totm nov 2023 SpaceX Discussion Thread

[Beccab]

14 minutes ago, kerbiloid said:

230?
Wiki says 185.

Thrust	~185 tf (1.81 MN; 410,000 lbf) for Raptor 1

25% of difference.

According to wiki, 185 * 33 / 1.5 ~= 4 000 t.

+/- 1000 t?

Well, let's go with 5 000 t.

(It would be nice of course, if he was decoding the abbreviations. It this case I would not need to recalculate "mf" as "m final" instead of "m fuel").

fuel : empty 3000 + 380 - 220 :  220 ~= 14.
Looks reasonable bor a booster, let's take it.

I honestly have no idea what does this techobubble mean at all, and why should be care about angles, when the author just said:

(Actually, 9.6, but who cares).

All angles are already included. This 9..9.6 km/s presumes the optimal angle.
The vertical-schmertical is a nonsense, the rocket is just moving by the optimal trajectory with nearly zero AoA and spending the energy against gravity and air drag.

All we need to know is

So,  we need the Starship initial mass ratio:

exp(6 000 / (370 * 9.8)) ~= 5.2

1620 /5.2 ~= 310 t.

So, if take the same ration for landing (380 : 220), the empty mass of Starship is 150 / 380 * 220 = 86 t.
The fuel mass = 1620 - 310 = 1310 t.
The fuel:empty = 1310 : 86 ~= 15.

So the aerobraking and deorbiting stage, with a reusable cargo bay, equipped with door mechanisms and so on, with command&control equip, with avionics, with heat protection, has greater fuel:dry mass ratio than the booster which reenters at an almost airplane 2 km/s speed? Seriously?

Is the cargo bay, where they put the payload, massless or what? The winglets? The tyles?

What do we have is a payload mass 160 t for a fully Starship's propulsion unit.
I.e. exactly what I said about Saturn (140 t, expendable).

Wait...
But as the initial mass of Starship is 1620 t, it requires 1620 / 230 = 7 raptors

But everywhere (in wiki, in video) it has just 3 raptors.

So, T/W is < 0.5, and the whole underthrusted thing dives into ocean after having lost 1 km/s of delta-V.

Kaboom! Splash-X !!!

***

Let's recalculate.

Thrust = 33 * 185 tf (according to wiki, rather than to the unknown source).

Launch mass at T/W = 1.5 (from the given) = 33 * 185 / 1.5 = 4 070 t.

Starship thrust = 3 * 185 tf.
T/W (from the online calculator) ~= 1.1.
Mass = 185*3/1.1 ~= 504 t.

Let it be 600 t. (Starship + fuel + cargo), as the given T/W is ~1.

Booster total mass = 4070 - 600 ~= 3470 t.

Compared to the 3 380 t from forum, it almost same. Bingo.

Buster fuel ratio: let's take the same = 3 470 / 3 380 * (3 380 - 220) ~= 3244 t.
Operational = 3244 * (3 380 - 380) / (3 380 - 220) ~= 3 180 t.

Booster delta-V ~= 340 * 9.8 * ln(4 070 / (4070 - 3 180)) ~= 5 065 m/s.

A little much for a booster, but let's take it, as 5 000 - (9 600 - 7 800) of loss ~= 3 200 m/s of resulting speed.

 

So, we need 4.6 km/s more from the upper stage.

Total mass = 600 t.

mass ratio = exp(4600 / (370 * 9.8)) ~= 3.55

Final mass =  600 / 3.55 ~= 170 t.

Spent fuel = 600 - 170 = 430 t.

Tank mass = 430 / 15 (see the booster) ~= 30 t.

So, the garage + cargo = 170 - 30 = 140 t.

Exactly Saturn V, but by 1 000 t heavier (because no hydrolox.

And see: we didn't substract a heatshield and wings.

If take the shuttle shape and mass ratio, a reusable stage would carry just 25% of the total mass as payload, so 140 / 4 ~= 35 t.

***

So, we can conclude that the NSF post was using an overestimated Raptor thrust for booster, twice overestimated thrust for Starship, spent no mass on heatshield, avionics, wings, etc,

and thus is a full nonsense is rersult.

