totm nov 2023 SpaceX Discussion Thread

[JoeSchmuckatelli]

35 minutes ago, RealKerbal3x said:

I'm surprised nobody has posted this yet.

 

I can't make out the image.  Thumbs up?

[RealKerbal3x]

1 minute ago, JoeSchmuckatelli said:

I can't make out the image.  Thumbs up?

It's highlighting the serial number on the engine bell of Raptor SN42. It's a Hitchhiker's Guide reference.

[RCgothic]

3 minutes ago, JoeSchmuckatelli said:

I can't make out the image.  Thumbs up?

42

[sevenperforce]

11 hours ago, JoeSchmuckatelli said:

The flare out starts @ +01:42.  You can see the flames go right to the foil packets.  Then they sort-of independently catch fire at +01:49.  At +01:55 you start to see some of the burned stuff fall out.

So I don't know what it was - and again, it did not affect the flight... but something burned.

It's hard to tell for sure, exactly. My guess is still that a good bit of unburned liquid methane was released at engine shutdown, spraying the inside of the skirt. Part of it went up in flames immediately but flamed out due to either fuel exhaustion or lack of oxygen. However, the skirt is still an extraordinarily volatile environment and so the remaining residues on the right-hand side ignited spontaneously a few seconds later. 

I feel like there's really nothing flammable in that skirt. (so much innuendo)

Speaking of which, I wonder exactly how long you would live if you tried to ride inside the skirt. Like, obviously you would die pretty fast, but...how fast?

4 minutes ago, tater said:

We knew it would be slow (from SpaceX sims), but it's still unexpected when you actually see it.

Really remarkable. As amazing as it was to watch the camera view live, it must have been an entirely different experience to watch it in person. 

From the wide-angle view, it REALLY looks like it's never going to actually flip -- that it's going to drop straight down and pancake. I'm sure that was a nail-biter.

32 minutes ago, paul_c said:

We don't know - and I suspect they didn't either, until yesterday - what the various hot gases, or exhausts, will do in the airflow when doing these not-seen-before-by-a-rocket maneouvers and whether they'll have a negative influence on other portions of the flight. My concern is the fuel flow during the landing phase is a new thing to get to grips with, and it was designed into the rocket using separate tanks (which it did switch over to) but the pressure/flowrates didn't work out as expected.

My most educated guess is that pressurizing the CH₄ header tank is going to be more of a challenge than they thought.

The CH₄ header tank is inside the CH₄ main tank, while the LOX header tank is independent of the LOX main tank. The CH₄ flow path goes through the header at all times. Presumably, then, they close valves between the CH₄ header and main at engine shutdown to ensure that it remains full of propellant at engine restart. The simplest solution at restart would be to reopen those valves immediately after ignition, allowing the autogenous pressurant in the main tank to provide pressure to the header:

In the diagrams above (which are obviously not to scale but aren't THAT bad), you can see the thin pressurant lines running from the engines to the tanks. The methane pressurant line runs straight to the main fuel tank, while the GOX line splits to pressurize both the main LOX tank and the header LOX tank (not shown).

Yesterday was the first time they ever did an in-air restart. Elon said outright "fuel header tank pressure was low during landing burn" so my guess is that the pressure in the main tank dropped faster than it was able to be replenished by the pressurant line. The easiest way to remedy this would be to split the methane pressurant line, just like the GOX pressurant line, and keep those valves closed between the fuel header tank and the fuel main tank.

14 minutes ago, RealKerbal3x said:

It's highlighting the serial number on the engine bell of Raptor SN42. It's a Hitchhiker's Guide reference.

I referenced this yesterday just before launch, LOL.

1 hour ago, Kerwood Floyd said:

Has anyone heard how high it actually got?

The test altitude was 12.5 km and it certainly followed the planned ascent properly so I'm guessing 12.5 km.

Also I did a thing for the public who doesn't understand this:

 

[JoeSchmuckatelli]

11 minutes ago, sevenperforce said:

... . 

I feel like there's really nothing flammable in that skirt. (so much innuendo) ;D

Speaking of which, I wonder exactly how long you would live if you tried to ride inside the skirt. Like, obviously you would die pretty fast, but...how fast?

... 

...... LOL.

Presuming you don't die from inhaled hot gas - this might be informative: https://www.google.com/amp/s/amp.iflscience.com/environment/stepbystep-death-lava-flow/

 

Has anyone seen anything about what debris survived the impact?  Would love to see their recovery report 

Edited December 10, 2020 by JoeSchmuckatelli

[tater]

@sevenperforce, I don't do tiktok, but nice summary.

 

Interesting to see what is stacked, and how this can related to fixing the CH4 header tank pressure issue. SN9 is obviously ready to fly, not sure what they can do to deal with the issue (unless it was already tweaked). 10 and 11 are similarly stacked in the critical area. The rest? Open books.

