Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 639953 times)

Offline Twark_Main

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1380 on: 08/31/2022 08:16 am »
If you don't care about all that math and you just want to skip straight to "the answer" (as if there ever was such a thing!  ::))...


If your depot doesn't reenter, Nomex blankets over MLI.


This also contributes some MMOD protection, which is a nice risk buy-down.

Offline LMT

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1381 on: 08/31/2022 02:26 pm »
(snip)
Btw SPHEREx is precisely the special case I described earlier: the cone always points up, so it never has a view of the Earth. It also needs to be located in a dusk/dawn polar orbit, such that it never has a view of the Sun. There are downsides to using a disk/dawn orbit for a depot: it's less efficient than launching eastward, and it has less flexibility for targeting a specific right ascension for departure.

Jumping in late to this discussion, so apologies if this has been said before.
The dusk-dawn SSO orbit is a limiting case, one that is particularly well suited to all-sky surveys like SPHEREX and WISE.
(And particularly unsuited to a depot from which to start interplanetary trajectories, as you said.)
There, the angle from the local vertical to the Sun is always near 90 degrees.  (probably >90 minus 23.5 degree inclination of the Earth's rotation with respect to its orbit minus ~7 degrees from the inclination to the pole.)
However, the same goal of never pointing the radiator at the Sun can be achieved at lower inclinations for which the precession does not match the orbital rate of the Earth, i.e. with a variable beta angle.

Take the other extreme, an equatorial orbit.
A depot in equatorial orbit oriented to the Local Velocity, Local Horizon (LVLH) would need an Earth shield and a sunshield.
This could be cylindrical, with axis pointed at the orbit poles, perpendicular to velocity and to the local zenith.
A cryoradiator could point out either end.
However, it's Field Of View would be limited to 90 - 23.5 =~66 degrees from the axis, to prevent the Sun from shining into it regardless of season.
(The beta angle is zero at the equinoxes, when the pane of the equator passes through the Sun, and grows to ~22 deg at the solstices.)
Such radiators are commonly made with "Etendue converters", non-imaging optics, sometimes implemented with Winston cones.  (See some one dimensional implementations here.)

For higher inclination orbits, the angle is reduced, and by conservation of Etendue, the far end of the "cone" gets proportionally larger.
So it's a trade between making the inclination high enough to go through the departure points and restricting the size.

So it's not just the spectral properties that influence the solar and Earth heating and the thermal radiation. 
The geometry is also important.

More to the point: 

- A sun-sync orbit could freeze a passive V-Groove depot solid.

- A low-inclination orbit doesn't just maximize depot payload.  It also melts ice.

Q:  Which liquid would you load in the exposed tank?
« Last Edit: 08/31/2022 02:30 pm by LMT »

Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1382 on: 08/31/2022 05:09 pm »
Just to clarify, the terminology of the thread (and the NASA HLS contract) is:

Tanker: Starship that launches fuel, either to an orbiting depot, or directly to another Starship to be refuelled.

Depot: An accumulator in orbit that is refuelled by a number of tanker-flights until it is full (or full enough). Then-and-only-then the mission vehicle launches and docks with the depot to take on a full (or full enough) propellant load for its mission.
So consider a specialized starship with extended tanks (and no cargo hold)--what I've been calling a "tanker." Is that still a tanker by your definition? (I would expect it to be.) If you launch it empty with a plan to fill it in orbit, does it turn into a depot? Even though it's the same vehicle?

Now consider a cargo starship with a couple of tanks of propellant in the cargo bay. Surely that's not also a tanker? It turns into a tanker when you put the tanks in the cargo hold, and it quits being one when you take them out?

Imagine that you launch that same cargo starship with empty tanks in the hold. Does that mean it magically turns into a depot as soon as it's in orbit--assuming the plan were to fill and then empty the tanks?

Surely it makes no sense to reclassify the launch vehicle merely based on the cargo in it!

Anyway, it seems to me like you're missing a term to distinguish bespoke hardware vs. multipurpose hardware. Unless I'm missing some other consideration . . .


Offline Luc

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1383 on: 08/31/2022 05:24 pm »
Rather than a specialized depot with coatings, what about an orbiting tubular sunshade/solar wing that starships “park in” - basically fly in formation with while exchanging/storing fuel? I’m not talking about anything elaborate, just a big, hollow milar structure with basic station keeping from one of their satellites.

