totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

1 hour ago, CatastrophicFailure said:

As I understand it, the arrangements is specifically so that the bells can be fixed to structure, details unknown, to help support them. Musk mentioned this in the past. 

These cutouts are "gulfs" with open coastline.
The round(ed) holes inside (which are to lighten the construction or to screw something there, or to let the wires pass through) are "lakes", with close coastline.

Both are stress concentrators, but the "lakes" weaken the structure less that the "gulfs" (like a pierced sheet of paper compared to a partially torn from one side if pull it apart).
If this was by design, they could drill more holes, but unlikely make the ring thinner by the cutouts.

Nobody attaches the nozzle to the hull. The support structure carries the combustion chamber with a short part of the nozzle, while the most part of the nozzle is attached to that.

1 hour ago, CatastrophicFailure said:

The engines on there now are likely as further developed and refined as S20 is to those older prototypes. And a full version 2.0 has already been spotted on site. Pretty sure there won’t be the same issues, if indeed they were issues. 

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.

Edited February 10, 2022 by kerbiloid

[Beccab]

4 minutes 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

I feel like I heard this one before. Like, a few million times

[kerbiloid]

32 minutes ago, Beccab said:

I feel like I heard this one before. Like, a few million times

Yes, and Saturn V was actually flying. So, probably you will hear this not once again before Starssip becomes new Saturn V three fourth of Saturn V, based on the payload mass.

[Flavio hc16]

7 hours ago, kerbiloid said:

Yes, and Saturn V was actually flying. So, probably you will hear this not once again before Starssip becomes new Saturn V three fourth of Saturn V  5 times the Saturn 5, , based on the payload mass to the moon. Or 20 Times/ish the Saturn 5, based on the mass to moon surface, Or 1000s times the mass of saturn 5, based on the mass per$ to LEO/GEO/TLI/LO/LS/TMO/MO/MS.

Fixed for you

Even if we consider it in non reusable mode: 300 tons to orbit at what? 1/10th of the price if not lower? So 20 times more efficient?

~[snip]~

Edited February 10, 2022 by Starhawk
Redacted by moderator

[kerbiloid]

1 hour ago, Flavio hc16 said:

300 tons to orbit at what?

300 tons is what? The Starship in total or what it can carry in a 9x10 m cargo bay?

[Rakaydos]

18 minutes ago, kerbiloid said:

300 tons is what? The Starship in total or what it can carry in a 9x10 m cargo bay?

300 tons paid cargo expendable. 150 tons reusable.

Saturn 5 was only 125 tons including the upper stage residuals, AND fully expendable

[RealKerbal3x]

This belongs here

 

[kerbiloid]

56 minutes ago, Rakaydos said:

300 tons paid cargo expendable. 150 tons reusable.

How much in the bay?

150 t of reusable = dry mass = empty mass + cargo mass.

As Starship is closer to a heatproof spaceplane rather than to a lightweight upper stage, it looks reasonable to take Shuttle as a reference.

105 t of dry mass (let's forget its small fuel tanks) = ~75 t of empty (60 t of the spaceplane itself + ~10 of the 2nd stage engines) + 30 t of cargo (overloaded) or 15 t of cargo (landable).

So, as the Space Shuttle cargo mass is ~30/105 .. 15 / 90 = 0.25 of dry mass

For Starship the cargo mass is ~150 * 0.25 ~= 40 t, i.e. two Protons or probably one Falcon Heavy.

Let's add, say, 15 t of cabin, and it's ~55 t.

150 t of reusable can't carry 300 t in the bay.

It's an expendable fairing + shroud.

So, 300 should be the total Starship mass, including fuel.

[Beccab]

4 hours ago, kerbiloid said:

How much in the bay?

150 t of reusable = dry mass = empty mass + cargo mass.

As Starship is closer to a heatproof spaceplane rather than to a lightweight upper stage, it looks reasonable to take Shuttle as a reference.

105 t of dry mass (let's forget its small fuel tanks) = ~75 t of empty (60 t of the spaceplane itself + ~10 of the 2nd stage engines) + 30 t of cargo (overloaded) or 15 t of cargo (landable).

