Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 384002 times)

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1220 on: 07/28/2022 08:46 pm »
So would it make the most sense to build a special docking station with something equivalent to two quick disconnect arms? It would sit between two starships, connected to both, and transfer fuel from one to the other exactly as the system does on the ground. Each starship would be responsible for the ullage burn (and keeping it balanced as the center of mass moved during fueling), but the pumps would be in the docking station. The docking station would need its own power, and big enough solar panels might be a problem, but perhaps big batteries would suffice with solar panels large enough to recharge them in 24 hours or so.

That certainly minimizes the plumbing (no change to either starship), and if you can use the same QD structure that's used on the ground, then even that's not a new part.

Does that all make sense? Or is that more or less what people have been talking about already and I'm just slow figuring it out? :-)
LoL. Yup. I think this one's been discussed. It's prime advantage is both the accumulated and the tanker would be exactly the same build.


Downside is it has no tanks, so there is zero chance of moving it if that becomes desirable, short of hitching a ride.


Which way is best? I doubt anybody at SpaceX really knows yet. I sure don't. That sucker's got to fly so it's working in a vacuum instead of us working in a vacuum.
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Online robot_enthusiast

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1221 on: 07/29/2022 03:00 am »
So would it make the most sense to build a special docking station with something equivalent to two quick disconnect arms? It would sit between two starships, connected to both, and transfer fuel from one to the other exactly as the system does on the ground. Each starship would be responsible for the ullage burn (and keeping it balanced as the center of mass moved during fueling), but the pumps would be in the docking station. The docking station would need its own power, and big enough solar panels might be a problem, but perhaps big batteries would suffice with solar panels large enough to recharge them in 24 hours or so.

That certainly minimizes the plumbing (no change to either starship), and if you can use the same QD structure that's used on the ground, then even that's not a new part.

Does that all make sense? Or is that more or less what people have been talking about already and I'm just slow figuring it out? :-)
The problem with that is that the system lacks the medium term storage needed to enable flexibility in the schedule for the accumulation flights. This desire for flexibility with the scheduling of tanker flights seems to have driven SpaceX down the path they are currently pursuing, with dedicated orbital-only depots. From all appearances, the depot ships will be based off of the tankers, with as few changes as possible to suit their needs. Deleted entry hardware, additional thermal insulation, possible extra tank capacity to account for boiloff, and hardware for propellant transfer with docked ships (compatible QD plate and likely dedicated ullage thrusters) seem to be their medium-long term solution to the problem. In the long term, once they've mastered active cooling solutions to allow for minimal boiloff over longer time periods, the potential limitations from being locked into a specific inclination will be minimized by putting tankers in every useful orbit. In the shorter term (ie. HLS contracts), the relatively low-cost nature of the depot design should allow missions to be profitable even with single-use depots.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1222 on: 07/29/2022 03:22 pm »
So would it make the most sense to build a special docking station with something equivalent to two quick disconnect arms? It would sit between two starships, connected to both, and transfer fuel from one to the other exactly as the system does on the ground. Each starship would be responsible for the ullage burn (and keeping it balanced as the center of mass moved during fueling), but the pumps would be in the docking station. The docking station would need its own power, and big enough solar panels might be a problem, but perhaps big batteries would suffice with solar panels large enough to recharge them in 24 hours or so.

That certainly minimizes the plumbing (no change to either starship), and if you can use the same QD structure that's used on the ground, then even that's not a new part.

Does that all make sense? Or is that more or less what people have been talking about already and I'm just slow figuring it out? :-)
The problem with that is that the system lacks the medium term storage needed to enable flexibility in the schedule for the accumulation flights. This desire for flexibility with the scheduling of tanker flights seems to have driven SpaceX down the path they are currently pursuing, with dedicated orbital-only depots. From all appearances, the depot ships will be based off of the tankers, with as few changes as possible to suit their needs. Deleted entry hardware, additional thermal insulation, possible extra tank capacity to account for boiloff, and hardware for propellant transfer with docked ships (compatible QD plate and likely dedicated ullage thrusters) seem to be their medium-long term solution to the problem. In the long term, once they've mastered active cooling solutions to allow for minimal boiloff over longer time periods, the potential limitations from being locked into a specific inclination will be minimized by putting tankers in every useful orbit. In the shorter term (ie. HLS contracts), the relatively low-cost nature of the depot design should allow missions to be profitable even with single-use depots.
Completely agree but for one point. We have logic'd through all the identifiable issue, often with divergent conclusions, but we have not seen a shred of hard evidence as to specifics of what SX really intends because right now their intentions are only general. 


