Author Topic: Starship performance improvements  (Read 14457 times)

Offline Nevyn72

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Re: Starship performance improvements
« Reply #40 on: 11/26/2023 05:44 am »
Ok, I'll go out on a limb;

My prediction:
1) Starship will be lengthened by one ring segment (10 meters) (part of Version 2).
4) Tower ex8tension (allow the Chopstick's added length necessary to lift the lengthened Version-2 Starship up another 10 meters):
I don't think the word "meter" means what you think it means.

So I made a mistake in my previous statement. I didn't mean to say 1 ring segment, but rather a 10-meter increase in length (approximately 30 feet). I apologize for the confusion. It will require multiple rings to achieve this extension. However, increasing the length will affect the tower's capacity. My prediction is that the tower will need to be modified to accommodate this additional length. Please note that the 10-meter measurement is an approximation and not exact.  IMHO.  So, let's just wait and see, it's just my prediction, I will be wrong somewhere.

10 metres would be at least 5 standard rings...
How would you distribute them among the ships' sections?

Offline catdlr

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Re: Starship performance improvements
« Reply #41 on: 11/26/2023 07:19 am »
Ok, I'll go out on a limb;

My prediction:
1) Starship will be lengthened by one ring segment (10 meters) (part of Version 2).
4) Tower ex8tension (allow the Chopstick's added length necessary to lift the lengthened Version-2 Starship up another 10 meters):
I don't think the word "meter" means what you think it means.



So I made a mistake in my previous statement. I didn't mean to say 1 ring segment, but rather a 10-meter increase in length (approximately 30 feet). I apologize for the confusion. It will require multiple rings to achieve this extension. However, increasing the length will affect the tower's capacity. My prediction is that the tower will need to be modified to accommodate this additional length. Please note that the 10-meter measurement is an approximation and not exact.  IMHO.  So, let's just wait and see, it's just my prediction, I will be wrong somewhere.

10 meters would be at least 5 standard rings...
How would you distribute them among the ships' sections?

That's what I wanted members to start a discussion on. Elon mentioned a 5-10 meter increase. So that may be one ring section for each tank? As for the number of bands per ring section, 4-5??. Maybe he wants to also increase the payload on top of that.

Nevyn72, Good question, Let's hope some smart minds get together to start directing that in this thread.

Looks like the number of RVACs are being discussed here:
https://forum.nasaspaceflight.com/index.php?topic=59953.msg2544001#msg2544001

and here:
https://forum.nasaspaceflight.com/index.php?topic=58758.msg2544006#msg2544006
« Last Edit: 11/26/2023 07:48 am by catdlr »
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Offline Barley

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Re: Starship performance improvements
« Reply #42 on: 11/26/2023 04:53 pm »
Yes, as Brigantine said, roll control on single engine upper stages is controlled by RCS. But it works fine in this case because there's only one source of thrust and its alignment is always straight through the center of mass. With multiple fixed engines not thrusting through the center of mass (Raptor vacuum engines) but rather around the periphery, there will always be slight misalignments and a roll motion will be induced. This doesn't happen with single engine upper stage because the thrust always pointing through the center of mass. And relying of differential thrust as your only yaw and pitch control isn't optimal either since turbopump engines don't react as fast as a gimballing engine does.
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.



Offline eriblo

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Re: Starship performance improvements
« Reply #43 on: 11/26/2023 06:47 pm »
Yes, as Brigantine said, roll control on single engine upper stages is controlled by RCS. But it works fine in this case because there's only one source of thrust and its alignment is always straight through the center of mass. With multiple fixed engines not thrusting through the center of mass (Raptor vacuum engines) but rather around the periphery, there will always be slight misalignments and a roll motion will be induced. This doesn't happen with single engine upper stage because the thrust always pointing through the center of mass. And relying of differential thrust as your only yaw and pitch control isn't optimal either since turbopump engines don't react as fast as a gimballing engine does.
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.
Not really. The center of mass of the stage will follow a curve in 3D space as the propellant decreases. If the tanks are symmetric this curve will be close to a straight line. How many engines can you align with a line?
« Last Edit: 11/26/2023 06:49 pm by eriblo »

Offline Brigantine

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Re: Starship performance improvements
« Reply #44 on: 11/26/2023 09:31 pm »
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.
To clarify, I was considering roll only, assuming a single engine with TVC (e.g. F9 S2 MVac), vs n fixed RVacs.
TVC will put the thrust vector running straight through CoM, even if it is mounted with some misalignment

At present, the RVacs can be fixed, because the RCs with TVC are still part of the picture.

