Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 818955 times)

Offline Norm38

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2640 on: 11/15/2024 08:38 pm »
We're not used to docking spacecraft where over half the mass is loose in the tanks.  That's not slosh, that's a couple of independent tsunamis in there.

The only predictable way to do this is get the ships on your fractional-g recipe ahead of time, never going into drift.  Align courses, and dock sideways, without ever dropping the acceleration.  And at that point, start moving fuel until done.

So the entire operation from before docking to after separation, is under this slight baseline acceleration (and the docking accelerations are lower)

Otherwise the effects of 100 ton propellant blobs hitting the sidewalls at random delays, off center, will be insane.

That's a useful concept.  Any LEO depot will need reboosting.  So refueling and reboost happen together.  The depot ends up full in a higher orbit.  The nearly empty tanker doesn't have much penalty heading back home.
If they don't need to go higher they can also do plane changes, phasing, whatever other orbital maneuvers the depot and tanker need to do.  Be creative.

Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2641 on: 11/15/2024 11:26 pm »
In no particular order

Atlas demonstrated disconnecting engines in-flight.

Why should we expect connecting engines will be easier than disconnecting them?

Why separate engines and tankage vs using on-orbit refilling?
I guess I wasn't clear. The assemblage of OTV and tanks would be the BEO depot rather than using an SS variation. It saves dry mass for missions to NRHO, LLO, mars and anywhere else a depot is needed other than LEO.

Okay, but...  same questions?

At most, the dry mass means you deliver 1-2 tonnes more propellant per engine removed. In reality it will be less, because some of those gains are lost to Oberth.

Seems like a lot of non-recurring R&D for a tiny benefit.
« Last Edit: 11/16/2024 02:17 am by Twark_Main »

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2642 on: 11/16/2024 05:50 pm »
In no particular order

Atlas demonstrated disconnecting engines in-flight.

Why should we expect connecting engines will be easier than disconnecting them?

Why separate engines and tankage vs using on-orbit refilling?
I guess I wasn't clear. The assemblage of OTV and tanks would be the BEO depot rather than using an SS variation. It saves dry mass for missions to NRHO, LLO, mars and anywhere else a depot is needed other than LEO.

Okay, but...  same questions?

At most, the dry mass means you deliver 1-2 tonnes more propellant per engine removed. In reality it will be less, because some of those gains are lost to Oberth.

Seems like a lot of non-recurring R&D for a tiny benefit.
That's 1-2 tons of propellant per engine that can be used for maneuvering. that's 5-10 tons if it replaces a 6 engine tanker and 8-16t if it has 9 engines.

The 1-2 tons is actually a lowball as the entire structure would be different. As cargo, the tanks won't have the stress of hauling propellant or supporting other structure through launch. No downcomer and the engine skirt wouldn't be having to support a full loaded SS through launch. Actually, on engine skirt needed. Think about all the stiffening that we can see and speculate on what might be there that we can't see.

There is a lot of dry mass that could go away and not hurt a depot. There is absolutely an R&D cost but ISTM, not much on the actual structure, assuming they don't want to bother wringing every gram out of it. SX has a lot of experience building stainless tanks by now - and a lot of knowledge from their highly entertaining 'not quite good enough' early tries.

Where the R&D needs to be is in the assembly. That where the novelty is.

Would it be worth it? IDK, but it is worth a look. How much dry mass can be cut? How much tankage can be reasonably assembled? How much R&D would be needed? These are some of the questions that translate into a go/no go.

RadMod keeps finding lunar scenarios where the current BLEO depot thinking is either very close or not quite sufficient. Early Mars missions can't depend on ISRU for return and will need propellant delivery. Once a tool is available new uses will be found. Especially if it cuts costs. These are the rest of the questions that play into a go/no go.


Edit: cleanup
« Last Edit: 11/16/2024 05:51 pm by OTV Booster »
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Online TheRadicalModerate

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2643 on: 11/20/2024 04:29 am »
Here's the new render for the depot/tanker docking.  We probably shouldn't read too much into this, but some things jumped out:

1) Kinda looks like the depot might not have RVacs, and they've been covered with some kind of insulation?