That amazing ship hasn't even made it to orbit yet. No responsible engineering organization that specializes in rapid iterative development would expend much energy optimizing a complex, not yet needed capability for a system that has only demonstrated a few of the many capabilities needed for that complex operation.


They've done what I call noodling. That's what we do here. The difference is they have more information and they can read our memos and we can't read theirs.

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Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1223 on: 07/29/2022 07:51 pm »
Given all this, it seems to me that there's a lot of functionality that's needed for refueling but probably isn't needed in any given Starship. Does it make sense for them to build a specialized "docking station" to handle all of that and avoid complicating the Starship design?

The rough idea is a sort of cylinder that two Starships dock to which has quick disconnect arms that reach down to attach to each one. Lacking a clear idea of a) how they dock and b) where the QD ports are going to be, I can't be more specific. The dock would handle all the ullage burns and would need solar panels to provide power to pump the propellants around and keep them cool.

That's a whole new structure that has to fit into a Starship and unfold itself in space, but maybe that's not so bad. It seems better than adding a whole lot of hardware to every Starship that would only be used during refueling. Does that all seem reasonable?

Offline groknull

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1224 on: 07/29/2022 08:32 pm »
Given all this, it seems to me that there's a lot of functionality that's needed for refueling but probably isn't needed in any given Starship. Does it make sense for them to build a specialized "docking station" to handle all of that and avoid complicating the Starship design?

The rough idea is a sort of cylinder that two Starships dock to which has quick disconnect arms that reach down to attach to each one. Lacking a clear idea of a) how they dock and b) where the QD ports are going to be, I can't be more specific. The dock would handle all the ullage burns and would need solar panels to provide power to pump the propellants around and keep them cool.

That's a whole new structure that has to fit into a Starship and unfold itself in space, but maybe that's not so bad. It seems better than adding a whole lot of hardware to every Starship that would only be used during refueling. Does that all seem reasonable?

Deployable free-flyers and tethered / robot arm deployed adapters have been discussed earlier in this thread.

IMO further discussion of those concepts is not unreasonable.  Formalization of each concept group may help discussion.  That would probably clarify assumptions, questions, benefits, and drawbacks.

e.g.
- <concept name> (to help identify which concept is being discussed)
- <general concept description> (deployable free flyer; arm deployed adapter; adapter attached to depot tanker; adapter attached to ferry tanker; gender bent depot tanker with GSE adapter; etc.)
- <free flyer. (yes | no)
- <orbit lifetime> (goes up with, comes home with depot tanker; stays in orbit for a refilling campaign; stays in orbit permanently; stays in orbit until obsolete, then retrieved)
- <includes thrusters> (yes | no)
- <thruster type(s)> (ion; cold gas; MethaLOX; MethOX; etc.)
- <plane change capable?> (yes | no; time required for the plane change)
- <includes batteries and solar arrays> (yes | no)
- <includes depot methane and LOX propellant tanks?> (yes | no)
- <extensible?> (fixed size, single purpose; modular - configuration on ground; modular - extensible in orbit)
- <evolution of, or adaptation of existing tech?> (Starlink bus, Dragon components, Dragon XL components, Starship components)
- <adaptable / intended for adaptation> (free flyer adapter intended to be used in multiple Earth orbits, plus around Mars; free flyer adapter is just an initial implementation of future general purpose ferry or work platform; etc.)
- <alignment with SpaceX goals> (If bespoke hardware, how does this help with getting to Mars?; Does this accelerate or delay Starship development or deployment?>
- <applicable timeframe> (When is this concept or version of concept valid?; When will evolving tech or a large number of Starships built make this concept obsolete?)

As OTV Booster and others have pointed out, SpaceX isn't showing all of their cards, and will change their hand to adapt to changing situations, so we don't have enough information to accurately guess what they are going to do.  We can, however, have a lot of fun playing with concepts and looking at the trade offs.

