totm nov 2023 SpaceX Discussion Thread

[Meecrob]

1 hour ago, lajoswinkler said:

The sentiment of the media is "haha, Musk couldn't make it go even with all that money, it went kaboom, serves him well". It's demeaning. There is much more to Starship than just "big rocket go to space". Like with Apollo, it's a thing all humans can share together. Mocking it is pathetic.

Just to be clear, I don't like Musk, but I love SpaceX.

When it works, you will be laughing. Don't let them get you down.

Its cool to hate Elon right now. He could cure cancer and people would still have a bone to pick. Not that he is amazing...In fact, Lets hear it for the CEO, Gwynne Shotwell!

Edited April 22, 2023 by Meecrob

[mikegarrison]

9 hours ago, CatastrophicFailure said:

Sorry but this is incorrect. SpaceX has a contract from NASA to develop a lunar variant specifically, and milestones related to that. This launch, and pretty much all Starship development up to this point, was entirely funded by SpaceX. 

The two are obviously not unconnected. Part of SpaceX's contract requires the lunar lander to actually get to the moon, and I'm pretty sure that without the Superheavy (and probably also Starship tankers and orbital fuel transfer) that can't happen. SpaceX committing to make the whole system work is part of what they contracted for.

[darthgently]

16 hours ago, Meecrob said:

An explosion is an exothermic reaction that propagates at greater than the speed of sound

Isn't that a detonation while an explosion is subsonic?

[kerbiloid]

(Probably, already was posted, but lazy to look through.)

Photos of post-launch launchpad.

The crater is 20 m in diameter and several meters deep.

https://pikabu.ru/story/nemnogo_podrobnostey_o_posleduyushchikh_planakh_na_puskovuyu_ploshchadku_starship_10168321

[darthgently]

15 hours ago, K^2 said:

I think we had an official flameout of what, six engines? It sounds like way more of them were underperforming.

I think they were running at 70% throttle initially, but may have throttled up was engines dropped out

[Meecrob]

27 minutes ago, darthgently said:

Isn't that a detonation while an explosion is subsonic?

With regards to piston engines at least, "detonation" is how you say "the fuel-air mixture in my combustion chamber is exploding, not burning rapidly."

With regards to this failure, its why it didn't look like say the Falcon 9 failure, compare this fireball to some of the SN8-15 flop test explosions...you can see the the fireball moves faster in the latter examples.

Conflagration is the technical term for subsonic releases of energy by combustion..I do like the one Scott Manley video on Saturn V engine start where he called the initial burning of the gases before full propellant pressure as "casual combustion"

Edited April 22, 2023 by Meecrob

[tater]

1 hour ago, mikegarrison said:

The two are obviously not unconnected. Part of SpaceX's contract requires the lunar lander to actually get to the moon, and I'm pretty sure that without the Superheavy (and probably also Starship tankers and orbital fuel transfer) that can't happen. SpaceX committing to make the whole system work is part of what they contracted for.

True, but they only get paid when the complete milestones (some payment for each milestone). So they have not gotten paid yet. Same as Commercial Crew.

EDIT: All the bidders got paid to create their bids in the first place—SpaceX was in fact paid the least, and Dynetics got the most. The payment for the white papers was inverse to the quality of the bids, lol.

 

Edited April 22, 2023 by tater

[mikegarrison]

49 minutes ago, Meecrob said:

With regards to piston engines at least, "detonation" is how you say "the fuel-air mixture in my combustion chamber is exploding, not burning rapidly."

With regards to this failure, its why it didn't look like say the Falcon 9 failure, compare this fireball to some of the SN8-15 flop test explosions...you can see the the fireball moves faster in the latter examples.

Conflagration is the technical term for subsonic releases of energy by combustion..I do like the one Scott Manley video on Saturn V engine start where he called the initial burning of the gases before full propellant pressure as "casual combustion"

The usual distinction is that "detonation" happens with a supersonic flame front, while "deflagration" happens with a subsonic flame front. This is also usually taken to be the difference between an explosion and a conflagration.

[tater]

 

[Exoscientist]

9 minutes ago, tater said:

 

!!!

 I wanted a separate static test stand for all 33 engine engines constructed because I had no confidence all 33 Raptors would burn for the full flight duration. The idea of damage to the pad from the demolished concrete from the thrust was not even on my radar. 

 But if the full test stand had been constructed, this is another major flaw that would have been picked up beforehand.

 Bob Clark 

 

[magnemoe]

1 hour ago, Meecrob said:

With regards to piston engines at least, "detonation" is how you say "the fuel-air mixture in my combustion chamber is exploding, not burning rapidly."

With regards to this failure, its why it didn't look like say the Falcon 9 failure, compare this fireball to some of the SN8-15 flop test explosions...you can see the the fireball moves faster in the latter examples.