2) As we've suspected for a while, it looks like the QD is the plumbing connection between depot and tanker.  However, also as discussed, there's some kind of a spacer / gender-bender between the two QDs.  It's not possible to tell if it's launched that way or not.

3) Docking is... interesting.  Looks like two pairs of struts with piston shock absorbers, which slide into sockets.  I can't tell whether the struts are part of the depot or part of the tanker, although the former would make more sense, but the piston telescoping seems to argue for the other way around.  I don't understand the two thinner struts that surround the strut with the piston.  Could they be used to deploy the strut?

4) It'd be nice to know how long the struts are when undocked.  I assume fairly long, because making a perfect 4-point docking seems like it'll be hard without something to take out the inevitable misalignments.  Looks like the docking sockets could handle the struts sliding into place from someplace closer to the midline.

5) Doesn't seem to be any extra hardware for cryocooling, and it looks like they're going for Solar White on the depot.

Update:  Here's the tweet from SpaceX:

https://x.com/SpaceX/status/1858991247312212112
« Last Edit: 11/20/2024 04:34 am by TheRadicalModerate »

Online DanClemmensen

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2644 on: 11/20/2024 04:34 am »
Here's the new render for the depot/tanker docking.  We probably shouldn't read too much into this, but some things jumped out:

1) Kinda looks like the depot might not have RVacs, and they've been covered with some kind of insulation?

2) As we've suspected for a while, it looks like the QD is the plumbing connection between depot and tanker.  However, also as discussed, there's some kind of a spacer / gender-bender between the two QDs.  It's not possible to tell if it's launched that way or not.

3) Docking is... interesting.  Looks like two pairs of struts with piston shock absorbers, which slide into sockets.  I can't tell whether the struts are part of the depot or part of the tanker, although the former would make more sense, but the piston telescoping seems to argue for the other way around.  I don't understand the two thinner struts that surround the strut with the piston.  Could they be used to deploy the strut?

4) It'd be nice to know how long the struts are when undocked.  I assume fairly long, because making a perfect 4-point docking seems like it'll be hard without something to take out the inevitable misalignments.  Looks like the docking sockets could handle the struts sliding into place from someplace closer to the midline.

5) Doesn't seem to be any extra hardware for cryocooling, and it looks like they're going for Solar White on the depot.
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Online TheRadicalModerate

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2645 on: 11/20/2024 04:35 am »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.

Offline Asteroza

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2646 on: 11/20/2024 06:00 am »
Depot has a very HLS look to it too, as if it was just missing some HLS leg hardware.

Offline Riccardo11

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2647 on: 11/20/2024 07:45 am »
Have our Starbase spotters found any evidence of the beginning of the tanker's construction?

Offline mordroberon

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2648 on: 11/20/2024 02:06 pm »
Depot has a very HLS look to it too, as if it was just missing some HLS leg hardware.

They have a few similarities, need to reject solar radiation, and don't need to survive atmospheric re-entry

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2649 on: 11/20/2024 08:12 pm »
Here's the new render for the depot/tanker docking.  We probably shouldn't read too much into this, but some things jumped out:

1) Kinda looks like the depot might not have RVacs, and they've been covered with some kind of insulation?

2) As we've suspected for a while, it looks like the QD is the plumbing connection between depot and tanker.  However, also as discussed, there's some kind of a spacer / gender-bender between the two QDs.  It's not possible to tell if it's launched that way or not.

3) Docking is... interesting.  Looks like two pairs of struts with piston shock absorbers, which slide into sockets.  I can't tell whether the struts are part of the depot or part of the tanker, although the former would make more sense, but the piston telescoping seems to argue for the other way around.  I don't understand the two thinner struts that surround the strut with the piston.  Could they be used to deploy the strut?

4) It'd be nice to know how long the struts are when undocked.  I assume fairly long, because making a perfect 4-point docking seems like it'll be hard without something to take out the inevitable misalignments.  Looks like the docking sockets could handle the struts sliding into place from someplace closer to the midline.

5) Doesn't seem to be any extra hardware for cryocooling, and it looks like they're going for Solar White on the depot.

Update:  Here's the tweet from SpaceX:

https://x.com/SpaceX/status/1858991247312212112
Here's a closeup of the connecting struts.

A couple of things to note.
- The thin struts look as if they're also extendable.
- The fairings are not mirror images.