Offline rakaydos

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1384 on: 08/31/2022 05:52 pm »
If you don't care about all that math and you just want to skip straight to "the answer" (as if there ever was such a thing!  ::))...


If your depot doesn't reenter, Nomex blankets over MLI.


This also contributes some MMOD protection, which is a nice risk buy-down.
Can you paint it shuttle-tank orange? Gotta have some nice clarity in the visuals when explaining it to 80 year old politicians.

Offline Twark_Main

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1385 on: 08/31/2022 06:59 pm »
- A sun-sync orbit could freeze a V-Groove depot solid.

- A low-inclination orbit doesn't just maximize depot payload.  It also melts ice.

It's almost like... it's a trade-off.

SSO + V-Groove is simply a bad trade compared to LEO 28° + MLI/Nomex. More complex sunshade design / deployment and a less efficient orbit.



Folks here love it when you and I get into it ( ::) ), so that's the last I'll say in this exchange. You get the last word, buddy!! I'll just pretend like you said I'm wrong by hyperlinking to your own post, and call it a day. ;)
« Last Edit: 08/31/2022 08:06 pm by Twark_Main »

Offline Asteroza

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1386 on: 08/31/2022 11:24 pm »
Rather than a specialized depot with coatings, what about an orbiting tubular sunshade/solar wing that starships “park in” - basically fly in formation with while exchanging/storing fuel? I’m not talking about anything elaborate, just a big, hollow milar structure with basic station keeping from one of their satellites.

An inflatable beam tensegrity structure with stretched mylar films would be fairly simple, and there are designs for UV cured inflatable booms so it stays stiff after the deployment gas leaks out. Either self deploy with an inchworm robot arm slipping it over the nose, or something that can be swung around from the freeflyer mating device that's been proposed here. However, the PR optics on what would be a shiny condom for Staship would, at the least, be a dangerous meme resource for our favorite memelord...

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1387 on: 08/31/2022 11:25 pm »
IIUC, the cargo/tanker has GSE up in the nose along with propellant tanks. It noses up to the QD plate on the receiving ship, its QD plate extends, and it pumps over the propellant from the cargo bay tanks. Is this right?
Maybe I've been messing the terms up. I think QD is the "quick disconnect," which is the female socket that's at the bottom of a Starship. GSE is the "ground support equipment." This is the male plug that goes into the QD when a starship is filled on the ground. A "gender bender" is an adaptor that's male on one side and female on the other, with plumbing crossed over as needed to make it work. (Otherwise it'll be the mirror image of what you want on one side or the other.) Are we in agreement here? (Sorry if I've been mixing them up before.)

Given that, I've been visualizing the tanker starship as having GSE instead of a QD at the bottom. They attach a gender bender on the ground to fill it up, but they pull that off and the GSE needs to retract into the starship before it launches. In space, it extends the GSE and mates with the QD on a standard starship.

Are we still together?

If you want one tanker to refill another, you'll have to somehow attach a gender bender to one of them. This is what a "free flyer" is good for. (Among other things)

For what I was envisioning, the "depot" in the cargo hold would consist of two small tanks plus GSE. You'd fill these tanks the same way you would a tanker starship. In space, the cargo door would open, the GSE would extend, and it would mate with the QD on the target vehicle.

The actual numbers will change as the ships capabilities evolve. Twark or Rad Mod or maybe Robo ran some numbers awhile back claiming that a tanker with a small stretch could load a total of 1600 or 1650t of propellant and deliver quite a bit more than 150t. A dedicated depot would most probably be a tanker variant with extra kit so this plays into supporting early Artemus missions where the extra propellant can be put to good use. Don't ask. It was a very detailed discussion.
I guess the real question is "how much more propellant?" If it's twice as much, then, yeah, I can see how it might be worth it. But if it's just 20% more, maybe not.

Perhaps I should go back through the earlier posts on the thread. I suspect they'd make a lot more sense to me now.

There is one point in your cargo/tanker idea where safety would be a concern. This may be where my brain fart happened. If a crewed ship needs refueling it should only happen once. Multiple small transfers each carry the same safety risks as one big gulp. This can be got around by waiting for the transfers to be finished before the crew launches and transfers over to the refueled ship. Another complexity, but maybe the best way.
Yeah, I thought about this too. That's where a bespoke depot seems to make the most sense. You fill it up--no matter how long it takes--and when it's got enough propellant, then you send up the crewed ship and fill it just once. That's the case where special reflectors and/or cryocoolers make sense as well--given how long the propellant has to survive in LEO--and all that extra hardware really does seem like it should be on a depot--not a starship.