Offline TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1225 on: 07/29/2022 09:01 pm »
Yet another half-baked geometrical thought:

If you put the depot's hardware (active side of the QD, cryocooler, pumps, etc.) in the ogive portion of the nose, it's straightforward to dock the depot and the other ship (either a lift tanker or a payload Starship to be refueled), dorsal-to-dorsal but nose-to-tail.  However, as has been pointed out, then you have to deal with ullage management in two different directions.

So what about this?  Imagine sort of a backwards chomper, i.e. a fairing door whose bottom is at about the level where the ogive portion of the nose begins, whose top is a bit below the level of the LOX header tank, and whose sides are roughly at the midline of the fairing.  Now put the whole fairing on an arm that can lift it clear of the depot and flip it over.  On the inside of the removed door are solar cells and docking hardware.  When a Starship wishes to use the depot, it slides into the (now concave) door segment and latches.  The active QD then extends from the open ogive space and connects to the Starship.

You now have both Starships pointing in the same direction, which removes the ullage issues.  What you've sacrificed is some amount of torsional stability between the two Starships.  Note that this is still a depot (or other kind of tanker) that can return to EDL, because everything will close up and stow, leaving the TPS alone.

I'm not quite sure I have the geometry right in the attached very bad picture.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1226 on: 07/29/2022 09:34 pm »
Given all this, it seems to me that there's a lot of functionality that's needed for refueling but probably isn't needed in any given Starship. Does it make sense for them to build a specialized "docking station" to handle all of that and avoid complicating the Starship design?

The rough idea is a sort of cylinder that two Starships dock to which has quick disconnect arms that reach down to attach to each one. Lacking a clear idea of a) how they dock and b) where the QD ports are going to be, I can't be more specific. The dock would handle all the ullage burns and would need solar panels to provide power to pump the propellants around and keep them cool.

That's a whole new structure that has to fit into a Starship and unfold itself in space, but maybe that's not so bad. It seems better than adding a whole lot of hardware to every Starship that would only be used during refueling. Does that all seem reasonable?
If you take that docking station and give it full sized tanks, it is a depot heavy. Tanks are the only thing missing from it.


The virtue I do see in a deployable docking station over a stay on orbit depot is that it has no raptors to waste. If it needs to change orbits it will need only one, saving that mass and the mass of the tanks.


On the down side, it's something new to design. Maybe that's a good trade.


A point in defense of the depot heavy which you might have missed is that no other ships need any changes. The depot would supply all the services of your docking station and all other ships would dress out plain jane. Well, maybe some attachment points which might also be needed for the docking station.


Still, saving the mass of the engines and tankage for orbit change does sound like a good trade if it can be designed to fit in and deploy from an SS. Mass shouldn't  be a problem.


Late thought. Somebody correct me if I've got this wrong. I think we're going to need a depot on high earth or lunar orbit. Under this plan that would mean a loaded tanker and a docking station. Is there anything outrageous about a docking station hitching a ride on a full tanker? It's has to attach anyway. It'll put the CoM a bit off the centerline but hey, that's why the engines gymbal.

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Online edzieba

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1227 on: 07/29/2022 10:27 pm »
Yet another half-baked geometrical thought:

If you put the depot's hardware (active side of the QD, cryocooler, pumps, etc.) in the ogive portion of the nose, it's straightforward to dock the depot and the other ship (either a lift tanker or a payload Starship to be refueled), dorsal-to-dorsal but nose-to-tail.  However, as has been pointed out, then you have to deal with ullage management in two different directions.

So what about this?  Imagine sort of a backwards chomper, i.e. a fairing door whose bottom is at about the level where the ogive portion of the nose begins, whose top is a bit below the level of the LOX header tank, and whose sides are roughly at the midline of the fairing.  Now put the whole fairing on an arm that can lift it clear of the depot and flip it over.  On the inside of the removed door are solar cells and docking hardware.  When a Starship wishes to use the depot, it slides into the (now concave) door segment and latches.  The active QD then extends from the open ogive space and connects to the Starship.

You now have both Starships pointing in the same direction, which removes the ullage issues.  What you've sacrificed is some amount of torsional stability between the two Starships.  Note that this is still a depot (or other kind of tanker) that can return to EDL, because everything will close up and stow, leaving the TPS alone.