I can't make heads or tails of this if the struts deploy from the depot (top) as I also expected, but it makes sense if they deploy from the tanker (bottom).

Assume the big strut (spacer strut) has something like a ball joint at the base (tanker end). Assume the small struts are also on the tanker side with the top ends attached towards the far end of the spacer strut. These would be positioning struts.

All three struts would have pressure chambers on either side of its piston to allow movement in both extension and retraction. When working in concert the positioning struts would move the assembly through a fore & aft arc. When working differentially the positioning struts would move the assembly laterally. Once the strut is hooked to the depot the spacer strut would take over to set the inter ship spacing. Conceivably, all three struts working in concert after hookup would have mild micro control authority to position the ships to help other connection points that can't quite reach.

The fairings are interesting. The depot side is perfectly set up for a receiving socket and the tanker side fairing has nothing to do with the positioning strut. The strut misses it entirely.

Heres my speculation. After disconnect, the strut assembly lays down not quite flat on the tanker pointing aft and then its base joint, riding on a carrier, retracts into the fairing as far as it can. This is also its launch position.

One last speculation. Some wires may have been crossed somewhere in the art department. I see no advantage and many disadvantages in putting the struts on the tanker. The depot makes more sense.

Edit: cleanup & a brightened up image
« Last Edit: 11/20/2024 08:19 pm by OTV Booster »
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Online TheRadicalModerate

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2650 on: 11/20/2024 09:08 pm »
The fairings are interesting. The depot side is perfectly set up for a receiving socket and the tanker side fairing has nothing to do with the positioning strut. The strut misses it entirely.

Heres my speculation. After disconnect, the strut assembly lays down not quite flat on the tanker pointing aft and then its base joint, riding on a carrier, retracts into the fairing as far as it can. This is also its launch position.

One last speculation. Some wires may have been crossed somewhere in the art department. I see no advantage and many disadvantages in putting the struts on the tanker. The depot makes more sense.

I've been wondering if maybe the struts are depot equipment that's designed to drag along the dorsal side of the tanker/LSS, until they're captured by the sockets behind the fairings on the tanker.  That doesn't explain the two thin struts, though.  Maybe they're sensors?

Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2651 on: 11/21/2024 02:23 am »
The fairings are interesting. The depot side is perfectly set up for a receiving socket and the tanker side fairing has nothing to do with the positioning strut. The strut misses it entirely.

Heres my speculation. After disconnect, the strut assembly lays down not quite flat on the tanker pointing aft and then its base joint, riding on a carrier, retracts into the fairing as far as it can. This is also its launch position.

One last speculation. Some wires may have been crossed somewhere in the art department. I see no advantage and many disadvantages in putting the struts on the tanker. The depot makes more sense.

I've been wondering if maybe the struts are depot equipment that's designed to drag along the dorsal side of the tanker/LSS, until they're captured by the sockets behind the fairings on the tanker.  That doesn't explain the two thin struts, though.  Maybe they're sensors?
I've gotta sleep on that but my first reaction to dragging along the hull is a shudder. ISTM that physical contact between two bodies free to move with 6 degrees of freedom (boats, planes or spaceships) needs to be done with controlled care.


What would the thin struts be sensing that can't be picked up some other way more easily? I doubt they're curb feelers.
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Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2652 on: 11/22/2024 04:29 am »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.


This isn't our first rodeo. Old-timers like us should be well aware that when a render looks egregiously dumb like that, what inevitably happens is that Elon says.

"That? Oh yeah, that's dumb, we just do <thing that made sense all along>."

I trust that this pattern will prevail in this instance too.

Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2653 on: 11/22/2024 04:41 am »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.


This isn't our first rodeo. Old-timers like us should be well aware that when a render looks egregiously dumb like that, what inevitably happens is that Elon says.

"That? Oh yeah, that's dumb, we just do <thing that made sense all along>."

I trust that this pattern will prevail in this instance too.

Just to immediately contradict myself, the logic might be to put the "active" (and failure-prone) parts on the tanker to minimize risk.

If the complex moving struts and/or gender changer on the depot gets damaged, then you can kiss the entire depot (and any previous refilling flights) goodbye. All wasted effort now! However if the fragile active components are on the tanker instead, if there's a failure you just write off one tanker flight, and you get the hardware back for failure analysis. This could easily be more valuable than carrying a few extra tonnes of propellant per tanker.

