Author Topic: Starship On-orbit refueling - Options and Discussion  (Read 630332 times)

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4532
  • Tampa, FL
  • Liked: 3378
  • Likes Given: 649
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2520 on: 04/02/2024 09:41 pm »
...The lowest viable SSO is 274 x 274 x 97.7°, and you want to launch from Kodiak.  So our delta-v budget is:

+475m/s to cover launching against Earth's rotation, plus azimuth changes (again, spreadsheet hacking involved)


...That swing from a 408m/s rotational advantage to a 475m/s disadvantage...

Are you sure you're not counting the same penalty twice?  What's the difference between the "launching against Earth's rotation" penalty and the "azimuth" penalty?

At 57.4° latitude, Kodiak's pure eastward velocity is only 250 m/s. Solving for azimuth via cos(inclination) = cos(latitude) × sin(azimuth), the launch azimuth is 194.1°. Sine of 194.1° is -0.24, so the downrange component of that eastward velocity is only 250 m/s × -0.24 = -61 m/s.


That's a far cry from -475 m/s.  Why the discrepancy I wonder?

Crap.  I did indeed double-count, but it's still 474m/s more, which puts the prop to orbit using unstretched tanks at 95.6t.  Spreadsheet screenshot for the azimuths and delta-v attached, and the real sheet's available here.

Two things you have wrong:

1) You left out the fact that, from LC-39A due east, you get 408m/s, so the LC-39A launch site starts with a 408-250=158m/s advantage over Kodiak

2) The eastward component is orbitalSpeed*sin(azimuth) - 250, not 250*sin(azimuth).  Then you have the big south/north component, which doesn't exist at all if you're launching to 28.6º from the Cape.

Update:  More accounting problems.  You got the right total answer for how much it costs beyond inertial orbital speed to launch from Kodiak, and I'm too stupid to figure out why.  But the way you did it, you still have to add in the whole 408m/s advantage you get from the Cape, which takes you to 474m/s more delta-v from Kodiak.  (We have minor geodetic differences, because I used average radius for equatorial speed, rather than equatorial radius.)

Update to the update:  It may just be a coincidence that you got close the right answer.  Even with our geodetic differences, you're still off by about 5m/s.  There may be an algebraic invariance lurking in here somewhere, but I can't find it.  I had the link up-thread, but here's the algorithm I'm using.

Note that this is still an approximation, because it assumes, even after biasing by however much the SuperHeavy provided to get you above most of the air and going mostly downrange, that there's no gravity drag incurred by the second stage.  So the actual azimuth and delta-v requirements will be somewhat different, but it's a decent apples-to-apples comparison of the delta-v budgets.

Also note that the true, rotationally-adjusted azimuth is a bit different from the inertial azimuth.  Doesn't really matter in the delta-v computation, but it'll be arctan(eastWestComponent/northSouthComponent).

(Update: Fixed southerly true azimuth computation.  Those pesky reflections!)
« Last Edit: 04/02/2024 10:37 pm by TheRadicalModerate »

Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4532
  • Tampa, FL
  • Liked: 3378
  • Likes Given: 649
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2521 on: 04/02/2024 10:04 pm »
Yow.

OK, thanks for putting so much effort into making that very clear.

Cheers, Martin

Per Twark, I made a double-counting mistake, which reduces but doesn't eliminate the horribleness.  See above.

Offline Greg Hullender

  • Full Member
  • ****
  • Posts: 621
  • Seattle
    • Rocket Stack Rank
  • Liked: 450
  • Likes Given: 343
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2522 on: 05/04/2024 06:09 pm »
NASA lays out how SpaceX will refuel Starships in low-Earth orbit, Ars Technica, 4/29/2024, 5:19 PM.

It's not a long read, but here are some highlights:

Quote
Right now, SpaceX is scheduled to attempt the first demonstration of a large-scale propellant transfer between two Starships in orbit next year. [Calendar 2025]
It was news to me that this is actually scheduled.

Quote
During these upcoming Starship test flights, engineers will measure the slosh of propellants inside the ship, along with tank pressures, and observe how the fluids respond to impulses from small thrusters. In microgravity, these small rocket jets provide "settling thrust" to guide the ship's liquid toward the outflow needed for refueling.
Everyone was pretty sure they'd use ullage engines, but this is the first time I've seen that confirmed.

