totm nov 2023 SpaceX Discussion Thread

[StrandedonEarth]

34 minutes ago, Terwin said:

As best as I understand it, it looked like the high-temp high-strength concrete should be strong enough for them to do a test flight before the water deluge system was ready to install.  

I would guess that it was not as strong as they thought, but considering that S0 was not damaged enough to delay the next launch, and they got useful data from the first launch, I suspect they are reasonably happy with the results of taking that risk.

TLDR: Another example of 'move fast and break stuff'

They were gathering data on what a heavy cargo lander might do to the local regolith...

[Spaceception]

On the subject of upgrades, I think the next focus will be on ease of manufacuring/reusability/lower costs, with marginal increases to performance. But transpirational cooling (or some other alternative/improved shielding) if it's still on the table, will be the last major change before Starship is (mostly) frozen in its design.

If it takes a similar amount of time as Falcon 9, the last upgrade should be around 2028/9 (if the next version flies in 2024). Maybe a couple years sooner if they leapfrog themselves/make a harder push.

[AckSed]

How expensive will it be to fly an expendable SuperHeavy and a reusable StarShip? Say they don't crack hot-staging, the refurbishment turns out to be uneconomic or whatever. This is an inverse of the usual paradigm, but I'm throwing ideas around.

[Minmus Taster]

26 minutes ago, AckSed said:

How expensive will it be to fly an expendable SuperHeavy and a reusable StarShip? Say they don't crack hot-staging, the refurbishment turns out to be uneconomic or whatever. This is an inverse of the usual paradigm, but I'm throwing ideas around.

Come to think of that, what is the price of a fully expended vehicle? I assume it's cheaper than a typical rocket of this size but probably not economical to have without it being reusable, especially with all the engines.

[Hotel26]

From a KSP point of view (knowing nothing and caring little about real life), I think delaying the flip until Starship has gained some decent separation (exhaust-wise) and then performing a much slower flip before full burn-back thrust is applied, ought to be considered.  So I can see some motivation to go faster (including being 'flashy').  If it meant beefing up some RCS control on the booster.  I can also imagine the usage of small, 'reserve' tanks that are kept full until the flip to avoid ullage problems.

The first two interesting issues might be a) how quickly the turbines slow down, b) how fast a flip could they actually withstand, c) what the atmospheric density is at flip altitude and what is required to prevent going 'unstable' during a slower flip.  

In any case, responding to AckSed above, way, way, too early to think about giving up, especially as the hot-staging concept itself has now been demonstrated.

 

35 minutes ago, AckSed said:

How expensive will it be to fly an expendable SuperHeavy and a reusable StarShip? Say they don't crack hot-staging, the refurbishment turns out to be uneconomic or whatever. This is an inverse of the usual paradigm, but I'm throwing ideas around.

 

5 minutes ago, Minmus Taster said:

Come to think of that, what is the price of a fully expended vehicle? I assume it's cheaper than a typical rocket of this size but probably not economical to have without it being reusable, especially with all the engines

Mmm, nope.  You'd (both) be completely throwing out the whole economic model of SpaceX, the sine qua non.

Edited November 25, 2023 by Hotel26

[mikegarrison]

20 minutes ago, Minmus Taster said:

Come to think of that, what is the price of a fully expended vehicle? I assume it's cheaper than a typical rocket of this size but probably not economical to have without it being reusable, especially with all the engines.

There is no "typical rocket of this size".

19 minutes ago, Hotel26 said:

From a KSP point of view (knowing nothing and caring little about real life), I think delaying the flip until Starship has gained some decent separation (exhaust-wise) and then performing a much slower flip before full burn-back thrust is applied, ought to be considered.  So I can see some motivation to go faster (including being 'flashy').  If it meant beefing up some RCS control on the booster.  I can also imagine the usage of small, 'reserve' tanks that are kept full until the flip to avoid ullage problems.

Every second before they boost back makes it harder to return to landing, and the whole premise of the booster is that it must return to landing.

[Hotel26]

2 hours ago, mikegarrison said:

Every second before they boost back makes it harder to return to landing, and the whole premise of the booster is that it must return to landing.

That's true with Super Heavy, isn't it, as I can't conceive of that object ever touching down on a barge at sea, even nearly empty.

Spoiler

(Of course, I am entertaining geographical solutions now.)

If Super Heavy just coasted and fired retro only to decelerate to touch-down, how far downrange could it go, from its current apogee?  Just needs an unused, privately-owned island (with a clear path to avoid overflight of any populated areas).