When the hardware is iterated enough that it's proven to be 99+% reliable, then surely they'll swap components over to the depot. But for early mission, what's depicted in the render could make more sense (at least as an interim configuration).
« Last Edit: 11/22/2024 05:15 am by Twark_Main »

Online TheRadicalModerate

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2654 on: 11/22/2024 04:48 am »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.


This isn't our first rodeo. Old-timers like us should be well aware that when a render looks egregiously dumb like that, what inevitably happens is that Elon says.

"That? Oh yeah, that's dumb, we just do <thing that made sense all along>."

I trust that this pattern will prevail in this instance too.

Why would any graphic artist generate something that fanciful?  The fact that this stuff changes from concept to concept--and the level of detail increases--implies that somebody's basing the render off of some particular CAD model.  That doesn't mean that the CAD drawing isn't dumb and will be disavowed later on, but I doubt the art department is using the Rectal Extraction Technique to produce these.

Offline Twark_Main

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2655 on: 11/22/2024 04:57 am »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.


This isn't our first rodeo. Old-timers like us should be well aware that when a render looks egregiously dumb like that, what inevitably happens is that Elon says.

"That? Oh yeah, that's dumb, we just do <thing that made sense all along>."

I trust that this pattern will prevail in this instance too.

Why would any graphic artist generate something that fanciful?  The fact that this stuff changes from concept to concept--and the level of detail increases--implies that somebody's basing the render off of some particular CAD model.  That doesn't mean that the CAD drawing isn't dumb and will be disavowed later on, but I doubt the art department is using the Rectal Extraction Technique to produce these.

Go back in your memory and we can easily find additional "fanciful" design choices in renders past. That doesn't mean SpaceX doesn't eventually come around.

But also see my follow-up post above, where I offer one possible explanation for what we're seeing.
« Last Edit: 11/22/2024 05:02 am by Twark_Main »

Offline Greg Hullender

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2656 on: 11/22/2024 03:34 pm »
It really makes you want to have a small habitation module so you can have an engineer on site to do inspections and make repairs as needed.

Online meekGee

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2657 on: 11/22/2024 09:16 pm »
All of the docking hardware needs to be on Depot, not tanker, because Depot must be able to transfer propellant to other Ship types, notably HLS.

Yup, that's my reasoning as well.  But it doesn't look like that's what's happening.


This isn't our first rodeo. Old-timers like us should be well aware that when a render looks egregiously dumb like that, what inevitably happens is that Elon says.

"That? Oh yeah, that's dumb, we just do &lt;thing that made sense all along&gt;."

I trust that this pattern will prevail in this instance too.

Why would any graphic artist generate something that fanciful?  The fact that this stuff changes from concept to concept--and the level of detail increases--implies that somebody's basing the render off of some particular CAD model.  That doesn't mean that the CAD drawing isn't dumb and will be disavowed later on, but I doubt the art department is using the Rectal Extraction Technique to produce these.
Remember how a graphics artist revealed the lower center engine on the upcoming F9?

These guys artisify stuff that's given to them by the engineers, they directly communicate with them, receive feedback, etc.

It doesn't mean that they're not working off of an old revision or one of many design branches, but it's typically not someone's imagination.
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Offline OTV Booster

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2658 on: 11/23/2024 02:14 am »
About that strut hardware. It looks like a workable system, just on the wrong ship. I expect early depots to only support one campaign then be disposed of. A robust depot mounted strut system designed for a dozen or so uses would most likely have less mass penalty than a lighter built one on each tanker. YMMV.
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Offline Norm38

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Re: Starship On-orbit refueling - Options and Discussion
« Reply #2659 on: 11/23/2024 05:23 pm »
Any thoughts on what these details are up near the nose?  Looks to be above the top dome. Remember how big this thing is, could those be an airlock and cargo bay door?  Notice the indicator lights.

The only thing that seems to be missing are docking ports for a couple dragons. Maybe they’re on the other side.
That entire nose could be a hab. No need for a header tank there.
« Last Edit: 11/23/2024 05:25 pm by Norm38 »

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