totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

18 hours ago, zolotiyeruki said:

Another option is to switch to slightly-trapezoidal tiles for the nose section, and arrange them in rows.  That way, you only have three types of tiles: hexagonal for the cylindrical portion, half-of-a-hexagons at the joint between the rings and the nose cone, and trapezoid.

Oh, that’s a VERY good idea. Especially because **gaps are okay** and this can take advantage of that property. The ogive will change in curvature but you can pick a trapezoidal shape that can be used in a number of ways. Trapezoids can be flipped alternately to create a mostly-even ring for the less curved sections and they can be stacked edge-to-edge to create a more curved section. 

If that doesn’t make sense here’s what I’m thinking....

For the less curved sections:

∆ ∇ ∆ ∇ ∆ ∇ ∆ ∇ ∆ ∇

For the more curved sections:

∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆ ∆

(those are triangles not trapezoids but you get the point)

[tater]

Small tiles make sense if you want them all the same, and need to cover a large, curved area—the have to be small enough with enough gap to form the curve.

Why not carbon-carbon like Shuttle leading edges? Make a single piece for the nose? There are no undercuts except the very tip where it wraps around. Even if it wraps past 50% of the circumference it can be lowered from above in construction. Yeah, expensive, but it gets reused.

[sevenperforce]

20 hours ago, Terwin said:

It *should* survive reentry naked, but without heat tiles it could negatively affect temper and other properties of the steel, especially as they intend to aerobreak from both the Moon and Mars(the shuttle never went faster than LEO).

Without something like transpirational cooling, I do not think an entirely unshielded stainless steel Starship could survive re-entry. It can survive the loss of a few tiles because that each hot spot will wax off heat to the cooler shielded areas around it, but it does need some degree of shielding. Just far less than the Shuttle.

3 minutes ago, tater said:

Why not carbon-carbon like Shuttle leading edges? Make a single piece for the nose? There are no undercuts except the very tip where it wraps around. Even if it wraps past 50% of the circumference it can be lowered from above in construction. Yeah, expensive, but it gets reused.

Reinforced carbon-carbon for the nose, the trailing edges of the fins, and any weirdly-shaped transition points. Makes perfect sense. 

1 hour ago, paul_c said:

There's obviously a sliding scale between number of distinct tile shapes and gap size. I imagine if they worked out a tolerable gap size, their inventory could be 10-12 variants, rather than thousands like the space shuttle.

I think they could get away with just four variants: hex files, truncated hex tiles, trapezoids, and right triangles. The right triangles edge the trapezoids. Gap size tolerances are pretty high tbh.

1 hour ago, paul_c said:

Of course, too big a gap negates (or renders inaccurate) a lot of the aerodynamics work if its done on a smooth stainless steel shell!

At the tile thicknesses we’re talking about, the aero properties are not going to be significant. Especially given airspeed. 

[tater]

5 minutes ago, sevenperforce said:

Reinforced carbon-carbon for the nose, the trailing edges of the fins, and any weirdly-shaped transition points. Makes perfect sense. 

I mean  the ENTIRE nose. Every single part of the nose that is not cylindrical. 1 piece.

[sevenperforce]

6 hours ago, RCgothic said:

As always an impressive diagram, but I'm pretty sure this ends up with a large number of different custom tiles.

The idea would be to have a single RCC “filler tile” shape that would fill the regularly-shaped gap created by iterations of this pattern. If the pattern repeats, the filler tile shape will repeat as well. So just three tile shapes: hex, filler, and nosecone.

But I like the trapezoid idea better. 

1 minute ago, tater said:

I mean  the ENTIRE nose. Every single part of the nose that is not cylindrical. 1 piece.

I think you would run into issues with size and attachment mechanism. Plus, a vibration-induced crack or latent manufacturing defect could destroy the entire nosecone and result in an instant RUD, whereas tiles are more fault-tolerant. 

