totm nov 2023 SpaceX Discussion Thread

[cubinator]

Third engine was also way out in the "out of the way" position.

[tater]

It makes me wonder if the best solution might be a header tank for each engine for landing.

[tater]

This comparison is really useful:

[JoeSchmuckatelli]

2 hours ago, RCgothic said:

Sure those are legs? Maybe looks like engine bell debris to me.

 

 

The way that they seem to float up and away makes me think it's something like foil or insulation that has a lot of surface area for the weight.  Landing legs should have dropped like a rock (or with the craft) 

[tater]

Yeah, maybe they weren't legs, they seems to come from the edge, but that view is better.

[xebx]

I bet Engine 2 blew off, you can see N°1 perfect restart and N°2 not going clean and parts (insulation ?) thrown away.

And the final maneuver was a little late, even if they have high twr they should keep a little more margin.

Another 95% success, not bad.

[JoeSchmuckatelli]

3 minutes ago, tater said:

This comparison is really useful:

If the frame timing is the same - 9 was falling a whole lot faster than 8 was before the flip maneuver 

[K^2]

2 hours ago, magnemoe said:

Landing is far more than one magnitude harder than flying who is about avoiding the ground  

Instructor: "You know that thing we've practiced not hitting for the past few lessons?"

Student: "Ground? Yes."

Instructor: "I want you to hit it this time. But gently."

Student: "Hit it? On purpose?"

Instructor: "Yes. But gently."

Edited February 3, 2021 by K^2

[xebx]

SN 8 timing : 04m38s top altitude/flip - 06m42s landing

SN 9 timing : 04m35s top altitude/flip - 06m26s landing

Edited February 3, 2021 by xebx

[ExtremeSquared]

3 minutes ago, xebx said:

SN 8 timing : 04m37s top altitude/flip - 06m42s landing

SN 9 timing : 04m35s top altitude/flip - 06m26s landing

Suggests there was ballast on this one. Maybe more fuel.

[mikegarrison]

3 hours ago, RCgothic said:

Sure those are legs? Maybe looks like engine bell debris to me.

 

 

Actually ....

SpaceX is so annoyed about Jeff Bezos deciding to compete with them that they are secretly planning to compete with Amazon. What we saw there is their first test of a new rocket-powered package delivery method.

[xebx]

18 minutes ago, ExtremeSquared said:

Suggests there was ballast on this one. Maybe more fuel.

Maybe a little more fuel yes, but the timings are very similar if you consider SN 9 did hit the ground faster/failed to reduce its velocity compared to SN8.

I'm surprised at the photo where even engine N°1 doesn't look nominal (like losing all thrust halfway in the maneuvre), maybe the engines weren't fed correctly, one engine should be enough for an empty starship.

Edited February 3, 2021 by xebx

[derega16]

Anyone know that the failed engine is a replaced one or not?

[StrandedonEarth]

[tater]

 

[kerbiloid]

Spoiler

Jingle bells, jingle bells...

Awaiting for the 28-nozzle version of it.

[sevenperforce]

This slow-mo is amazing.

I was certain that the white cloud was the header tank. Looks like I was right. 

[kerbiloid]

Spoiler

Where is petunia?

 

[kerbiloid]

Btw, has somebody made a screenshot from this last video and look carefully at the tail section.

Isn't it a wider cylinder under a conical interstage?

[Flying dutchman]

Media is being stupid again in my country.

They're saying that because Starship crashed, it wouldn't be wise for spacex to facilitate Space tourist missions in the near future.

 

They clearly don't know that those people are launching on Falcon 9/dragon..

 

[derega16]

1 hour ago, Flying dutchman said:

Media is being stupid again in my country.

They're saying that because Starship crashed, it wouldn't be wise for spacex to facilitate Space tourist missions in the near future.

 

They clearly don't know that those people are launching on Falcon 9/dragon..

 

It kinda like "because Titanic sank we shouldn't use ship anymore"

[RealKerbal3x]

I really like Scott's analysis of this. This is a completely different issue to SN8 for sure - it could be a defect localised to the engine that failed to start.

 

[AVaughan]

A week or two ago I read something on social media (not sure where, maybe in this thread), that suggested that SpaceX had loaded more fuel in SN8 than they were authorised to.   Maybe that is what the FAA was upset about. 

 

13 hours ago, sevenperforce said:

I really only worried about two things: aerodynamic control authority during unpowered descent and the engine plumbing reliability at relight. At least the first seems to be a non-issue.

My best guess is that there’s another propellant flow issue. With the 1-2 relight they do, it almost looks like the torque from the first engine startup might have introduced unexpected slosh in the lines to its companion.

Fluid management is hard. 

Personally I'm worried about the downcomers and header tanks.  Especially that long downcomer from the nose.  Fluid mechanics is complicated.  With a fluid that is already close to its boiling point, it might only take a small (potentially localised) pressure drop to cause some of that fluid to potentially boil and create gas bubbles.  Turbulent flow in the downcomer or even just sloshing as starship flips might be enough.  You also need to consider heat transfer from the downcomer pipes to the fuel.  I have no idea how well the downcomers are insulated, but there is probably going to be at least some heat transfer from the support brackets to the downcomer, then to the fuel/oxygen.  If the liquid is already at its boiling point, then that means that gas bubbles might form in the downcomers.  (If that happens during re-entry, then how do you get those bubbles out before the engines ingest them?)