You're correct in expecting the depot to have what you call female and what I call gender bent GSE. My terminology comes from electronics adapters (called gender benders) used to reverse a cables gender.
Yep. I've soldered RS232 cables for this purpose myself, although not since Jimmy Carter was president. :-)

A depot would have only the one QD plate. It's the free flyer that would have two of the same gender as the ground side GSE.  One side would mount to a tanker with standard QD plate that becomes a temporary accumulator. The other would mate to the tankers (also standard QD plate) arriving to fill the accumulator, and ultimately to the receiving ship (also with standard QD plate). Keep in mind, the free flyer and depot are not complimentary. The are competing concepts with the same goal.

What you call a command module is pretty much what the free flyer would be. It packs in whatever functionality a depot needs but allows plain Jane tankers to become storage tanks (accumulators). If you build the command module into a tanker you have - a depot. The free flyer concept that's been thrown around would be a new design with all that implies.
Ah, that makes sense, although the gender combinations are a little challenging. E.g. if you want one tanker to fill another, you need a twisted female-female free flyer. But if you want a tanker to fill a regular starship, you need a straight-through male-female one. And if you know you'll always have a free flyer, then you want to make all starships female and all free flyers twisted male-male.

IMO it's way too early for hard decisions in depot vs free flyer, let alone the variants. Just gonna set back and enjoy the show.
Sure, but it's a lot easier to enjoy the show if you start off knowing what language they're speaking! :-)
Let's not sweat terminology unless it hinders communications rather than help it. As long as we end up on the same page, the specific label is unimportant. We're working on it.

I've been a bit loose on QD plate and GSE. The QD plate that is part of the ship might arguably be considered GSE. It depends where you want to split that hair. Part of the launch tower GSE is a QD plate. Following your convention it would be male. The one on the ship, female.

In the spirit of keeping hardware as common as possible, all ships would have a female QD plate so that all ships can properly mate to the male GSE QD plate on the tower. The problem is that a depot needs a QD plate that will mate to the tower GSE so it can be filled and launched. It must be female. Then, to mate to any other ship, it's QD plate must be male, because other ships QD plates are female. From this, arise all discussion of gender benders and related.

Ideally, the depot would be the only ship with major adaptions specific to refueling. Something has to be done and whatever it is, it logically should be done on the tanker depot. Or better yet, on the ground equipment. That's where the idea of a gender bender on the towers GSE QD plate comes in.

The ground GSE is male. Ships are ordinarily female. The depot needs to be male to do its job on orbit.  So an adapter (gender bender), female on both faces, is mounted between the ground side QD plate and the depot side QD plate. It stays on the ground.

I envision the depot QD plate to be in a bit of a dog house sticking out of the ship. This would allow some stand-off between the ships. If necessary, it could be designed to extend. This would preclude using the QD plate connection as a firm connection between ships so if they need to do a tight lashup, the lashup would need be elsewhere.

The most reasonable alternative IMO, is the free flyer. Simple version is a cube with male QD plates on either side. It needs pumps, plumbing, smarts, thrusters to maneuver and fuel. If small enough it might launch in the truncated cargo bay of the first tanker to act as an accumulator. Ity bitty bay door opens and it exits and works it's way down the hull and one of its male QD plates does unmentionable intimate things to the normal female QD plate on the tanker accumulator. And they lived happily ever-after.

If too large, it has to find another ride. The heavy version would have PV, radiator, cryocooler, and/or some MLI. Might have substantial tankage to allow orbit changes. It would need another ride.

These are IMO, the direction SX will be looking. In usual fashion they'll start simple, maybe something like the rig and tankage in the cargo bay. But these two designs or something like them, will be what they'll be looking at as the final product.

Refueling is central to what SX wants to do, not to mention that it is (I think) a formal milestone in the Artemus contract. This implies they will start bending metal as early as possible. Maybe two or three launches following the first reasonably successful (sub)orbital flight will see the first attempt.

This will still be early enough in the overall starship development process that even if they can recover a ship successfully, the changes will be coming too fast to bother except as a test of reflight. Well, maybe once they get a StarLink system unkinked they'll reuse them out of practicality as soon as possible.

