene of the accident, instead of just owning a shop. 

Notably, SpaceX seems to do all their assembly on the ground. I can't see any reason that would be so important (or so unavoidable) that they'd be motivated to spend a lot more money by changing that.


I think for the time being, 69 position will be left to kids smashing together their Starship toys. Maybe there is a real reason IRL, but I just can't see it, personally...

[InterestedEngineer]

In mammals, there's only one type of fluid being transferred, so I think that analogy has some severe limits.

Now a binary reproductive fluid would make an interesting sci-fi story, but that's way off topic...

[Twark_Main]

Now I know why they call it "the gripping hand."     ( ͡° ͜ʖ ͡°)


Seriously though, I think the, uh, specifics of biology aren't actually followed here. For example we don't actually follow the rule that the fluid can only ever flow from the male side of the connector to the female side. That would be kind of weird to enforce such a rule, honestly.

For me, an "androgynous" connector is where the exact same connector is used on both sides of the connection. A "hermaphroditic" connector has distinct male and female connectors, but they're arranged so that male and female connectors are in the proper place when the interface plate is mated.

Note that an interface plate can simultaneously use both androgynous and hermaphroditic connectors. If you want a self-mating interface plate, you arrange the androgynous connectors along the mirror line, and you arrange the hermaphroditic male/female connectors in matched pairs opposite each-other across the mirror line.

[DanClemmensen]

Now I know why they call it "the gripping hand."     ( ͡° ͜ʖ ͡°)


Seriously though, I think the, uh, specifics of biology aren't actually followed here. For example we don't actually follow the rule that the fluid can only ever flow from the male side of the connector to the female side. That would be kind of weird to enforce such a rule, honestly.

For me, an "androgynous" connector is where the exact same connector is used on both sides of the connection. A "hermaphroditic" connector has distinct male and female connectors, but they're arranged so that male and female connectors are in the proper place when the interface plate is mated.

Note that an interface plate can simultaneously employ both androgynous and hermaphroditic connectors. If you want to design a self-mating interface plate, you would arrange the androgynous connectors along the mirror line, and you'd arrange the hermaphroditic male/female connectors in matched pairs opposite each-other across the mirror line.

In the IDSS example, IDSS is declared to be "androgynous". That defines the system as a whole. The individual sub-elements are not separately androgynous. Instead, they are paired.
    https://commons.wikimedia.org/wiki/File:IDSS_rev_d.png
I think the terminology is getting in the way of actual understanding of the interface system as a whole.

[Twark_Main]

Precisely. The connectors and the interface plate are separate things. You can have an androgynous interface plate with hermaphroditic connectors, or a hermaphroditic interface plate with androgynous connectors. Or the interface plate can be neither hermaphroditic nor androgynous, even if it contains hermaphroditic or androgynous connectors or both.

How very clear!   

edit: This is different from self-mating. The Dragon docking port was (until recently) "androgynous" but not "self-mating."

edit2: This is also different from active vs passive role. The reason the Dragon docking port wasn't self-mating is (partly) because it didn't have the hardware to perform the passive docking role.

[OTV Booster]

Precisely. The connectors and the interface plate are separate things. You can have an androgynous interface plate with hermaphroditic connectors, or a hermaphroditic interface plate with androgynous connectors. Or the interface plate can be neither hermaphroditic nor androgynous, even if it contains hermaphroditic or androgynous connectors or both.

How very clear!   

You might add in that they're mating back to back. Not sure where that leaves us.

[DanClemmensen]

Precisely. The connectors and the interface plate are separate things. You can have an androgynous interface plate with hermaphroditic connectors, or a hermaphroditic interface plate with androgynous connectors. Or the interface plate can be neither hermaphroditic nor androgynous, even if it contains hermaphroditic or androgynous connectors or both.

How very clear!   

edit: This is different from self-mating. The Dragon docking port was (until recently) "androgynous" but not "self-mating."

edit2: This is also different from active vs passive role. The reason the Dragon docking port wasn't self-mating is (partly) because it didn't have the hardware to perform the passive docking role.

