totm nov 2023 SpaceX Discussion Thread

[CatastrophicFailure]

Actual question:

in all those videos of the launch, what were those little puffs that could be seen in the plume, that would then spread out? Like here:

that little puff that kinda looks like an eye...

[sevenperforce]

5 minutes ago, CatastrophicFailure said:

Actual question:

in all those videos of the launch, what were those little puffs that could be seen in the plume, that would then spread out? Like here:

that little puff that kinda looks like an eye...

Cold-gas RCS puffs from the nitrogen thrusters on the first stage.

[CatastrophicFailure]

9 minutes ago, sevenperforce said:

Cold-gas RCS puffs from the nitrogen thrusters on the first stage.

That close to the front of the second stage plume, tho?

[cubinator]

6 minutes ago, CatastrophicFailure said:

That close to the front of the second stage plume, tho?

The first stage stays pretty close to the second stage for a while.

[sevenperforce]

46 minutes ago, CatastrophicFailure said:

That close to the front of the second stage plume, tho?

TWR on the upper stage is pretty poor; it pulls away rather slowly. The plume gases are racing away from the MVac at 3400 m/s, so they rapidly envelop the first stage.

Plus, you're seeing it from VERY far away, so distances are deceiving.

[IncongruousGoat]

1 hour ago, sevenperforce said:

Note that while GEO comsats typically need very little station-keeping fuel, they still need an engine to circularize from GTO to GEO, and they also need enough dV to remove themselves into a high graveyard orbit at the end of their lives. In contrast, LEO comsats don't really need to circularize, and they don't need fuel for a terminal graveyard orbit insertion, but they do have a lot more station-keeping needs because of the higher drag in low orbit.

Actually, GEO satellites need more station-keeping fuel than one would expect because geostationary orbits aren't stable, primarily due to gravitational influence from the Moon. It's not quite as bad as LEO, but it's not insignificant.

[1101]

Cold-gas RCS puffs from the nitrogen thrusters on the first stage.

Looking on the footage posted upthread:

 

An extremely close up view at around 4 minutes shows some faint puffs between First and 2nd stages, presumably the Fairings?

[CastleKSide]

Id like to see someone more knowledgeable than myself go through the footage piece by piece and explain each of the events.. for instance there is the time when the contrail cuts out early on. Is that staging or just going behind a cloud?

 maybe sync to the official livestream? Is there any way to find the timestamp of the footage? 

[tater]

Contrails are formed as a function of available moisture to condense. In this case, visibility is also a factor and could have varied based on available light (a distant background cloud could cast a shadow on part of a contrail).

That said, I would think the skips are largely related to passing through small areas that have less available moisture. There was only the one staging, clearly visible.

[PakledHostage]

1 hour ago, tater said:

Contrails are formed as a function of available moisture to condense. 

But combustion products include plenty of H2O, so there's never going to be a shortage of moisture to condense... But it is a good question. Maybe, as you say, there was a cloud boyond the horizon that was casting a shadow, or maybe some atmospheric condition was preventing the available moisture from condensing? You often see aircraft up in the flight levels trailing little or no contrail, even though significant quantities of water is also present in jet aircraft exhaust.

[Cheif Operations Director]

4 hours ago, sevenperforce said:

TWR on the upper stage is pretty poor; it pulls away rather slowly. The plume gases are racing away from the MVac at 3400 m/s, so they rapidly envelop the first stage.

Plus, you're seeing it from VERY far away, so distances are deceiving.

English lol

I understood what you said but what is MVac? 

[tater]

16 minutes ago, PakledHostage said:

But combustion products include plenty of H2O, so there's never going to be a shortage of moisture to condense... But it is a good question. Maybe, as you say, there was a cloud boyond the horizon that was casting a shadow, or maybe some atmospheric condition was preventing the available moisture from condensing? You often see aircraft up in the flight levels trailing little or no contrail, even though significant quantities of water is also present in jet aircraft exhaust.

Yeah, but since the contrail stops in places, it’s clearly the result of the local air, and not a function solely of combustion products, since the engines only narrowly throttle.

[PB666]

I know what caused this. Its not the Contrails per say.

When the rocket reached a certain altitude it was in the sunlight, this is what caused the smoke tails to glow. You can clearly see the smoke even though its not glowing, just much less bright. The reason is that the sun was blocked from reaching it, it could be a cloud or some other obstruction on the horizon.