StarLink launch, as it stands now, looks like it will be a candidate for a dedicated variant. If a big tank tanker adds only 20% propellant it gives six tankers worth for the launch of five tankers. Actually, better than that because there is zero cargo handling & fueling other than normal propellant loading. This is another variant candidate.

If starship were isogrid construction and Boeing were doing the work, variants would be out of the question without five years lead time and a ton of money. Not sure if that's a metric ton or not. This is SX. This whole shebang started with a water tower construction company doing contract work to build Hoppy in the open, within spitting distance of the beach. The whole point is to optimize operations, not keep the fabrication costs as low as possible. Fabrication costs are important but it's only a means to an end and they seem to have it well in hand.

There may be some unlabeled opinions above.  :D


Edit, changed word.
« Last Edit: 08/31/2022 11:29 pm by OTV Booster »
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Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1388 on: 09/01/2022 12:04 am »
Well, maybe once they get a StarLink system unkinked they'll reuse them out of practicality as soon as possible.
Of course! I see it now! The free flyer will be a modified StarLink satellite! (Inspired by the folks above who assured me that it's always easier to modify something you've already built.) :-)

Seriously, I have to say the Free Flyer is certainly the cleanest option, if it can be made to work. Then you don't make any changes to your base starships, and you can always put up specialized depots later, if you want to. Everything except a free flyer would have female QD plates--even the depots.

Then the question is: what is the simplest possible free-flyer design?


Offline LMT

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1389 on: 09/01/2022 01:45 am »
SSO + V-Groove is simply a bad trade compared to LEO 28° + MLI/Nomex.

No, the sun-sync orbit was never a requirement of V-Groove passive radiators, just your misreading.  Posters seem unfamiliar with V-Groove, despite long heritage.  Mass-efficiency is hard to beat.

And it's methane in the exposed tank, because...?

Rather than a specialized depot with coatings, what about an orbiting tubular sunshade/solar wing that starships “park in” - basically fly in formation with while exchanging/storing fuel? I’m not talking about anything elaborate, just a big, hollow milar structure with basic station keeping from one of their satellites.

Well, a single-layer sunshade or parallel-layering sunshade wouldn't give cryogenic temperature in LEO; you'd need more complex structural units, like V-Groove.  Example:  Compare the V-Groove middle-shield temperatures to inner-shield temperatures in Bhandari et al. 2020 figures.  By inference, single-shield temperature would be even higher.

...the Free Flyer is certainly the cleanest option, if it can be made to work. Then you don't make any changes to your base starships, and you can always put up specialized depots later, if you want to.

If you built for Martian fleet support, you could arrange a "free-flying structure" also for passive liquid water storage, docks, cargo warehouses, stevedore services, and other protected fleet facilities, giving a more valuable, multi-purpose depot. 

E.g., the VLEO "Terrestation" concept.
« Last Edit: 09/01/2022 02:42 am by LMT »

Offline Paul451

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1390 on: 09/01/2022 04:26 am »
Just to clarify, the terminology of the thread (and the NASA HLS contract) is:
Tanker: Starship that launches fuel, either to an orbiting depot, or directly to another Starship to be refuelled.
Depot: An accumulator in orbit that is refuelled by a number of tanker-flights until it is full (or full enough). Then-and-only-then the mission vehicle launches and docks with the depot to take on a full (or full enough) propellant load for its mission.
So consider a specialized starship with extended tanks (and no cargo hold)--what I've been calling a "tanker." Is that still a tanker by your definition? (I would expect it to be.) If you launch it empty with a plan to fill it in orbit, does it turn into a depot? Even though it's the same vehicle?
Now consider a cargo starship with a couple of tanks of propellant in the cargo bay. Surely that's not also a tanker? It turns into a tanker when you put the tanks in the cargo hold, and it quits being one when you take them out?
Imagine that you launch that same cargo starship with empty tanks in the hold. Does that mean it magically turns into a depot as soon as it's in orbit--assuming the plan were to fill and then empty the tanks?
Surely it makes no sense to reclassify the launch vehicle merely based on the cargo in it!
Anyway, it seems to me like you're missing a term to distinguish bespoke hardware vs. multipurpose hardware. Unless I'm missing some other consideration . . .

Dude, I wasn't trying to get into some debate on Plutonic [Platonic] ideals. I was just letting you know that you are using terminology that has been used differently previous in the thread (and in the HLS contract); and judging by some replies, it's likely to cause confusion.

