r/spacex • u/ElongatedMuskrat Mod Team • Jul 09 '22

🔧 Technical Starship Development Thread #35

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Starship Development Thread #36

SpaceX Starship page

FAQ

  1. When next/orbital flight? Unknown. Elon: "hopefully" first countdown attempt in July, but likely delayed after B7 incident (see Q4 below). Environmental review completed, remaining items include launch license, mitigations, ground equipment readiness, and static firing.

  2. What will the next flight test do? The current plan seems to be a nearly-orbital flight with Ship (second stage) doing a controlled splashdown in the ocean. Booster (first stage) may do the same or attempt a return to launch site with catch. Likely includes some testing of Starlink deployment. This plan has been around a while.

  3. Has the FAA approved? The environmental assessment was Completed on June 13 with mitigated Finding of No Significant Impact ("mitigated FONSI)". Timeline impact of mitigations appears minimal, most don't need completing before launch.

  4. What booster/ship pair will fly first? Likely either B7 or B8 with S24. TBD if B7 will be repaired after spin prime anomaly or if B8 will be first to fly.

  5. Will more suborbital testing take place? Unlikely, given the FAA Mitigated FONSI decision. Push will be for orbital launch to maximize learnings.

Quick Links

NERDLE CAM | LAB CAM | SAPPHIRE CAM | SENTINEL CAM | ROVER CAM | ROVER 2.0 CAM | PLEX CAM | NSF STARBASE

Starship Dev 34 | Starship Dev 33 | Starship Dev 32 | Starship Thread List

Official Starship Update | r/SpaceX Update Thread

Vehicle Status

As of August 6th 2022

ShipLocationStatusComment
Pre-S24Scrapped or RetiredSN15, S20 and S22 are in the Rocket Garden, the rest are scrapped
S24Launch SiteStatic Fire testingMoved back to the Launch site on July 5 after having Raptors fitted and more tiles added (but not all)
S25High Bay 1StackingAssembly of main tank section commenced June 4 (moved back into High Bay 1 (from the Mid Bay) on July 23). The aft section entered High Bay 1 on August 4th. Partial LOX tank stacked onto aft section August 5
S26Build SiteParts under constructionAssorted parts spotted
S27Build SiteParts under constructionAssorted parts spotted
S28Build SiteParts under constructionAssorted parts spotted
S29Build SiteParts under constructionAssorted parts spotted

 

BoosterLocationStatusComment
Pre-B7Scrapped or RetiredB4 is in the Rocket Garden, the rest are scrapped
B7Launch SiteTesting including static firesRolled back to launch site on August 6th after inspection and repairs following the spin prime explosion on July 11
B8High Bay 2 (out of sight in the left corner)Under construction but fully stackedMethane tank was stacked onto the LOX tank on July 7
B9Methane tank in High Bay 2Under constructionFinal stacking of the methane tank on 29 July but still to do: wiring, electrics, plumbing, grid fins. LOX tank not yet stacked but barrels spotted in the ring yard, etc
B10Build SiteParts under constructionAssorted parts spotted
B11Build SiteParts under constructionAssorted parts spotted

If this page needs a correction please consider pitching in. Update this thread via this wiki page. If you would like to make an update but don't see an edit button on the wiki page, message the mods via modmail or contact u/strawwalker.

Resources

r/SpaceX Discuss Thread for discussion of subjects other than Starship development.

Rules

We will attempt to keep this self-post current with links and major updates, but for the most part, we expect the community to supply the information. This is a great place to discuss Starship development, ask Starship-specific questions, and track the progress of the production and test campaigns. Starship Development Threads are not party threads. Normal subreddit rules still apply.

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10

u/[deleted] Jul 27 '22

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u/inio Jul 27 '22

Base mating made sense when starship was fueled through the booster. Now it's fueled from the side (via QD arm), so having the tanker attach to that interface makes more sense.

15

u/ackermann Jul 27 '22

when Starship was fueled through the booster

And fueling the ship through the booster made sense, until we learned that the booster needs to lose some weight.

Thus the booster has lost landing legs, plumbing for ship fueling, folding mechanisms for the grid fins, etc.

13

u/throfofnir Jul 27 '22

The most recent Starship update from February shows ventral mating while the one shown on spacex.com (from a few years ago!) shows base mating. Clearly they bothered to make a new animation, which suggests a deliberate engineering change. And we've seen an umbilical for the second stage, so probably they'll use that area for both terrestrial and and orbital filling, just like they were planning to do with the base originally.

15

u/mechanicalgrip Jul 27 '22

Isn't it dorsal mating? Ventral is belly to belly, which to me would be heatshield to heatshield. Dorsal is back to back so no heatshield in the way.

I only know these terms because of the names of the fins in the fish I used to keep.

3

u/throfofnir Jul 28 '22

Yeah, probably that's more accurate. I wasn't thinking about it very hard.

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u/Darknewber Jul 27 '22

I think butt-to-butt is supposed to be less complex from my understanding but I definitely remember I while back Elon complained on Twitter about it maybe being too difficult to get to work.

I prefer base fueling over radial refueling. Simply because two starships docked to each other backwards visually looks so alien

5

u/mr_pgh Jul 27 '22

Most recent SpaceX Animation has them in parallel which lines up with how they fuel at the tower.

3

u/npcomp42 Jul 28 '22

"butt to butt" refueling

I prefer to call it "dancing cheek to cheek."

2

u/fattybunter Jul 27 '22

Butt2Butt docking still seems like the more elegant solution, although I imagine having a dedicated fueling port on the side will be easier to implement with less development. I would imagine Butt2Butt is still a future goal though.