So, as the Space Shuttle cargo mass is ~30/105 .. 15 / 90 = 0.25 of dry mass

For Starship the cargo mass is ~150 * 0.25 ~= 40 t, i.e. two Protons or probably one Falcon Heavy.

Let's add, say, 15 t of cabin, and it's ~55 t.

150 t of reusable can't carry 300 t in the bay.

It's an expendable fairing + shroud.

So, 300 should be the total Starship mass, including fuel.

For the third time, no, it is not. As the others have already said quite clearly 150 tons is the cargo fully reusable, NOT the dry mass + cargo. ~[snip]~

Edited February 10, 2022 by Starhawk
Redacted by moderator

[RealKerbal3x]

Just now, kerbiloid said:

How much in the bay?

150 t of reusable = dry mass = empty mass + cargo mass.

As Starship is closer to a heatproof spaceplane rather than to a lightweight upper stage, it looks reasonable to take Shuttle as a reference.

105 t of dry mass (let's forget its small fuel tanks) = ~75 t of empty (60 t of the spaceplane itself + ~10 of the 2nd stage engines) + 30 t of cargo (overloaded) or 15 t of cargo (landable).

So, as the Space Shuttle cargo mass is ~30/105 .. 15 / 90 = 0.25 of dry mass

For Starship the cargo mass is ~150 * 0.25 ~= 40 t, i.e. two Protons or probably one Falcon Heavy.

Let's add, say, 15 t of cabin, and it's ~55 t.

150 t of reusable can't carry 300 t in the bay.

It's an expendable fairing + shroud.

When Starship's max reusable payload mass is quoted as 150t, that doesn't include the mass of the vehicle itself. It can put itself + 150t of payload into orbit.

[kerbiloid]

The Raptor thrust is ~180 tf.

30+ engines ~= 5 500 tf of thrust, i.e. ~4 500 t of total launch mass.

The fuel is hydrocarbon, no hydrogen.

So, the launch mass of SH+SS ~= 1.5 N1 launch mass (also hydrocarbon fuel) or ~1 UR-700 (hypergolic, with a little less ISP).

This means payload of 140 .. 150 t to LEO.

As the Raptors are definitely more effective than the old NK-33 or RD-270, let it be twice.

Exactly 150+ t of total mass is what we have for the payload, plus 150 for the upperstage included.

That's all. a 150 t reusable (if lucky) craft with 50 t  of payload.

14 minutes ago, RealKerbal3x said:

When Starship's max reusable payload mass is quoted as 150t, that doesn't include the mass of the vehicle itself. It can put itself + 150t of payload into orbit.

They are juggling with payload mass since the project beginning. Originally it was 550.

And they never made the mass distribution  clear.

Upd.

The Shuttle cargo bay. 18 m long, 4.6x4.6 m wide.

Cross-section area = 4.6 * 4.6 ~= 20 m².

Starship, a squared corridor in the cylindric hull: (9 / sqrt(2) )² ~= 40 m², twice as Shuttle. So at average cargo density it's twice as capable.

On the published picture it's a little longer. Say, same 18 m (i.e. two diameters and not longer than a raiload car, because the cargo should be delivered by standard roads, cars, and trailers)

30 t * twice = 60 t.

So, again we get the maximum payload value of 60 t.

So, everything tells us that its cargo mass is ~55 t.

***

If replace the cargo bay and the cabin with a shroud, its payload mass should be ~150 t,

(But without Starship, only with its engines and tanks).

***

So, SH/SS is 1.5 times heavier than Saturn with same payload, rather exotic landing tower, and rather doubtful chain of engines.

Just a worse version of Saturn wannabe reusable.

Edited February 10, 2022 by kerbiloid

[Beccab]

4 hours ago, kerbiloid said:

They are juggling with payload mass since the project beginning. Originally it was 550.