I'm not quite sure I have the geometry right in the attached very bad picture.
This is what I've been proposing. The folding multi-use load-bearing fairing can probably be omitted for a simpler non load bearing panel, and the QD arm itself used for local grappling and mating. No need for two pieces of added hardware that can extend, actuate, and latch, when you can use one.
Depending on the final 'chomper' geometry (would need to be able to fold far enough to clear, but this may be needed for payload deployment anyway) this could even mean the QD assembly is entirely self-contained within the payload bay, so the depot/tanker can have that unit removed (and the extra plumbing blanked off) and the vehicle be used for payload launches when no depots or tankers are needed in order to pay for itself, rather than sitting around doing nothing.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1228 on: 07/29/2022 11:54 pm »
Yet another half-baked geometrical thought:

If you put the depot's hardware (active side of the QD, cryocooler, pumps, etc.) in the ogive portion of the nose, it's straightforward to dock the depot and the other ship (either a lift tanker or a payload Starship to be refueled), dorsal-to-dorsal but nose-to-tail.  However, as has been pointed out, then you have to deal with ullage management in two different directions.

So what about this?  Imagine sort of a backwards chomper, i.e. a fairing door whose bottom is at about the level where the ogive portion of the nose begins, whose top is a bit below the level of the LOX header tank, and whose sides are roughly at the midline of the fairing.  Now put the whole fairing on an arm that can lift it clear of the depot and flip it over.  On the inside of the removed door are solar cells and docking hardware.  When a Starship wishes to use the depot, it slides into the (now concave) door segment and latches.  The active QD then extends from the open ogive space and connects to the Starship.

You now have both Starships pointing in the same direction, which removes the ullage issues.  What you've sacrificed is some amount of torsional stability between the two Starships.  Note that this is still a depot (or other kind of tanker) that can return to EDL, because everything will close up and stow, leaving the TPS alone.

I'm not quite sure I have the geometry right in the attached very bad picture.
Yes. Much better than catawompus. My objections are some quibbles, and some not so quibbly.


That door. You're trying to make the inside diameter, probably with reinforcement, mate up to the outside diameter. Won't work, although if there were some mating surfaces that lined up with the edges it might. On the other hand, do you really want a hinged hatch as part of a latching arrangement? Maybe edzieba is right and nothing more than the QD is needed to attach. I don't agree but...


I think you came up with some numbers on the amount of power needed to run a cooler. Don't remember what they were except they were big. I don't think what you're showing would be enough. If EDL is intended, Solar white paint is out. I'm not seeing an easy sun shade deploy. Same for PV. Maybe cheap flexible throwaway PV? Put it conformal over the heat tiles and let it burn away? Where does the radiator go?


They changed the methane header again. It's up in the nose these days. Also, do you remember the boxy reinforcing rings we saw on the early builds? That may have changed. If it hasn't, there isn't very much room up there. I've no idea of the size of a cryo cooler. Maybe it'll fit. If not, the tanks may not stretch to 1600t without a full ship stretch.


The big deploy stuff, PV, radiators and sun shade, are a big reason I see the depot as something different than a plain jane tanker. Or maybe a docking station and an accumulator tanker. If it needs a cryo cooler it will need both PV and radiator. Maybe it can get away with just a sun shade. That needs to deploy. It's gotta have something or that propellant will boil off.


Edit to add: with the methane header moved up to the nose there's an easy tapoff point. I think this system would demand active pumping. Gotta think on this some more.
« Last Edit: 07/30/2022 12:01 am by OTV Booster »
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Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1229 on: 07/30/2022 01:06 am »
Yet another half-baked geometrical thought:

If you put the depot's hardware (active side of the QD, cryocooler, pumps, etc.) in the ogive portion of the nose, it's straightforward to dock the depot and the other ship (either a lift tanker or a payload Starship to be refueled), dorsal-to-dorsal but nose-to-tail.  However, as has been pointed out, then you have to deal with ullage management in two different directions.