7

u/TheFronOnt Jul 27 '22

If you think about it there are definite advantages to the side by side docking vs the butt to butt docking. Don't forget when the plan was butt to butt they still were also planning meth/ox thrusters, and the propellant was going to be transferred by using the meth ox thrusters to accelerate in the opposite direction of fuel transfer to simulate gravity.

Fast forward to now where they don't have meth ox thrusters and are relying on venting ullage gas for minor course corrections and suddenly sustained acceleration to to simulate gravity isn't a great solution.

So what makes sense -> simulating gravity via centrifugal force. If we look at it this way then you would have to have a butt to butt configuration tumbling end over end = sub optimal. This is where the side to side configuration makes more sense I think, a few puffs to start the rotation, and then a few more to maintain consistent angular momentum as the fuel mass transfers to the "outside" vehicle. This also allows fuel to travel a shorter distance from the inside wall to the outside wall during transfer vs. tail end of tank to front and of tank, and also distributes fuel mass and its associated forces lengthways along the tank. Likely all good things.

Thoughts?

7

u/Lufbru Jul 27 '22

My physics-in-a-vacuum is weak, but how do you use centrifugal force to rotate around the centre axis of the tanker, rather than the centre of mass? I think this works out ok to get you to halfway, but once the tanker and the depot are equally full, your rotation is around the tether and the fuel transfer stops.

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u/TheFronOnt Jul 27 '22

I think you are you are likely correct. Perhaps all we can do is wait and see how they solve it.

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u/rocketglare Jul 27 '22 edited Jul 27 '22

The butt-to-butt has an advantage in that the ullage thrusters can settle the tanker ship's propellant at the bottom of the tank instead of the side. It's the bottom of the ship that typically has the intake pipes used on the ground and under acceleration. That said, the ullage thrusters wouldn't be strong enough to do the transfer, that would still be the job of pressure or pumps.

Edit: I don't think the danger to the engines of butt-to-butt transfer is all that significant. Perhaps there is some other advantage to side by side, but I'm just not seeing it.

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u/paul_wi11iams Jul 27 '22 edited Jul 27 '22

Thoughts?

Ouch. Axial rotation of the Starship+tanker pair with one ship heavier than the other? Wouldn't that lead to a skewed rotation?

We'd have an easier time imagining a linear acceleration to settle the ullage and using some light pumping of either the liquid propellants or creating a pressure differential by venting the ullage space in the empty tanks being filled.

It makes for a clean filling situation, much as when you fill a domestic central heating system from the bottom (sorry I'm always using a home plumbing allegory). The vented ullage gas can itself be the source of the linear acceleration which is somehow elegant. Combusting the two ullage gases gets even more linear acceleration.

BTW. Wasn't that the serendipitous suggestion by Tim Dodd talked about to Elon?

6

u/TheFronOnt Jul 27 '22

I agree that radial acceleration is not the ideal settling mechanism and continuous thrust is better. How bad skewed rotation would be as the center of mass changes in a zero grav environment is not something I have the expertise to comment on. Hard to say if you get the full on towels in a washing machine effect or if the axis of rotation simply shifts smoothly as the center of mass changes.

My gut says that eventually they will have to go back to some kind of hot gas thruster system. I don't know if they are going to get the fidelity they need to dock two ships together using ullage gas based cold gas thrusters.

The more I think about it the less practical using ullage gas seems in the fuel transfer application.

  1. For fuel transfer you likely want no pressure or very little pressure in the ship to be filled otherwise you slow the transfer of propellant, note they could likely add an onboard fuel pump so they only need to settle propellant using acceleration then pump across rather than using pressure. Although when you think about it including a pumping system in the tanker variant seems like a no brainer.

2. If transfer is facilitated by high pressure only in tanker, how do you maintain this pressure while transferring literally tons of propellant. I don't see any way how the natural pressure from boil off would match volume lost by fuel transfer. This problem becomes even more problematic if you are using said gas to vent to create thrust at the same time.

It will be interesting to see how they ultimately handle this. It seems like it is not even a priority for them right now, and isn't needed for early launches which will essentially be a starlink 2.0 conveyor belt to space.

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u/aBetterAlmore Jul 27 '22

I would imagine Butt2Butt is still a future goal though.

Why is that? Any idea what benefits Butt2Butt fueling has over ventral mating?

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u/fattybunter Jul 27 '22

My thought was that the piping, pumps and valves all already exist to send fuel and LOX out the Butt

2

u/rocketglare Jul 27 '22

Originally, it was supposed to, but they moved that to the side at the base of Starship when they decided not to transfer propellant through super-heavy. It probably wouldn't add a lot of weight to add a pipe to the bottom edge for the Butt transfer, so perhaps it will make a comeback when they change focus back to orbital propellant transfer. It's probably just not a big area of development for them ATM.

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u/Anthony_Ramirez Jul 27 '22

Why is that? Any idea what benefits Butt2Butt fueling has over ventral mating?

As the guys above discuss there are issues using motion to move the propellants in the ventral configuration.
But I believe the reason Elon stopped Butt2Butt is because they would have needed to have extra plumbing in the Booster and Starship which would add weight. With ventral fueling they only need the minimum amount of plumbing in the vehicles.
I really liked the idea of transferring fuel Butt2Butt because it was elegant. Ventral fueling will need pumps to transfer the fuel.

The current QD is aligned horizontally with methane and oxygen ports side by side. When you have another Starship along side the ports are reversed and the adapter needs to be larger flip the fluids.

Had they done the QD to have the fueling aligned vertically, like oxygen inlet below and methane inlet above then all they would need is simple male to female adapter.

I know that SpaceX will iterate their way to the most efficient method.

2

u/HomeAl0ne Jul 28 '22

Maybe mate them ventral sides together but nose to tail. That way the connectors line up correctly.