totm nov 2023 SpaceX Discussion Thread

[Meecrob]

As was already explained, this is flight test. Its a bizarre environment if you have not been there before. Some companies won't move an inch until they have simulated thousands of hours of CFD, and some like SpaceX learn from screwing up. We have debated the pro's and con's of both approaches before, but suffice to say, SpaceX is firmly on the path of destroying everything in the name of progress, so a few tiles falling off is an easy way to show them where they need to improve...or they could simulate all the loads with CFD, but in order to make that accurate, they would have to put strain gauges and vibration gauges all over starship, then pour that data into a computer.  But then they would have to physically install those sensors...they went the route of just installing the heat shield and "we will improve as we go" because as anyone who has dealt with CFD will tell you, its scary accurate, until it screws up....as in encounters a situation humans did not program enough input into it. That's why they still actually fly things...nobody trusts computers fully.

Edited October 25, 2021 by Meecrob
Not my best keyboard skills

[RealKerbal3x]

10 minutes ago, Deddly said:

why don't they do the static fire before they attach the tiles?

Because installing all of the tiles takes a really long time, and from what we've seen it's easier to install the majority of the tiles before the various sections are stacked and welded together.

Besides, S20 only lost about 7 tiles when it did its static fire. That's a pretty good going rate considering that this is the first ship to receive a full heat shield.

[Meecrob]

6 minutes ago, RealKerbal3x said:

Besides, S20 only lost about 7 tiles when it did its static fire. That's a pretty good going rate considering that this is the first ship to receive a full heat shield.

I'm still waiting on someone to count all the tiles and tell me what percent fell off...


Edited: jokingly...I'm not trying to be a jerk. I'm just saying that all things considered a first prototype of a heat shield designed to be flawed and iterated on only losing like less than 10 tiles ain't bad for a first try.

Edited October 25, 2021 by Meecrob

[Beccab]

26 minutes ago, Deddly said:

Yes, steel has a higher melting point than aluminium, but I still expect that SpaceX will not be content with any tiles falling off in flight.

As I said before in this thread STS-1 survived with 16 tiles completely missing and STS-27 with over 700 damaged tiles and a critical one loss (but protected by the aluminium frame of an antenna). Losing a few tiles is a problem, but usually not critical considering both the steel frame and the protective layer under the heat shield.

26 minutes ago, Deddly said:

People here are saying that the stresses of flight are probably less than the static fire because of the sound, hence my question - why don't they do the static fire before they attach the tiles?

This is still the first flight of a very much in development program. The procedure will change countless times as it continues, but for now they want to find the limits and possible issues and putting the tiles is a good way of doing that. Putting on tiles is also very time consuming, and when they start reusing starships they are going to have to always SF them with the heat shield on (until they start removing the static fire, like on F9)

10 minutes ago, Meecrob said:

I'm still waiting on someone to count all the tiles and tell me what percent fell off...

There you go:

Being pessimistic, the count is too high by 200 and 7 tiles fell off. This means that it has lost the 0.045% of the total tiles during the static fire

If we have to be cynical, Columbia lost more than 2,000 of its 21,000 tiles when being trasported on the SCA in 1979, or almost 10%

Edited October 25, 2021 by Beccab

[Meecrob]

11 minutes ago, Beccab said:

 This means that it has lost the 0.045% of the total tiles during the static fire

...for a prototype, that's airliner rates of failure...I get that that number isn't the vehicle as a whole, but this is encouraging to say the least!

(Thanks for the numbers, man!)

Edit: "airliner rate of failure" does not equal crash.

Edited October 25, 2021 by Meecrob

[mikegarrison]

8 hours ago, grawl said:

To clarify as well, my answer was an attempt at a lighthearted comment with a touch of humor.

In no way I believe it is a good idea to do QA on Starship this way. Final QA that is. But for a tile's laying process validation test ? Yes, of course.

I thought that was obvious. Darn, maybe I should have add some smileys.

OK, sorry that I misread your intent.

[MKI]

The other thing that hasn't been tested, is the impact of losing a tile on Starship. Losing a tile on the Shuttle was vastly more risky due to the nature of the Shuttles internal structure, as its was aluminum. The same can't be said for Starship due to its size (more surface area), and internal structure (steel), so losing tiles should be less risky overall.

Losing a tile on the Shuttle in the wrong place could end the mission. I'm not sure what the "wrong" place would be for a missing tile on Starship. Possibly near the fins. I'm sure someone ran a simulation to know where the highest risk places are. 

 

Overall though, putting a thing and thing together where they don't fall off isn't exactly a super complex engineering challenge. Its striking a balance between doing it cheaply, easily, quickly and reliably that really needs to be testing "live" to find the kinks the process. 

 

 

 

 

[AtomicTech]

8 minutes ago, MKI said:

The other thing that hasn't been tested, is the impact of losing a tile on Starship. Losing a tile on the Shuttle was vastly more risky due to the nature of the Shuttles internal structure, as its was aluminum. The same can't be said for Starship due to its size (more surface area), and internal structure (steel), so losing tiles should be less risky overall.

Losing a tile on the Shuttle in the wrong place could end the mission. I'm not sure what the "wrong" place would be for a missing tile on Starship. Possibly near the fins. I'm sure someone ran a simulation to know where the highest risk places are. 