 

Edited November 25, 2023 by Hotel26

[tater]

Zack Golden says that FTS actually triggered on SH as soo as the last engine was starved and shut down, the flash literally begins at the FTS location he said.

[CatastrophicFailure]

15 hours ago, mikegarrison said:

Every second before they boost back makes it harder to return to landing, and the whole premise of the booster is that it must return to landing.

It’s all about finding that balance point. SH started its flip almost immediately after separating, much closer, relatively, than an F9 booster. My own theory is it got kicked around faster than expected by the blast from SS, which just amplified the issues with slosh, “water hammer,” turbines, etc. If the solution really is to just wait a few more seconds, with a bit more throttle, before beginning the flip, that seems preferable to adding more mass with baffles or other structural changes. 

As always, they have the data, we just have armchairs. 
 

16 hours ago, Minmus Taster said:

Come to think of that, what is the price of a fully expended vehicle? I assume it's cheaper than a typical rocket of this size but probably not economical to have without it being reusable, especially with all the engines.

IIRC SS/SH is figured to be  cheaper to manufacture than F9, or cheaper per kilo even expended, or something like that. 
 

 

On 11/23/2023 at 12:03 PM, Mikki said:

...a bit off-topic the recent events at SpaceX...

I would slap some wings to SH and weld a proper cone on top (Blast cone hehe) and land SH like a glider...

Hoverslam is nice and all, mechazilla is great but i think landing like a plane would be more logical.

Or is this tube too bottom heavy to glide at all? 

Wouldn’t work, without a ground-up redesign. Superheavy can’t go horizontal, ever, it’s not designed for it. And wings, especially big wings, are heavy. SpaceX are the raining champs of propulsive booster landing, they’ll figure this out. And likely already have. 

[mikegarrison]

36 minutes ago, CatastrophicFailure said:

It’s all about finding that balance point.

Yes, obviously if it increases the percentage chances of success, then delay or slow down the rotation. I was just reacting to the suggestion that the only reason they were doing it quickly was to show off.

36 minutes ago, CatastrophicFailure said:

IIRC SS/SH is figured to be  cheaper to manufacture than F9

This (almost) can't possibly be true.

The claims that were being tossed around was that the cost per flight would ultimately be lower than F9 due to a substantial increase in reusability. A claim that I found dubious.

Consider, for instance, prop-fans v. high-bypass turbofans. People were predicting things like a 50% increase in efficiency from the prop-fans back in the 1980s, but it's been 40 years and the propfans are still not in service. Meanwhile the efficiency of the high-bypass turbofans has almost increased to the point where the propfans were predicted to be, so now for the prop-fans to succeed they need to be competing against the current turbofans, not those of the 1980s.

As F9 gets more and more reusable and cheaper and cheaper to fly, SH has to compete against the newer, better F9 costs, not the F9 costs that existed when SH was conceived.

Edited November 25, 2023 by mikegarrison

[RCgothic]

1 hour ago, mikegarrison said:

This (almost) can't possibly be true.

The claims that were being tossed around was that the cost per flight would ultimately be lower than F9 due to a substantial increase in reusability. A claim that I found dubious.

Not just lower per flight, single digit millions per flight. An order of magnitude less per flight and two orders of magnitude per kg.

[tater]

1 hour ago, RCgothic said:

Not just lower per flight, single digit millions per flight. An order of magnitude less per flight and two orders of magnitude per kg.

The cost of the stack is probably north of $100M at the moment. ~$1M/engine, and a few hundred grand in steel. That's under $50M, so I'm assuming $50M+ in slop for labor, etc.

[RCgothic]

Requires reuse, definitely. A reused stage costs basically nothing per flight compared to a new one and F9 still expends S2 each flight, so if SS SH can manage full reuse it wins.

Expendable vs expendable certainly there's no way Superheavy can come in under F9. It's over 4x the engines even if the structure breaks even for welded steel vs machined aluminium isogrid.

Edited November 25, 2023 by RCgothic

[JoeSchmuckatelli]

F9 reusable is putting, what?  ~ 20 tons into space?

Presuming SX gets SS working in 2024... just how long is it going to have to compete on F9 levels of lift?

(I kinda suspect that 'if you build it, they will come' is a factor.  Give SX a reliable heavy-lift craft, and very soon folks will come knocking asking to put comparatively large & heavy stuff into space).

...

Of course, that depends on someone inventing a need / service for large structures, craft or missions... but presuming we don't decide to immolate ourselves; it's likely to happen)

[darthgently]

1 minute ago, JoeSchmuckatelli said:

F9 reusable is putting, what?  ~ 20 tons into space?