16 hours ago, paul_c said:

How about making the tiles half as thick each as they need to be; then attaching twice the number in 2 layers? Curved sections will have big(ger) gaps but with all the tiles overlapping it still leaves the 1 tile thickness. For a sufficiently small gap, it would be approachable to engineer the situation to accommodate this with heat transfer thru the structure?

Sort of a Dragonskin body armor approach, eh?

It’s not a bad idea but I don’t think it would work out. Attachment becomes an issue because there is less space to work with. You are introducing an entirely new degree of vibrational freedom which needs to be accounted for. And hot spots will form between overlapping tiles because the tiles do not conduct heat well (that is their purpose after all).

[kerbiloid]

They should make a starship of clay and break it from nose.

Then gather the debris and reproduce them as tiles. 

So, they will match the pattern of breaking forces.

[Brotoro]

I was under the impression that Reinforced Carbon Carbon was relatively heavy stuff.

[tater]

14 minutes ago, sevenperforce said:

I think you would run into issues with size and attachment mechanism. Plus, a vibration-induced crack or latent manufacturing defect could destroy the entire nosecone and result in an instant RUD, whereas tiles are more fault-tolerant. 

Possible, but it's not like it could not have a composite substrate that is vibration tolerant. If you eliminate the undercut sections (those as unique parts, though very few of them), attachment could be the same glue/mechanical used for the tiles.

Obviously the RCC used was susceptible to damage (Columbia leading edge), and even a bird strike could be an issue (assuming there are any at an altitude where the velocity is high).

I'm assuming they are welding pins on that have a small bulb at the tip, and have a cast in place fastener in the tiles with an undercut to grab the pins, BTW, has anyone seen a super close up?

1 minute ago, Brotoro said:

I was under the impression that Reinforced Carbon Carbon was relatively heavy stuff.

Yeah, SS has margin though, at a certain point is seems like "get it working, then refine" makes a certain amount of sense. I assume the tiles are not light, either, though.

[RealKerbal3x]

This is a Raptor that was removed from SN8 during its test campaign. Interesting.

[Spaceception]

25 minutes ago, RealKerbal3x said:

This is a Raptor that was removed from SN8 during its test campaign. Interesting.

Did they repair it or something then? It must not have been too serious if they're using it again.

[RealKerbal3x]

Just now, Spaceception said:

Did they repair it or something then? It must not have been too serious if they're using it again.

They must have repaired and/or upgraded it.

SN39 was removed after SN8's first static fire, which seemed pretty norminal.

[YNM]

1 hour ago, tater said:

I mean  the ENTIRE nose. Every single part of the nose that is not cylindrical. 1 piece.

Perhaps either cost or reuse rate + damage probability would make problems with that. With small tiles they're cheaper I assume.

[grungar3x7]

Remember, the main reason for hex tiles in the first place, is to prevent hypersonic plasma being channeled in a straight line...

 

I'm not sure of a solution to the curvature problem, personally, but trapezoids and half hexes don't seem to be the answer, considering the reason for initial shape choice.

[JoeSchmuckatelli]

Another resource: How to Cover a Monolithic Dome with Tile or Rock | Monolithic Dome Institute

and this 'fish scale' design is cool: Dome Tile | MCA Tile (mca-tile.com)

 

[CatastrophicFailure]

3 hours ago, sevenperforce said:

The idea would be to have a single RCC “filler tile” shape that would fill the regularly-shaped gap created by iterations of this pattern. If the pattern repeats, the filler tile shape will repeat as well. So just three tile shapes: hex, filler, and nosecone.

But I like the trapezoid idea better. 

3 hours ago, tater said:

Could they shield the nosecone with simply different sizes of tiles? There’s pictures on NSF of SN11, below the big tiled area are smaller patches of test tiles and one such patch does indeed have some smaller hex tiles one the edge. There’s some obvious gaps but not bad. 