Quote
Engineers will also monitor the boil-off rates of the methane and liquid oxygen in space. Over time, cryogenic liquids transition to a gaseous state without insulation or other measures to prevent boil-off. SpaceX and NASA officials want to know how much of the propellant will be lost from boil-off to know how many refueling tankers they need to launch for a Starship lunar landing mission.
Everyone was pretty sure they'd have to research boil-off mitigation, but, again, it's nice to see it confirmed.



Quote
Both ships involved in the refueling demo will also have thermal insulation and vacuum jacketing around internal plumbing to limit boil-off.
So neither will be a "vanilla" Starship--whatever that means. :-)

Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.

Quote
Computer models and flight data from numerous rockets show it is possible to gain control over cryogenic boil-off, tank pressures, and propellant settling in space. But no one has ever attempted to flow cryogenic propellants from one spacecraft to another in orbit.

"In my mind, all the technical issues associated with cryo transfer in space are solved," said George Sowers, former chief scientist at SpaceX rival United Launch Alliance and a longtime proponent of depoting propellants in space. "It’s just a matter of demonstrating it and fine-tuning the technology and the procedures. So, I think we’re on the cusp. I’m happy to see SpaceX taking the steps to make it work.
This is an optimistic take that I'd definitely like to believe!

Quote
Once the two Starships come together, they will connect using the same ports SpaceX uses to load propellants on the launch pad. Then, SpaceX will fine-tune tank pressures and fire propellant settling thrusters. "At that point, they'll open up and let the propellant flow."

The propellants will flow from one vehicle to the other using a pressure differential, or "delta," between the donor tank and the recipient tank. This is a simpler solution than relying on pumps.

"The fundamental flow mechanism is because of the pressure delta across the umbilical," Kshatriya said.
(Emphasis mine.) This point has been debated here a few times. Nice to know what they're actually doing--to start with, anyway.

Quote
The results of this refueling demonstration will allow SpaceX and NASA engineers to calculate how many refueling tankers they will need to fill up a Starship heading for the Moon. SpaceX's current estimate is approximately 10 refueling launches for one Artemis landing mission, but there are error bars on each side of this number.
This is pretty much the same number everyone here has come up with.


Offline TheRadicalModerate

  • Senior Member
  • *****
  • Posts: 4532
  • Tampa, FL
  • Liked: 3378
  • Likes Given: 649
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2523 on: 05/04/2024 09:02 pm »
Everyone was pretty sure they'd use ullage engines, but this is the first time I've seen that confirmed.

This is a nit, but let's avoid the term "ullage engines".  It's ambiguous, because it's not clear if it's referring to "ullage" in terms of a settling thruster (as you seem to be using it), or if it's referring to an engine being driven off of ullage gases.  Both are in play in this discussion.

Quote
Quote
Both ships involved in the refueling demo will also have thermal insulation and vacuum jacketing around internal plumbing to limit boil-off.
So neither will be a "vanilla" Starship--whatever that means. :-)

Not necessarily true.  "Internal plumbing" isn't the same as full tankage insulation.  It may make sense just to make all the QD connections insulated for all cases and have done with it. 

Even a vanilla Starship will need to receive prop from a depot.  The problem is that a substantial amount of prop will be boiled off as the transfer plumbing chills down.  If you can maintain that plumbing in a nominally cold state, it'll reduce losses by quite a bit.

On the other hand, a Starlink / pez-dispenser Starship won't ever receive prop.  That might be the special case.

Re: Starship On-orbit refueling - Options and Discussion
« Reply #2524 on: 05/04/2024 09:28 pm »
Would someone please help?
Afaik, a simple sunshade would allow all of any depot to radiate to outer space at near 0 degrees K.
Where is the heat to be managed coming from?

Offline eriblo

  • Full Member
  • ****
  • Posts: 1414
  • Sweden
  • Liked: 1704
  • Likes Given: 278
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2525 on: 05/04/2024 09:32 pm »
Would someone please help?
Afaik, a simple sunshade would allow all of any depot to radiate to outer space at near 0 degrees K.
Where is the heat to be managed coming from?
Earth.

Offline Bob Shaw

  • Full Member
  • ****
  • Posts: 1435
  • Liked: 733
  • Likes Given: 676
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2526 on: 05/04/2024 10:10 pm »
Both Earth and the Moon are substantial re-radiators of heat from the Sun. India’s first Lunar orbiter was, IIRC, damaged by heat from the Moon on daylight passes. As well as protecting from the Sun there will need to be protection from other parts of the spacecraft operating environment.