The realistic value is 140 t as fully expendable and ~50 t as reusable if the Boca-Chica shamans had improved the heat protection so much, otherwise 35.

And see, we have treated the fuel tanks as steel-skinned and requiring no heat protection.

Otherwise the reusable Starship is impossible at all (which is most probable).

As the Soviets found out, 5 acoustic sources are better that 30+.

Currently it's in only in PR. N-1 at least tried four times.

Gas physics stays same.

Two options: everyone else but you is wrong or you are wrong. What conclusion you take from this is up to you

[tater]

 

 

Call Starship 100t dry all in (entirely reasonable, I've done the math on the steel in other posts discussing SS variant tugs, etc). 1200t props. 100t cargo (in ADDITION to SS mass, obviously).

Total stack mass is 5200, and I will call the booster 120t dry.

The booster has a total of 3980 m/s of dv with the full SS on top. All the drag, and most gravity losses are in the boost phase. MECO will be something >2 km/s. Once staged, it requires very little props to boostback and land. So 2.something to almost 3 km/s, how much dv does our SS have?

If the Isp is 350 for SS (ave), then it has 6679 m/s—the whole SS, and 100t cargo.

If the Isp is ~360, it has 6869.

If they can get it to 370 (3 @ 356 and 6@378), then it has 7060 m/s.

 

 

Note I used the SL Isp for the booster, but in vacuum, the Isp is not 330, but 356, and the actual Isp will average slightly higher than 330. The total stack dv could be as high as 4100+ m/s depending on that average.

Edited February 10, 2022 by tater

[tater]

So total stack dv with 100t of actual payload (not including Starship, since no one does that) is >10.6 km/s.

Edited February 10, 2022 by tater

[kerbiloid]

42 minutes ago, RealKerbal3x said:

Most upper stages have a TWR < 1 and get to orbit just fine. Starship is no different.

0.8 .. 1.1, and Starship is two-staged, so more 1.1 than 0.5.
On their official site 1.1.

***

Okay, let's calculate again (skipping the intermediate explanations, as they stay same).

Booster thrust = 33 * 230 = 7 590 tf.

T/W = 1.5

Total launch mass =  7590 / 1.5 ~= 5 060 t.

Starship:
Thrust = 9 * 230 = 2 070  tf.

T/W = 1..1.1

Starship total mass = 2 070 / (1 .. 1.1) ~= 1 900 .. 2 100 t.

Booster total mass = 5 060 - (1 900 .. 2 100) = 2 960 .. 3 160 t.

Let's take the booster = 3 380 t from the example, it looks reasonable.

So, Starship total mass = 5 060 - 3 380 = 1 680 t.

T/W = 2 070 / / 1 680 ~= 1.23, a little great for the upper stage, but let's have in mind the 6 instead of 9 on the intermediate version.

***

Booster operational fuel: 3 000 t, ISP = 340 s.

Booster delta-V = 340 * 9.8 * ln(5 060 / (5 060 - 3 000)) ~= 3 000 m/s, of 9 600 required (or 9 000 from the example).

***

Starship:
Total mass = 1 680 t.
Required delta-V = 6 600 (or 6 000) m/s,
ISP = 370 s.

Mass ratio = exp(6 600 (or 6 000) / (370 * 9.8)) = 6.2 (or 5.2).

Final mass = 1680 / (6.2 or 5.2) = 270 or 320 t.

Operational fuel mass = 1 680 - 270 or 320 = 1410 or 1 360 t.

Tank + engines mass (from booster) = (1410 or 1 360 t) / 14.5 ~= 97 or 94 t.

So, the garage + avionics + heat protection + cargo = 1 680 - (1410 + 97 or 1 360 + 94) = 1 680 - (1507 or 1454) = 173 or 226 t.

Shuttle:
total = 105 overloaded - 30 + 15 = 90 t.
cabin ~ 10 t.
booster engines ~10 t.
cargo = 15 t.

So, garage + avionics + heat protection = 90 -10 -10 -15 ~= 55 t.
Payload = 15 t (landable in case of emergency) or 30 (if Shuttle is lost) + 10 t of cabin + 10 t of engines = 35 .. 50 t.
So, full payload to total "what to land" mass ~= (35..50:55) = 0.6..0.9.