[edit: Words are hard]

For example, your concept only replaces the tankers, it doesn't replace the depot. You are instead using the mission HLS as the accumulator. That just transfers the cost of thermal management/boil-off losses to the HLS, it doesn't solve it.
« Last Edit: 09/02/2022 05:35 am by Paul451 »

Offline Greg Hullender

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1391 on: 09/01/2022 01:43 pm »
Dude, I wasn't trying to get into some debate on Plutonic ideals.
Only if we're planning to refill the Starship with magma. :-)

I was just letting you know that you are using terminology that has been used differently previous in the thread (and in the HLS contract); and judging by some replies, it's likely to cause confusion.
Do you have a link to the part of the HLS contract you're talking about?

I did see a post (way back) trying to impose the definition you're talking about, and I think I saw one or two people try to use it, but I'm not convinced that it's a) widely used or b) particularly useful.

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1392 on: 09/01/2022 02:14 pm »
Well, maybe once they get a StarLink system unkinked they'll reuse them out of practicality as soon as possible.
Of course! I see it now! The free flyer will be a modified StarLink satellite! (Inspired by the folks above who assured me that it's always easier to modify something you've already built.) :-)

Seriously, I have to say the Free Flyer is certainly the cleanest option, if it can be made to work. Then you don't make any changes to your base starships, and you can always put up specialized depots later, if you want to. Everything except a free flyer would have female QD plates--even the depots.

Then the question is: what is the simplest possible free-flyer design?
Wellll, it depends on the needs. That's what the discussion about heat rejection and solar white paint is all about. If they can cycle a tanker to the accumulator every 15 minutes (yeah, right) then get the receiving ship in there right after the final tanker, the basic cube free flyer would be fine. If it's two weeks between tankers it's a whole different problem. How long does it take to transfer a tanker load? How often can they launch a tanker? Lots of moving parts. One SpaceX sized step at a time.


You were joking about modifying a StarLink for the free flyer. There is some truth there. The first Ford Mustang was a Falcon with a few inches added to the frame, a bigger engine and sexier bling. Any overlap in needs between StarLink and free flyer can be carried over in hardware and software. Just don't expect gross physical structure to carry over.


My gut says they'll shoot for either a free flyer or a full tilt depot but not cross over from one to the other unless they hit a wall or decide to add capabilities beyond propellant transfer. Which is better? Too many unknown at this time. Thermal and its mitigation is at the top of the list.
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Offline docmordrid

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1393 on: 09/01/2022 02:59 pm »
As regards Starlink customization, SpaceX is already doing it.

https://twitter.com/Sandra_I_Erwin/status/1313225103392546816

Sandra Erwin @Sandra_I_Erwin
Breaking news: SpaceX, L3Harris win Space Development Agency contracts to build missile-warning satellites. SpaceX is developing a new satellite for DoD based on the Starlink design. SpaceNews
« Last Edit: 09/01/2022 03:03 pm by docmordrid »
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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1394 on: 09/01/2022 04:36 pm »
Some insight on research on atmospheric thermal behavior that seems pertinent.

https://www.nasaspaceflight.com/2022/08/jpss-2-testing-complete/

Quote
Lastly, the Clouds and Earth’s Radiant Energy System (CERES) instrument will measure the energy being absorbed and emitted by Earth’s atmosphere. CERES is currently flying on Suomi NPP and NOAA-20 and previously helped scientists understand the links between absorption and energy emissions that affect energy balances.
« Last Edit: 09/01/2022 04:37 pm by OTV Booster »
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Offline edzieba

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1395 on: 09/01/2022 05:11 pm »
A 'free flyer' is a needless complexity. Since:
- an adapter will only ever do anything when right next to (and in contact with) a Starship
- is only ever needed when a Starship is transferring propellants to another Starship
- that situation (prop transfer) only ever needs to occur between a tanker and a depot, and a depot and a 'target' Starship
- any adapter (free flyer or not) needs to be launchable by a Starship or smaller vehicle
- therefor any adapter by definition can be launched by a Starship
You can eliminate all redundant free-flight hardware (power, propulsion, avionics, control, position sensing, etc) by attaching the adapter to a Starship, ideally the depot. That way the adapter is launched by the Depot Starship rather than by an entirely separate launch of its own, so the propellant 'cost' for the combined depot launch is lower overall than with a separate launch. If the 'free flight' adapter is intended to launch with the depot anyway, then it is a direct mass and complexity (and cost and development time) saving to eliminate the free flight capability and leave just the adapter attached.