Edited December 10, 2020 by tater

[Kerwood Floyd]

45 minutes ago, sevenperforce said:

 

The test altitude was 12.5 km and it certainly followed the planned ascent properly so I'm guessing 12.5 km.

 

I asked because it wasn't clear to me how properly it followed the planned ascent.  I didn't know if both of the engine outages during the ascent were planned. If they weren't then it probably fell significantly short of 12.5 km. On the other hand if it actually came within a margin of error of 12.5 km then I guess they were planned.

[RealKerbal3x]

3 minutes ago, Kerwood Floyd said:

I asked because it wasn't clear to me how properly it followed the planned ascent.  I didn't know if both of the engine outages during the ascent were planned. If they weren't then it probably fell significantly short of 12.5 km. On the other hand if it actually came within a margin of error of 12.5 km then I guess they were planned.

The engine shutdowns were planned and it looked like it reached apogee:

 

[Kerwood Floyd]

Ok then. Thanks

[sevenperforce]

20 minutes ago, tater said:

@sevenperforce, I don't do tiktok, but nice summary.

Interestings to see what is stacked, and how this can related to fixing the CH4 header tank pressure issue. SN9 is obviously ready to fly, not sure what they can do to deal with the issue (unless it was already tweaked). 10 and 11 are similarly stacked in the critical area. The rest? Open books.

It's also entirely possible that they already have a separate autogenous press line running to the CH₄ header tank and the valves remain closed the entire time after MECO, in which case it was a different problem. 

The more I think about it, the more I feel like the use of pressurant accumulator tanks will solve a lot of problems for Starship.  They can feed the hot-gas thrusters directly and can provide full head pressure to the header tank even before Raptor relight. They'll need them for the landing engines on Lunar Starship, too, so why not just build them into the overall design?

[tater]

LOL

 

[StrandedonEarth]

34 minutes ago, tater said:

LOL

 

That was perfect LOL 

“I wonder if it’ll be friends with me?”

Well not when you scorch it with that big green flame...

[tater]

Douglas Adams was awesome.

[Brotoro]

2 hours ago, Kerwood Floyd said:

I asked because it wasn't clear to me how properly it followed the planned ascent.  I didn't know if both of the engine outages during the ascent were planned. If they weren't then it probably fell significantly short of 12.5 km. On the other hand if it actually came within a margin of error of 12.5 km then I guess they were planned.

The ascent profile wasn't at all like I was expecting to see, so it sure had me wondering at the time. I expected a jump up to 12.5 klicks, then a transition to belly flop for a vertical descent. Instead it did that long slide off to the side, where it seemed to be translating quite a way. After the sequential shutdowns of the engines (which I hadn't expected, and which look pretty violent as unburned propellant makes flames all over the place, and the engines gimbal hard and fast to handle the transients and park the other nozzle out of the way), I thought, "Aw, hell, they've lost two engines, so it isn't going to be able to do a safe landing... so they must be translating out over the water to ditch it into the gulf." So I was expecting to see the remaking engine gamely try to perform the flip-around before seeing it splash in the water. In those close shots of the tracking cameras, you don't have a good sense of where the ship is relative to the landing pad.

[JoeSchmuckatelli]

This is what I was looking for 

 

F

Edited December 10, 2020 by JoeSchmuckatelli

[NSEP]

 

[RCgothic]

haha

 

 

[sevenperforce]

I did a careful pixel count of the entire descent from the first frame when the ground came into view, all the way down to impact, then converted to time and altitude based on measured pixel counts of the height of the rocket. Here's the raw data:

Spoiler

Time (sec)	Altitude (m)
-2.667	79.8
-2.633	78.3
-2.600	76.8
-2.567	76.4
-2.533	74.5
-2.500	73.4
-2.467	73.4
-2.433	72.3
-2.400	70.8
-2.367	70.4
-2.333	70.4
-2.300	68.6
-2.267	68.6
-2.233	67.5
-2.200	66.7
-2.167	65.6
-2.133	64.5
-2.100	63.7
-2.067	62.2
-2.033	61.5
-2.000	60.8
-1.967	59.3
-1.933	58.5
-1.900	57.4
-1.867	56.7
-1.833	55.2
-1.800	54.4
-1.767	53.3
-1.733	52.6
-1.700	51.8
-1.667	50.3
-1.633	49.2
-1.600	48.5
-1.567	47.3
-1.533	46.6
-1.500	45.5
-1.467	44.4
-1.433	43.6
-1.400	42.5
-1.367	41.4
-1.333	40.6
-1.300	39.5
-1.267	38.4
-1.233	37.3
-1.200	36.5
-1.167	35.4
-1.133	34.3
-1.100	33.5
-1.067	32.8
-1.033	31.7
-1.000	29.8
-0.967	29.8
-0.933	28.7
-0.900	27.2
-0.867	27.2
-0.833	25.7
-0.800	23.9
-0.767	23.9
-0.733	22.7
-0.700	22.0
-0.667	20.9
-0.633	19.8
-0.600	18.6
-0.567	17.5
-0.533	16.4
-0.500	15.7
-0.467	14.9
-0.433	13.4
-0.400	13.0
-0.367	11.6
-0.333	11.2
-0.300	9.7
-0.267	7.5
-0.233	7.5
-0.200	6.7
-0.167	4.5
-0.133	4.5
-0.100	3.4
-0.067	2.2
-0.033	1.1
0.000	0.0

Putting this into a scatter chart produces a pretty clear signal.

