totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

13 hours ago, CatastrophicFailure said:

How about the National Team lander’s photocopied switches for... parachutes. 

Also, closeup of SN7.1’s fate:

 

Yep, I'm pretty sure that's exactly what they were going for.

[Elthy]

It didnt even rip at the welds, realy impressive.

[sevenperforce]

28 minutes ago, Elthy said:

It didnt even rip at the welds, realy impressive.

Exactly.

My somewhat-informed materials science take: Ductile yield strength and fracture propagation in cold-rolled steel are extremely well-understood. Weld failures, on the other hand, are dependent on many, many difficult-to-predict variables. In order for their digital models to accurately predict the vehicle's response to transitive stresses, they needed to be sure that their welds were substantially stronger than the bare steel, in all failure modes. If they are certain that the bare steel will fail before their welds do, then their computer modeling is much simpler and much more accurate.

What we see here is that ductile failure and fracture propagation took place entirely within the bare steel regions, preferentially along areas where the bare steel was stressed (but not by the welds themselves). It's particularly notable when you see the torn steel on the left with a fracture that passed across the weld without traveling down it.

[sevenperforce]

Oh my god this is beautiful. 
 

 

The glorious Mach diamonds. The roar. The utter power of the biggest vacuum engine ever constructed.

THEY BUILT A VACUUM ENGINE THAT CAN BE TESTED AT SEA LEVEL. Seriously this is freaking amazing. 

[cubinator]

They should release some full duration ultra-high quality rocket firing audio...

[IncongruousGoat]

38 minutes ago, sevenperforce said:

THEY BUILT A VACUUM ENGINE THAT CAN BE TESTED AT SEA LEVEL. Seriously this is freaking amazing. 

It's... less exciting than you'd think, actually. From what we can see of the nozzle, it doesn't look like they played with the nozzle geometry to try and reduce flow separation (as was done on the RS-25), and from the shape of the plume, the engine is very over-expanded at sea level. It looks like they just worked out the size of the biggest nozzle they could mount on Raptor's combustion chamber that wouldn't tear itself to pieces when fired at sea level, and went with that. It's a compromise design, sacrificing some tens of seconds of specific impulse in vacuum for the ability to fire the engine at sea level, probably for abort capability and landing redundancy reasons.

44 minutes ago, sevenperforce said:

The utter power of the biggest vacuum engine ever constructed.

It's only the biggest if you don't count the M-1 (http://astronautix.com/m/m-1.html). Which, to be fair, never got as far as an all-up test, but it seems like it was at least put together at some point.

 

None of which is to say the test isn't exciting. It's very exciting. It's another piece of SS/SH in action, and the fact that they went with a relatively short nozzle helps answer a lot of open questions about low-altitude abort scenarios and landing contingency plans. Also, it's Raptor, and Raptor is an amazing engine. So yes, hype.

[RCgothic]

And it wasn't an unsupported test, which helps explain its sea level durability a little, but maybe not entirely:

 

Edited September 25, 2020 by RCgothic

[Nothalogh]

6 hours ago, sevenperforce said:

Oh my god this is beautiful. 
 

 

The glorious Mach diamonds. The roar. The utter power of the biggest vacuum engine ever constructed.

THEY BUILT A VACUUM ENGINE THAT CAN BE TESTED AT SEA LEVEL. Seriously this is freaking amazing. 

It's funny, not even the usual shills and detractors can come up with a way to spin these engines negatively

[RCgothic]

An expansion ratio of 107:1 (Elon says it could get a little bigger) is not exceptional for a vacuum engine, but it is amazing at sea level. High chamber pressure really helps!

RVac knocks the socks off RS-25 (67:1) as a sustainer engine but not a pure vacuum engine like MVac (1:165) or RL10(1:280). There are still trade offs like being able to fire at sea level, fit in the engine bay, and regeneratively cool a nozzle that large.

But the number of things this Raptor is great at (if not exceptional) certainly beats every other engine. It seemingly has no weaknesses.

[tater]

 

[tater]

 

The people on top give some sense of scale to what a "mockup" of lunar starship will offer in terms of "room for activities." LOL

 

[RCgothic]

9 minutes ago, tater said:

 

The people on top give some sense of scale to what a "mockup" of lunar starship will offer in terms of "room for activities." LOL

 

I'm looking forward to a new video of an astronaut lapping the circumference in zero g!