It surely would help if you used numbers about the rocket we're talking about, not ITS. It's as if I said "With the Saturn V they were juggling with payload mass since the project beginning. Originally it was 210 tons." when 210 its the estimate for C-8

4 hours ago, kerbiloid said:

Exactly 150+ t of total mass is what we have for the payload, plus 150 for the upperstage included.

That's all. a 150 t reusable (if lucky) craft with 50 t  of payload.

Your math makes zero sense. For the first half you use payload estimates (95 tons for the N1), then suddenly at some point they become for dry mass+payload

4 hours ago, kerbiloid said:

Just a worse version of Saturn wannabe reusable.

~[snip]~

Edited February 10, 2022 by Starhawk
Redacted by moderator

[Elthy]

The star ship presentation is at 03:00 here, as i have to wake up at 07:00 i wont watch it live. Hopefully i manage to shield myself from spoilers before i have the time for it.

BTW: I want to remind some of you of the option to ignore users, helpful if someone isnt directly violating the forum rules but is spewing the same useless nonsense all the time. You can find it here: https://forum.kerbalspaceprogram.com/index.php?/ignore/

[Beccab]

1 minute ago, Elthy said:

BTW: I want to remind some of you of the option to ignore users, helpful if someone isnt directly violating the forum rules but is spewing the same useless nonsense all the time. You can find it here: https://forum.kerbalspaceprogram.com/index.php?/ignore/

Thank you

[kerbiloid]

4 hours ago, Beccab said:

Originally it was 210 tons." when 210 its the estimate for C-8

S-8 is not S-5.
S-5 was 135 t always.

The early SS/SH hype was about 500+ t to LEO.

4 hours ago, Beccab said:

Your math makes zero sense. For the first half you use payload estimates (95 tons for the N1), then suddenly at some point they become for dry mass+payload

I compare a kerolox rocket to another kerolox rocket without SpaceX magic.

~[snip]~

(I guess, methalox is closer to the kerolox, rather than to the hydrolox, isn;t it?)

Edited February 10, 2022 by Starhawk
Redacted by moderator

[RealKerbal3x]

20 minutes ago, kerbiloid said:

The early SS/SH hype was about 500+ t to LEO.

That was for fully expendable ITS, a very different and much larger vehicle.

[Lukaszenko]

1 hour ago, kerbiloid said:

How much in the bay?

....

For Starship the cargo mass is ~150 * 0.25 ~= 40 t, i.e. two Protons or probably one Falcon Heavy.

...

So, 300 should be the total Starship mass, including fuel.

You forgot to add the mass of the launch tower and the fuel tanks and the access road. 

So you see, the real payload to orbit is actually deep in the negatives.  It's why we're having all these Starlink satellites falling down, and this is just the beginning. 

[tater]

 

 

https://launchercalculator.com/?rocket=SX5

You have to express stage 2 as a % of total vehicle mass if you want to noodle around (odd choice, but whatever).

[kerbiloid]

1 minute ago, Lukaszenko said:

You forgot to add the mass of the launch tower and the fuel tanks and the access road. 

So you see, the real payload to orbit is actually deep in the negatives.  It's why we're having all these Starlink satellites falling down, and this is just the beginning. 

I forgot to add the mass of SpaceX mana which lets a 350 s ISP hydrocarbon + LOx rocket lift threetimes greater mass than earlier.

Just now, tater said:

You have to express stage 2 as a % of total vehicle mass if you want to noodle around (odd choice, but whatever).

Quote

Assumed payload mass	kg
2nd stage to Rocket mass ratio

What is "payload" and the "2nd stage"?

That's why I would prefer a simple calculation here rather than magic Musk numbers.

[Jacke]

4 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.

That's because the F-1 started development in 1955 and was first fired in 1957.  Engines, especially large ones, take a long time to develop and perfect.  This is all before any of the Saturn rockets started development (Saturn I in 1957, Saturn V in 1961/1962).  The Saturn V adopted using the F-1 engine because it was the working solution for its first stage.

