totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

1 hour ago, cubinator said:

I have heard that the separation was not actually attempted because the vehicle was in such an off-nominal trajectory.

The description from those on the inside is that the separation WAS commanded but didn't happen for some reason.

The Starship is already supposed to have an abort mode for Superheavy failures. Granted, it might not have been programmed in yet, but trajectory issues alone wouldn't have been a reason not to attempt separation.

49 minutes ago, Vl3d said:

1 hour ago, sevenperforce said:

My working theory is that . . . MECO is not commanded until latch release is confirmed, and so in this case latch release never happened and so the booster kept pushing through the flat spin because it didn't know what else to do.

That's a huge assumption.

FTFY.

It's not an assumption; it's just one possible theory.

34 minutes ago, CBase said:

1 hour ago, sevenperforce said:

My working theory is that due to thrust shortfall, the attempted separation happened lower in the atmosphere than planned, resulting in significant aerodynamic torque on the stack during the flat spin, which in turn placed too much shear force on the latches for them to open properly.

Do you really think this would have been the case on all latches on all sides ? Visually there was no seperation happing at all.

It may have been that the set of aerodynamic forces and torques and the type of latches involved caused only one of the latches to seize, but it was in a position where it acted like a hinge and thus kept the stack connected:

The gray arrow is the direction of travel, and the blue arrows are wind. At the moment of commanded separation (when Starship is pointed straight down in my graphic) the separation latches on the leeward side of the interstage are under slight compression (somewhat balanced by centrifugal force), while the latches on the windward side are under tension only. If they're under too much tension (because of higher than expected drag) then perhaps they wouldn't be able to retract, and so they would remain seized.

This could explain the split-second image of Starship after Superheavy FTS but before Starship FTS, when the remains of the Superheavy interstage appear to be dangling from the aft of Starship by a single latch:

35 minutes ago, CBase said:

@sevenperforce thank you for this great explanation

1 hour ago, sevenperforce said:

It's a really very aggressive maneuver.

If this wasn't SpaceX, I would think anyone bringing up this manoveur as being completely nuts

I showed the (secondhand) source this image, and he's said it's the right idea but without a complete flip -- going back to the drawing board.

[Exoscientist]

2 hours ago, sevenperforce said:

This article is almost two years old now and has obsolete information.

There is no pusher stage separation mechanism. There is, however, a separation mechanism -- latches holding the booster and the starship together. When it's time to separate, those latches open.

That article talks about a "small but significant" flick. Apparently it's much more than that:

Just before MECO, Superheavy gimbals hard left and places the entire stack into a flat spin, and the spin continues under full gimbal for almost 270 degrees before MECO and separation are commanded simultaneously. Once separation occurs, both vehicles continue to rotate and drift apart. Starship rotates for almost another 90 degrees before igniting its engines and straightening out, while Superheavy does another 270 degrees before starting the boostback. It's a really very aggressive maneuver.

My working theory is that due to thrust shortfall, the attempted separation happened lower in the atmosphere than planned, resulting in significant aerodynamic torque on the stack during the flat spin, which in turn placed too much shear force on the latches for them to open properly. Separation and MECO happen simultaneously, but MECO is not commanded until latch release is confirmed, and so in this case latch release never happened and so the booster kept pushing through the flat spin because it didn't know what else to do.

The other possibility is that the latches were just fine, but because of the higher drag, the rotation rate never got high enough for the computer to command separation at all.

 By separation mechanism I mean one of the methods used before on staged rockets that mechanically separates the stages, not simply using centrifugal force. 
 

  Robert Clark

Edited April 21, 2023 by Exoscientist

[CatastrophicFailure]

Could the near-total loss of hydraulic power at that point have any effect on the latches?

[magnemoe]

5 minutes ago, CatastrophicFailure said:

Could the near-total loss of hydraulic power at that point have any effect on the latches?

Could be, not sure how hydraulic pressure is generated here.  Also if latches and grind fins are hydraulic. If so having an separate system for top would make some sense to avoid long lines. 
If so long lines and need of serious gimbal and you probably get low pressure up at top.  

[tater]

53 minutes ago, darthgently said:

And, significantly, Unity take notes here, the craft did *not* squiggle about like a spaghetti noodle

Let's hear it for autostrut.

[sevenperforce]

16 minutes ago, CatastrophicFailure said:

Could the near-total loss of hydraulic power at that point have any effect on the latches?

I don't think so. There's no confirmation that the booster actually fully lost hydraulic power at any point, and latches seem like the sort of thing that would get redundant loops.

If I recall, one Falcon 9 was lost because of a hydraulic loss on the grid fin drivers, so they put in a backup hydraulic to make the grid fins dual redundant. The latches probably operate off the same hydraulic system as the grid fins, which makes them independent of the engine hydraulic unit.