So what about this?  Imagine sort of a backwards chomper, i.e. a fairing door whose bottom is at about the level where the ogive portion of the nose begins, whose top is a bit below the level of the LOX header tank, and whose sides are roughly at the midline of the fairing.  Now put the whole fairing on an arm that can lift it clear of the depot and flip it over.  On the inside of the removed door are solar cells and docking hardware.  When a Starship wishes to use the depot, it slides into the (now concave) door segment and latches.  The active QD then extends from the open ogive space and connects to the Starship.

You now have both Starships pointing in the same direction, which removes the ullage issues.  What you've sacrificed is some amount of torsional stability between the two Starships.  Note that this is still a depot (or other kind of tanker) that can return to EDL, because everything will close up and stow, leaving the TPS alone.

I'm not quite sure I have the geometry right in the attached very bad picture.
This is what I've been proposing. The folding multi-use load-bearing fairing can probably be omitted for a simpler non load bearing panel, and the QD arm itself used for local grappling and mating. No need for two pieces of added hardware that can extend, actuate, and latch, when you can use one.
Depending on the final 'chomper' geometry (would need to be able to fold far enough to clear, but this may be needed for payload deployment anyway) this could even mean the QD assembly is entirely self-contained within the payload bay, so the depot/tanker can have that unit removed (and the extra plumbing blanked off) and the vehicle be used for payload launches when no depots or tankers are needed in order to pay for itself, rather than sitting around doing nothing.
I think the advantages of stretch tanks have been well established. That would make the tanker a different variant than a dry cargo SS. Indeed, having a special cargo hatch for a refueling QD plate, either for a depot variant or all tankers for commonality, would demand it be a variant. The current StarLink deployment slot shows that SX is not shy about optimizing the design to fit the mission. The upshot of this is that if they left an accumulator on orbit it would only impact the tanker fleet, not the dry cargo fleet. The tanker is probably the simplest and least expensive variant they will ever have.


It looks like they will need two accumulators for Artemus but it's not clear that they will need two tanker fleets. Until the first Mars push there's no clear reason that they'd need more than one tanker fleet. Indeed, unless SS is a total reuse flop, there's every reason to believe their production capacity will be greater than the demand. A few accumulators that stay on orbit will not put any launch strain in SX.


If the accumulator is going to stay on orbit it needs no fins or heatshield. At this point it is yet another variant and can be called a depot. Why do half measures. Ditch the second QD plate in the nose and permanently deploy any PV, radiators, sun shade, thrusters and anything else it needs and be done with it.


It won't start out this way. They'll play around with two ships with overlapping  missions. Then move to a dry cargo ship and a tanker, moving further ahead on each trial, adding only what they need. Eventually they'll have it figured out.


Then they'll either build a full tilt depot or a docking station. I'm warming to the docking station.



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Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1230 on: 07/30/2022 04:07 am »
If you take that docking station and give it full sized tanks, it is a depot heavy. Tanks are the only thing missing from it.
Actually, I was thinking of the docking station as also being a way for crew to move from one Starship to another as well. My thought was that although you want to bring up the crew after you've already got your mission vehicle fully fueled, you really don't want to transfer all that fuel from one vehicle to another if you can help it. But if the docking station is a tube that two Starships dock to, why not make it a passageway for the crew and small amounts of last-minute cargo?

Not sure if that's really necessary, but it makes the station rather different from yet another Starship variant.

Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1231 on: 07/30/2022 04:12 am »
- <thruster type(s)> (ion; cold gas; MethaLOX; MethOX; etc.)
- <plane change capable?> (yes | no; time required for the plane change)
Two questions: First, do ion engines provide anything like the thrust required for ullage? I know it doesn't take much, but even so.
Second, I thought the cost of plane changes in LEO was prohibitive. Is that really on the table?

Offline Nomadd

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1232 on: 07/30/2022 04:57 am »
- <thruster type(s)> (ion; cold gas; MethaLOX; MethOX; etc.)
- <plane change capable?> (yes | no; time required for the plane change)
Two questions: First, do ion engines provide anything like the thrust required for ullage? I know it doesn't take much, but even so.
Second, I thought the cost of plane changes in LEO was prohibitive. Is that really on the table?
That would be like a butterfly trying to move an elephant.
 Inclination changes are hard. Plane changes just take time. Most Starlinks go to different planes than they start out in.
« Last Edit: 07/30/2022 05:00 am by Nomadd »
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Offline Ionmars

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1233 on: 07/30/2022 10:25 am »
Following the suggestion of groknull I outlined this RPOD concept for comparative discussion.