Conflagration is the technical term for subsonic releases of energy by combustion..I do like the one Scott Manley video on Saturn V engine start where he called the initial burning of the gases before full propellant pressure as "casual combustion"

This, detonation is also why an piston engine is more effective than an gas turbine, its hoped that rotating detonation engines can close this gap. 

[king of nowhere]

Why can't they use tungsten in the base? it's got a high enough melting temperature that it would survive the flames, it's also notable for staying hard at high temperature, and it's surprisingly cheap for its relative rarity. I assume there is a good reason for not using it, probably it doesn't work somehow. but why?

[magnemoe]

3 minutes ago, Exoscientist said:

!!!

 I wanted a separate static test stand for all 33 engine engines constructed because I had no confidence all 33 Raptors would burn for the full flight duration. The idea of damage to the pad from the demolished concrete from the thrust was not even on my radar. 

 But if the full test stand had been constructed, this is another major flaw that would have been picked up beforehand.

 Bob Clark 

An full duration burn is a bit overkill, engines are tested for long burns individually but I doubt even falcon 9 first stage does full duration burns. 
Yes it would catch most of the issues in this test launch but it would be an major construction project. I think you needed an lake or huge pool to burn down into. 

Now as I suggested they are working on a water cooled steel plate below the tower but it was not ready. Might have it extend a bit past the pad however. even with lips directing the flame up. 
 

[55delta]

2 hours ago, Meecrob said:

Lets hear it for the CEO, Gwynne Shotwell!

Very much so!

[lajoswinkler]

36 minutes ago, king of nowhere said:

Why can't they use tungsten in the base? it's got a high enough melting temperature that it would survive the flames, it's also notable for staying hard at high temperature, and it's surprisingly cheap for its relative rarity. I assume there is a good reason for not using it, probably it doesn't work somehow. but why?

It's very difficult to work with and it's extremely dense.  Welding out in the open is nearly impossible, it has to be done either in vacuum or with very high electrical beam currents under helium. There is really no need for it. It can be done with steel.

[darthgently]

3 hours ago, Meecrob said:

With regards to piston engines at least, "detonation" is how you say "the fuel-air mixture in my combustion chamber is exploding, not burning rapidly."

With regards to this failure, its why it didn't look like say the Falcon 9 failure, compare this fireball to some of the SN8-15 flop test explosions...you can see the the fireball moves faster in the latter examples.

Conflagration is the technical term for subsonic releases of energy by combustion..I do like the one Scott Manley video on Saturn V engine start where he called the initial burning of the gases before full propellant pressure as "casual combustion"

My understanding after some reading is that an explosion can be either subsonic or supersonic.  As you note, a conflagration is subsonic.   From what I've read detonation refers to a supersonic pressure wave that initiates an explosion that would not have easily happened from a subsonic pressure wave 

[CatastrophicFailure]

5 hours ago, StrandedonEarth said:

I have to wonder if the mount could have handled the rocket shutting down and settling back onto the OLM after that blast, although I imagine a lot of the damage was done after release.

I’m given to think it definitely could not, so they deliberately programmed the stack to move away from it if at all possible. Any kind RUD on/near the pad would have been way worse. 

4 hours ago, mikegarrison said:

The two are obviously not unconnected. Part of SpaceX's contract requires the lunar lander to actually get to the moon, and I'm pretty sure that without the Superheavy (and probably also Starship tankers and orbital fuel transfer) that can't happen. SpaceX committing to make the whole system work is part of what they contracted for.

A good analogy here is Boeing starting development on the 767 and then getting a contract to also develop the K-767. “No” public money is going into that initial development. 

[lajoswinkler]

1 hour ago, darthgently said:

My understanding after some reading is that an explosion can be either subsonic or supersonic.  As you note, a conflagration is subsonic.   From what I've read detonation refers to a supersonic pressure wave that initiates an explosion that would not have easily happened from a subsonic pressure wave 

It's "deflagration", not conflagration. Deflagrations and detonations are types of explosions, however low end deflagrations can't be really called explosions (otherwise a paper caught on fire could be called one), but there isn't a strictly defined lower end AFAIK.

You got it correct, detonations have supersonic fronts. I've heard people consider detonations to be true explosions, but that's just semantics.

[mikegarrison]

46 minutes ago, CatastrophicFailure said:

A good analogy here is Boeing starting development on the 767 and then getting a contract to also develop the K-767. “No” public money is going into that initial development. 

Not really. The 767 was first flying in the 1980s. The KC-46 was developed more than 30 years later.

While it is highly unlikely that the contract for the lunar lander is paying all the development costs for the Starship, it is paying for some of them.

[tater]

29 minutes ago, mikegarrison said:

While it is highly unlikely that the contract for the lunar lander is paying all the development costs for the Starship, it is paying for some of them.