It appears that for the last 2.5 seconds of flight, it was dropping toward the pad at an essentially constant speed, with the thrust of the dying engine exactly balancing the pull of gravity.

 

[JoeSchmuckatelli]

Grin - threads like this give me hope for humanity.

[RCgothic]

Edit: tweet scrubbed, email address visible.

 

SN9SN9 rollout on Monday? Odd that an email would be leaked though.

 

Edited December 10, 2020 by RCgothic

[JoeSchmuckatelli]

Someone is going to have to change her email address; not cool to post that on twitter, btw

[RCgothic]

1 minute ago, JoeSchmuckatelli said:

Someone is going to have to change her email address; not cool to post that on twitter, btw

Good catch, editing out.

[magnemoe]

6 hours ago, sevenperforce said:

It's hard to tell for sure, exactly. My guess is still that a good bit of unburned liquid methane was released at engine shutdown, spraying the inside of the skirt. Part of it went up in flames immediately but flamed out due to either fuel exhaustion or lack of oxygen. However, the skirt is still an extraordinarily volatile environment and so the remaining residues on the right-hand side ignited spontaneously a few seconds later. 

I feel like there's really nothing flammable in that skirt. (so much innuendo)

Speaking of which, I wonder exactly how long you would live if you tried to ride inside the skirt. Like, obviously you would die pretty fast, but...how fast?

Really remarkable. As amazing as it was to watch the camera view live, it must have been an entirely different experience to watch it in person. 

From the wide-angle view, it REALLY looks like it's never going to actually flip -- that it's going to drop straight down and pancake. I'm sure that was a nail-biter.

My most educated guess is that pressurizing the CH₄ header tank is going to be more of a challenge than they thought.

The CH₄ header tank is inside the CH₄ main tank, while the LOX header tank is independent of the LOX main tank. The CH₄ flow path goes through the header at all times. Presumably, then, they close valves between the CH₄ header and main at engine shutdown to ensure that it remains full of propellant at engine restart. The simplest solution at restart would be to reopen those valves immediately after ignition, allowing the autogenous pressurant in the main tank to provide pressure to the header:

In the diagrams above (which are obviously not to scale but aren't THAT bad), you can see the thin pressurant lines running from the engines to the tanks. The methane pressurant line runs straight to the main fuel tank, while the GOX line splits to pressurize both the main LOX tank and the header LOX tank (not shown).

Yesterday was the first time they ever did an in-air restart. Elon said outright "fuel header tank pressure was low during landing burn" so my guess is that the pressure in the main tank dropped faster than it was able to be replenished by the pressurant line. The easiest way to remedy this would be to split the methane pressurant line, just like the GOX pressurant line, and keep those valves closed between the fuel header tank and the fuel main tank.

I referenced this yesterday just before launch, LOL.

The test altitude was 12.5 km and it certainly followed the planned ascent properly so I'm guessing 12.5 km.

Also I did a thing for the public who doesn't understand this:

Questionable how relevant this is for return from orbit. Skin will be boiling hot during reentry so I don't see much methane and LOX will stay liquid in the main tanks.
More likely you will use pressure difference to top up the header tanks once you reach orbit. close the valves and either dump the liquid methane and oxygen in main tanks or let it boil off during reentry. 

[CatastrophicFailure]

5 hours ago, sevenperforce said:

It's also entirely possible that they already have a separate autogenous press line running to the CH₄ header tank and the valves remain closed the entire time after MECO, in which case it was a different problem. 

The more I think about it, the more I feel like the use of pressurant accumulator tanks will solve a lot of problems for Starship.  They can feed the hot-gas thrusters directly and can provide full head pressure to the header tank even before Raptor relight. They'll need them for the landing engines on Lunar Starship, too, so why not just build them into the overall design?

May, of course, be missing some significant bits, but... for what it’s worth...

 

 

Edited December 10, 2020 by CatastrophicFailure
Image stolen from Twitter

[RCgothic]

Careful, some Twitter handles are not forum safe.

6 minutes ago, CatastrophicFailure said:

May, of course, be missing some significant bits, but... for what it’s worth...

 

Elon and Gwynne take a tour. Pieces on a truck already.

 

 

Edited December 10, 2020 by RCgothic