Presuming SX gets SS working in 2024... just how long is it going to have to compete on F9 levels of lift?

(I kinda suspect that 'if you build it, they will come' is a factor.  Give SX a reliable heavy-lift craft, and very soon folks will come knocking asking to put comparatively large & heavy stuff into space).

...

Of course, that depends on someone inventing a need / service for large structures, craft or missions... but presuming we don't decide to immolate ourselves; it's likely to happen)

The silicon water and integrated circuit manufacturers are quite interested in zero G.  Also putting compute resources in orbit powered by solar (or nuke) is another interest as the projected power requirements for where computation demand is going would put a big strain on terrestrial generation.  3D printing, both biological and nonbiological, on very tiny scales is another area that zero G holds out much promise (organs, nanoscale tech, etc)

So "the cloud" could end up literally above our heads and above the actual clouds

[JoeSchmuckatelli]

10 minutes ago, darthgently said:

"the cloud" could end up literally above our heads and above the actual clouds

A very good point.   Data sector of the economy is likely to be a continuous growth sector for the foreseeable future. 

One concern is latency, though. (I started speculation about large scale geosynchronous data farms and then realized that would only be good for relatively static data given signal travel times) 

Honestly - I hope to see orbital manufacturing become viable, if only to see what the smart folks can come up with! 

Made in Space 

Had to share this; look at the last entry from my google search:

Idiocracy

[Exoscientist]

 Given the Raptors repeated history of leaking fuel and catching fire I was surprised the booster was able to complete its portion of the ascent with no engine failures.

 Hypothesis: the booster flew without engine failures because it throttled down to < 75%. The Starship had engine failures because it ran at ~90%, like the booster did on the first test flight with its multiple engine failures.

Two separate observers found fairly constant propellant flow rate, and therefore throttle, before where the booster begins to prepare for stage separation. Rocket thrust is given by (thrust) = (exhaust speed)*(propellant flow rate). So can get degree of throttle by propellant flow rate.

 The graphs give the percentage of propellant remaining vs time. From this we can calculate the percentage change rate as the slope. For the booster it’s about 0.5%/s, 0.005/s as a decimal. Then given the total propellant load of 3,400 tons, in absolute term that propellant flow rate is 17 tons per second.

 But the full thrust propellant flow rate  for each Raptor v2 can be calculated as:

props flow rate = thrust/exhaust speed = 230,000*9.81/(327*9.81) = 700 kg/s.  Then for all 33 engines on the booster that’s 33*700 kg/s = 23,100 kg/s, 23.1 tons/s. Then the throttle down for the booster amounted to: 17/23.1 = .736, less than 75%.

 For the Starship, from the first image below, in its second graph we see from 4 minutes to 8 minutes, 240 seconds, the propellant level dropped from  ~80% to ~5%, for a percentage rate drop of 75/240, 0.313%/s. Then the absolute flow rate for a 1,200 ton prop load is 3.756 tons per second. But for the 6 engines the flow rate at full thrust would be 6*700 = 4,200 kg/s, 4.2 tons/s. Then the throttle is .894, ~90%.

 Note that throttling down to 75% also correspondingly drops the combustion chamber pressure from 300 bar to about 225 bar, allowing the Raptor to operate without leaks. 

 But this reduced thrust would also mean the SuperHeavy/Starship could carry less payload. I estimate a drop in payload to ca. 100 tons reusable. In such a scenario, the 16 refueling launches needed for a Starship HLS would be increased to 24 launches.

  Robert Clark

 

[tater]

28 minutes ago, Exoscientist said:

 Hypothesis: the booster flew without engine failures because it throttled down to < 75%. The Starship had engine failures because it ran at ~90%, like the booster did on the first test flight with its multiple engine failures.

Alternately, this guy was hammering the engines:

 

Edited November 26, 2023 by tater

[Royalswissarmyknife]

4 hours ago, JoeSchmuckatelli said:

Had to share this; look at the last entry from my google search:

Idiocracy

Just searched it up on Bing and I can confirm it does say this.

Spoiler

Please be written by AI.

AI seemed to do a better Job

AI's Result Below:

A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth’s rotation on its axis, which is 23 hours, 56 minutes, and 4 seconds (one sidereal day)1. This synchronization of rotation and orbital period means that, for an observer on Earth’s surface, an object in geosynchronous orbit returns to exactly the same position in the sky after a period of one sidereal day1.

