Jump to content

SpaceX Discussion Thread


Skylon
 Share

Recommended Posts

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:

press-flow-path.png

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:

 

Link to comment
Share on other sites

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 by JoeSchmuckatelli
Link to comment
Share on other sites

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

 

Eo2HKkvUYAERFN1?format=jpg&name=4096x409

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 by tater
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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:

 

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

plummet.png

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.

 

Link to comment
Share on other sites

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:

press-flow-path.png

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. 

Link to comment
Share on other sites

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...

NYblmjc.jpg

 

 

Edited by CatastrophicFailure
Image stolen from Twitter
Link to comment
Share on other sites

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 by RCgothic
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...