Concept: Landing Docking Posts

Where posted:  Short series beginning at p. 55 Reply #1086, with sketches.

Description: Accumulator/depot in orbit is visited by SS resupply tankers and SS outgoing ships. They  land dock on three posts jutting from the accumulator, whose projecting ends are in the same plane as a plumbing connector plate on the ventral surface of the accumulator. Each visiting ship has a corresponding connector plate that automatically joins to the accumulator plate upon landing docking, requiring no other robotic arms or gadgets.

Free flyer: no

Orbital lifetime: Until obsolete

Includes thrusters?  Use thrusters of standard Starships

Plane change capable: Not addressed, but assumes appropriate orbital position around a planetary body that serves multiple missions.

Batteries and solar arrays: Not addressed, but beefed up arrays and batteries would allow accumulator to recharge batteries of a visiting ship while receiving or providing propellants.

Both LOX and CH4 tanks? Yes. Accumulator is a standard SS tanker with strap-on posts that automatically erect in space.

Modular: No extensions in space are planned other than erecting the posts.

Adaption of other existing tech: No. Minimal changes to Starship, assuming SS is “existing” tech.

Adaptable to multiple orbits: Only to the extent that any standard SS could theoretically change to a different orbit.

Alignment with SpaceX goals: Refueling in space is required. This is one approach.

Edited: landing changed to docking
« Last Edit: 07/30/2022 11:31 am by Ionmars »

Offline rsdavis9

Re: Starship In-orbit refueling - Options and Discussion
« Reply #1234 on: 07/30/2022 12:06 pm »
If you take that docking station and give it full sized tanks, it is a depot heavy. Tanks are the only thing missing from it.
Actually, I was thinking of the docking station as also being a way for crew to move from one Starship to another as well. My thought was that although you want to bring up the crew after you've already got your mission vehicle fully fueled, you really don't want to transfer all that fuel from one vehicle to another if you can help it. But if the docking station is a tube that two Starships dock to, why not make it a passageway for the crew and small amounts of last-minute cargo?

Not sure if that's really necessary, but it makes the station rather different from yet another Starship variant.

Eventually, like in the future.

The fuel transfer and cargo moving will be the same thing.
Sort of like the 7/11 of space.
I like the idea of nose docking to a slowing rotating hub. That way ullage is free.
Now just have connectors on the hub for fuel and people/cargo.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1235 on: 07/30/2022 06:57 pm »
This is what I've been proposing. The folding multi-use load-bearing fairing can probably be omitted for a simpler non load bearing panel, and the QD arm itself used for local grappling and mating. No need for two pieces of added hardware that can extend, actuate, and latch, when you can use one.

I still don't think you can get sufficient rigidity (torsional or otherwise) from a one-point latch, or even a multi-point latch with the attachments within a short distance of one another.  The nice thing about using the inside of the door as the second point of contact is that it's simple and far enough away from the active QD to be rigid.

Quote
Depending on the final 'chomper' geometry (would need to be able to fold far enough to clear, but this may be needed for payload deployment anyway) this could even mean the QD assembly is entirely self-contained within the payload bay, so the depot/tanker can have that unit removed (and the extra plumbing blanked off) and the vehicle be used for payload launches when no depots or tankers are needed in order to pay for itself, rather than sitting around doing nothing.

Largely agree here, although I still think that we're going to see an LSS with 1500t-1600t tanks, and you might as well use that layout for lift tankers and depots.  But if everything remains at 1200t, then yes, you could conceivably have a single propulsion section layout that was good for everything.

We know that there are going to be several different noses.  In order that they'll appear:

1) The Pez Dispenser is only good for Starlinks or third-party birds that conform to Starlink form factor and specs.

2) There's going to be a tanker/depot nose, unless the free-flyer is viable.  (I've come to the conclusion that it would only be a solution of last resort, with a payload kit being far, far preferable.)

3) There's going to be an LSS hatch + crew module version.

4) There's going to be some chomper-like version for deploying bulky payloads into microgravity.

