totm nov 2023 SpaceX Discussion Thread

[Beccab]

https://rascal.nianet.org/wp-content/uploads/08-MIT-2022-RASCAL-Technical-Paper.pdf

This year's RASC (Revolutionary AeroSpace Concepts) awards have been released, and the winner of the Mars ISRU section (by a team of MIT students) is particularly interesting - it uses three cargo starship to produce 100 tons of methane per year from the martian surface. It's not ambitious enough to support human flights to and from the surface, but it's definitely a great starting point

Also:

 

 

 

Edited June 27, 2022 by Beccab

[tater]

 

[Beccab]

17 minutes ago, tater said:

 

Oh nice, looks like it's painted now!

[Brotoro]

Ship 24 needs a little cubesat that it can very slowly spit out before pirouetting so that the cubesat can quickly photograph tile condition before re-entry.

[CatastrophicFailure]

3 hours ago, Beccab said:

Oh nice, looks like it's painted now!

What'chall think, here? Just cosmetic or some sort of lower-heat spray-on thermal protection?

[RCgothic]

5 hours ago, Beccab said:

Oh nice, looks like it's painted now!

Pretty sure that's just shadow on the heat shield and reflection of the high bay door on the leeward side.

[tater]

28 minutes ago, RCgothic said:

Pretty sure that's just shadow on the heat shield and reflection of the high bay door on the leeward side.

No, it's painted.

Look at the edges of the hex tiles.

The sort of "stripe" on the right is a reflection, though.

[JoeSchmuckatelli]

31 minutes ago, tater said:

, it's painted

I'm assuming for a purpose and not just looks?

Depending on type, a gallon of paint weighs 6-12 pounds.  I thought part of the reason for stainless was to not have to paint it 

[tater]

16 minutes ago, JoeSchmuckatelli said:

I'm assuming for a purpose and not just looks?

Depending on type, a gallon of paint weighs 6-12 pounds.  I thought part of the reason for stainless was to not have to paint it 

The weight is meaningless in the context of Starship assuming it's just to clean up the edges visually.

[Beccab]

 

[tater]

 

[tater]

 

[mikegarrison]

18 hours ago, tater said:

The weight is meaningless in the context of Starship assuming it's just to clean up the edges visually.

Vehicle weight is never "meaningless".

[Beccab]

45 minutes ago, mikegarrison said:

Vehicle weight is never "meaningless".

It kinda is for B7/S24 - the payload is extremely light (one Starlink V2), and so is TWR at liftoff with 1.5. Lots of margin to reach a low, elliptical orbit

[tater]

5 hours ago, mikegarrison said:

Vehicle weight is never "meaningless".

In this context negligible would have been a better world choice, but for this vehicle, meaningless, as it will have ballast as payload. Cargo supposed to be >100t, actual cargo 0, so the paint mass doesn't matter at all (and no payload dispenser hardware that must have a higher mass than paint).

We're talking about the black paint squaring off the gaps left by the hex edges. Tiles are ~30cm? So the 1/2 tile gaps are ~0.039m² each. Guestimate with the couple areas that the not tile edges, but just slopes to make it look cool makes total paint areas maybe 3m². That's about 0.39 kg of paint (assuming 100 micron layer). Note that they could also do the same thing visually with 1/2 tiles—which would mass substantially more.

0.39kg kg of paint on a vehicle that masses 100,000+ kg empty. That's about like me being concerned about having a single unpopped corn kernel in my pocket.

We could nearly triple the paint and it's like me having a paperclip in my pocket.

 

Edited June 28, 2022 by tater

[tater]

 

[mikegarrison]

1 hour ago, Beccab said:

It kinda is for B7/S24 - the payload is extremely light (one Starlink V2), and so is TWR at liftoff with 1.5. Lots of margin to reach a low, elliptical orbit

Having margin doesn't mean weight is meaningless. Any vehicle weight means less margin.

I'm not saying this amount of weight is going to cause a failure or anything. I'm just saying that the idea that a flight vehicle is already heavy so a little more weight doesn't matter is just not how aerospace works. Weight always matters. If nothing else, any weight you save on the vehicle itself means more payload capacity.

Now for a specific flight test article, that's fine. I'm not saying they shouldn't paint this booster or whatever. I'm just saying that the weight is never "meaningless".

[StrandedonEarth]

16 minutes ago, mikegarrison said:

Now for a specific flight test article, that's fine. I'm not saying they shouldn't paint this booster or whatever. I'm just saying that the weight is never "meaningless".