Starship doesn't have a LES, and is declared human-rated, and has no "hard landing option" due to no gears, It either lands together with human cabin, or crashes.

In Starship the landing mass is up to = 173 or 226 t, including ~95 t of tanks and engines (see above).

Garage + avionics + heatshield + payload = (173 or 226) - 95  = 78 or 131 t.

They can't return it without garage, avionics, and heatshield, as they are parts of the Starship,

Payload / (garage, avionics, and heatshield) in Shuttle = 0.6 .. 0.9.
So, 0.9

Payload = 70 or 118 t.

So, if magically reduce the delta-V loss from 9.6 km/s to 9.0 km/s, it can take 118 t max.

If take 9.6 km/s the reusable Starship payload is ~ 70 t.

As original sixpack of the Raptors provides 2/3 of full thrust, so delta-V loss is greater, the 6 Raptor-2 version may have ~60 payload.

***

(All of that is under assumption that 33 Raptors hadn't get into resonance and explode, and Starship had revamped into proper shape with proper heatshield, and that the thin and bulky tanks of Starship hadn't crashed.)

Actually, 75% of that in best case.

34 minutes ago, Beccab said:

wo options: everyone else but you is wrong or you are wrong. What conclusion you take from this is up to you

Read the calculation, updated after the @RealKerbal3x's notes.

Edited February 10, 2022 by kerbiloid

[Starhawk]

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[Rakaydos]

8 hours until we get the latest official numbers.

[mikegarrison]

People, working from marketing releases and press releases and public data to determine technical details of an aerospace vehicle is a difficult, specialized job. It requires experienced engineers to essentially reverse-engineer the design and then adjust it to match the known data. When we do it where I work, it takes months. And then when we get new data, we do it again to refine our work.

It is not something you are going to get right in a post on this board. So I suggest you stop fighting about who is right, because I am quite confident that the answer is "none of you". Not unless one of you is secretly a SpaceX engineer with access to data that you probably shouldn't be sharing publicly anyway.

Edited February 10, 2022 by mikegarrison

[tater]

^^^ yeah, the best anyone can do using the stated specs is to guess a vehicle dry mass (4mm steel, plus geometry gives a lower bound adding in engines at 1-2t per), estimate or accept propellant mass data (densities are known, and so with geometry, so this is possible to first order as well, or take the quoted tonnage at face value). Then calculate the dv of the SS, then the stack with SS on top (which I did above).

I'll have to take their word on the thrust and I_sp figures—what choice do I have there?

Looks to me that a 100t payload AND a 100t ship has about 10.6 km/s of dv. That is sufficient for LEO with a 1+ km/s margin (and some is certainly required for reuse, which I did not bother to calculate).

To be very clear, "back of the envelope." This is first order stuff, I would not presume to do more than a ballpark. Their stated payload mass seems plausible to me in short.

Edited February 10, 2022 by tater

[Jacke]

6 hours ago, kerbiloid said:

Why did they start this at all, when smaller ones were easier to use?

Development started in 1955 when launch vehicles of larger size were envisioned.  Most clustering in the US at the time was 3 engines on Atlas.  And there are benefits going to larger engines rather than more of them.

[tater]

 

[Beccab]

Just now, tater said:

 

99% it's a raptor 1 and a raptor 2

Also, they're installing lights around SN15/16 and mounting a stage in front of the full stack

[Minmus Taster]

4 minutes ago, Beccab said:

mounting a stage in front of the full stack

OMG Starship has 3 stages :O :O :O   #CONFIRMED

I wonder what the lights are for considering the presentation seems to be under 420

[magnemoe]

12 hours ago, kerbiloid said:

It was much easier to put 30 smaller engines on the Saturn-V 1st stage rather than develop F-1.

But for reasons they preferred the headache of making a bigger engine.

Other times other solutions, back then electric cars was an pretty stupid idea for obvious reason like only lead acid batteries. 
Engines blew up who took out other engines so its better to use fewer larger ones. Russia had more problems making larger engines so they fueled multiple from one turbopump. 
Falcon 9 has 27 engines and no issues and as I know its has just been one Merlin engine fail during launch. 