If SpaceX is using superchilled Methalox, then given the short flight duration of the test flights, this might not be an issue atm.  But something keeps happening the engines during the flip, and I'm guessing they are ingesting gas.

9 hours ago, tater said:

It makes me wonder if the best solution might be a header tank for each engine for landing.

That might be a good idea from a reliability perspective.  It might not even be much heavier than the current design.   For a theoretical spherical pressure tank, tank mass is actually proportional to volume, (https://en.wikipedia.org/wiki/Pressure_vessel#Spherical_vessel).  So 3 small tanks with shorter and simpler plumbing to  the engines might not  add a significant mass cost.  It would mean a higher surface area to volume ratio, which suggests higher heat transfer, which implies more boiloff.  (Assuming the header tanks are located within the main tanks, if those tanks are depressurised and hence effectively a vacuum, then the surface area to volume ratio might be mostly insignificant.  Thermal transfer via the mounts/pipes might be the dominant concern).

I wonder whether carrying more fuel and doing a single engine flip at a higher altitude would allow them to successfully land and hence run more tests per prototype and get better data on how the fuel is behaving (sloshing?) in the tanks and downcomers during the flip.  (If needed they could do the flip, then ignite a second engine to decelerate after fuel has stabilised).   Plus they probably want to inspect some Raptor engines after a flight.  Of course, there is still the issue of whether one engine can provide enough torque to flip in a reasonable time.

If they are willing to consider a redesign, then maybe 3 sets of header tanks.   One set for each engine.  (So 6 header tanks total).  If you still do a 2 engine flip, then that gives you a spare engine and header tank/downcomer set, for partial redundancy.  It also implies a 50% increase in fuel/header tank mass.   

Next rearrange the plumping.   Dedicated piping between each set of header tanks and their associated engine.  Make that piping as short (and straight)as practical.   (Although not vertical, because we also want to move the header tanks somewhat dorsal of vertically above their engine).   

Consider a Starship in the bellyflop position at roughly terminal velocity.  At that point the fuel is experiencing roughly one G, directed roughly dorsal.  Next consider a Starship that is in the process of executing the flip.  Again the fuel is experiencing acceleration from the engines, directly rough aft.   So you want the downcomer oriented so that it slopes down from the tank to the engines at all times when in the lower atmosphere.  That way any gas bubbles that do form, will rise into the header tank, and not end up trapped in the downcomer.   My guess-estimate from this overly simplistic analysis is that you want the downcomer oriented roughly 45 degrees dorsal of vertical.   Obviously SpaceX could do a better analysis and design a solution that optimises the ability of any gas bubbles that do form to migrate back into the tanks, baffles to make sure that gas is never sucked into the tank outlet from fluid sloshing around, and good fluid flow rates after ignition. 

 

8 hours ago, ExtremeSquared said:

Suggests there was ballast on this one. Maybe more fuel.

Or a slightly slower average ascent rate,  to a lower altitude before the transition to skydiving.  (Or a combination of course).

 

2 hours ago, Flying dutchman said:

Media is being stupid again in my country.

They're saying that because Starship crashed, it wouldn't be wise for spacex to facilitate Space tourist missions in the near future.

 

They clearly don't know that those people are launching on Falcon 9/dragon..

 

They probably don't even care.  Most media outlets, only care about page (read ad) views per dollar spent on wages/salaries.  So an unresearched but sensational article churned out by someone with zero knowledge in the field is cheaper and faster to write, and will probably earn about as much money as better article that is properly researched.  (There are exceptions, but they are generally written by authors who are already knowledgeable in the relevant field and targeted at audiences who are actually want decent information).

 

53 minutes ago, derega16 said:

It kinda like "because Titanic sank we shouldn't use ship anymore"

Maybe more like "because of what happened to the Hindenburg, we shouldn't use hydrogen airships"?

Personally I think Starship's flip and propulsive land manoeuvre will be more dangerous than a well designed and tested capsule landing under parachute for many years.   (Probably permanently).   Sort of like comparing hydrogen filled airships to helium ones.  If an engine ingests gas during the flip, then there is a high chance that engine will fail, and if all engines share a common downcomer, then attempting to emergency start another engine risks feeding it the same gas.

 

[kerbiloid]

Looking at the SNx swinging before landing, the most hard part of the interflight refurbishment will be to wash it from inside.

But Falcon/Dragon have much longer and better history than Starship, so if Starship is Hindie, then Falcon is a bunch of helium balloons.

[YNM]

13 hours ago, xebx said:

SN 8 timing : 04m38s top altitude/flip - 06m42s landing

SN 9 timing : 04m35s top altitude/flip - 06m26s landing

Is it correct though that SN8 went to 12.5 km and SN9 only went up to 10 km ? I know that SN9's altitude was announced in the livestream but for SN8 there wasn't any.

Edited February 3, 2021 by YNM