Author Topic: SpaceX Starship/Super Heavy Engineering General Thread 4  (Read 1798968 times)

Offline InterestedEngineer

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4180 on: 11/29/2022 04:47 pm »
I have looked for this question/answer but I can't seem to find it.

Can SH fire all 33 engines without a full load of propellant or some added weight during a static fire?  That's a lot of up thrust on the clamps with a relatively light stage if not.  Just curious.

I don't think so.

The OLM (and its hold downs), need to be able to hold down 2,500t  (1.5x thrust/weight ratio) for launch with all 33 engines as part of normal operations.  That's 7,500t of thrust with 5,000t mass of fully fueled Starship+Booster.

the recent 14 engine Static fire IMHO likely tested about 20% margins on that number (~3,000t net thrust), which is about what one would expect for a margins test.

A fully fueled booster should weigh in at 3,600t (5,000-1,400). 

I doubt they would want to stress the OLM with 7,500 - 3,600 ~= 3,900t of net upwards force.  That would be 1.6x normal operational load.

For a full 33 engine static fire I think Starship will need to be on top and loaded with at least nitrogen close to capacity.

Offline su27k

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4181 on: 11/30/2022 01:33 am »
I have looked for this question/answer but I can't seem to find it.

Can SH fire all 33 engines without a full load of propellant or some added weight during a static fire?  That's a lot of up thrust on the clamps with a relatively light stage if not.  Just curious.

I think insider on reddit says it doesn't need Starship on top to do the 33 engines static fire, probably needs a full load of lox at least. Also there's an animation somewhere showing temporary struts can be added to each hold down clamp to strengthen them so that they can take more force during static fire, so it's likely SpaceX has thought about this and designed accordingly.

Offline edzieba

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4182 on: 11/30/2022 09:43 am »
For a full 33 engine static fire I think Starship will need to be on top and loaded with at least nitrogen close to capacity.
Or the tried-and-tested method from the Starship static fire campaigns: pile some rolls of steel on top.

Offline skyflyer81

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4183 on: 11/30/2022 03:02 pm »
Why is everyone assuming that they have to run all the engines at 100% throttle to prove they work?

Don't Raptor 2s throttle all the way down to 40%? I don't know if thrust/throttle is linear, but a back of napkin assumption is the 7500t thrust at 100% would be around 3000t thrust at 40% which wouldn't require any hold down at all.

I think I remember something about the outer 20 not throttling, I know they don't gimbal, but I can't find it.

Offline RoboGoofers

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4184 on: 11/30/2022 03:15 pm »
Why is everyone assuming that they have to run all the engines at 100% throttle to prove they work?

Don't Raptor 2s throttle all the way down to 40%? I don't know if thrust/throttle is linear, but a back of napkin assumption is the 7500t thrust at 100% would be around 3000t thrust at 40% which wouldn't require any hold down at all.

I think I remember something about the outer 20 not throttling, I know they don't gimbal, but I can't find it.
Can Raptors start up at 40%, though?

Online eriblo

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4185 on: 11/30/2022 03:21 pm »
Why is everyone assuming that they have to run all the engines at 100% throttle to prove they work?

Don't Raptor 2s throttle all the way down to 40%? I don't know if thrust/throttle is linear, but a back of napkin assumption is the 7500t thrust at 100% would be around 3000t thrust at 40% which wouldn't require any hold down at all.

I think I remember something about the outer 20 not throttling, I know they don't gimbal, but I can't find it.
That is outdated, all Raptor 2 SL engines are the same, the only difference is the gimbal or fixed mount and that they do not attach gimbal actuators to the outer ones.

The reason for the assumption of 100% thrust unless explicitly stated otherwise is that that is how they will be operated. The engines might have been tested individually but the whole booster has not so you do not necessary know how to extrapolate lower thrust performance to full throttle.

Offline InterestedEngineer

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4186 on: 11/30/2022 04:17 pm »
I have looked for this question/answer but I can't seem to find it.

Can SH fire all 33 engines without a full load of propellant or some added weight during a static fire?  That's a lot of up thrust on the clamps with a relatively light stage if not.  Just curious.

I think insider on reddit says it doesn't need Starship on top to do the 33 engines static fire, probably needs a full load of lox at least. Also there's an animation somewhere showing temporary struts can be added to each hold down clamp to strengthen them so that they can take more force during static fire, so it's likely SpaceX has thought about this and designed accordingly.

That's a hilariously wrong take.

You can add temporary struts to add to the hold down capabilities, but what got added to the booster?  One is pushing, one is pulling.

if you are going to stress something 3x beyond its required operating load there would be extra mass involved just for a test.

Anything added to the booster would add mass.   Very unlikely to happen.

Offline Grandpa to Two

Who says you have to static fire all the engines at once? If they do half and then the other half, if everything looks good then launch.
"All truths are easy to understand once they are discovered; the point is to discover them" Galileo Galilei

Offline AU1.52

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4188 on: 11/30/2022 08:57 pm »
Who says you have to static fire all the engines at once? If they do half and then the other half, if everything looks good then launch.