[mikegarrison]

1 hour ago, tater said:

^^^ yeah, the best anyone can do using the stated specs is to guess a vehicle dry mass (4mm steel, plus geometry gives a lower bound adding in engines at 1-2t per), estimate or accept propellant mass data (densities are known, and so with geometry, so this is possible to first order as well, or take the quoted tonnage at face value). Then calculate the dv of the SS, then the stack with SS on top (which I did above).

I'll have to take their word on the thrust and I_sp figures—what choice do I have there?

Looks to me that a 100t payload AND a 100t ship has about 10.6 km/s of dv. That is sufficient for LEO with a 1+ km/s margin (and some is certainly required for reuse, which I did not bother to calculate).

To be very clear, "back of the envelope." This is first order stuff, I would not presume to do more than a ballpark. Their stated payload mass seems plausible to me in short.

The way it is done is to use PD design tools to basically create the design yourself. See how close you came to the data you know, and redo it in a loop until it converges.

PD design tools are not really "back of the envelope", but in a sense they are a more sophisticated, calibrated version of "back of the envelope". They still are not a detailed design, which is the step you do once a PD design gets the go-ahead for further development.

Sometimes you come up with the answer that the claimed performance is unlikely to be achieved, and that's also an educational outcome.

It's different with a design that is actually in service, because in that case if you come up with the answer that the performance can't be achieved and yet it is clearly being achieved in service, then you know your tools need fixing. Real world data trumps all.

[Meecrob]

15 hours ago, mikegarrison said:

That's what I was thinking, but if they are that sensitive to the local wind, then, um, did they really pick the right place for their spaceport?

Anyway, I've worked on tests at night, for multiple reasons (schedule, temperature requirement, low ambient noise, and even, yes, wind). But when doing something like this for the first time, typically you really would want to do it in the daylight if at all possible.

I say this totally in jest, but perhaps this is why Boeing currently seems to be plagued with being late?

Full disclosure, I've worked in flight test, and @mikegarrison is correct; it is standard practice to not leave anything to chance, such as a situation where low lighting levels could impact operations. SpaceX seems to really want to re-write all the rules here!
 

Fingers crossed it doesn't end up biting them in the butt!

[tater]

1 hour ago, mikegarrison said:

PD design tools are not really "back of the envelope", but in a sense they are a more sophisticated, calibrated version of "back of the envelope". They still are not a detailed design, which is the step you do once a PD design gets the go-ahead for further development.

I meant here. Not professionally.

(really more to the conversation about if the numbers we see in press releases are plausible or not)

 

 

 

[tater]

Music going.

 

[Spaceception]

Getting some reel footage now

 

Idk, the beat almost reminds me of the song irresistible, but it's not quite right

Edited February 11, 2022 by Spaceception

[ExtremeSquared]

Was this filmed yesterday? All the captions are clearly finished already.

[cubinator]

1 minute ago, ExtremeSquared said:

Was this filmed yesterday? All the captions are clearly finished already.

The ship wasn't on the booster until after midnight today.

[ExtremeSquared]

1 minute ago, cubinator said:

The ship wasn't on the booster until after midnight today.

Must just be heavily time-delayed. The captions are clearly human-generated and showing up before the words. If youtube does live human-generated captions it could be just a minute or two delayed, though.

[Minmus Taster]

Amazing new animation, not wildly available online now sadly  I'm sure it will be posted in the next few days.

Edit: Seems I spoke to soon

 

 

[Wizard Kerbal]

Just want to check - will I get banned for making fun of the refueling . . . position?

[Rakaydos]

Just now, Wizard Kerbal said:

Just want to check - will I get banned for making fun of the refueling . . . position?

"I mean, it's a fluid transfer, y'know?

[Minmus Taster]

5 minutes ago, Wizard Kerbal said:

Just want to check - will I get banned for making fun of the refueling . . . position?

 

2 minutes ago, Rakaydos said:

"I mean, it's a fluid transfer, y'know?

It worked well for me when I did it, but I'd keep it subtle just to be safe  

TDH to help convey our thoughts on that whole thing.

And as long as we're talking about TDH: