totm nov 2023 SpaceX Discussion Thread

[Meecrob]

1 hour ago, sevenperforce said:

Oh, it is clearly way, way too large. No question about that. I was just trying to design it in KSP which is inherently difficult since I don't have Tweakscale installed.

Using active hydraulic control for auto-leveling allows shock absorbers to also be the auto-levelers. The best part is no part.

I'm thinking along the lines of combining all those things actually are two parts, not zero parts.  A hydraulic actuator with shock absorbing capability is inherently heavier and not as optimal. My thought is make shock absorbers just do shock absorption, and have a mechanical gear extend mechanism, simply because weight is clearly an objective and we have been doing this for like 100 years. There is a reason planes do not have triple hydraulic actuators as opposed to two fixed posts and one hydraulic actuator. I hate to relate it to planes though. I know its a different regime, but I feel that weight is the exact reason the gear sucks so much on starship right now. Actually I think I just outed myself there, I think the gear sucks! haha. With reference to my idea of ratcheting, what say you of that...the logic would be basically weight dependant and "amount of legs touched down" dependant. Set up a sawtooth array of metal and have an electromagnet be the interference to stop travel. The actual gear though....I spent my brainpower thinking of this part...just like likes on this forum, I spread myself too thin haha

[tater]

SN11 (BN1 parts behind).

 

[SOXBLOX]

21 hours ago, sevenperforce said:

It was the kaboom that launched it in the air, not the 3 bar of ullage pressure. The kaboom was probably 100 bar or more.

I watched Scott Manley's analysis after posting...and he said it was the fuel pressure. IDK.

[Spaceception]

I hope we see BN1 fully stacked over the next few weeks. I suppose they'll do that after rolling out SN11, and they'll do that before stacking SN15's nose and fins.

[CatastrophicFailure]

There’s that hindsight thing again... 

 

[StrandedonEarth]

9 minutes ago, CatastrophicFailure said:

There’s that hindsight thing again... 

 

Any confirmation of intentionally allowing it to RUD?

Oh, and, I couldn't resist. Hope someone picks up on it and retweets it....

 

[CatastrophicFailure]

6 minutes ago, StrandedonEarth said:

Any confirmation of intentionally allowing it to RUD?

I’m more interested in how well the thermal tiles survived that bump, personally. If they held on, that’s a really good sign that the mounting system is maturing. 

[Brotoro]

It seems like SpaceX should make a big vertical test stand where they can do full-length firings of Starships and Super Heavies just to test multiple Raptors under various combinations and situations. Or maybe they think it's cheaper to just test them in flight.

[tater]

No way they wanted a RUD. Zero probability.

 

 

[RyanRising]

1 hour ago, CatastrophicFailure said:

There’s that hindsight thing again... 

 

I had no idea they could land the thing on two Raptors. Either they’ve gotten the Raptors to throttle lower already, or the ship even in this state is a lot heavier than I thought it was. >160t, for two 200t-f raptors at 40%? Yikes. No wonder they’re trying to make the thing even more of a balloon tank than it already is it that’s the case.

 

EDIT: or does that mean they’ll attempt a suicide burn?

Edited March 6, 2021 by RyanRising

[JcoolTheShipbuilder]

Just wondering, when will sn11 launch? About a month?

[Clamp-o-Tron]

1 hour ago, tater said:

No way they wanted a RUD. Zero probability.

 

 

Not a particularly great render TBH. It falls into the uncanny valley of not being quite true to the real SN10 and having lots of effort put into it.

The sky is clearly a stock image, the creator went WAY overboard on the engine flares in the first pic, and the rest of the vehicle just doesn’t look right.

[Jacke]

2 hours ago, Brotoro said:

It seems like SpaceX should make a big vertical test stand where they can do full-length firings of Starships and Super Heavies just to test multiple Raptors under various combinations and situations. Or maybe they think it's cheaper to just test them in flight.

The problem with a full stage static test is it doesn't necessarily give a lot more experience than a single engine lengthy test fire.  It doesn't load and stress the vehicle as much as an actual flight, and is much more expensive than a single engine lengthy test fire.  Being held on the pad with all engines firing only happens for at most a few seconds for a live flight.

These are about the equivalent of a cross between boilerplate tests and the Saturn I test series, which started out with just the first stage and dummy upper stages.  Saturn I had a lot of changes with respect to previous launch vehicles (much larger rocket, upgraded engines, 8 engines with cross-feed piping to 9 tanks and engine-out adaptable flight) and started off after static tests with only a live first stage and dummy upper stages.

With Starship, SpaceX is following an equivalent test program as adapted to what is being developed new for it as well as its critical performance needs.  The SN are not true flight articles but test flight articles made in an equivalent manner but not up to the standards required of even uncrewed launch vehicles.  They can do this because the tests are focused on short flight durations, low altitude flight, flight transitions, and landings without any payload.

When SpaceX gets to producing closer to the actual true flight articles, then full stage static tests are likely prior to test flights.

Edited March 6, 2021 by Jacke

[tater]

1 hour ago, JcoolTheShipbuilder said:

Just wondering, when will sn11 launch? About a month?

It moves to the pad Monday. Cryo proof, then statice fire...

Launch in 1-2 weeks?

SN11 will do the 3 engine flip, and 2 engine landing.

 

Gotta wonder what is up with SN15. The lack of a nose tip, for example.

 

Edited March 6, 2021 by tater

[magnemoe]

7 hours ago, sevenperforce said:

It's a surprisingly compact solution. Like I said, I was able to do it in actual KSP without any clipping.

But trying to move them inside the skirt is actually really tough. There are enough internal parts to make it a challenging fit. And you lose more of the wide stance than you would think.

Bulges will however be an problem here, note you can reduce the bottom cargo holds a lot, I see them as a bit pointless however for moonship they could be nice for eva stuff if you could lower them down for access from ground. 
Another thing is to bring the pairs between engines closer together. One final tricks might be to have the tip point a bit downward and have this work as the initial dampening. 
Only issue I see with this design is dampening and having the tips make contact first might help here, the cylinder doing the tilting is very long granted it will not be an cylinder all the way 

[RealKerbal3x]

 

[sevenperforce]

10 hours ago, CatastrophicFailure said:

There’s that hindsight thing again... 

 

Looks like Elon had been playing stock KSP and was surprised by the switch to RO.

Thinking about throttle settings. With two engines that’s definitely a suicide burn. But not all suicide burns are created equal. I am guessing that the flip will be timed such that the suicide burn will be achieved at or near minimum throttle for both engines, so if one has a thrust shortfall the other can throttle up to compensate.

This is really the inherent problem with these landings...all this stuff is literally rocket science. Having three engines for redundancy is great because it allows these options but that doesn’t necessarily fix problems with timing. If something goes bad on a plane, you typically have plenty of time to come up with a solution, and there’s no mission-critical system that undergoes a bunch of transients right at touchdown. 

[paul_c]

Pragmatically, I think they need to get to a point where they can have the TWR <1 with good control; as well as TWR>1 obviously. And don't forget there will be a not insignificant ground effect too.

Whether this is achieved with greater reliability, 2 engines (ie redundancy), RCS assistance, depends on a number of things being engineered or developed to a point further down the line than they're at now. Things like an engine not producing thrust when commanded to, is obviously a major issue which they can't have happen too often, if at all.

Once they have the control in the 0.8 > TWR > 1.2 'zone', the landing gear issue is rendered somewhat moot. So is the post-landing explosion scenario - they could in theory, hover 5cm above the pad at TWR=1.000 and land safely with almost no fuel remaining. Obviously this is inefficient on fuel so later on, they will want to coordinate the whole de-orbit, approach, landing to use less fuel but still retain the good amount ((reserve) fuel for) of control.

[RealKerbal3x]

30 minutes ago, sevenperforce said:

Thinking about throttle settings. With two engines that’s definitely a suicide burn. But not all suicide burns are created equal. I am guessing that the flip will be timed such that the suicide burn will be achieved at or near minimum throttle for both engines, so if one has a thrust shortfall the other can throttle up to compensate.

Yeah, sounds reasonable. If we take 40% as Raptor's minimum thrust (and that's a figure from months ago, undoubtedly they've reduced that since then) then two engines on minimum throttle produce the same thrust as a single engine on 80% thrust. And throttling up an engine is a lot simpler than starting a different one, so this should provide engine redundancy throughout the entire flip and landing burn sequence.

[RealKerbal3x]

Looks like SN16's leg skirt is being scrapped. Maybe this is for new legs.

Edit: SN16's leg skirt is already attached to its aft dome. Maybe this was SN17's or something.

Edited March 6, 2021 by RealKerbal3x

[tater]

1 hour ago, sevenperforce said:

This is really the inherent problem with these landings...all this stuff is literally rocket science. Having three engines for redundancy is great because it allows these options but that doesn’t necessarily fix problems with timing. If something goes bad on a plane, you typically have plenty of time to come up with a solution, and there’s no mission-critical system that undergoes a bunch of transients right at touchdown. 

Yeah, it really is a 1 shot thing.

Makes me wonder about engine choice, to be honest. Ideally you's have the Earth landing engines such that it would nominally land with all burning, and sink rate controlled by throttle. Engine outs such that remaining engines can throttle up.

If Raptor can't throttle deep enough, I wonder if they could make a different version with less thrust for landing.

[Brotoro]

7 hours ago, RealKerbal3x said:

 

No mention of the fact that half of the legs were flapping in the breeze?

[RCgothic]

Anyone else reading Liftoff by Eric Berger? I'm 7 chapters in and folding it hard to put down. I'd have loved to have worked for SpaceX in those early days.

[CatastrophicFailure]

Build plan for Spacex Boca Chica Starbase, Tx:

 

 

[Flying dutchman]

I wonder why the engine wasn't producing the requested thrust on landing, plume seems alright to me..

 

Perhaps a faulty sensor? A stuck throttle valve should prevent them from shutting the engine down right, so that wouldn't be it..

Edited March 7, 2021 by Flying dutchman