[Nightside]

4 minutes ago, RCgothic said:

I'm looking forward to a new video of an astronaut lapping the circumference in zero g!

On magnetic roller skates? Or do you mean on the inside?

[RCgothic]

7 minutes ago, Nightside said:

On magnetic roller skates? Or do you mean on the inside?

The inside. Hang on, let me dig out the Skylab video (largest diameter hab ever lofted). There's a good video of astronauts lapping the interior, and Starship will be better because it's 50% bigger.

At 4m radius you can simulate 1g at a running speed of 6.25m/s!

 

Edited September 25, 2020 by RCgothic

[DDE]

6 hours ago, Nothalogh said:

It's funny, not even the usual shills and detractors can come up with a way to spin these engines negatively

There's always the sour grapes cope.

Sincerely, a former detractor.

[Nothalogh]

1 hour ago, DDE said:

There's always the sour grapes cope.

Not really, because it still makes Lockheed and Boeing look like either chumps or swindlers

[sevenperforce]

1 hour ago, DDE said:

There's always the sour grapes cope.

Spoiler

Sincerely, a former detractor.

Sometimes I just marvel that Glushko designed a version of the RD-270 which would have run on PENTABORANE and pushed 340 s AT SEA LEVEL.

Now THAT would have been just beyond.

[magnemoe]

4 minutes ago, sevenperforce said:

Sometimes I just marvel that Glushko designed a version of the RD-270 which would have run on PENTABORANE and pushed 340 s AT SEA LEVEL.

Now THAT would have been just beyond.

Well https://en.wikipedia.org/wiki/Pentaborane(9) has the 12 score in the fire diamond who is impressive. 

 

[CatastrophicFailure]

2 hours ago, tater said:

The people on top give some sense of scale to what a "mockup" of lunar starship will offer in terms of "room for activities." LOL

I really want to see footage of people just moving around in lunar (or Martian) gravity. 

No heavy space suits, nothing to encumber them. Would one walk across a 9-ish meter room or just sort of single-bound it? Would that be practical inside with some sort of ceiling? The Apollo LEM wasn’t nearly big enough inside for anything like that.
 
Oh and water. I want to see how a sizable bowl of liquid behaves in low gravity, if only because it’s never really been done AFAIK. 
 

And of course, sooner or later we need to send cats to the Moon. The Moon needs a Cat a Room. 

[sevenperforce]

12 minutes ago, magnemoe said:

Well https://en.wikipedia.org/wiki/Pentaborane(9) has the 12 score in the fire diamond who is impressive. 

Lovely discussion points on pentaborane-9 from this and other sources:

• "Problems with this fuel include its toxicity and its characteristic of bursting into flame on contact with the air."
• "...reacts violently with some fire suppressants, notably with water."
• "Its acute toxicity is comparable to some nerve agents."
• "It is difficult to extinguish a pentaborane fire. Structural firefighting clothing will NOT provide adequate protection."
• "In humans, minor intoxication has been reported to cause various central nervous system (CNS) symptoms, some of which are dizziness, drowsiness, blurred vision, fatigue, muscle spasms, hallucinations, memory loss, behavioral changes, poor judgment, lethargy, confusion, inability to concentrate, headache, nausea, vomiting, and feelings of constriction in the chest."
• "With severe intoxication...spasms, convulsions, agitation, hallucinations, hepatitis, destruction of skeletal muscle, coma, and death."
• "In case of spillage ignition, the area should be deluged with water. The water will not extinguish the fire but is of value in cooling surrounding equipment and facilities."
• "In conclusion, the best way to decontaminate a spill area is ignition of the pentaborane."
• "We find as a matter of law...that the release of pentaborane creates problems of uniqueness and magnitude and constitutes an unnecessary, extraordinarily and inherently dangerous hazard."

[Guest]

Pentaborane is rather pricey, too. Ultimately, it's similar to problems with fluorine oxidizer - more trouble than it's worth, and expensive to boot. Pentaborane isn't quite as expensive as fluorine, but still, it's not something trivial. LOX, LH2, kerosene and methane all have the advantage of being cheap and as common as dirt. The first two are in the air and water, the latter are produced by oil industry in massive volumes (especially methane, which is basically waste). If you want affordable, reusable space vehicle, exotic fuels or oxidizers bring you no closer to that goal.

