totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

2 minutes ago, tater said:

Might be wrong, I thought he said they'd not throttle—I bet I'm mixing it up with the fixed SL raptors on SH.

Right, makes sense.

Back during the 2016 IAC presentation, I believe Elon said the vacuum Raptors would use differential throttle for pointing on orbit. From reporting on that presentation: "Per the notional design of the Tanker/Spaceship, only the three SL Raptors in the center of the vehicle are capable of gimbaling for precise attitude control during ascent and landing maneuvers. Differential throttling on the outer Vac engines is employed for control during in-space maneuvering."

I don't think it was in any of the slides, though; just something he said.

[tater]

Yeah, and in some talk where he said the outer SH engines would be fixed to the skirt, he said they were easier since they didn't have to throttle or gimbal. I mixed the 2 up.

Regardless, the intermediate version that we have pics of up the thread (the Rvac they test fired at SL) is probably perfectly capable of getting SS to orbit just those. The must underperform SL Raptors in thrust within some altitude (ambient pressure) range, but since they should be better in all ways up high, and the vehicle is also lighter as they go, it seems like a non-issue (besides which Elon talked about a stripped version with just 3 engines, right?).

Edited February 13, 2021 by tater

[RCgothic]

40 minutes ago, RyanRising said:

Definitely more him agreeing to six vacuum engines than coming out with it himself, but it's still some validation on the idea.

 

6 hours ago, RCgothic said:

Elon has previously agreed a pure tanker with stretched tanks and 9 raptors (6Vac, 3SL) might make sense.

Yup. 

[RyanRising]

5 hours ago, RCgothic said:

Yup. 

I may need to get more sleep, thanks

[tater]

 

[YNM]

Good to hear they're satisfied enough with the falling-aerodynamic data to start actually try stick the landing. When they'd land it from that position it'll be a new step of the game.

Edited February 13, 2021 by YNM

[tater]

[Spaceception]

A couple weeks to go in February, I wonder if they'll push to have Superheavy stacked by the end of the month.

[tater]

 

[RealKerbal3x]

Reason to be cautiously optimistic: 

 

[zolotiyeruki]

"Master the flip"?  It seems to me that they've already got a pretty good handle on the maneuvering algorithms.  They're 2 for 2 on that part.  It's the engines that are currently giving them trouble.

Speaking of which, did SpaceX ever say why the second engine didn't light on SN9?

[kerbiloid]

Spoiler

 

[RealKerbal3x]

47 minutes ago, zolotiyeruki said:

"Master the flip"?  It seems to me that they've already got a pretty good handle on the maneuvering algorithms.  They're 2 for 2 on that part.  It's the engines that are currently giving them trouble.

Speaking of which, did SpaceX ever say why the second engine didn't light on SN9?

Yeah, the flip seemed to work just fine on SN8. The only reason it didn't really work on SN9 was that only one engine was ever lit and there wasn't enough torque from that one engine gimballing to correct for the angular velocity from the flip.

And no, they only ever said that the engine failed to relight.

[tater]

 

[Silavite]

There's a pretty good chance of freezing rain overnight in Boca Chica.

Quote

Excerpt from NWS Brownsville Forecast Discussion

Model soundings still lean toward a classic warm nose freezing rain
signature late Sunday evening through Monday morning, however, snow
flurries or brief periods of light snow, mainly across Zapata and
Jim Hogg counties, may be possible Monday morning as cooler air
aloft arrives. Flyovers, interchanges, bridges, and elevated
surfaces will likely become icy in any precipitation Sunday night
into Monday morning. This may occur even when surface temperatures
are a degree or two above freezing. As a result, travel should be
avoided Sunday night through Monday morning.

The facility's proximity to the coast may help to prevent the ground from freezing, but exposed surfaces (like the entirety of SN10...) will likely get covered in a thin icy glaze.

[coyotesfrontier]

3 hours ago, Silavite said:

The facility's proximity to the coast may help to prevent the ground from freezing, but exposed surfaces (like the entirety of SN10...) will likely get covered in a thin icy glaze.

For most aircraft that might be a problem, but rockets are a different story 

[Silavite]

8 minutes ago, coyotesfrontier said:

For most aircraft that might be a problem, but rockets are a different story 

True, something built to hold cryogenic liquids should probably be fine. Even icing on the control surfaces shouldn't be a huge deal since they're more like spoilers. I think that the only risk would be buildup of ice on the joints such that the control surfaces are unable to actuate (if they were crazy enough to try and fly in such conditions).

Edited February 14, 2021 by Silavite

[mikegarrison]

The main problems with ice on airplanes is that it ruins the aerodynamic shaping of the surfaces and is heavy. Rockets are certainly susceptible to at least the latter issue.

I might also point out that the shuttle losses were caused by (or at least partially caused by):

a) cold weather, and

b) ice buildup on the tank insulation.

For what that's worth.

Edited February 14, 2021 by mikegarrison

[magnemoe]

20 minutes ago, mikegarrison said:

The main problems with ice on airplanes is that it ruins the aerodynamic shaping of the surfaces and is heavy. Rockets are certainly susceptible to at least the latter issue.

I might also point out that the shuttle losses were caused by (or at least partially caused by):

a) cold weather, and

b) ice buildup on the tank insulation.

For what that's worth.

Now one problem with starship might be water behind the tiles if it freezes and expand. 

[xebx]

On 2/13/2021 at 7:41 AM, tater said:

 

 

Did i hear 30Tons header tank (Lox) ? i'm surprised : (or is it 13T ?)

- they only need 11T total to desorbit and land safely, why would they put so much fuel in the top ?

- the only reason i see is to have more weight in the top, that gives a better balance during atmo reentry, this explains why they need bigger flaps at the top compared to my simulations. It also gives more margin for fueled trajectory correction.

- previoulsly i extrapolated the header tank volume and weight from photos, and ended with a 25-30m3 ->20-25T Lox, i thought it was too much, but why not.

- It could also explain why the terminal velocity seems to be around 87m/s : i found 76 m/s with 10T remaining fuel. With 35T remaining fuel Starship probably ends at 85-90 m/s.

 

I'm curious about this, i will have to retest Starship reentry, will 25T added fuel for landing increases the temperatures ? (Starship 116T vs 141T)

 

Edited February 14, 2021 by xebx

[CastleKSide]

@xebx what kind of system are you using for these simulations? Custom programming or some kind of flight sim?

[tater]

Scrub, weather.

 

[sevenperforce]

We’ve...

...got...

...a...

SUPERHEAVY GRIDDDDD FINNNNNN!!!!!!!!

 

 

[Clamp-o-Tron]

Just now, tater said:

Scrub, weather.

 

They ought to be consulting with those Russians and their Soyuz. Might help their launch cadence if they can launch in the rare Florida blizzard!

[xebx]

23 hours ago, CastleKSide said:

@xebx what kind of system are you using for these simulations? Custom programming or some kind of flight sim?

KSP RSSRO (and Principia), procedural tank has a setting "tank-sep-starship" (stir-welded), add to this Raptors (small tweaks : SL 108% = 1921kN, Vac 105% = 2055kN) and procedural fairing (density 0.12), and the result is very close to/can be crossed with known data (wikipedia, etc).

There are some limitations (for ex : small wings are not flaps) and possible inaccuracies,  but so far it looks fine.

Edited February 15, 2021 by xebx