totm nov 2023 SpaceX Discussion Thread

[IncongruousGoat]

8 minutes ago, tater said:

You think they deploy to form a sort of meta-engine bell?

I went and consulted a friend of mine who's studying fluid dynamics as to the whole meta-nozzle thing, and got back an answer of "That wouldn't work at all". If it have a central protrusion of some sort it could act as an aerospike, but that's not what's going on here.

It could be that SpaceX decided that they didn't need the extra specific impulse, but I find that to be unlikely given the number of times they've emphasized that BFR/BFS isn't a big, dumb booster.

[RedKraken]

All sea-level engines give up 20s of Isp .... payload would be130t to orbit....and maybe 120t to mars surface.

[Nibb31]

A meta-nozzle might not work as well as  a proper vacuum nozzle, but it might be a good enough compromise to make the reduction of engines worthwhile.

Those petals might also be for protecting the engines from debris during landing.

 

[tater]

Again, this might be the LEO version, in this case used for a lunar return mission, for "real" BLEO they perhaps make a vac engine version.

[IncongruousGoat]

1 minute ago, RedKraken said:

All sea-level engines give up 20s of Isp .... payload would be130t to orbit....and maybe 120t to mars surface.

Well, they could be optimized for a regime somewhere in the middle, like the LR-105 was, or they could have a funky nozzle geometry that allows them to operate well at all altitudes, like the RS-25. I suspect it's the former, though, given how much of a mess the development of the RS-25 was.

1 minute ago, Nibb31 said:

Those petals might also be for protecting the engines from debris during landing.

This seems more likely. That and TPS for the engines during re-entry.

[AVaughan]

Those engine bells look larger than the sea level engine bells on earlier renders. eg 

So they might be some sort of intermediate engine.  Hopefully the briefing will provide more details.

 

Edit: also a commenter on Arstechnica's thread said " Elon's claims that the BFS ship will be capable of single stage to orbit missions with a modest payload mass."  I've not seen that claim before, but it would suggest that BFS is capable of single stage suborbital antipodal flights, with a "modest" payload (100 passengers?).

Edited September 14, 2018 by AVaughan

[RedKraken]

Single engine design across booster and spacecraft will speed up development a lot and add quite a bit of safety factor.

And the sL engine is way more robust than the vac. Less likely to be damaged by landing/takeoff debris.

Could be a smart way to hit project goals sooner.

[Scotius]

Is it me, or is BFR evolving to be more and more like a spaceplane? VTOL spaceplane to be more precise

Also, this - from the old (1950) movie "Destination Moon":

 

Looks like history is making a full circle, eh?

[magnemoe]

7 hours ago, IncongruousGoat said:

It looks like someone took the old 7-engine design for ITS and drew it on a BFS airframe, and then added a Shuttle-style tailfin for good measure. I highly suspect it was produced by a third party that's been out of the loop for a couple of years.

Oh, wait. Now that you've pointed that out...

This is very strange.

Yes, that is done by someone with little idea that they do, BFR upper stage with an shuttle style tail fin larger than the two fins it has. 
And why do an full power burn around the moon? Eiter to enter orbit / land or for gravity assist. 

[Xd the great]

5 hours ago, IncongruousGoat said:

I went and consulted a friend of mine who's studying fluid dynamics as to the whole meta-nozzle thing, and got back an answer of "That wouldn't work at all". If it have a central protrusion of some sort it could act as an aerospike, but that's not what's going on here.

It could be that SpaceX decided that they didn't need the extra specific impulse, but I find that to be unlikely given the number of times they've emphasized that BFR/BFS isn't a big, dumb booster.

BFR is not a big dumb booster. It is a reuseable, cheap big dump booster.

[sh1pman]

41 minutes ago, Xd the great said:

BFR is not a big dumb booster. It is a reuseable, cheap big dump booster.

Big smart booster.

[Xd the great]

9 hours ago, sh1pman said:

 

They should hire elon as their guide.

7 minutes ago, sh1pman said:

Big smart booster.

Technically yeah. 

 

Could those skirts be landing legs/docking ports for refueling?

[Nefrums]

It looks like the "wings" can move.  If they can tilt a lot it could, together with  the top fin, make ship fairly stable reentering belly first. 

Could it be that the entire engine segment is movable?    So that they can slide it deeper into the body?   That would move CoM, something that would simplify the flipping maneuver. and it could also make the skirt around the engine act as a vacuum nozzle (not sure that could work) 

Edited September 14, 2018 by Nefrums

[Xd the great]

35 minutes ago, Nefrums said:

It looks like the "wings" can move.  If they can tilt a lot it could, together with  the top fin, make ship fairly stable reentering belly first. 

Could it be that the entire engine segment is movable?    So that they can slide it deeper into the body?   That would move CoM, something that would simplify the flipping maneuver. and it could also make the skirt around the engine act as a vacuum nozzle (not sure that could work) 

I think the skirt is a heat shield

[NSEP]

9 hours ago, IncongruousGoat said:

I'm of the opinion that Elon is just messing with us at this point. That render doesn't make much sense as a new version of BFR for a number of reasons, not least of which that it lacks any sea-level-optimized nozzles, which makes it incapable of landing on Earth. This is Elon Musk's Twitter account, people. It's not exactly a reputable news source. Hopefully this will all be cleared up in the stream on Monday.

Its litterly shrouded in darkness, lets just wait and see what the SpaceX people have to say about it.