[kerbiloid]

Just now, Jacke said:

the F-1 started development in 1955

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

[Beccab]

NSF thread: https://forum.nasaspaceflight.com/index.php?topic=55430.msg2323970#msg2323970


TL;DR: 160T cargo capacity for Starship (becoming 180 if the booster lands downrange, which is irrelevant here but it was worth mentioning since it was the original question of the thread I linked)

And no, kerbiloid, this is not payload+dry mass. No payload estimate of any rocket includes dry mass, not even of the Shuttle

[Rakaydos]

Just now, kerbiloid said:

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

As the soviets found out, just because a bigger engine is more unstable than several smaller ones, means nothing if your control systems for multiple smaller engines cant be tested.

That's where SpaceX's advantage over the N1 lies- fire, refire, test, retest, simulate and validate, and be willing to make mistakes AND fix them after they make themselves obvious, well before they actually get used.

There's nothing magical about the 3 engines more that the N1 had over the Falcon Heavy. It's all about 50 years of computer tech getting better.

[kerbiloid]

1 hour ago, Beccab said:

NSF thread: https://forum.nasaspaceflight.com/index.php?topic=55430.msg2323970#msg2323970

Quote

Booster:  230T * 33 = 7,500T  thrust

230?
Wiki says 185.

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

25% of difference.

Quote

Booster:  230T * 33 = 7,500T  thrust
Max takeoff mass = 7500  / 1.5 = 5,000T

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

+/- 1000 t?

Well, let's go with 5 000 t.

Quote

3km/sec deltaV for booster
220T Booster dry weight.
380T pre-boost-back weight for Booster (includes boost-back and landing fuel)
3 km/sec = 340 * 9.8 * ln (5000/mf),  solve for mf = 2000 tons, which includes the booster and Starship.

(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.

Quote

We don't know what the angle is, but Falcon 9 ranges from 45deg to 30deg
https://www.reddit.com/r/spacex/comments/7wlk5j/falcon_9_and_falcon_heavy_trajectories_and/
Taking 37deg as an average, the horizontal component of the velocity that has to be canceled is cos37 * 1.7 = 1.4km/sec
Vertical component is free, we have gravity in our favor.
1.4km/sec + 0.5km/sec (landing) = 1.9km/sec deltaV
1.9km/sec = 353 * 9.8 * ln(mass_ratio).  Solve for mass_ratio = 1.73

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

Quote

9 km/sec to get to orbit (includes gravity losses)

(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

Quote

6km/sec deltaV for Starship
<...>
370 avg ISP for Starship

So,  we need the Starship initial mass ratio:

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

Quote

So we have 2000 tons at MECO traveling at 1.7km/sec, and 2000-380 = 1620T of Starship.

6km/sec = 370 * 9.8 * ln (1620/mf), solve for mf = 310 tons

1620 /5.2 ~= 310 t.

Quote

310 - 150 = 160T cargo capacity for Starship.
150T de-orbit weight for Starship (includes deorbit and landing fuel, no payload coming down)

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).

Quote

> 1.0x thrust/weight at Starship at second stage ignition

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).

1 hour ago, Rakaydos said:

As the soviets found out, just because a bigger engine is more unstable than several smaller ones, means nothing if your control systems for multiple smaller engines cant be tested.

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

1 hour ago, Rakaydos said:

That's where SpaceX's advantage over the N1 lies- fire, refire, test, retest, simulate and validate, and be willing to make mistakes AND fix them after they make themselves obvious, well before they actually get used.

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

1 hour ago, Rakaydos said:

It's all about 50 years of computer tech getting better.

Gas physics stays same.

Edited February 10, 2022 by kerbiloid

[RealKerbal3x]

8 minutes ago, kerbiloid said:

230?
Wiki says 185.

230t thrust is for the new Raptor 2 iteration, the wiki thrust is for the previous version.

8 minutes ago, kerbiloid said:

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.

The current version of Starship has 6 Raptors (3 sea-level, 3 vacuum), increasing to 9 engines later on (3 sea-level, 6 vacuum). All engines will be running during the second-stage ascent to reduce gravity losses.

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

Edited February 10, 2022 by RealKerbal3x