There is a deeper problem with Dragon-to-Dragon mating: the opened nosecone is on the axis of androgyny and extends past the plane of the port. This means the two nosecones will bang into each other. It's conceptually easy to add the passive hardware to the active IDSS. It's not clear how to move the nosecones.

[InterestedEngineer]

Now I know why they call it "the gripping hand."     ( ͡° ͜ʖ ͡°)


Seriously though, I think the, uh, specifics of biology aren't actually followed here. For example we don't actually follow the rule that the fluid can only ever flow from the male side of the connector to the female side. That would be kind of weird to enforce such a rule, honestly.

It's not weird at all if there's a lip formed when one connector slides over another.  Fluid flow in on direction is un-impeded, the other has to cross a lip and go into a narrower pipe, which can cause issues such as inreased friction, turbulence, etc.

Now many connections in piping are flush-fit so it wouldn't be relevant, but it's not always true.

I don't know how this kind of coupling works in rockets

[Twark_Main]

I always assumed that if they needed to do an emergency D2 docking in space, they would just use the contingency nose cone jettison pyrotechnics.

How do we know they have contingency nose cone jettison pyrotechnics? Well, the button that says "Jettison Nose Cone" under "Pyros" is probably a clue...   

[Paul451]

The distinction between androgynous (one pipe/connector for each of methane/oxygen, through which prop can go both ways) and hemaphroditic connectors (having separate male and female connectors on both ships) is a pretty useful one imo. Specifically, if people could stop saying androgynous when you mean hemaphroditic, that would increase clarity.

It's possible to have all three of "one pipe and connector each for methane and oxygen, and "prop can go both ways," and "have separate male and female connectors on both ships." For example it can have a male connector for LOX and a female connector for CH4 (and vice versa on the depot). Is that androgynous or hermaphroditic or both or neither?

Neither, it's single gendered for each prop. Hence it can only connect to the opposite gendered ship/GSE, but cannot connect to another similar ship.

Mike's discussion of gender/non-gender applies to each fluid and gas connection separately. But the reasoning then applies to all fluids and gases for each vehicle.

Non-gendered plumbing means two similar/identical plumbed ships can connect to each other.

The two ways of doing that are: a) having two connectors (one of each gender) on each ship (for each fluid/gas), one connector for inflow, one for outflow (for each fluid/gas). Or b) having only one connector for each fluid/gas, which can connect to a copy of itself.

(a) requires twice as many connectors, and associated valves, etc, and requires docking orientations that explicitly reverse the orientation of the connectors, but tends to be easier to engineer and less fail prone. (b) requires more complex internal plumbing to allow completely reversible fluid/gas flow, is thus more complex to engineer, but is easier to orient and has a smaller external footprint.

(Note that a "third option", having an externally mounted adapter on each connector to flip the gender, isn't really a separate option. It requires the internal plumbing of option (b), it just makes the physical connectors easier.)

Mike is calling option (b) "androgynous" and option (a) "hermaphroditic". But IMO, the second term is unnecessary, both are "androgynous" systems, and it's up to the speaker to explain the method; single or paired connectors.

[Twark_Main]

The two ways of doing that are: a) having two connectors (one of each gender) on each ship (for each fluid/gas), one connector for inflow, one for outflow (for each fluid/gas).

Why does it need to be "one for inflow, one for outflow"? Why not just plumb then in parallel?

The nice thing about plumbing them in parallel is that you can split the shutoff valve into two smaller valves. This way if one of the connectors fails to seal you can still proceed with the fuel transfer (just at half the flow rate).

(a) requires... docking orientations that explicitly reverse the orientation of the connectors

This is equally true for both options (a) and (b), really.

(b) requires more complex internal plumbing to allow completely reversible fluid/gas flow, is thus more complex to engineer

The current QD labels them as "LOX Tank Fill/Drain" and "CH4 Tank Fill/Drain," so it's already reversible in the current design.

(Note that a "third option", having an externally mounted adapter on each connector to flip the gender

Ahh yes, the ever-popular Transvestite option.

isn't really a separate option. It requires the internal plumbing of option (b), it just makes the physical connectors easier.)

Ahh, yes, the ever-popular Transvestite option.   

