Starship specs - weight, volumes, etc

[InterestedEngineer]

Maybe, but Starship suffers from much of the same problems as Shuttle and for the same reason. Its performance rapidly decreases beyond the lowest LEO orbit because the dry mass of the upper stage is very high, because it’s a reentry vehicle (heavy heatshield, aerosurfaces/“wings”, etc) with an integrated payload bay.

So the difference in performance between different LEO orbits is much larger than you might think.

Stretching the booster and doing down range booster landing would significantly mitigate this problem, tho.

the difference between 185km and 400km for the 45 degree inclination is 124t - 108t = 16t `evolved`.

Not a huge difference.

I do wish that tool showed its work, at least the staging velocities and altitudes, so we could check its work.

[Robotbeat]

It’s not a big difference because you’re using the wrong numbers. You should pick an inclination equal to the launch site latitude for the reference orbit and equal to about 53deg for the Starlink case, as that’s the thing Elon is using.

And if you think a big dogleg is being used, try Florida instead of Boca Chica.

[xcelr8]

It's difficult to know sometimes what Elon really means in his messages. They can often have multiple interpretations. Thanks for pointing out the impact on payload from the orbit parameters. Definitely the performance will decrease as orbital altitude and inclination increase, especially for something as massive as the Ship.

My take is that Elon was referring generally to performance to Starlink orbit altitude, since the actual orbits can vary significantly for Starlink. I have no way to know that for certain though. The impact on payload will be less dramatic for increase in orbit altitude of that magnitude (185 - 400 km) than for inclination.

Another source from Elon that I'm referencing is his Starship update from last year

At a little after 19 minutes in this video he starts discussing the different Starship versions. Starship 2 (V2) would be able to deliver over 100t payload and what was described as Starship 3 at that time would be able to deliver over 200t. That V3 had the stretched propellant tanks, a much larger stack height. This has now been deferred until later. The current V3 which is to fly by the end of this year is much closer to V2 in the amount of propellant mass on the Booster and Ship.

Another thing Elon discussed prior to the Starship versions was the progression of Raptor. As a part of this, he mentioned that they are shooting to achieve 330t SL thrust eventually for Raptor, which would give a total liftoff thrust for the later Starship version of over 10,000t. This is consistent with the number of engines on the Booster being maintained at 33, which is what he showed a few weeks ago.

[Ludus]

There is also the fact that keeping SH Raptors at 33 while upgrading Starship to 9 (with 6 vacuum filling up the obvious available space) lets the whole system have 42 which at least for that version would be something Elon would find amusement in.

[InterestedEngineer]

There is also the fact that keeping SH Raptors at 33 while upgrading Starship to 9 (with 6 vacuum filling up the obvious available space) lets the whole system have 42 which at least for that version would be something Elon would find amusement in.

I suspect Raptor 3 came in slightly ahead of thrust level expectations, so they didn't need to go 35 or more.

A 6% increase in the predicted thrust for Raptor3 would be enough.

[wannamoonbase]

There is also the fact that keeping SH Raptors at 33 while upgrading Starship to 9 (with 6 vacuum filling up the obvious available space) lets the whole system have 42 which at least for that version would be something Elon would find amusement in.

I suspect Raptor 3 came in slightly ahead of thrust level expectations, so they didn't need to go 35 or more.

A 6% increase in the predicted thrust for Raptor3 would be enough.

I went the other way, that Raptor 3 didn't shrink as much as they wanted and they don't have the room to pack 2 more in (yet).  If there was room for more engines you can bet Elon would insist on including them.

[xvel]

god, this has nothing to do with "Elon insisting", you just calculate the performance with 33 and with 35 engines and see what's better, added thrust from more engines is beneficial at first after liftoff, but for the end of the burn, boostback and landing they are a dead weight, at some point it doesn't make sense to add more, it doesn't increase the performance or even decreases it.

[Brigantine]

more engines is beneficial at first after liftoff, but for the end of the burn, boostback and landing they are a dead weight, at some point [...] it doesn't increase the performance or even decreases it.

If you've already fixed the tank size, then maybe. (e.g. no more height in the Gigabay)
If the tanks can still stretch, then it's a very simple more thrust more better, even if the boostback burn needs more delta-V

[xvel]

more engines is beneficial at first after liftoff, but for the end of the burn, boostback and landing they are a dead weight, at some point [...] it doesn't increase the performance or even decreases it.

If you've already fixed the tank size, then maybe. (e.g. no more height in the Gigabay)
If the tanks can still stretch, then it's a very simple more thrust more better, even if the boostback burn needs more delta-V

Yes that is correct, if the height is not fixed it would be TWR not number of engines that matters, anyway, I did not do any approximate calculations for this but I guess that difference for 33 vs 35 engines even if 35 is better now may be close to insignificant and is just not worth it and then there are other factors like smaller gimballing range or center group of engines being further off center

[lamontagne]

Update based on latest NSF update video on Florida permitting, (relevant snapshot below)

https://youtube.com/watch?v=CWYryy9vZJo

Estimate SECO mass:  150_{starship+header_tanks} + 200_cargo = 350t
estimated MECO mass:  (2650 + 350) + (200 + 500)  = 3700
estimated launch mass:  (2650 + 350) + (200 + 4100) = 7300

At average Isp for Booster of 340, and 369 for Starship, that gives deltaVs for the launch phase of:
Booster:  340*9.81 * ln(7300/3700) = 2.27km/sec
Starship: 369 * 9.81 * ln(3000/350) = 7.78km/sec

Total deltaV = 10km/sec, which is in excess of the nominal 9.2km/sec for LEO.  The extra may be for going to different orbits, bad assumptions above, etc.

So 200t to LEO is what that model of starship seems perfectly capable of.  Also note the emphasis of far more deltaV on the upper stage than on the booster.  The booster's job is basically to get a Starship full of fuel to altitude and with a trajectory such that cosine/gravity losses are small.

TWR at liftoff will be 10,500/7300 = 1.44.

TWR Starship immediately after startup is 0.95.

Great update.  Perhaps the difference is landing propellant?  I don't see any allocation for it in your table.

[Brigantine]

landing propellant?

Ship: included in the 150 ton "Starship + header tanks"
Booster: looks like 500 tons of prop retained at staging for boostback and landing

Re: delta-V to LEO, IMO it's natural it would be a bit higher than a well-balanced EELV. It looks like spending much more time sitting between (horizontal velocities) maybe 1,900 m/s (inertial) at staging and e.g. 4,000 m/s where gravity is still sinking your vertical velocity by about 6.7m/s². (depending on assumptions about altitude). Superheavy doesn't do all that much work.

[lamontagne]

landing propellant?

Ship: included in the 150 ton "Starship + header tanks"
Booster: looks like 500 tons of prop retained at staging for boostback and landing

Re: delta-V to LEO, IMO it's natural it would be a bit higher than a well-balanced EELV. It looks like spending much more time sitting between (horizontal velocities) maybe 1,900 m/s (inertial) at staging and e.g. 4,000 m/s where gravity is still sinking your vertical velocity by about 6.7m/s². (depending on assumptions about altitude). Superheavy doesn't do all that much work.

You're quite right, i'd missed that.  Thanks, now it all works out.