5) I expect to see a jettisonable fairing for expendable deep space missions, but that one will probably wait a while.

It's possible that the chomper and the tanker nose will be the same, but I'd put my bet on it being unique, and designed to work with a 1500t (of propellant) propulsion section. 

I think you came up with some numbers on the amount of power needed to run a cooler. Don't remember what they were except they were big. I don't think what you're showing would be enough. If EDL is intended, Solar white paint is out. I'm not seeing an easy sun shade deploy. Same for PV. Maybe cheap flexible throwaway PV? Put it conformal over the heat tiles and let it burn away? Where does the radiator go?

I think the cooling numbers were associated with a self-contained Sabaitier/electrolysis/RWGS plant for Mars.  That's considerably more challenging.  I haven't learned how to model heating in VLEO.

That said, there's an awful lot to be said for brute force.  If you can deploy enough PV and heat rejection, then you don't need anything other than bare-metal tanks.  And if you're going to swing most of the top of the nose out of the way, you're looking at at least a 6m x 6m trapezoidal hole.  You can deploy an awful lot of stuff out of a hole like that--even if it it contains active QD and docking hardware.  And it's not like PV and radiators with large surface areas are low-TRL technologies.  As for cryocoolers:  they're sized for the job, usually as multi-stage systems to keep efficiency up.  Again, you're talking about hundreds of m³ of space in the nose, even with stretched tanks.

It would be, admittedly, a bit a of Rube Goldberg, especially if you want to fold everything back up for recovery.  But if you can't do that, you can probably jettison the PV and radiators for recovery, or you can simply leave the depot on orbit.  Eventually, there will be a recoverable design.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1236 on: 07/31/2022 05:05 am »
A problem we're having is that we don't have a clue what boiloff rates to expect and what the various mitigation might give us. That impacts the BFS (Big Floppy Stuff) a depot or accumulator might need. PV, radiators and sunshield. There's also Solar white paint and spray on foam. That last isn't all that popular but it's there to look at.

I found this 2020 thesis on modeling boiloff mitigation. https://repository.tudelft.nl/islandora/object/uuid:f1e1c77e-f5be-4e6b-a813-e7f955760603/datastream/OBJ/download

It's 143 pages long and in the abstract it has an interesting comment.
Quote
Due to a lack of experimental and flight data of existing spacecraft, the Boil-off Monte Carlo program is not validated.

Even the real rocket scientists have only a hypothetical understanding of the problem. My bets are that we might see a StarLink launch or three that explore boiloff mitigation. Might see one with solar white and one with spray-on foam. Rotisserie spins. Anything that's quick, easy and on point.

Edit: cleanup and add: maybe just settin there for a day keeping the shiny side to the heat and a day with the tiles to the heat. Start and end each test with mild acceleration to get a quick n dirty on boiloff.



« Last Edit: 07/31/2022 05:38 am by OTV Booster »
We are on the cusp of revolutionary access to space. One hallmark of a revolution is that there is a disjuncture through which projections do not work. The thread must be picked up anew and the tapestry of history woven with a fresh pattern.

Offline OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1237 on: 07/31/2022 05:41 pm »
Found an on point paper from 2006. Only 8 pages. Maybe somebody already linked it already. It's worth the read. https://www.ulalaunch.com/docs/default-source/extended-duration/settled-cryogenic-propellant-transfer-2006-4436.pdf


Broadly, it covers most everything we've been talking about except the SpaceX specific QD hookup. The most interesting points are:
- a list of the TRL's of the sub tasks
- settling thrust of down to 2x10^-5g already demonstrated.



We are on the cusp of revolutionary access to space. One hallmark of a revolution is that there is a disjuncture through which projections do not work. The thread must be picked up anew and the tapestry of history woven with a fresh pattern.