[mikelepage]

For the record, my observation was that in doing a search on "androgynous" throughout this thread, people were using it in at least two different senses. The number of people talking at cross-purposes was particularly high at points where people were referring to QD adapters with both male and female components as "androgynous" where others were thinking "androgynous" meant something as magically simple as it is in KSP. I think using "hemaphroditic" in the first case is clarifying. YMMV.

Linking back to my actual question...

In any case, I was trying to recall whether we reached any consensus about whether we thought the 4-points-of-contact shown in the attached video (credit: SpaceX website) contained any kind of plumbing for prop transfer? And I see we have two camps for and against.

For a while I have been thinking that the 4 probe-drogue setup is purely a mechanical linkage such that the two ships' QD interfaces can be brought together for prop transfer, but in looking at this screen capture of what's on the SpaceX website currently, it's evident that there are two components to each of the 4 points. I could easily believe that the bulky longer one with the probe is there to handle the physical loads, and - once the ships are firmly linked - the narrow one adjacent in each set can extend for prop transfer.

Attaching a shortened version of the video for reference. It would be interesting if anyone had any of the older SpaceX renders to figure out how long the narrow "needle-like" component (present in each of 4 points) has been included in the renders, because when zoomed out, they just look like they could be part of the larger structure.

[eriblo]

[...]

Linking back to my actual question...

In any case, I was trying to recall whether we reached any consensus about whether we thought the 4-points-of-contact shown in the attached video (credit: SpaceX website) contained any kind of plumbing for prop transfer? And I see we have two camps for and against.

For a while I have been thinking that the 4 probe-drogue setup is purely a mechanical linkage such that the two ships' QD interfaces can be brought together for prop transfer, but in looking at this screen capture of what's on the SpaceX website currently, it's evident that there are two components to each of the 4 points. I could easily believe that the bulky longer one with the probe is there to handle the physical loads, and - once the ships are firmly linked - the narrow one adjacent in each set can extend for prop transfer.

Attaching a shortened version of the video for reference. It would be interesting if anyone had any of the older SpaceX renders to figure out how long the narrow "needle-like" component (present in each of 4 points) has been included in the renders, because when zoomed out, they just look like they could be part of the larger structure.

I've just interpreted those as strut/actuators reinforcing/positioning the four connecting struts/probes perpendicular to the main hinge direction. Somewhat similar to the stabilizers on the chopsticks. It makes little sense for any of the four docking points to be involved in propellant transfer as that would be a lot of extra plumbing for no obvious reason.

[mikelepage]

[...]

Linking back to my actual question...

In any case, I was trying to recall whether we reached any consensus about whether we thought the 4-points-of-contact shown in the attached video (credit: SpaceX website) contained any kind of plumbing for prop transfer? And I see we have two camps for and against.

For a while I have been thinking that the 4 probe-drogue setup is purely a mechanical linkage such that the two ships' QD interfaces can be brought together for prop transfer, but in looking at this screen capture of what's on the SpaceX website currently, it's evident that there are two components to each of the 4 points. I could easily believe that the bulky longer one with the probe is there to handle the physical loads, and - once the ships are firmly linked - the narrow one adjacent in each set can extend for prop transfer.

Attaching a shortened version of the video for reference. It would be interesting if anyone had any of the older SpaceX renders to figure out how long the narrow "needle-like" component (present in each of 4 points) has been included in the renders, because when zoomed out, they just look like they could be part of the larger structure.

I've just interpreted those as strut/actuators reinforcing/positioning the four connecting struts/probes perpendicular to the main hinge direction. Somewhat similar to the stabilizers on the chopsticks. It makes little sense for any of the four docking points to be involved in propellant transfer as that would be a lot of extra plumbing for no obvious reason.

Reattaching the diagram from Roy_H's post showing separate pipes for equalising fuel and oxidiser ullage gas pressure across HLS and depot ships. Not sure if this type of setup is known or just speculated, but there have been other, similar diagrams elsewhere upthread. Seems to me that having those links closer to the forward part of the ships - through the 4 points - could actually minimise total plumbing pipe length, and keep the QD for launch site refuelling.