[RCgothic]

I'm hearing Clamps were hydraulic release. Makes sense.

 

Edit: that's what I guess for not releasing before posting.

Edited April 21, 2023 by RCgothic

[Geonovast]

1 minute ago, sevenperforce said:

If I recall, one Falcon 9 was lost because of a hydraulic loss on the grid fin drivers, so they put in a backup hydraulic to make the grid fins dual redundant. The latches probably operate off the same hydraulic system as the grid fins, which makes them independent of the engine hydraulic unit.

B1050, the first Falcon 9 (non-heavy) I watched live... which they did recover, it just never flew again.

I think there's a pretty good argument against having the staging latches and the grid fins on the same hydraulic loop.  One system is mission critical, the other is not.  Adding a "non-essential" system to an essential one will open up more points of failure for the essential system.

[magnemoe]

21 minutes ago, Geonovast said:

B1050, the first Falcon 9 (non-heavy) I watched live... which they did recover, it just never flew again.

I think there's a pretty good argument against having the staging latches and the grid fins on the same hydraulic loop.  One system is mission critical, the other is not.  Adding a "non-essential" system to an essential one will open up more points of failure for the essential system.

Agree or I would say have SS have an secondary detachment system who might well be destructive, as long as it don't damage SS engines or critical structure, in case superheavy brick itself. 
Or move system to SS but some creative use of explosive bolts are probably lighter. 

Again once they start flying important payloads abort options for SS will be an selling point, and yes payloads most major science or communication satellites are very expensive so having an abort modes would be nice. Return to launch site or redirect to Europe or Africa is the two obvious ones. Redirect to orbit awaiting urgent refueling is an future one. 

[Deddly]

2 hours ago, sevenperforce said:

Just before MECO, Superheavy gimbals hard left and places the entire stack into a flat spin, and the spin continues under full gimbal for almost 270 degrees before MECO and separation are commanded simultaneously. 

Considering they want to ultimately send thousands of people to Mars on this system, that maneuver seems like a nauseating mistake to me. 

[AckSed]

17 hours ago, sevenperforce said:

God, what an amazing, beautiful thing it will be when we see that.

I... Excuse me? The flip was planned? They were going to do a supersonic hammer-throw with a building-sized rocket to avoid fitting a normal separation mechanism.

The HELL? This is Philip Bono levels of far-out. SpaceX, you have flabbered my gast most thoroughly, and I salute you.

[Kartoffelkuchen]

24 minutes ago, AckSed said:

I... Excuse me? The flip was planned? They were going to do a supersonic hammer-throw with a building-sized rocket to avoid fitting a normal separation mechanism.

The HELL? This is Philip Bono levels of far-out. SpaceX, you have flabbered my gast most thoroughly, and I salute you.

Yeah, it's pretty nuts to think about. However, not as crazy from an aerodynamic perspective with air density and thus dynamic pressure being very, very low at that altitude and, compared to reentry velocities, low speed at stage seperation. I was much more worried about the aerodynamic stability during ascend leading up to Max-Q, since with the flaps being deployed, that will quickly generate a huge momentum if you deviate even just a little from your velocity vector.

When we're talking about the actual stage seperation mechanism, I'm not really sure what the benefits to doing it this flippy way would be, except for a lower structural mass. But I'm sure they have their reasons, or we will very quickly let them see switching their strategy. Rapid iteration in aerospace is always exciting to watch

Edited April 21, 2023 by Kartoffelkuchen

[CastleKSide]

How would there be lower structure weights with this insanity?  I can see a simpler coupling but wouldn't that be outweighed by needed to strengthen the entire stack?

 

I also like the term supersonic hammer throw. We really have gone full #humansarespaceorcs

[sevenperforce]

37 minutes ago, AckSed said:

18 hours ago, sevenperforce said:

God, what an amazing, beautiful thing it will be when we see that.

I... Excuse me? The flip was planned? They were going to do a supersonic hammer-throw with a building-sized rocket to avoid fitting a normal separation mechanism.

The HELL? This is Philip Bono levels of far-out. SpaceX, you have flabbered my gast most thoroughly, and I salute you.

I've since received updated information and I've updated the graphic accordingly.

It's more like this:

Note that all of this is in the yaw axis. So less Pugachev's Cobra, more Crazy Ivan. Except the stack yaws 90° to port before commiting to the Ivan, and the booster then does a 270° Crazy Ivan but releases the Starship a third of the way through. 

[Exoscientist]

3 hours ago, sevenperforce said:

Holy crap. This does not look good.

Those pilings are 150 feet deep, but still -- that's absolute devastation.