[HvP]

On 2/5/2021 at 8:10 AM, Elthy said:

SpaceX still has a problem, even if they try the three engine burn next time. If the issue was with the fuel supply another engine wouldnt help, if the problem was in the engine itself then they seem to have issues with Raptors reliability. The second one is propably worse, since those are way more complex to develop/modify.

This seems like a fair assessment to me.

The whole point of Starship, of course, is to be able to recover and reuse engines for multiple flights. For this experiment to work the Raptors don't just have to not fail for one flight, they have to perform for multiple flights and not cause a mission failure in those future flights.

The Merlin engines have shown that they can be refurbished easily enough to fly reliably and economically. Will they get there with the Raptor?

Edited February 6, 2021 by HvP

[Flying dutchman]

54 minutes ago, HvP said:

Will they get there with the Raptor?

I think they eventually Will, yes.

[mikegarrison]

11 hours ago, Elthy said:

Obviosly it would be easier with one tile for everything, but that wont be possible. Dont forget that the Spaceshuttle was build in another era with conservative NASA design. I guess even on the last flights most stuff regarding the tiles was done by hand, including inventory and ordering new ones. But if you automate the process most of the (expensive) work is done by the computer. Modern manufacturing has no issue with that if you design the process properly in the first place.

I work for a modern aerospace manufacturing company, and I know how important it is for us to standardize and simplify everything we possibly can.

[tater]

1 hour ago, mikegarrison said:

I work for a modern aerospace manufacturing company, and I know how important it is for us to standardize and simplify everything we possibly can.

Yeah, and as goofy as it might seem to at least some of us, it's important to realize that SpaceX is serious about Mars. I'm a SpaceX fan, but I have not drunk the Mars Kool-Aid. They have some with breakfast every morning. Musk talks about 1000 Starships... at the same time. Yeah, goofy—but they want something scalable, and that means simplicity and standardization, and in numbers that look like airliner level numbers of airframes (spaceframes?).

[paul_c]

Were there 1000 747s?

[Brotoro]

There were 1,562 747s.

[tater]

Again, me observing that SpaceX thinks they need 1000s of SS to colonize Mars is not the same as me thinking that is likely—but that idea informs their decision making, kooky or not.

[mikegarrison]

55 minutes ago, Brotoro said:

There were 1,562 747s.

The 747 is still in production, although not for much longer.

[xebx]

Starship will need heat shield tiles on 55% of its surface : Temperature 1500K just for LEO  reentry.

 

Spoiler

 

Notes :

- Starship dry weight : 108T + 11T fuel + 2T Biprop. for desorbit and landing. (300m/s DeltaV should be more than enough for landing lol)

- According to AeroGUI in RSSRO with procedural wings+tank+fairing, Starship has Lift/Drag ratio around 5, but when i look at item UI debug it's 1:1 or 3:4.

- 8kN RCS are needed to keep control of the ship between mach 5 and 1.1, for some reason it's not 100% stable at these speeds, but maybe it's different with flaps (wings are arranged in V to simulate flaps here, and CoM and CoL are finely tuned) or with different pitch adjustment.

- Starship final velocity : 76m/s (very close to current SpaceX tests), in the end there is a good margin for safe landing.

- The 3 Raptors SL have been throttled down to 67%, so they have same SLTwr as 2 Raptors + redundancy.

- This Starship delivers 118Tons payload in LEO 200km, SH has 36 Raptors SL 109% thrust, it helps.

 

 

I highly doubt it will reentry direct from Lunar or Mars orbit, the velocities are another story : from 12000 m/s to 18000 m/s. (4x temperatures compared to LEO)

AFAIK Starship arrival from Mars will be at Lunar Gateway (it saves around 2200 m/S DeltaV), and Lunar Starship is all white.

 

 

Edited February 11, 2021 by xebx

[kerbiloid]

Pinhead.

Spoiler

They should make pin-shaped tiles and cover the rocket head densely, like with nails for yoga.

Spoiler

This will standardize and simplify the tiles as much as possible.

A voxel heat protection.