totm nov 2023 SpaceX Discussion Thread

[Ultimate Steve]

1 minute ago, tater said:

 

So either lazy rendering, or there are no extendable landing legs.

[Spaceception]

So, 2028... Does that mean the date for a crewed Mars landing has slipped 4 years? Because I imagine a base can be built in the first crewed mission. Gives them more time to test everything though, which is good. And a date I was honestly expecting.

Edited September 21, 2018 by Spaceception

[Scotius]

I have flashbacks to old, cheesy sci-fi movies and pictures from 1940-50'ies

[Spaceception]

Just now, Scotius said:

I have flashbacks to old, cheesy sci-fi movies and pictures from 1940-50'ies

It's almost the same pic from a couple years ago, but I can't help feeling the same. There's just something so awesome about that pic, and it looks so tantalizingly close as well.

[Brotoro]

21 minutes ago, Ultimate Steve said:

So either lazy rendering, or there are no extendable landing legs.

Or, the extendable parts of the legs retract after landing.

[cubinator]

21 minutes ago, Ultimate Steve said:

So either lazy rendering, or there are no extendable landing legs.

No extendable landing legs. There's probably some suspension for right on landing, though.

[tater]

49 minutes ago, Green Baron said:

I meant he could have explained some features of the ship but it turns out he only has blabla. Which makes me ask myself, how much is real about the bfr at this time.

Just my impression ....

How about the engines for example ?

Heretic's question, eh ?

He showed a Raptor test at 200 tons thrust (1779 kN). He thought they'd get it to 300.

That's already ~4X Merlin.

18 minutes ago, Spaceception said:

So, 2028... Does that mean the date for a crewed Mars landing has slipped 4 years? Because I imagine a base can be built in the first crewed mission. Gives them more time to test everything though, which is good. And a date I was honestly expecting.

No way a base like that gets built the first landing. 2028 for something that spectacular is insanely optimistic. Heck, it's optimistic to happen in a few decades, IMO.

The other image he tweeted:

 

[Spaceception]

6 minutes ago, tater said:

No way a base like that gets built the first landing. 2028 for something that spectacular is insanely optimistic. Heck, it's optimistic to happen in a few decades, IMO.

 

Oh, no, I meant more like basic equipment, habs, something like the start of a base. I wasn't talking about the picture's version. I agree that'll take awhile.

[magnemoe]

5 hours ago, Mad Rocket Scientist said:

Yes, they are. Thankfully someone asked during the presentation. They could be replaced with vacuum engines to increase payload to mars, at the cost of the easily accessible aft cargo. It just about matched up about with our predictions.

The ground level engines has some benefits, first it give an better abort and engine out profiles, this also apply to landings. you get more cargo space cargo volume is more than an restriction than mass outside the tanker. And the vacuum engines takes more work. 

[tater]

I'll consider belief in a date for a base after they've actually flown BFS to space.

With people.

 

1 minute ago, magnemoe said:

The ground level engines has some benefits, first it give an better abort and engine out profiles, this also apply to landings. you get more cargo space cargo volume is more than an restriction than mass outside the tanker. And the vacuum engines takes more work. 

I don't see abort as a thing unless they make a test version for that.

Note that the Raptor was supposed to have a chamber pressure closer to 250 bar, but he sadi the current one is running around 300.

Someone at NSF was pixel counting the YT video, and said that the engine diameter was ~1.1 m. Final was supposed to be 1.3 in earlier statements. It's certainly not the old, 1/3 scale model, that's for sure.

[sh1pman]

These renders are super lazy. Same pics we had last year, but with fins.

There’s never enough BFR renders for me.

[Green Baron]

1 hour ago, tater said:

He showed a Raptor test at 200 tons thrust (1779 kN). He thought they'd get it to 300.

That's already ~4X Merlin.

He talked about the possibility. Is there a newer version of the engine since the 2017 downsized "development raptor" ?

Edited September 21, 2018 by Green Baron

[RedKraken]

I'd be surprised if they moved away from the 1.3m bell from the 2017 design.

Changing to 30 MPa / 200t  was a surprise....   but a welcome one.

Are we talking ~2000kN? I thought elon would be talking metric tonnes.

And 30/25 * 170t comes out at 204t for a very rough approximation.

Are we still dealing with 334s - 361s isp of the 2016  engine?

Edited September 21, 2018 by RedKraken

[tater]

13 minutes ago, Green Baron said:

He talked about the possibility. Is there a newer version of the engine since the 2017 downsized "development raptor" ?

It's a new engine.

NSF was reporting a new engine int he test stand a while ago.

2016:

 

2018 (moved to the right time stamp):

 

 

[sevenperforce]

2 hours ago, tater said:

It's a new engine.