That is to say the sun caused them to glow, the contrails are always there, too much moisture and too low of a pressure and temperature, when the sun could not reach them they could not glow.

Edited December 24, 2017 by PB666

[Cheif Operations Director]

Launch Time would be significant. Because of the suns Location seeing as the sun just set your theory is pretty good.

[SuperFastJellyfish]

1 hour ago, Cheif Operations Director said:

English lol

I understood what you said but what is MVac? 

The vacuum version of the Merlin engine on the second stage.

[Cheif Operations Director]

3 minutes ago, SuperFastJellyfish said:

The vacuum version of the Merlin engine on the second stage.

Ahh I thought you were talking about a scientific term or phenomenon and I was like wha?

[PakledHostage]

4 hours ago, tater said:

Yeah, but since the contrail stops in places, it’s clearly the result of the local air, and not a function solely of combustion products, since the engines only narrowly throttle.

That was my point, yes.

[tater]

As I said (along with @PB666) it could also be far background clouds, but I haven't looked at the LA videos in any deatil to see if it's just lack of illumination, or breaks in contrails.

Here in New Mexico, where the air is pretty variable, we sometimes have horizon to horizon contrails, but often see breaks in them as the aircraft enter and leave zones of different humidity.

[Nibb31]

6 hours ago, Cheif Operations Director said:

English lol

I understood what you said but what is MVac? 

Merlin Vacuum, the upper stage engine.

[Scotius]

I keep thinking about fairing recovery method. With a ship armed with a big net. Could it possibly be used to recover second stage of Falcon? It would require some sort of heat shield on the front, and a drogue parachute on the end. Stage would re-enter, slow down in atmosphere protected by heat shield, then chute would pop and slow it even more - to a velocity allowing net to grab it without being shredded to bits. No need for landing legs, fuel reserve and other things cutting into dV or payload capability of the stage. What do you guys think - is it even remotely possible?

[CatastrophicFailure]

4 minutes ago, Scotius said:

What do you guys think - is it even remotely possible?

And if it misses, you suddenly have a significant quantity of aerosolized kerosene in possibily the worst place for a fire on earth, and lots of sparks. 

The big challenge is keeping the fragile engine bell pointed the right way, a heat shield on the “nose” of the stage would be extremely unstable with the heavy engine at the back. 

[PakledHostage]

1 hour ago, tater said:

As I said (along with @PB666) it could also be far background clouds, but I haven't looked at the LA videos in any deatil to see if it's just lack of illumination, or breaks in contrails.

Here in New Mexico, where the air is pretty variable, we sometimes have horizon to horizon contrails, but often see breaks in them as the aircraft enter and leave zones of different humidity.

That was my point, yes.

[Scotius]

18 minutes ago, CatastrophicFailure said:

And if it misses, you suddenly have a significant quantity of aerosolized kerosene in possibily the worst place for a fire on earth, and lots of sparks. 

The big challenge is keeping the fragile engine bell pointed the right way, a heat shield on the “nose” of the stage would be extremely unstable with the heavy engine at the back. 

Est modus in rebus . Airbrakes deployable into the airstream behind the stage. They would turn entire contraption into a giant dart

[mikegarrison]

10 hours ago, PakledHostage said:

You often see aircraft up in the flight levels trailing little or no contrail, even though significant quantities of water is also present in jet aircraft exhaust.

Contrails have very specific atmospheric requirements. Yes, there is water vapor in engine exhaust, but there is also heat. (In fact, this is why more efficient engines are more prone to contrails -- because they have less waste heat.)

This was studied way back in WW2 when contrails were life-threatening to bombers. The eventual result was what is now called the Schmidt-Appleman Criterion. Here are some slides from DLR showing a derivation of it. http://www.forum-ae.eu/system/files/12_contrail-formation-fundamentals.pdf

Bottom line is that it actually does matter whether there is already water in the air or not, even though the fuel combustion supplies a lot of water. You can kind of think of it as the air having to be very nearly ready to make a cloud, and then the engine comes along and pushes it over the edge.

[Listy]

This excellent close up footage quite clearly shows little puffs of gas coming from the fairings at around 1:50. (The whole video is quite spectacular!)