For a vehicle this size, it may as well be meaningless, as it amounts to a bit of noise on the mass chart. Nonetheless, a negligible burp of thrust (that looked like a tiny bit of noise on the thrust graph, and was overlooked) from the new Merlin 1-C is what caused re-contact and doomed the third flight of the Falcon 1

[RCgothic]

If it's there to help re-radiate heat from these edge boundaries then it might save the weight of an extra row of tiles or an extra thickness of steel.

In those circumstances the paint could be mass negative.

[mikegarrison]

49 minutes ago, StrandedonEarth said:

For a vehicle this size, it may as well be meaningless, as it amounts to a bit of noise on the mass chart. Nonetheless, a negligible burp of thrust (that looked like a tiny bit of noise on the thrust graph, and was overlooked) from the new Merlin 1-C is what caused re-contact and doomed the third flight of the Falcon 1

It's not.

Seriously, I don't know what SpaceX's processes are like, but absolutely we track weight a lot closer than this where I work, and we build some very heavy flight vehicles.

[SunlitZelkova]

46 minutes ago, mikegarrison said:

It's not.

Seriously, I don't know what SpaceX's processes are like, but absolutely we track weight a lot closer than this where I work, and we build some very heavy flight vehicles.

I think tater and co just mean within the context of our amateur space enthusiast discussions it is “meaningless”, not that it doesn’t need to be paid attention by the engineers.

[tater]

3 hours ago, mikegarrison said:

I'm not saying this amount of weight is going to cause a failure or anything. I'm just saying that the idea that a flight vehicle is already heavy so a little more weight doesn't matter is just not how aerospace works. Weight always matters. If nothing else, any weight you save on the vehicle itself means more payload capacity.

If the whole thing was painted, or the paint was a non-trivial thickness some sort of applied TPS) then yeah, the mass might start being meaningful. From that pic is seems like it's more of an aesthetic choice to make the edges look straight though. Literally less than a gallon (sprayed)—if my ballpark is close, then under 1 pint of paint.

Thinking about small weight changes, presumably the vehicle can deal with that anyway, as on descent it is often venting, and the mass vented probably exceeds total paint mass even if the whole thing was painted—with different boiling points the LOX vs CH₄ must vent at different rates, throwing the CM off—which the vehicle must actively compensate for with the flaps during EDL.

2 hours ago, mikegarrison said:

It's not.

Seriously, I don't know what SpaceX's processes are like, but absolutely we track weight a lot closer than this where I work, and we build some very heavy flight vehicles.

I'm sure they've fed the sub-1kg paint mass into their model of the vehicle, but it's inconsequential compared to even the empty mass of the vehicle, much less the loaded mass.

We've also seen some tile sections that seem to be applied with adhesive. We've also seen the variability in surface on the steel—it's certainly improved with each vehicle, but they still have skin that is not perfectly smooth. Since the tiles are ceramic, and are smooth/straight within each hexagon, any gap in the steel substrate would be filled with any adhesive they use on those areas. That thickness is possible multiple mm, vs a 0.1 mm paint coat. They might make some model assumptions about that, but it seems like in practice they cannot possibly know the exact weight distribution of any such adhesive to some fraction of a gram per m² unless they are weighing the adhesive mixed before and after, then doing areas they are tightly tracking—maybe they are. "This particular adhesive-applied section is 2.3 m², and used 317g of adhesive."

Did they weigh and record any material between Shuttle tiles? (were those caulked?)

Edited June 28, 2022 by tater

[tater]

Or weld masses. On Starship, even a slightly thicker weld on a few parts of it could easily exceed 390g of decorative paint.

[mikegarrison]

40 minutes ago, tater said:

Or weld masses. On Starship, even a slightly thicker weld on a few parts of it could easily exceed 390g of decorative paint.

This is part of the reason why welds are not traditionally used on airplanes.

These days welds are done by machine and are extremely consistent. If you use friction stir welding, it's not even an additive process.

[tater]

16 minutes ago, mikegarrison said:

This is part of the reason why welds are not traditionally used on airplanes.

These days welds are done by machine and are extremely consistent. If you use friction stir welding, it's not even an additive process.

Yeah, for most of SS they have gone to robots, but if you look at some of the other stuff on there... some of it looks a lot less precise. Better and better, but still sorta rough around the edges.

SS is 4mm thick. A 2mm wire 16m long is 390g, so slight weld variations might easily equal the pretty symmetric paint mass.

Dunno, maybe it has some functional TPS component—elastomeric, and covers the edge of the "fluff" they have between the tiles and steel? They'd still want decent surface area to bond, so might as well make the hex edges a straight line?