totm nov 2023 SpaceX Discussion Thread

[RCgothic]

Or maybe the extended flip staging manoeuvre they had planned previously was just that much of a performance penalty.

[darthgently]

The newer lunar Starship has the landing engines even higher up.  Is there a remote possibility of a notion that the upper portion might become optionally detachable from the main tank lower and hop to the surface to remain there as a base module?  The crew would have a much safer egress/ingress height if so.

If it could reliably do a lunar gravity-well redock with the landed main tanks.... ok, I'm dreaming now...

 

[tomf]

9 hours ago, darthgently said:

Maybe they are losing parts and complexity related to stage 2 ullage? Not sure

But if they can maintain continuous thrust it would make a difference.  Try it in KSP, you'll see

But 10%? When the starship still needs RCS that could do the job and you need to add the extra mass of shielding the second stage.

And as for the idea that the craft is slowing down and needs to speed back up again, that energy is always going to be lost to gravity. There will be a loss to the oberth effect from burning the fuel higher but I can't believe that a few seconds difference makes more than a fraction of a percent.

[darthgently]

13 minutes ago, tomf said:

But 10%? When the starship still needs RCS that could do the job and you need to add the extra mass of shielding the second stage.

And as for the idea that the craft is slowing down and needs to speed back up again, that energy is always going to be lost to gravity. There will be a loss to the oberth effect from burning the fuel higher but I can't believe that a few seconds difference makes more than a fraction of a percent.

Tell the Russians all of this, lol

[AckSed]

Maybe it works, maybe it doesn't, maybe they should concentrate on finishing something... but they're trying it. I think that's laudable.

[darthgently]

1 hour ago, AckSed said:

Maybe it works, maybe it doesn't, maybe they should concentrate on finishing something... but they're trying it. I think that's laudable.

Hot staging works, but isn't easy.  As for finishing something,  they are developing the design from data gathered en route.  So they are finishing the design as they finish the rocket(s).  Hard to compare to standard industry methodology so "finish" means something different.  Apples and oranges

Edited June 25, 2023 by darthgently

[Nuke]

3 hours ago, AckSed said:

Maybe it works, maybe it doesn't, maybe they should concentrate on finishing something... but they're trying it. I think that's laudable.

testing every possible thing until something sticks is a good way to move quickly, if they dont get regulated into oblivion first because of all the explosions. 

Edited June 25, 2023 by Nuke

[Meecrob]

I think we are reading too much into this "10%" thing. People have been raising the issue of no launch abort capability for years; detractors and fanboys alike. Then SpaceX brings out a design that ostensibly has the ability to perform a pad abort, and everyone is laser focused on something else.

I find it hilarious, because in most other designs, the addition of a launch abort capability would decrease performance.

[mikegarrison]

I see this as part of the whole "design as we go" thing. I suspect their flight test convinced them that the "flip to separate" idea had too many risks. So now they are moving on the the next idea.

[CatastrophicFailure]

Going back to engine nozzles, this makes the shorty make a little more sense. Seems like it’d be way quicker to produce, if nothing else:

 Tweet deleted, here's the same video:

 

Edited June 25, 2023 by CatastrophicFailure

[Nuke]

2 hours ago, mikegarrison said:

I see this as part of the whole "design as we go" thing. I suspect their flight test convinced them that the "flip to separate" idea had too many risks. So now they are moving on the the next idea.

seems like an unnecessary stress on the payload, especially if that payload is humans. hot staging is a better known quantity, since its been used a lot by the russians. how many instances of hot stage failures resulting in explosions have their been?

[mikegarrison]

25 minutes ago, Nuke said:

seems like an unnecessary stress on the payload, especially if that payload is humans. hot staging is a better known quantity, since its been used a lot by the russians. how many instances of hot stage failures resulting in explosions have their been?

How many hot-staged boosters have ever been reused?

It's not a gimme.

[CastleKSide]

I wouldn't be surprised if in 2 years they start testing thier kickflip again. SpaceX is not as reluctant to make sweeping design changes as other companies are. Just look at how much evolution the F9 went thru. Block 5 is a very different beast than Block 1 or whatever the early versions were called. 

This reads to me like when they fed the launch test data into the computers and updated/re-validated the models risk profiles changed enough for them to go "let's try some other options."  Whether they stick with I'd say is an open question. Frankly they have enough production capacity to test multiple versions at once, not to mention the test articles already built.

They want this thing flying sooner rather than later and I'd bet we see them try everything they can

[CatastrophicFailure]

Good thread on stuff:

 

[magnemoe]

12 hours ago, tomf said:

But 10%? When the starship still needs RCS that could do the job and you need to add the extra mass of shielding the second stage.

And as for the idea that the craft is slowing down and needs to speed back up again, that energy is always going to be lost to gravity. There will be a loss to the oberth effect from burning the fuel higher but I can't believe that a few seconds difference makes more than a fraction of a percent.

I assume moonship will do like mechjeb landing autopilot does, stop landing burn say 100 meter so the main engines don't disturb the ground, ship is no  at  0 velocity relative to the ground then switch to landing engines. 
The landing engines then land it. Now I say it likely the landing engines will rotate the craft, and for safety you will ignite the landing engines before turning off the main. 

[magnemoe]

2 hours ago, mikegarrison said:

How many hot-staged boosters have ever been reused?

It's not a gimme.

I assume hot staging is an abort option if an first stage fail.  Reinforce the upper dome say heat resistant material on top or an extra steel plate to take most of the engine flames or both. 
No it will not be an standard abort system but better than nothing. 
First stage will do an burn back then hover to  burn off most of its fuel before landing, it will not do the belly flop as it has more fuel than it need. 
This could also be useful for expensive payloads not only human launches. 

[Nuke]

2 hours ago, mikegarrison said:

How many hot-staged boosters have ever been reused?

It's not a gimme.

yea but the failure rates are a good starting point for determining if it is a good idea or not. if instances of explosions or pressure loss on the tanks are zero or of such low probability that you can effectively ignore it, then it becomes worth considering. then it would take actually testing it to see if its viable or stupid or results in a maintenance problem that affects turn around and thus launch cadence. since you separate with fuel in the tanks, the possibility exists of actively cooling the interstage with cryogenic fuel for a couple seconds while you start your engines. the potential benefits of hot staging, should it work as designed, are still worth investigating.

Edited June 25, 2023 by Nuke

[tater]

 

[Brotoro]

Such tiny vent holes.

[tater]

22 hours ago, mikegarrison said:

I see this as part of the whole "design as we go" thing. I suspect their flight test convinced them that the "flip to separate" idea had too many risks. So now they are moving on the the next idea.

They seem to have had the other ideas in the can already as well.

[mikegarrison]

26 minutes ago, tater said:

They seem to have had the other ideas in the can already as well.

Yeah, I'm sure they did. Separation motors, springs like they use in Falcon ... I'm sure they thought of a bunch of ideas before choosing to try the flip thing.

I suspect the flight test revealed to them that the problem with the flip is that if they lose control of the booster stage then they lose the whole thing, because the upper stage was relying on the booster to have the thrust and control authority to execute the flip.

Edited June 26, 2023 by mikegarrison

[sevenperforce]

1 hour ago, mikegarrison said:

I suspect the flight test revealed to them that the problem with the flip is that if they lose control of the booster stage then they lose the whole thing, because the upper stage was relying on the booster to have the thrust and control authority to execute the flip.

Put very succinctly and accurately. Bravo.

[tater]

 

[bigyihsuan]

1 hour ago, tater said:

Deleted video.

[Spaceception]