 

Overall though, putting a thing and thing together where they don't fall off isn't exactly a super complex engineering challenge. Its striking a balance between doing it cheaply, easily, quickly and reliably that really needs to be testing "live" to find the kinks the process. 

 

 

 

 

True!

[mikegarrison]

38 minutes ago, MKI said:

The other thing that hasn't been tested, is the impact of losing a tile on Starship. Losing a tile on the Shuttle was vastly more risky due to the nature of the Shuttles internal structure, as its was aluminum. The same can't be said for Starship due to its size (more surface area), and internal structure (steel), so losing tiles should be less risky overall.

On the other hand, the skin is also the fuel tank. So any heating (or worse, burn-through) is directly impacting the fuel and oxidizer.

[tater]

The acoustic environment of a static test on the suborbital pad is not the same as launch. We'll have to wait and see, it's not like they don't think about this stuff.

[Deddly]

57 minutes ago, MKI said:

losing tiles should be less risky overall.

I would certainly expect so! Less likely to end in RUD, but I'm sure some damage would occur, which is no good for a reusable craft. So I would imagine they will work to ensure that this does not happen, even if they know if would not result in loss of mission. 

[cubinator]

As long as it gets me from one planet to another in one piece, I'm pretty happy.

[magnemoe]

27 minutes ago, mikegarrison said:

On the other hand, the skin is also the fuel tank. So any heating (or worse, burn-through) is directly impacting the fuel and oxidizer.

The tanks will be empty during reentry, yes they will be pressurized who add a lot of strength, an burn through will loose that. 
Now I image max braking as in max-q during reentry will be after the main thermal load and you start getting into thicker air. 
An burn trough in the LOX header tank in the nose would be bad but also unlikely as you will rater boil off LOX you have to vent. 
Loosing structural pressurization is bad for the belly flop, loosing LOX is bad for landing and even bad if you have an abort system and it would use the header tank LOX. 

[RCgothic]

They'll be somewhat empty. For non-high performance missions it might be worth keeping some residual fuel for emergency cryogenic cooling. Deceleration would hold the fuel residuals against the windward tank wall.

[mikegarrison]

34 minutes ago, magnemoe said:

The tanks will be empty during reentry, yes they will be pressurized who add a lot of strength, an burn through will loose that. 
Now I image max braking as in max-q during reentry will be after the main thermal load and you start getting into thicker air. 
An burn trough in the LOX header tank in the nose would be bad but also unlikely as you will rater boil off LOX you have to vent. 
Loosing structural pressurization is bad for the belly flop, loosing LOX is bad for landing and even bad if you have an abort system and it would use the header tank LOX. 

If the tanks are empty during re-entry, there is going to be a crash. There has to be something in the tanks for propulsive landing to work.

[Silavite]

3 hours ago, mikegarrison said:

On the other hand, the skin is also the fuel tank. So any heating (or worse, burn-through) is directly impacting the fuel and oxidizer.

The CH4 header tank is ensconced in the center the larger LOX/CH4 bulkhead, so it is relatively well-insulated. The LOX header tank, on the other hand, is right at the nose (where the highest head loads will likely be). I'd imagine that losing a tile covering the LOX header tank could be very dangerous indeed.

[StrandedonEarth]

Well now, ain’t that a….

 

[CatastrophicFailure]

How to toilet train your Dragon… 

[cubinator]

Oof. That's worse than the Apollo 10 turd incident.

[Beccab]

7 hours ago, mikegarrison said:

If the tanks are empty during re-entry, there is going to be a crash. There has to be something in the tanks for propulsive landing to work.

The main tanks are empty. There is a single, small spherical tank in the nose, the header tank, that provides fuel for landing

[Beccab]

After that is done and the aerocovers are mounted, the booster should be ready for flight barring testing (cryo and SF)
 

For those who don't know, austin was one of the first people ever do start documenting the Boca Chica SpaceX development, together with Mary and Nomadd. I think he also was one of the original residents but don't quote me on that, I only know for sure that Mary is

[RCgothic]

Yes, the header tanks will be full. But the main tanks won't necessarily be completely empty. As I said, might not be a bad idea to have some cryogenic residuals in the main tanks for the first couple of flights at least.

Happy Austin is following his passions, but it'll be a loss to the community if he can't report anymore.

[kerbiloid]

10 hours ago, MKI said:

Losing a tile on the Shuttle was vastly more risky due to the nature of the Shuttles internal structure, as its was aluminum. The same can't be said for Starship due to its size (more surface area), and internal structure (steel), so losing tiles should be less risky overall.

Then the steel hull is overthickened.

Otherwise if it can go without the tiles, why these efforts about tiling.

[Beccab]

34 minutes ago, kerbiloid said:

Then the steel hull is overthickened.

Otherwise if it can go without the tiles, why these efforts about tiling.

That's like saying that the shuttle was overthickened because it survived when it lost some tiles. Most of the times you don't crash if your car has a flat tire, but that doesn't mean you should go around without tires

Edited October 26, 2021 by Beccab

[kerbiloid]

46 minutes ago, Beccab said:

That's like saying that

as the aluminium hull was enough, then the steel hull is excessive, as it still need the tiles.

The original claim was: "The hull is made of steel, thus doesn't need tiles".