NSF was reporting a new engine int he test stand a while ago.

<snip>

2018 (moved to the right time stamp):

<snip>

Looks to be a 70-75 second test fire, by my count.

Mach diamonds not nearly as pronounced as on the devscale engine. Suggests that they really are going all-out with sea level engines, rather than designing a compromise nozzle with a converging-diverging-converging bell like the SSMEs. 

The fact that they expect to be able to do a lunar free return (roughly 2.8 km/s out of LEO) without refueling, combined with the fact that they expect upwards of 100 tonnes to LEO in cargo configuration, can provide some degree of guesstimate as to how much "payload" they expect to comprise in a dozen passengers and their cabins, etc..

The mechanics of that flip are going to be challenging. Makes more sense now than it did before, though.

[Xd the great]

I guess that spaceX will build a sfs, with 3m in diameter and mount it on a falcon 9 for testing. Or falcon heavy. 

[Spaceception]

29 minutes ago, Xd the great said:

I guess that spaceX will build a sfs, with 3m in diameter and mount it on a falcon 9 for testing. Or falcon heavy. 

I thought that would pull too many resources from actually developing the BFR? And that will be handled in the mock-up version next year.

[cubinator]

42 minutes ago, Xd the great said:

I guess that spaceX will build a sfs, with 3m in diameter and mount it on a falcon 9 for testing. Or falcon heavy. 

Too hard, not worth it because the physics don't even scale quite nicely enough. They seem to be doing well enough constructing a full size test article.

[Mad Rocket Scientist]

5 hours ago, magnemoe said:

The ground level engines has some benefits, first it give an better abort and engine out profiles, this also apply to landings. you get more cargo space cargo volume is more than an restriction than mass outside the tanker. And the vacuum engines takes more work. 

I wonder if an almost dry BFS could abort during launch on earth. If you're refueling it anyway...

[Xd the great]

25 minutes ago, Mad Rocket Scientist said:

I wonder if an almost dry BFS could abort during launch on earth. If you're refueling it anyway...

I doubt it. Assuming the bfr uses a launch profile similar to a falcon 9, stage seperation at 6000km/h, about 6000m/s delta v will be needed. Which is about 2/3 delta V of a full bfs. 

So, at most the bfs will be half empty. I did not do the math, but rely on kerbal ecperience for this.

[Mad Rocket Scientist]

1 minute ago, Xd the great said:

I doubt it. Assuming the bfr uses a launch profile similar to a falcon 9, stage seperation at 6000km/h, about 6000m/s delta v will be needed. Which is about 2/3 delta V of a full bfs. 

So, at most the bfs will be half empty. I did not do the math, but rely on kerbal ecperience for this.

The new landing profile looks like it might reduce landing DV for a RTLS abort. I wonder whether BFS could survive a splashdown. I'll run the numbers sometime, but I suspect that the BFS is TWR limited for aborts.

[tater]

2 hours ago, Xd the great said:

I guess that spaceX will build a sfs, with 3m in diameter and mount it on a falcon 9 for testing. Or falcon heavy. 

Doubt it.

They're all-in for BFS.

Seriously, from a business standpoint their goal is functioning BFR in a similar timeframe as NG hits the market.

 

[Xd the great]

Seriously, how does elon plan on making the bfr stable during launch? It has wings in the middle and cnards in front.

[StrandedonEarth]

1 hour ago, Xd the great said:

Seriously, how does elon plan on making the bfr stable during launch? It has wings in the middle and cnards in front.

Wings in the middle are no big deal, and the canards are small. Computer guidance can handle it easily.

Bear in mind that modern fighter jets are on the edge of stability, to make them more agile. Fly-by-wire allows the computer to keep it going in the direction the pilot wants it to, within limits.

[Nibb31]

4 hours ago, Xd the great said:

Seriously, how does elon plan on making the bfr stable during launch? It has wings in the middle and cnards in front.

They are not wings, they are fins. Unlike something like DreamChaser, they do not generate lift, and since they are symmetric, they should be pretty much neutral.

The canards are also symmetrical and can be trimmed to be neutral. If anything, they should help stability. After all, fins on the front of a rocket are nothing new.

Now, vertically launching with a spaceplane on top (X-20 DynaSoar, DreamChaser, or Hermes) is much more problematic, because those vehicles are designed to generate lift on re-entry. You are going to need strong control authority to keep it flying straight.

That's why the Space Shuttle flew to orbit "upside down". It could use some of the lift generated by the wings to rotate the flight curve rather than fight the lift with the engine gimballing.

You just have to keep in mind that although it looks like it has wings, the BFS is not a spaceplane.

Edited September 22, 2018 by Nibb31