One of the reasons for the SpaceX selection (aside from merit, and proof of actually delivering on contracts with NASA, unlike BO) was that NASA thought that SpaceX was pitching in far more on dev.

The BO bid (National Team/whatever) was initially ~$10B vs the far lower SpaceX bid. As I recall, NASA expected both vehicles to cost a similar amount (closer to the BO amount), so SpaceX was seen as doing the majority of the dev themselevs, vs BO not pitching in enough. Bezos then said he'd throw in a few billion—too little, too late.

Also, for the money, SpaceX is also developing a launch vehicle—so I think NASA was also considering just the estimated cost of the lander itself.

[mikegarrison]

6 minutes ago, tater said:

One of the reasons for the SpaceX selection (aside from merit, and proof of actually delivering on contracts with NASA, unlike BO) was that NASA thought that SpaceX was pitching in far more on dev.

The BO bid (National Team/whatever) was initially ~$10B vs the far lower SpaceX bid. As I recall, NASA expected both vehicles to cost a similar amount (closer to the BO amount), so SpaceX was seen as doing the majority of the dev themselevs, vs BO not pitching in enough. Bezos then said he'd throw in a few billion—too little, too late.

Also, for the money, SpaceX is also developing a launch vehicle—so I think NASA was also considering just the estimated cost of the lander itself.

I am not trying to say that SpaceX is developing Starship entirely on NASA money, or that they were not going to develop it if they hadn't won that contract. But they are using that contract to help subsidize developing it. It's all quite reasonable, but it would be wrong to say there is no NASA money in Starship.

[Codraroll]

3 hours ago, darthgently said:

My understanding after some reading is that an explosion can be either subsonic or supersonic.  As you note, a conflagration is subsonic.   From what I've read detonation refers to a supersonic pressure wave that initiates an explosion that would not have easily happened from a subsonic pressure wave 

An explosion is technically just a term for something coming apart. In design, you often come across "exploded views" of an object, where its parts are drawn apart to show how it's put together. Explosions don't have to feature any chemical reactions at all. If a gas tank suddenly bursts due to overpressure, one'd have to be a pedant to say it didn't explode. Language-wise, if it has a loud bang and pieces going in different directions, it's enough to qualify as an explosion for most purposes. "Detonation" and "deflagration" are terms that really only are relevant to situations where the term "explosion" is too generic to be of any use anyway. It's like using the word "animal" in discussions of zoologic taxonomy. Too imprecise to even bother with, vs. the more specific terms.

[Meecrob]

6 hours ago, magnemoe said:

This, detonation is also why an piston engine is more effective than an gas turbine, its hoped that rotating detonation engines can close this gap. 

We would have to define parameters to determine which combustion cycle is more effective...except for fuel to noise conversion: turbines win every time!

 

@lajoswinklerre: deflagration - Thanks, I just keep walking right into these stupid mistakes, don't I?

Edited April 22, 2023 by Meecrob

[mikegarrison]

8 hours ago, magnemoe said:

This, detonation is also why an piston engine is more effective than an gas turbine, its hoped that rotating detonation engines can close this gap. 

 

2 hours ago, Meecrob said:

We would have to define parameters to determine which combustion cycle is more effective...except for fuel to noise conversion: turbines win every time

Both of these statements are problematical, although @Meecrob is correct about defining parameters.

First, you have to define what you mean by "efficiency", but I will assume we are probably talking about thermal cycle efficiency. Next, you have to define what pressures and temperatures you are using. Assuming an air-breathing engine with sea level standard day inlet conditions, you have specified the cold side temperature and pressure. So you need to specify the pressure ratio, which (assuming reasonable compression efficiencies) will give you the hot side temperatures and pressures.

Given that, then you have to specify the cycles. Gas turbines are usually Brayton cycle. Gasoline is usually Otto cycle. Diesel is usually Diesel cycle (go figure...). But if you supercharge or turbocharge or use afterburner/reheat then you have different cycles.

Anyway, given all that, if you had the same pressures and temperatures, then the Otto cycle and the Brayton cycle have the same efficiency! Neither is "more efficient" than the other. The Diesel cycle is less efficient.

But ... very often Diesel cycles have higher pressure ratios than Otto or Brayton cycles, which is why a real Diesel cycle engine might well have higher efficiency than the others. But ... gas turbines work well at altitude while Diesel and Otto cycle engines do not, unless they are super- or turbo-charged. And ... well, there are also many other real-world differences too.

Bottom line is that it simply is not true, in a general sense, that either "piston engines are more efficient" or that "turbines win every time".

Edited April 23, 2023 by mikegarrison

[JoeSchmuckatelli]

I was looking at the Moon to Mars thing and it dawns on me. 

SX really needed the 'engines shatter concrete and blowback destroys engines' thing with the launch table. 

I mean, sure you can model stuff and game it out - but nothing proves that landing a ship on the main engines might need rethinking like just destroying them on takeoff.