 
 There seems to be universal agreement that not having flame diverters was a mistake. As the “Angry Astronaut” puts it, the launch should be considered a success but major improvements need to be made, 
 

 

[CatastrophicFailure]

21 minutes ago, Kartoffelkuchen said:

Yeah, it's pretty nuts to think about. However, not as crazy from an aerodynamic perspective with air density and thus dynamic pressure being very, very low at that altitude and, compared to reentry velocities, low speed at stage seperation. I was much more worried about the aerodynamic stability during ascend leading up to Max-Q, since with the flaps being deployed, that will quickly generate a huge momentum if you deviate even just a little from your velocity vector.

This flip would/should have happened much higher, too… like 100km instead of only 40, so essentially in vacuum. 
 

It sounds pretty crazy, but… structurally, I wonder if it’s a bit like a barrel roll in an aircraft? In a properly executed barrel roll, the aircraft only experiences a constant 1G, so there’s virtually no unusual structural strain (why even an airliner can do it).

Anyways, maybe the flip isn’t as violent as it seems by description, if done right. Even like half a G would be plenty to separate the stack and wouldn’t need much additional structure. With all their F9 boost backs, SpaceX does have a lot of experience (read: DATA) flying rockets at unusual attitudes. 

[sevenperforce]

20 minutes ago, CatastrophicFailure said:

This flip would/should have happened much higher, too… like 100km instead of only 40, so essentially in vacuum. 
It sounds pretty crazy, but… structurally, I wonder if it’s a bit like a barrel roll in an aircraft? In a properly executed barrel roll, the aircraft only experiences a constant 1G, so there’s virtually no unusual structural strain (why even an airliner can do it).

An exoatmospheric Crazy Ivan should have very little structural strain -- aerospace members are usually stronger in tension than they are in compression.

Here's a crude gif:

Remember that this is a top-down view, not a side view.

[Terwin]

I figured that a chunk of the reason to do the 'hammer toss' would be to transfer additional energy from the booster to starship.

After release, Super-heavy wants to turn around and slow down, while Starship wants to speed up more, so any sort of momentum transfer should save dV for both.

Center of mass is probably still inside SH, due to all of the engines at the base, but Starship should have a majority of the remaining weight, so this little maneuver may transfer a significant amount of inertia from one to the other.  Even a few dozen m/s transferred might save tons of fuel, and those would be tons of fuel at stage separation that did not need additional dry-mass.

[kerbiloid]

in mid-air.

[tater]

17 minutes ago, Terwin said:

Center of mass is probably still inside SH, due to all of the engines at the base, but Starship should have a majority of the remaining weight, so this little maneuver may transfer a significant amount of inertia from one to the other.  Even a few dozen m/s transferred might save tons of fuel, and those would be tons of fuel at stage separation that did not need additional dry-mass.

CM is still in Starship. Assume 100t cargo, 100t vehicle, and 1200t props. SH is now 200t of vehicle—including the engines—pus whatever the residual props are. I doubt it needs >1000t of props for boostback and landing from the ~3400t it started with.

[sevenperforce]

26 minutes ago, Terwin said:

I figured that a chunk of the reason to do the 'hammer toss' would be to transfer additional energy from the booster to starship.

After release, Super-heavy wants to turn around and slow down, while Starship wants to speed up more, so any sort of momentum transfer should save dV for both.

Wait, did SpaceX buy Spinlaunch?

[tater]

For reference, the 39A flame trench appears to be ~42 feet deep, and the crawler height varies from 20-26 feet.

So the distance from the bottom of Shuttle/Saturn to the floor of the trench is on the order of 18.9m to 20.7m. OLM is apparently ~17m.

So slightly shorter, but not by a huge amount.

[AckSed]

1 hour ago, sevenperforce said:

An exoatmospheric Crazy Ivan should have very little structural strain -- aerospace members are usually stronger in tension than they are in compression.

Here's a crude gif:

Remember that this is a top-down view, not a side view.

I see. Now it's a rocket-powered, robotic returning spear-thrower.
The spear is also an orbital rocket.

Man what.

[lajoswinkler]

I'm very disappointed by the lying, sensationalist news outlets that filled the world with titles saying that Starship exploded. It did not "explode".

It survived all that tumbling, went off course and then flight termination system broke the vehicle apart. If it weren't for FTS, Starship would probably fall as one piece into ocean.

I mean, even Scott Manley uses this misleading, spiteful expression. What the hell?

 

Also, Musk seems to be adamant on not using flame trenches and that's just idiotic.

Edited April 21, 2023 by lajoswinkler

[Geonovast]

You don't need fire for an explosion.

FTS may have been what triggered it, but it still exploded from the fact that it was pressurized.  This is why it breaks up into an incomprehensible number of pieces, not like... 3.