totm nov 2023 SpaceX Discussion Thread

[tater]

Wiki (little other data) shows that SL to Vac I_sp gain is around 20 seconds.

They guess 356 for the regular Raptor, and guess 375 for vac optimized.

The dv for the spaceship (using the empty dry mass after burning props) is ~9.6 km/s for the SL version, and  10.1 km/s for vac optimized.

Half a km/s is nothing to sneeze at, but given proposed mission parameters, does it matter?

Edited September 14, 2018 by tater

[Ultimate Steve]

A thing about the lack of solar... On the NSF forum someone found the url/filename and it reads https://www.spacex.com/sites/spacex/files/bfr1_moon1_nosolar_all_engines.jpg suggesting that either this is the render with no solar panels or a version of the BFR with no solar panels.

 

[Rakaydos]

3 minutes ago, Ultimate Steve said:

A thing about the lack of solar... On the NSF forum someone found the url/filename and it reads https://www.spacex.com/sites/spacex/files/bfr1_moon1_nosolar_all_engines.jpg suggesting that either this is the render with no solar panels or a version of the BFR with no solar panels.

 

It also implies there's a version where some number of the engines are obscured.

[DAL59]

not mine

[tater]

^^^ I think that all 3 fins are the same size, contrary to that image (which I posted as well, earlier).

 

https://www.spacex.com/sites/spacex/files/bfr1_moon1_nosolar_all_engines.jpg

[sh1pman]

Squad needs to hunt the guy who makes SpaceX renders to do part revamps.

[Xd the great]

Without gridfins, how will bfs be able to land accurately?

Edited September 15, 2018 by Xd the great

[SuperFastJellyfish]

...with...real...fins...   

[Xd the great]

16 minutes ago, SuperFastJellyfish said:

...with...real...fins...   

So like the BO new shepard?

[tater]

Does anyone know about the fluid dynamics of engines in clusters?

Ie: when a series of engines are around a center engine, how does that act on the exterior ones? Could the center engine function in effect as an aerospike/plug, entraining the exhaust of the radial engines?

[Mad Rocket Scientist]

4 minutes ago, tater said:

Does anyone know about the fluid dynamics of engines in clusters?

Ie: when a series of engines are around a center engine, how does that act on the exterior ones? Could the center engine function in effect as an aerospike/plug, entraining the exhaust of the radial engines?

I recall there being some talk of a "virtual aerospike" like this on the ITS booster. You might want to take a look at this: https://www.reddit.com/r/spacex/comments/5ad34y/virtual_aerospike_discussion_background_in/

[SuperFastJellyfish]

46 minutes ago, Xd the great said:

Without gridfins, how will bfs be able to land accurately?

The reimagined BFS from the image above appears to have canards near the nose similarly positioned where Falcon 9's grid fins are.

Edited September 15, 2018 by SuperFastJellyfish

[sh1pman]

9 minutes ago, SuperFastJellyfish said:

The reimagined BFS from the image above appears to have canards near the nose similarly positioned where Falcon 9's grid fins are.

And I think, with these fancy new fins it will be able to glide pretty well before landing. 

Edited September 15, 2018 by sh1pman

[tater]

31 minutes ago, sh1pman said:

And I think, with these fancy new fins it will be able to glide pretty well before landing. 

[sh1pman]

Rare drawing of a BFS mounted on the side of the booster.

(or it’s something completely different)

[sevenperforce]

2 hours ago, tater said:

Does anyone know about the fluid dynamics of engines in clusters?

Ie: when a series of engines are around a center engine, how does that act on the exterior ones? Could the center engine function in effect as an aerospike/plug, entraining the exhaust of the radial engines?

Visually, we see little evidence of such effect in the Falcon 9 launches. Then again, inward gimbal on skirt engines is very limited so they may not be able to gimbal inward enough.

As far as I understand the fluid dynamics...which is not much, admittedly, but probably about as much as anybody here...it's a valid approach. Might squeeze out an extra 2-3% more thrust. Keep in mind that a full-size engine bell is only 5% more thrust and carries with it a bunch of extra dry mass.

1 hour ago, sh1pman said:

Rare drawing of a BFS mounted on the side of the booster.

(or it’s something completely different)

That's something completely different.

[Nibb31]

10 hours ago, Rakaydos said:

It also implies there's a version where some number of the engines are obscured.

Or it implies that there might be a version of the rendering where some other number of engines is firing.

[Xd the great]

10 hours ago, Ultimate Steve said:

A thing about the lack of solar... On the NSF forum someone found the url/filename and it reads https://www.spacex.com/sites/spacex/files/bfr1_moon1_nosolar_all_engines.jpg suggesting that either this is the render with no solar panels or a version of the BFR with no solar panels.

 

P2P hopping wont require solar panels either.

[magnemoe]

12 hours ago, Rakaydos said:

It also implies there's a version where some number of the engines are obscured.

Could be an shot with just 1 or 3 burning, it would be more realistic given that all 7 would give over one g fully loaded but also less dramatic and would probably confuse some.
Solar panels are not out, don't think they would be out then you used main engines as they are fragile and it would probably also look less cool 

[NSEP]

What if BFR lands horizontally on Earth and vertically on low or no atmosphere planets like Mars or the Moon?

I know, its a dumb idea. It might explain the lack of any SL engines. (Although it has been said those engines were SL engines.)

[tater]

6 hours ago, Nibb31 said:

Or it implies that there might be a version of the rendering where some other number of engines is firing.

This.

[cubinator]

27 minutes ago, NSEP said:

What if BFR lands horizontally on Earth and vertically on low or no atmosphere planets like Mars or the Moon?

I know, its a dumb idea. It might explain the lack of any SL engines. (Although it has been said those engines were SL engines.)

Need a much larger landing area for horizontal, so a runway is much more expensive to build than a landing platform, and SpaceX has already nearly perfected vertical propulsive landings on pinpoint targets with Falcon 9. BFR EDL is at its core a scaled-up version of that. Horizontal landing capability would just add extra complexity and delay the ship's deployment, and if the ship can pull TWR>1 then it should be just fine doing a vertical landing.

[tater]

It's not landing horizontally.

[Xd the great]

1 hour ago, NSEP said:

What if BFR lands horizontally on Earth and vertically on low or no atmosphere planets like Mars or the Moon?

I know, its a dumb idea. It might explain the lack of any SL engines. (Although it has been said those engines were SL engines.)

Having wheels that poke through the heatshield is much more of a headache than doing retropropulsive landings. Plus it will look like the old space shuttles.

[Ultimate Steve]

Someone on Reddit or somewhere did some digging or something, and discovered that the file was last modified in July, meaning this render could be 2 months old already if that is correct... I wonder how much the design has changed since then.