[tater]

So they have a racetrack up the dorsal spine of SS. Presumably at some point covered (not for SN8, but for orbital versions).

Wonder if the vehicle could get asymmetric legs?

Legs tucked inside on the windward (ventral) side, under the TPS, and something more F9 like on the dorsal surface? Not F9 legs, but widespread, using as much vertical space as needed to fold.

[RealKerbal3x]

28 minutes ago, tater said:

So they have a racetrack up the dorsal spine of SS. Presumably at some point covered (not for SN8, but for orbital versions).

Wonder if the vehicle could get asymmetric legs?

Legs tucked inside on the windward (ventral) side, under the TPS, and something more F9 like on the dorsal surface? Not F9 legs, but widespread, using as much vertical space as needed to fold.

Perhaps a smaller version of the 2016 ITS landing legs?

It seems like they're trying to minimise disrupting the shape of the heat shield (presumably so they don't need a zillion different shapes and sizes of tiles like Shuttle had), but the last set of official renders we got showed a bulge in the aft heat shield, presumably to smooth out the landing leg housing.

So maybe a return to three large wide-stanced deployable landing legs could be possible. Quick mockup of what that might look like in MS Paint:

Obviously the legs would be more smoothed into the main fuselage than they appear here, but I imagine it looking something like this if they went back to the large ITS-style legs.

Edit: Just realised I got the engine config the wrong way up, but that doesn't really matter

Edited September 25, 2020 by RealKerbal3x

[magnemoe]

1 hour ago, sevenperforce said:

Lovely discussion points on pentaborane-9 from this and other sources:

• "Problems with this fuel include its toxicity and its characteristic of bursting into flame on contact with the air."
• "...reacts violently with some fire suppressants, notably with water."
• "Its acute toxicity is comparable to some nerve agents."
• "It is difficult to extinguish a pentaborane fire. Structural firefighting clothing will NOT provide adequate protection."
• "In humans, minor intoxication has been reported to cause various central nervous system (CNS) symptoms, some of which are dizziness, drowsiness, blurred vision, fatigue, muscle spasms, hallucinations, memory loss, behavioral changes, poor judgment, lethargy, confusion, inability to concentrate, headache, nausea, vomiting, and feelings of constriction in the chest."
• "With severe intoxication...spasms, convulsions, agitation, hallucinations, hepatitis, destruction of skeletal muscle, coma, and death."
• "In case of spillage ignition, the area should be deluged with water. The water will not extinguish the fire but is of value in cooling surrounding equipment and facilities."
• "In conclusion, the best way to decontaminate a spill area is ignition of the pentaborane."
• "We find as a matter of law...that the release of pentaborane creates problems of uniqueness and magnitude and constitutes an unnecessary, extraordinarily and inherently dangerous hazard."

An pretty old chemistry joke, yes its very toxic but that is not an problem as it detonates on contact with air. 
And its an difference between a few gram in an lab and kiloton on an launchpad, 6 order of magnitude explains it. 

 

[zolotiyeruki]

1 hour ago, CatastrophicFailure said:

I really want to see footage of people just moving around in lunar (or Martian) gravity. 

No heavy space suits, nothing to encumber them. Would one walk across a 9-ish meter room or just sort of single-bound it? Would that be practical inside with some sort of ceiling? The Apollo LEM wasn’t nearly big enough inside for anything like that.

Well, you could do the math.  Let's say you've got a 50cm vertical jump on earth (because that makes the math easy).  0.5 = 1/2*9.8*t^2, and your fall time is about 1/3 second, and your vertical speed is 1/3*9.8 ~= 3.3m/s.  On the moon, with roughly 1.6m/s^2 gravity, your fall time would be about 2 seconds, so you'd make it 1/2*1.6*2^2 ~= 3.2 m off the floor.

That's a standing jump, upwards.  If you launched at a 45 degree angle, your initial vertical velocity would be .707*3.3 = 2.3m/s, which works out to a fall time of about 1.5 seconds.  If we neglect air resistance, you'd fly 1.5s * 2 * 2.3 = 6.9 meters.  If you're a bit more athletic, or you get a running start, then yeah, crossing a 9m room in a single bound is within the realm of possibility.