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1396 on: 09/01/2022 06:02 pm »
A 'free flyer' is a needless complexity. Since:
- an adapter will only ever do anything when right next to (and in contact with) a Starship
- is only ever needed when a Starship is transferring propellants to another Starship
- that situation (prop transfer) only ever needs to occur between a tanker and a depot, and a depot and a 'target' Starship
- any adapter (free flyer or not) needs to be launchable by a Starship or smaller vehicle
- therefor any adapter by definition can be launched by a Starship
You can eliminate all redundant free-flight hardware (power, propulsion, avionics, control, position sensing, etc) by attaching the adapter to a Starship, ideally the depot. That way the adapter is launched by the Depot Starship rather than by an entirely separate launch of its own, so the propellant 'cost' for the combined depot launch is lower overall than with a separate launch. If the 'free flight' adapter is intended to launch with the depot anyway, then it is a direct mass and complexity (and cost and development time) saving to eliminate the free flight capability and leave just the adapter attached.
IIRC, you expect that the two ships need little gap between them and the QD connection is the only connection needed. No other supports necessary. If I have this right, and your conjectures are correct, this can be a very simple system. While I very much respect the technical skill you bring to the table, I have to disagree. I'd be gobsmacked if it ends up that easy.


Gobsmacked, but not unhappy.
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 TheRadicalModerate

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1397 on: 09/01/2022 11:25 pm »
A 'free flyer' is a needless complexity. Since:
- an adapter will only ever do anything when right next to (and in contact with) a Starship
- is only ever needed when a Starship is transferring propellants to another Starship
- that situation (prop transfer) only ever needs to occur between a tanker and a depot, and a depot and a 'target' Starship
- any adapter (free flyer or not) needs to be launchable by a Starship or smaller vehicle
- therefor any adapter by definition can be launched by a Starship
You can eliminate all redundant free-flight hardware (power, propulsion, avionics, control, position sensing, etc) by attaching the adapter to a Starship, ideally the depot. That way the adapter is launched by the Depot Starship rather than by an entirely separate launch of its own, so the propellant 'cost' for the combined depot launch is lower overall than with a separate launch. If the 'free flight' adapter is intended to launch with the depot anyway, then it is a direct mass and complexity (and cost and development time) saving to eliminate the free flight capability and leave just the adapter attached.
IIRC, you expect that the two ships need little gap between them and the QD connection is the only connection needed. No other supports necessary. If I have this right, and your conjectures are correct, this can be a very simple system. While I very much respect the technical skill you bring to the table, I have to disagree. I'd be gobsmacked if it ends up that easy.


Gobsmacked, but not unhappy.

We're sorta re-litigating some stuff, but this is ultimately about torsional load.  I doubt that a single set of bellows hoses will support the torques that an almost-full depot can exert against a completely full lift tanker (which should be worst case), but you can build some kind of reinforcing truss around the plumbing that takes up the loads.

As that truss gets wider, the individual loads on any of its connecting pins obviously go down.  So the question is whether they go down enough that a single subunit (i.e., plumbing, docking guides, and connecting pins) can support the worst-case torsion.  If not, then you need two subsystems, separated by as much distance as you can manage, and things are complicated.

However, in either case, I don't see a free-flyer helping out much, unless it's two connecting systems mounted on either end of a long truss.  And... that's just a kludge.

(Note:  If it's truly flying free, then it has propulsion.  Even if you want some fairly robust structure, you can deploy an awful lot of stuff from a payload bay.  Some kind of robot that walks end-over-end would probably do fine, and it's still vastly simpler than a true free flyer.  But even that is overkill.)

A quick summary:  We've talked about four different geometries (cheesy diagrams attached):

1) The old-timey tail-to-tail docking (apparently abandoned).

2) Dorsal-to-dorsal, nose-to-nose, aligned docking (what the most recent aspirational artwork showed).  No connectors shown, and this would require something that deployed. (Free flyer, walker, extender, something in a chine--who knows?  It's not my fave.)

3) Dorsal-to-dorsal nose-to-tail, overlapped docking.  This could be androgynous, but it can also have full plumbing coming out of one payload bay and a stub that just stabilizes things in the other.  (I think I've given up on this one.)