Offline Greg Hullender

  • Full Member
  • ****
  • Posts: 621
  • Seattle
    • Rocket Stack Rank
  • Liked: 450
  • Likes Given: 343
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2527 on: 05/05/2024 05:50 pm »
This is a nit, but let's avoid the term "ullage engines". 
Fair enough. I'd still like to know what kind of settling engines they're going to use. If it's cold gas, they may end up using up a significant fraction of the propellants.

Quote
"Internal plumbing" isn't the same as full tankage insulation.  It may make sense just to make all the QD connections insulated for all cases and have done with it. 

Even a vanilla Starship will need to receive prop from a depot.  The problem is that a substantial amount of prop will be boiled off as the transfer plumbing chills down.  If you can maintain that plumbing in a nominally cold state, it'll reduce losses by quite a bit.

On the other hand, a Starlink / pez-dispenser Starship won't ever receive prop.  That might be the special case.
Could be. I wonder what sort of insulation they have in mind and how much mass we're talking about.

It's also interesting that they didn't talk about a) Solar White (or other) coating on the depot to reduce solar heating and b) heatshield between depot and the Earth to reduce heating from the Earth.

I keep thinking that is a) is good enough then you could focus on b) and not worry about the sun except to the extent that it reflects off the heat shield and gives the depot a double-whammy of insolation. That is, the depot would orbit the Earth, rotating once per orbit such that the depot was always tangent to its orbit. (That is, it always points in the direction it's going.) That should give you the minimum footprint for a heatshield (just slightly larger than the depot itself). The only problem I see (if it is a problem) is that sometimes the sun will shine "under" the depot, reflect off the back of the heat shield, and roast the depot.

Anyway, the article doesn't talk about either issue. I just hope SpaceX has it figured out! :-)


Offline Greg Hullender

  • Full Member
  • ****
  • Posts: 621
  • Seattle
    • Rocket Stack Rank
  • Liked: 450
  • Likes Given: 343
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2528 on: 05/05/2024 05:54 pm »
Both Earth and the Moon are substantial re-radiators of heat from the Sun. India’s first Lunar orbiter was, IIRC, damaged by heat from the Moon on daylight passes. As well as protecting from the Sun there will need to be protection from other parts of the spacecraft operating environment.
Just to clarify, in case Etudiant gets confused: the moon is only a problem if you're close to it. Obviously a depot in low-Earth-Orbit won't need a moon shade, and a depot orbiting the moon wouldn't need an Earth shade.

Offline Jim

  • Night Gator
  • Senior Member
  • *****
  • Posts: 37647
  • Cape Canaveral Spaceport
  • Liked: 21727
  • Likes Given: 429
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2529 on: 05/05/2024 08:32 pm »
This is a nit, but let's avoid the term "ullage engines". 
Fair enough. I'd still like to know what kind of settling engines they're going to use. If it's cold gas, they may end up using up a significant fraction of the propellants.


It is only needed during the actual transfer.  Also, there will be a lot of gas generated during the transfer ops.

Offline Greg Hullender

  • Full Member
  • ****
  • Posts: 621
  • Seattle
    • Rocket Stack Rank
  • Liked: 450
  • Likes Given: 343
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2530 on: 05/06/2024 12:05 am »
It is only needed during the actual transfer.  Also, there will be a lot of gas generated during the transfer ops.
Sure, but the question is "how long will the transfer take?"

Offline Thrustpuzzle

  • Member
  • Posts: 79
  • Liked: 155
  • Likes Given: 341
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2531 on: 05/06/2024 04:47 am »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.

Offline tyrred

  • Full Member
  • ****
  • Posts: 928
  • Seattle
  • Liked: 756
  • Likes Given: 21208
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2532 on: 05/06/2024 06:51 am »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.

Dorsal or ventral?

Offline Twark_Main

  • Senior Member
  • *****
  • Posts: 3767
  • Technically, we ALL live in space
  • Liked: 1950
  • Likes Given: 1220
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2533 on: 05/06/2024 08:47 am »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.

Dorsal or ventral?

Dorsal = back.  Ventral = belly.