Online edzieba

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1238 on: 08/01/2022 12:59 pm »
Largely agree here, although I still think that we're going to see an LSS with 1500t-1600t tanks, and you might as well use that layout for lift tankers and depots.  But if everything remains at 1200t, then yes, you could conceivably have a single propulsion section layout that was good for everything.
The Lunar Starship is the only vehicle that would need more than one 'standard' Starship's worth of propellant to be transferred, and those will be launching maybe once a year, if that. The rest of the time, a standard capacity Starship is sufficient as a tanker or depot for all regular launches (albeit most launches will likely require zero tankers, let alone a depot).
Rather than using a custom stretch depot Starship that may-or-may-not be able to ever deorbit (and even if it can, that's a lot of extra R&D work to make sure it actually works) and require s abunch of unique handling equipment and procedures to accommodate its greater size; for that once-a-year occasion that actually requires that capacity you can launch two regular sized depots instead.

In terms of cost and time, it's always preferable to make more copies of the same item than to make more one-off custom item variants whenever you can possibly help it.

Offline TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1239 on: 08/01/2022 06:33 pm »
Largely agree here, although I still think that we're going to see an LSS with 1500t-1600t tanks, and you might as well use that layout for lift tankers and depots.  But if everything remains at 1200t, then yes, you could conceivably have a single propulsion section layout that was good for everything.
The Lunar Starship is the only vehicle that would need more than one 'standard' Starship's worth of propellant to be transferred, and those will be launching maybe once a year, if that. The rest of the time, a standard capacity Starship is sufficient as a tanker or depot for all regular launches (albeit most launches will likely require zero tankers, let alone a depot).
Rather than using a custom stretch depot Starship that may-or-may-not be able to ever deorbit (and even if it can, that's a lot of extra R&D work to make sure it actually works) and require s abunch of unique handling equipment and procedures to accommodate its greater size; for that once-a-year occasion that actually requires that capacity you can launch two regular sized depots instead.

In terms of cost and time, it's always preferable to make more copies of the same item than to make more one-off custom item variants whenever you can possibly help it.

I think this is less work (and less manufacturing cost) than you think.  The overall length of the Starship doesn't change, just where you put the LOX/LCH4 bulkhead and the LCH4 dome.  Remember that, to a first-order approximation, you're just stacking ring segments, domes/bulkheads, and noses.  Changing the order of how these segments are stacked is trivial.  (Changing their plumbing and wiring is less than trivial, but it's still pretty easy.)

If you divide the manufacturing into a propulsion section, a nose, and various accoutrements, you can build everything you need:

1) Propulsion Section:
a) Short 1200t
b) Long 1550t.

2) Nose Section (long goes on short propulsion, short on long propulsion):
a) Starlink Pez Dispenser (long nose)
b) Tanker and/or Depot (short nose)
c) LSS nose (short nose)
d) Large micro-gravity payload nose "chomper" (long nose)
e) Jettisonable fairing for deep space expendable mission (probably short nose)
f) A crew launch nose (long nose, and possibly exotic escape system).

3) Various accoutrements:
a) TPS and bare metal surface.
b) Solar white surface.
c) Elonerons.
d) Header tanks.
e) Landing legs.
f) Lunar thruster package.

From these you make:

A) Vanilla Starship
Short propulsion
Pez dispenser or chomper long noses.
TPS/bare metal surface.
Elonerons, header tanks.
Cadence (first 5 years of operations):  20/yr Pez, 10/yr chomper.

B) Tanker (EDL-capable)
Long propulsion
Tanker short nose (with or without depot kit, depending on application)
TPS/bare metal surface
Elonerons, header tanks.
Cadence: 10/yr

Note that you can make a non-EDL depot with no elonerons, no headers, and solar white surface.

C) Lunar Starship
Long propulsion
LSS short nose with crew module, cargo deck, and crew access
Solar white surface.
Thrusters, landing legs.
Cadence: 1/yr

D) Deep-space "StarKicker"
Long propulsion
Short jettisonable fairing nose
No accoutrements at all
Cadence: 1/yr

E) Crew-Launch Starship
Short Propulsion
Long nose (possibility with exotic escape capabilities)
TPS/bare metal surface.
Header tanks, elonerons.
Possibly landing legs for aborts.
Cadence (first 5 years): 0/yr

All the real work is in the nose variants, and even then everything fits into either a long or short version.  Bear in mind that they must do the long propulsion version for LSS.  Once you have the tooling built for that, why wouldn't you use it when it made your life easier?
« Last Edit: 08/02/2022 12:07 pm by TheRadicalModerate »

Tags: Depot HLS 
 

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