And they may have already static fired all but 1 of them. 7 + 14 + 11 = 32.

Offline DanClemmensen

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4189 on: 11/30/2022 09:22 pm »
Who says you have to static fire all the engines at once? If they do half and then the other half, if everything looks good then launch.
Static fires are for testing the system, not the individual engines or even the individual propellant flow paths. In the abstract some full-system anomalies may not show up in partial-system tests.

Online steveleach

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4190 on: 12/01/2022 08:15 am »
Who says you have to static fire all the engines at once? If they do half and then the other half, if everything looks good then launch.
Static fires are for testing the system, not the individual engines or even the individual propellant flow paths. In the abstract some full-system anomalies may not show up in partial-system tests.
You make it sound like a binary thing: test everything together, or not. I don't think it is as simple as that.

As a trivial example, they presumably won't test all the engines at the same time as testing the hold-down clamp release mechanisms, because that would result in an actual launch.

They will test the things that can they can practically test, and take a risk on the rest.

The best test would be all 33 engines to 100% thrust, with a Starship stacked on top of the booster. And if that test is looking good, why not just release the hold-down clamps and let it go to orbit?

Offline DanClemmensen

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4191 on: 12/01/2022 02:55 pm »
Who says you have to static fire all the engines at once? If they do half and then the other half, if everything looks good then launch.
Static fires are for testing the system, not the individual engines or even the individual propellant flow paths. In the abstract some full-system anomalies may not show up in partial-system tests.
You make it sound like a binary thing: test everything together, or not. I don't think it is as simple as that.

As a trivial example, they presumably won't test all the engines at the same time as testing the hold-down clamp release mechanisms, because that would result in an actual launch.

They will test the things that can they can practically test, and take a risk on the rest.

The best test would be all 33 engines to 100% thrust, with a Starship stacked on top of the booster. And if that test is looking good, why not just release the hold-down clamps and let it go to orbit?
Agreed. The only full system test would include a launch. You arrange your earlier tests to try to test as many aspects of the system as you can in a cost-effective manner. I was responding to the post that asked if the three tests covered 32 of the 33 engines which seemed to assume that this was important.

Offline Barley

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4192 on: 12/01/2022 08:56 pm »
The best test would be all 33 engines to 100% thrust, with a Starship stacked on top of the booster. And if that test is looking good, why not just release the hold-down clamps and let it go to orbit?
So you have more than a few ms to analyze the data.
So you can do the test without bothering about a launch window, landing zone, range readiness and most of the associated bureaucracy.  (You probably still need the FTS and some bureaucracy.)

Not that they need to do that, it depends on what they are uncertain about and want to test,

Offline FutureSpaceTourist

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4193 on: 12/14/2022 07:11 am »
twitter.com/csi_starbase/status/1602827502786846721

Quote
Hey #StarshipAddicts, I hope yal are ready for Part 2!

If you are wondering what the REAL reason is behind the most significant delay to the 1st Starship Orbital Test Flight, then you don't want to miss this!

Premier starts at 7:30pm (CST)
🔗:

https://twitter.com/csi_starbase/status/1602827502786846721

Quote
Warning: This episode contains an extreme level of speculation. Nearly 100%

If anything I've covered here is proven to be incorrect, I will address it in a follow up investigation. This is an important topic to get right. These conclusions should NOT be considered as fact.

« Last Edit: 12/14/2022 09:44 am by FutureSpaceTourist »

Offline JamesH65

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4194 on: 12/14/2022 12:09 pm »
Why would anyone watch something that is advertised as almost 100% speculation?

Offline RamsesBic

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4195 on: 12/14/2022 01:52 pm »
Why would anyone watch something that is advertised as almost 100% speculation?

They do when his speculations are correct as often as they have been shown to be.

Offline InterestedEngineer

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4196 on: 12/14/2022 05:06 pm »
Why would anyone watch something that is advertised as almost 100% speculation?

Because Zack is an engineer, not a salesman.

If you want to be persuaded by over-optimism, then follow a sales guy.

if you want stuff to work because of a proper level of pessimism, then follow an engineer.

Elon is the one rare mix of both that works.

Offline equiserre

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4197 on: 12/14/2022 07:05 pm »
Why would anyone watch something that is advertised as almost 100% speculation?

An engineer puts in a lot of effort to make educated guesses, explaining his reasoning, and calls it 100% speculation? thatīs pretty good for some Youtube entertainment




Offline Tangilinear Interjar

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4198 on: 12/15/2022 04:02 pm »
Why would anyone watch something that is advertised as almost 100% speculation?

Why would anyone read a Space forum where everything is pretty much 100% speculation? 🙄

Offline Robotbeat

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Re: SpaceX Starship/Super Heavy Engineering General Thread 4
« Reply #4199 on: 12/15/2022 05:24 pm »
LOL, that’s a totally fair point.

My real gripe is with the annoying click-bait tactics. Regular old forum speculation is fine, and CSI_Starbase is often pretty informative.
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