SpaceX Starship/Super Heavy Engineering General Thread 4

[edzieba]

https://twitter.com/csi_starbase/status/1589099001575804928

Stabilizer pins have been added onto the brand new booster transport stand. As far as we know, B9 and up will not use this same mechanism. So this transport stand is likely being prepared for B7 to be taken back off of the OLM soon.  B7's transport stand was donated to B9

📸:S0Z

In addition to booster aerocovers having been delivered recently (late October) with the pin cutouts in place, and Booster 9's aft dome being rolled to the mega bay with unfaired structures in the correct location to host the pin sockets, all boosters (including B9 onwards) have the internal bracing needed for the alignment pins: they use the same structural hardpoints and bracing that allow the aft sections to be lifted and flipped from two points (rather than using an external support ring) during the dome sleeving process.
The assumption appears to be that if Booster 9 has eliminated the hydraulic TVC powerpacks that it must therefore also have eliminated the alignment pin sockets that are located over the top of the powerpacks, but that's not a particularly good assumption: nothing about the sockets requires the powerpacks to be present, either the sockets could be mounted to their hardpoints without the powerpack behind (acting as a spacer over empty space), or just mounted closer to the tank skin, with the pins extending slightly further to mate.
Also, it would be very odd to spend the time to install new hydraulic pin assemblies to a new transport stand for a single use with B7, rather than performing the same manual guy-wire alignment they have multiple times in the past (including with B7 after the chopstick hydraulic failure).

[InterestedEngineer]

Cool idea on how to prevent ullage collapse - floating balls that insulation ullage gas from the cryogenic liquids:

https://forum.nasaspaceflight.com/index.php?topic=57685.0

[ulm_atms]

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.

[InterestedEngineer]

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.

[su27k]

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.

[edzieba]

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.

[skyflyer81]

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.

[RoboGoofers]

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?

[eriblo]

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.

[InterestedEngineer]

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.

[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.

[AU1.52]

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.

[DanClemmensen]

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.

[steveleach]

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?

[DanClemmensen]

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.

[Barley]

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,

[FutureSpaceTourist]

twitter.com/csi_starbase/status/1602827502786846721

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

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.

[JamesH65]

Why would anyone watch something that is advertised as almost 100% speculation?

[RamsesBic]

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.

[InterestedEngineer]

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.