[sh1pman]

What if they decided to use some kind of expandable engine skirt, like DeltaIV second stage RL-10? That way they can make any of these 7 Raptor engines vacuum- or sea level-optimized, depending on the situation. 

[NSEP]

8 minutes ago, sh1pman said:

What if they decided to use some kind of expandable engine skirt, like DeltaIV second stage RL-10? That way they can make any of these 7 Raptor engines vacuum- or sea level-optimized, depending on the situation. 

Thats what i thought of too.

[Nibb31]

The petals look like they could be some sort of inflatable device. A ballute maybe ? Or a landing device ?

I'm having problems imagining telescopic landing stilts that extend out of the fins. Without feet or pads, the weight/surface area ratio is going to cause problems on unprepared terrain, and even prepared terrain. The whole ship could weigh several hundred tons and that entire weight will press on a total surface area of about 1 square meter.

[sh1pman]

7 minutes ago, Nibb31 said:

The petals look like they could be some sort of inflatable device. A ballute maybe ? Or a landing device ?

Or blast protection. 

[tater]

 

 

49 minutes ago, Nibb31 said:

The petals look like they could be some sort of inflatable device. A ballute maybe ? Or a landing device ?

I'm having problems imagining telescopic landing stilts that extend out of the fins. Without feet or pads, the weight/surface area ratio is going to cause problems on unprepared terrain, and even prepared terrain. The whole ship could weigh several hundred tons and that entire weight will press on a total surface area of about 1 square meter.

I think they only need extend enough to cover small terrain changes. Think shock absorbers, not long, spindly legs.

[kerbiloid]

If use an aerospike with central body, they could make the central body a hollow telescopic cylinder, protected from bottom with a "solid" (i.e. not tiled) heatshiled.

Inside the inner cyilnder (with a gateway in the side) they could place stairways and elevator.

So, the outer cylinder (which is the central body of the main engine nozzle) is immovable.
The circle of flames from the mini-nozzles around the external cylinder wraps around it and runs down.

In "flight" state the inner cylinder is retracted, and the wide (several meters) round heatshield beneath the bottom, attached to the inner cylinder, protects all this thing from below when aerobraking.

In "landed" state the inner cylinder extends down, from the outer cylinder.
The heatshield nearly touches the ground (say, 1 m above the ground).
When the inner cylinder is extended down, the gateway in its side is visible from outside of the external cylinder.
On the engine cooling down, they can walk throw the gateway to the vertical well inside the rocket, getting up and down by stairs or elevator. Without external doors, trusses, etc.

So, the immovable fins would be not engines, but massive fins/radiators/landing legs/RCS/other stuff.

Any power cables, fuel pipes, etc, would also run inside through this extended nozzle and its central well.

The nosecone with a cabin can be either a conical rescue capsule, or a separate orbital craft.

At least this would eliminate that ugly scaffold-looking tower on BFS pictures.

Also this can turn a rocketship into a planetary "wet workshop" right after the landing.

Edited September 14, 2018 by kerbiloid

[sevenperforce]

9 hours ago, AVaughan said:

Those engine bells look larger than the sea level engine bells on earlier renders. eg 

So they might be some sort of intermediate engine.  Hopefully the briefing will provide more details.

If you count pixels you can see that the depicted engine bells are exactly 1.3 meters, so they are standard SL engines.

I imagine the depiction of a burn in cislunar space is probably just artistic license. You'd need a lot of refueling trips to do an orbital mission.

While the original reusable Falcon 9 upper stage was designed with a translatable engine, the complexity is far too great. Thrust structure concerns alone would make it utterly unmanageable.

I like going back to three landing points. Four landing points means instability if you land on a surface that isn't completely flat. And those big fins look 

Those petals are curious. I can see them folding down to act as debris impingement protection for the engine bells. One really unlikely (but exciting) possibility is that they protrude to act as an inside-out aerospike nozzle and the six engines in the ring gimbal outward to make that happen.

Getting the wings to fold and unfold correctly is a problem. If they don't fold out properly after entry, you can't land. Though perhaps with those new forward canards, the vehicle would have enough pitch control to do a survivable unpowered belly-first splashdown in the event of a critical failure.

[magnemoe]

17 minutes ago, tater said:

 

 

I think they only need extend enough to cover small terrain changes. Think shock absorbers, not long, spindly legs.

Ok anybody else who think lambda shuttle?

And yes it become more and more of an space plane. 
Except that the BFS looks more like an freight ship, the lambda makes me think gunship. 

1 hour ago, Nibb31 said:

The petals look like they could be some sort of inflatable device. A ballute maybe ? Or a landing device ?

I'm having problems imagining telescopic landing stilts that extend out of the fins. Without feet or pads, the weight/surface area ratio is going to cause problems on unprepared terrain, and even prepared terrain. The whole ship could weigh several hundred tons and that entire weight will press on a total surface area of about 1 square meter.

The shock absorbers pads will be around an meter in diameter,  it only look small because the bfr is so huge. You could add something fold out here for better landing on say the Moon. 

And yes I was wrong about the fins and the engines. 

[tater]

14 minutes ago, sevenperforce said:

I imagine the depiction of a burn in cislunar space is probably just artistic license.

So is the fact that the Earth and Moon are apparently each lit by a different sun

 

[tater]

12 minutes ago, tater said:

So is the fact that the Earth and Moon are apparently each lit by a different sun

 

Unless that's supposed to be a lens flare... maybe it it is. Hard to tell in a tweet.