SpaceX Starship/Super Heavy Engineering General Thread 5

[Overtone]

What's the cone angle for a supersonic shock wave at Booster reentry velocities?

Perhaps the shock coming off the inside edge of the grid fin rectangles may impact the new hot staging ring.  In the velocity range where the grid fin openings are choked, there's going to be a lot of power in the edge shocks. 

[eriblo]

What's the cone angle for a supersonic shock wave at Booster reentry velocities?

Perhaps the shock coming off the inside edge of the grid fin rectangles may impact the new hot staging ring.  In the velocity range where the grid fin openings are choked, there's going to be a lot of power in the edge shocks.

Reentry will likely be around Mach 4 so around 15° ( sin^-1(1/M ) ). Choked flow would be when you approach transonic speeds just before the landing burn starts so there will be much less heating.

[FutureSpaceTourist]

The drawing ZG uses is off by 30º between the inner and outers, so it makes it look like less room than there will actually be.

https://twitter.com/felixschlang/status/1678610291452530689

Center engines adjusted for better gimbaling range.

I don’t know how much clearance is needed between adjacent Rvacs and so whether it’s practical to have them spaced to leave bigger gaps for the center engines to gimbal into.

[DigitalMan]

That's pretty nice. If I recall, the center engines protrude down a bit further than the outer engines, yes? It brings up the question of what is maximum gimbal range and does that support it? Would there be plume impingement on the outer bells?

I like the idea from an earlier picture to position pairs of engines close together on the flat sides of the center triangle. Besides providing much more gimbal area it could provide more structural support for the outer engines.

Down side of the other idea is if one of the outer engines goes, it would probably take its pair with it.

[rsdavis9]

We also need room for legs eventually.

Legs may go on outside. Bad for tiles and reentry.
Legs go between paired vac raptors.

[Overtone]

What's the cone angle for a supersonic shock wave at Booster reentry velocities?

Perhaps the shock coming off the inside edge of the grid fin rectangles may impact the new hot staging ring.  In the velocity range where the grid fin openings are choked, there's going to be a lot of power in the edge shocks.

Reentry will likely be around Mach 4 so around 15° ( sin^-1(1/M ) ). Choked flow would be when you approach transonic speeds just before the landing burn starts so there will be much less heating.

Thanks that's very informative.  It suggests that a ring structure capable of surviving raptor startup during hot staging will have no trouble with reentry shocks.

[greybeardengineer]

We also need room for legs eventually.

Legs may go on outside. Bad for tiles and reentry.
Legs go between paired vac raptors.

Commonality of OML is very desirable so my bet is on inside the skirt mounted legs. Going to electric TVC SL Raptors should clear space on the inner skirt walls and that will help.

[OTV Booster]

We also need room for legs eventually.

Legs may go on outside. Bad for tiles and reentry.
Legs go between paired vac raptors.

Commonality of OML is very desirable so my bet is on inside the skirt mounted legs. Going to electric TVC SL Raptors should clear space on the inner skirt walls and that will help.

The more I think on it the more I like paired Rvacs. The crewed variants are highest priority for 6 vac engines (LAS) and they're the ones that'll need legs. One potential difficulty with legs mounted inside the skirt, especially if they follow the earlier design, is too narrow a base for easy stability.


The big downside of paired engines is fratricide, as mentioned earlier. Maybe the best fix for this is for Raptor to become as reliable as Merlin. Big shoes to fill. It'll be awhile.


How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.


A late thought on 'legs through the skirt.' Will there ever be circumstances where an SS on legs would need to fire the vac engines? I can't think of any but if it's there it would complicate the design.

[Lee Jay]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

[Eer]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Darmok, with his arms open wide ...

[Lee Jay]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Darmok, with his arms open wide ...

Shaka, when the walls fell.

[clongton]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Darmok, with his arms open wide ...

Shaka, when the walls fell.

Picard and Dathon at El-Adrel, <pause> Mirab, with sails unfurled.
Sometimes I wonder when Elon puts his engineering cap on, if he thinks in Tamarian.

[warp99]

We also need room for legs eventually.

Legs may go on outside. Bad for tiles and reentry.
Legs go between paired vac raptors.

Commonality of OML is very desirable so my bet is on inside the skirt mounted legs. Going to electric TVC SL Raptors should clear space on the inner skirt walls and that will help.

My take is that 9 engine Starships will just be for tankers and perhaps Starlink launchers. 

Crew Starships such as HLS and both Crew and Cargo Mars Starships will have 6 engines and therefore have plenty of space for 6 fold out legs between the three vacuum Raptors.  Six is the minimum number that gives good leg redundancy and has much better slope stability than designs with lower numbers of legs. 

HLS can have legs that fold out from fairings on the outside of the engine bap but Starships with TPS will need to have legs that fold out from inside the bay. 

[Robotbeat]

That makes no sense because much of the reason to have 9 engines is margin and pad abort.

[Nomadd]

That makes no sense because much of the reason to have 9 engines is margin and pad abort.

And redundancy. Losing a vacuum engine on a Mars mission would be awkward with only three of them.

[volker2020]

9 Engines will:
 - provide pad abort capacity
 - add redundancy
 - improve acceleration by 50%
 - thereby shorten time to reach LEO and thereby reduce gravity looses
 - thereby increasing total payload
 - allow to stretch star ship to even higher capacity.

I guess it really feels great for SpaceX to have an engine with such a great thrust to weight ratio.   

[OTV Booster]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Wow! All them little holes dropping the weight but keeping the stiffness. Use the skirt as landing legs and ditch the open hotstaging interstage all in one go. The engine bay would be heavy but loosing the legs compensates a bit.


This started out as a sarcastic response but there might actually be something there.

[Lee Jay]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Wow! All them little holes dropping the weight but keeping the stiffness. Use the skirt as landing legs and ditch the open hotstaging interstage all in one go. The engine bay would be heavy but loosing the legs compensates a bit.


This started out as a sarcastic response but there might actually be something there.

Sarcastic?  What does that mean?

[edzieba]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Wow! All them little holes dropping the weight but keeping the stiffness. Use the skirt as landing legs and ditch the open hotstaging interstage all in one go. The engine bay would be heavy but loosing the legs compensates a bit.


This started out as a sarcastic response but there might actually be something there.

Holes in the ship-attached interstage are no good, the interstage protects the engines from plasma impingement during entry. However, a solid 'expanding' interstage a-la Sea Dragon's upper stage, where the interstage flowers out to form the vacuum nozzle bell...

[Asteroza]

How much complexity/weight would it add for the interior leg assemblies to be structural members of the skirt and 'disconnect' in some way when it's time to splay out and deploy for landing? Some mechanisms come to mind but I'm working way beyond my pay grade here. I'd bet there are dozens of general solutions, some of which might be applicable.

Build the skirt like a giant vegetable steamer.

Wow! All them little holes dropping the weight but keeping the stiffness. Use the skirt as landing legs and ditch the open hotstaging interstage all in one go. The engine bay would be heavy but loosing the legs compensates a bit.


This started out as a sarcastic response but there might actually be something there.

Holes in the ship-attached interstage are no good, the interstage protects the engines from plasma impingement during entry. However, a solid 'expanding' interstage a-la Sea Dragon's upper stage, where the interstage flowers out to form the vacuum nozzle bell...

I thought the Sea Dragon's extended upper stage nozzle was a jiffypop stovetop popcorn style setup, where the folded/pleated nozzle was draped over the interstage/first stage though before inflating (something like the airmat nozzle designs)? But some Sea Dragon images show the upper stage engine exposed, so how would the interstage segment in that area fall away when the rest of the nozzle is draped over the booster is problematic...