4) Dorsal-to-dorsal, noses in the same direction, but overlapped docking, with the payload bay of one close to the tail QD of the other.  In this case, the single grapple and the plumbing are all that's taking the torsional loads.

OTV Booster seems to be on Team #2.  I think edzieba and I are mostly on Team #4 (although we disagree on whether the torsional loads are a problem).  I used to like #3, but I think #4 does everything it does and is simpler, moments of inertia permitting.

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1398 on: 09/01/2022 11:33 pm »
RRM3 (Robotic Refueling Mission-3) Flex Hose Robotic Demonstration on ISS

« Last Edit: 09/01/2022 11:34 pm by LMT »

Online OTV Booster

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Re: Starship In-orbit refueling - Options and Discussion
« Reply #1399 on: 09/02/2022 02:03 am »
A 'free flyer' is a needless complexity. Since:
- an adapter will only ever do anything when right next to (and in contact with) a Starship
- is only ever needed when a Starship is transferring propellants to another Starship
- that situation (prop transfer) only ever needs to occur between a tanker and a depot, and a depot and a 'target' Starship
- any adapter (free flyer or not) needs to be launchable by a Starship or smaller vehicle
- therefor any adapter by definition can be launched by a Starship
You can eliminate all redundant free-flight hardware (power, propulsion, avionics, control, position sensing, etc) by attaching the adapter to a Starship, ideally the depot. That way the adapter is launched by the Depot Starship rather than by an entirely separate launch of its own, so the propellant 'cost' for the combined depot launch is lower overall than with a separate launch. If the 'free flight' adapter is intended to launch with the depot anyway, then it is a direct mass and complexity (and cost and development time) saving to eliminate the free flight capability and leave just the adapter attached.
IIRC, you expect that the two ships need little gap between them and the QD connection is the only connection needed. No other supports necessary. If I have this right, and your conjectures are correct, this can be a very simple system. While I very much respect the technical skill you bring to the table, I have to disagree. I'd be gobsmacked if it ends up that easy.


Gobsmacked, but not unhappy.

We're sorta re-litigating some stuff, but this is ultimately about torsional load.  I doubt that a single set of bellows hoses will support the torques that an almost-full depot can exert against a completely full lift tanker (which should be worst case), but you can build some kind of reinforcing truss around the plumbing that takes up the loads.

As that truss gets wider, the individual loads on any of its connecting pins obviously go down.  So the question is whether they go down enough that a single subunit (i.e., plumbing, docking guides, and connecting pins) can support the worst-case torsion.  If not, then you need two subsystems, separated by as much distance as you can manage, and things are complicated.

However, in either case, I don't see a free-flyer helping out much, unless it's two connecting systems mounted on either end of a long truss.  And... that's just a kludge.

(Note:  If it's truly flying free, then it has propulsion.  Even if you want some fairly robust structure, you can deploy an awful lot of stuff from a payload bay.  Some kind of robot that walks end-over-end would probably do fine, and it's still vastly simpler than a true free flyer.  But even that is overkill.)

A quick summary:  We've talked about four different geometries (cheesy diagrams attached):

1) The old-timey tail-to-tail docking (apparently abandoned).

2) Dorsal-to-dorsal, nose-to-nose, aligned docking (what the most recent aspirational artwork showed).  No connectors shown, and this would require something that deployed. (Free flyer, walker, extender, something in a chine--who knows?  It's not my fave.)

3) Dorsal-to-dorsal nose-to-tail, overlapped docking.  This could be androgynous, but it can also have full plumbing coming out of one payload bay and a stub that just stabilizes things in the other.  (I think I've given up on this one.)

4) Dorsal-to-dorsal, noses in the same direction, but overlapped docking, with the payload bay of one close to the tail QD of the other.  In this case, the single grapple and the plumbing are all that's taking the torsional loads.

OTV Booster seems to be on Team #2.  I think edzieba and I are mostly on Team #4 (although we disagree on whether the torsional loads are a problem).  I used to like #3, but I think #4 does everything it does and is simpler, moments of inertia permitting.
Yeah we've been down this road before but I now see something that confuses me more than usual.

Quote
I doubt that a single set of bellows hoses will support the torques that an almost-full depot can exert against a completely full lift tanker...
I don't think anybody is suggesting bellows hoses would be structural. They just carry fluid. Am I misunderstanding?
« Last Edit: 09/02/2022 02:03 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.

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