A special case of geosynchronous orbit is the geostationary orbit, which is a circular geosynchronous orbit in Earth’s equatorial plane with both inclination and eccentricity equal to 01. A satellite in a geostationary orbit remains in the same position in the sky to observers on the surface1. Communications satellites are often given geostationary orbits so that the satellite antennas that communicate with them do not have to move, but can be pointed permanently at the fixed location in the sky where the satellite appears1.

The geosynchronous orbit was popularised by the science fiction author Arthur C. Clarke, and is thus sometimes called the Clarke Orbit1. The first geosynchronous satellite was designed by Harold Rosen while he was working at Hughes Aircraft in 19591.

 

Edited November 26, 2023 by Royalswissarmyknife

[RKunze]

5 hours ago, darthgently said:

Also putting compute resources in orbit powered by solar (or nuke) is another interest as the projected power requirements for where computation demand is going would put a big strain on terrestrial generation. 

Errm - no. If you can power a computing center from solar cells in orbit, you can just as well power it from solar cells on earth. You just need a bit more than double the cell area (double because it's night approximately half the time, and a bit more to compensate for atmospheric loss) and a bit of energy storage (if you put the thing somewhere dry near the equator, 12 hours worth of storage is enough). The added costs for more cell area and energy storage are more than compensated by not having to launch those things to orbit, not having to launch either a repair crew or a replacement computing center to orbit every time some of the hardware breaks down,  and not needing extra expensive radiation hardened compute hardware (to keep said hardware from breaking down immediately) and sophisticated radiator arrays (to keep the whole thing from overheating).

Edited November 26, 2023 by RKunze

[Hotel26]

1 hour ago, RKunze said:

If you can power a computing center from solar cells in orbit

Split the difference then: keep it on Earth and power it with nuke.  That would be the scientific solution.

[RKunze]

1 minute ago, Hotel26 said:

Split the difference then: keep it on Earth and power it with nuke.  That would be the scientific solution

 

If you want to use the most expensive way to generate the needed electrical energy, go ahead.

There's a reason almost nobody is building commercial fission power plants anymore. Those things are just too expensive to build, to expensive to run, and too expensive to get rid of after they go out of service...

 

[darthgently]

1 hour ago, RKunze said:

Errm - no. If you can power a computing center from solar cells in orbit, you can just as well power it from solar cells on earth. You just need a bit more than double the cell area (double because it's night approximately half the time, and a bit more to compensate for atmospheric loss) and a bit of energy storage (if you put the thing somewhere dry near the equator, 12 hours worth of storage is enough). The added costs for more cell area and energy storage are more than compensated by not having to launch those things to orbit, not having to launch either a repair crew or a replacement computing center to orbit every time some of the hardware breaks down,  and not needing extra expensive radiation hardened compute hardware (to keep said hardware from breaking down immediately) and sophisticated radiator arrays (to keep the whole thing from overheating).

Errm, the dark period is far shorter in LEO than 12 hours.   The difference in battery materials quantity would be dramatic (i.e. lithium mining etc).  The atmospheric loss is very significant.  The terrestrial grid is already strained and woefully inadequate for projected electrification of transportation much less added compute.  Latency from LEO can be as low as Starlink.  Compute demand is projected to  vastly increase.  

What if every next gen Starlink sat had big compute and storage capability on board?

Edited November 27, 2023 by darthgently

[RKunze]

3 minutes ago, darthgently said:

Errm, the dark period is far shorter in LEO than 12 hours. 

Yes. Thats why you only need the energy storage on the ground.

5 minutes ago, darthgently said:

The atmospheric loss is very significant

Not really. 1350 W/m² above the atmosphere vs around 1100 at sea level.

7 minutes ago, darthgently said:

What if every next gen Starlink sat had big compute and storage capability on board?

They'd overheat because cooling things in space is hard and computing generates lots of waste heat, and they'd lose stored data like crazy, because at compute center storage densities, every cosmic ray particle that hits the storage hardware flips several bits at once...

[darthgently]

14 minutes ago, RKunze said:

Yes. Thats why you only need the energy storage on the ground.

That is a lot of lithium

14 minutes ago, RKunze said:

Not really. 1350 W/m² above the atmosphere vs around 1100 at sea level.

That is over a 30% difference.  When has a 30%+ efficiency increase ever been considered insignificant by any power engineer?  Wow.

Heat and shielding would indeed be challenges.  But there are many challenges to doing it terrestrially, like sourcing that much backup storage materials for a lot more batteries, real estate for (more than in space) panels, and inadequate grid capacity

14 minutes ago, RKunze said:

 

Edited November 27, 2023 by darthgently