Offline eriblo

  • Full Member
  • ****
  • Posts: 1414
  • Sweden
  • Liked: 1704
  • Likes Given: 278
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2534 on: 05/06/2024 10:21 am »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.
Dorsal or ventral?
Dorsal = back.  Ventral = belly.
Yes, belly to belly is wrong but it is also better at describing the concept to a layman than back to back which is ambiguous in English (likely due to human bipedalism).

Offline InterestedEngineer

  • Senior Member
  • *****
  • Posts: 2437
  • Seattle
  • Liked: 1845
  • Likes Given: 3042
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2535 on: 05/06/2024 03:55 pm »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.
Dorsal or ventral?
Dorsal = back.  Ventral = belly.
Yes, belly to belly is wrong but it is also better at describing the concept to a layman than back to back which is ambiguous in English (likely due to human bipedalism).

English has no problem with back to back, it's in lots of sword fighting movies

https://hinative.com/questions/19556164

Offline Twark_Main

  • Senior Member
  • *****
  • Posts: 3767
  • Technically, we ALL live in space
  • Liked: 1950
  • Likes Given: 1220
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2536 on: 05/06/2024 05:33 pm »
Quote
The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet.
Again, no surprise, but nice to see confirmation.
The Ars Technica article is wrong. The mating will be back to back. Belly to belly would be significantly complicated by all the plumbing and docking hardware that would have to penetrate the heat tiles covering the bellies.
Dorsal or ventral?
Dorsal = back.  Ventral = belly.
Yes, belly to belly is wrong but it is also better at describing the concept to a layman than back to back which is ambiguous in English (likely due to human bipedalism).

"Dorsal" is from Latin "dorsum" meaning... back. "Ventral" is from Latin "venter" meaning... belly or abdomen.   ???

#LatinMakesTheSameWordsFancy   ::)
« Last Edit: 05/06/2024 06:14 pm by Twark_Main »

Online notthebobo

  • Member
  • Posts: 11
  • Liked: 17
  • Likes Given: 66
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2537 on: 05/06/2024 05:42 pm »
My apologies for the non-technical reference, but all the back-to-back and belly-to-belly talk is begging for this soundtrack.



The old timers may appreciate the reference and the younger crowd will benefit from learning it :)

Offline Twark_Main

  • Senior Member
  • *****
  • Posts: 3767
  • Technically, we ALL live in space
  • Liked: 1950
  • Likes Given: 1220
Re: Starship On-orbit refueling - Options and Discussion
« Reply #2538 on: 05/06/2024 06:15 pm »
My apologies for the non-technical reference, but all the back-to-back and belly-to-belly talk is begging for this soundtrack.

[snip]

The old timers may appreciate the reference and the younger crowd will benefit from learning it :)

Didn't even click the link, but I know which one.  ;)

As someone whose jukebox brain has had that song running around since last night, thanks for democratizing the pain!  ;D



Anyway, if we really want to eliminate ambiguity we should determine the official Starship coordinate system (per signage spotted by ring watchers), not substitute no-less-ambiguous Latin synonyms. Then we can just say "+Z side" or "-Z side," or whatever it turns out to be.

https://forum.nasaspaceflight.com/index.php?topic=39215.0

Falcon coordinate system attached for reference.

« Last Edit: 05/06/2024 06:36 pm by Twark_Main »

Offline mikelepage

  • Full Member
  • ****
  • Posts: 1241
  • ExodusSpaceSystems.com
  • Perth, Australia
  • Liked: 872
  • Likes Given: 1385
Re: Starship In-orbit refueling - Options and Discussion
« Reply #2539 on: 05/08/2024 08:19 am »
Just seeing the slide from the Ars Technica article above, it makes me think SpaceX must be deep in the weeds of designing the cryogenic fluid transfer systems by this point, but the recent presentation by Musk had virtually zero detail on this. I guess there's no need to give the competition any more information than absolutely necessary.

One question I have: I think we know that prop transfer will use the same QD port on starship as when it is on the pad, right? But these aren't androgynous. So doesn't that mean the two starships can't be perfectly aligned in their back-to-back configuration, as is depicted in all the artwork? (as this would put two "female" QD ports opposite each other).

Does that mean there will be a "male" QD port present on tanker and depot starships? And if so, where would you put this? You could build it into the existing port, but it might be easier when further forward, in the payload bay area of those starship variants. This could put the chaser starship (active navigation/passive docking/donating propellant) roughly half a length or more behind the target starship (passive navigation/active docking/receiving propellant).


Tags: HLS 
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1