If you took an MVac and removed TVC, you would have pitch and yaw problems. But the roll problems would still be comparatively low, because the moment it isn't 'distance behind CoM' x angular misalignment x thrust, it's only 'positional misalignment' x angular misalignment x thrust. (a single engine is nominally positioned right on the roll axis)
« Last Edit: 11/26/2023 09:36 pm by Brigantine »

Offline catdlr

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Re: Starship performance improvements
« Reply #45 on: 11/26/2023 11:26 pm »
Cross post from https://forum.nasaspaceflight.com/index.php?topic=59871.msg2544151#msg2544151

Scott on his viewpoint on IFT-2 starship second stage starting at 11:00 ending at 15:00 (after reporting all the other worldwide launches, IFT-2 first stage, and hot stagging)

« Last Edit: 11/27/2023 01:06 am by catdlr »
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Offline Jim

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Re: Starship performance improvements
« Reply #46 on: 11/27/2023 01:20 am »
Yes, as Brigantine said, roll control on single engine upper stages is controlled by RCS. But it works fine in this case because there's only one source of thrust and its alignment is always straight through the center of mass. With multiple fixed engines not thrusting through the center of mass (Raptor vacuum engines) but rather around the periphery, there will always be slight misalignments and a roll motion will be induced. This doesn't happen with single engine upper stage because the thrust always pointing through the center of mass. And relying of differential thrust as your only yaw and pitch control isn't optimal either since turbopump engines don't react as fast as a gimballing engine does.
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.


A single engine has to be able to gimbal.



« Last Edit: 11/27/2023 01:20 am by Jim »

Online chopsticks

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Re: Starship performance improvements
« Reply #47 on: 11/27/2023 03:07 am »
Yes, as Brigantine said, roll control on single engine upper stages is controlled by RCS. But it works fine in this case because there's only one source of thrust and its alignment is always straight through the center of mass. With multiple fixed engines not thrusting through the center of mass (Raptor vacuum engines) but rather around the periphery, there will always be slight misalignments and a roll motion will be induced. This doesn't happen with single engine upper stage because the thrust always pointing through the center of mass. And relying of differential thrust as your only yaw and pitch control isn't optimal either since turbopump engines don't react as fast as a gimballing engine does.
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.
No, I'm also assuming imperfect alignment on a single engine as well. But it doesn't matter because the single point of thrust (gimballing) is always going to be pointing through the COM and no roll motion will be imparted.

Offline Twark_Main

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Re: Starship performance improvements
« Reply #48 on: 11/27/2023 04:05 am »
Yes, as Brigantine said, roll control on single engine upper stages is controlled by RCS. But it works fine in this case because there's only one source of thrust and its alignment is always straight through the center of mass. With multiple fixed engines not thrusting through the center of mass (Raptor vacuum engines) but rather around the periphery, there will always be slight misalignments and a roll motion will be induced. This doesn't happen with single engine upper stage because the thrust always pointing through the center of mass. And relying of differential thrust as your only yaw and pitch control isn't optimal either since turbopump engines don't react as fast as a gimballing engine does.
Your assuming perfect alignment for a single engine, but imperfect alignment for multiple engines.  Something is wrong with that picture.
No, I'm also assuming imperfect alignment on a single engine as well. But it doesn't matter because the single point of thrust (gimballing) is always going to be pointing through the COM and no roll motion will be imparted.


This assumes exactly zero angular momentum ("swirl") in the exhaust plume gases, which generally is not a valid assumption.
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Online chopsticks

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Re: Starship performance improvements
« Reply #49 on: 11/27/2023 04:12 am »
Sorry, I should have said minimal then. I think you knew what I meant.

Online chopsticks

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Re: Starship performance improvements
« Reply #50 on: 11/27/2023 04:14 am »
Point is, whatever roll motion imparted by a single engine is going to much less than multiple engines mounted at the periphery.

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