Apparently, it has now been decided to have 33 engines on Super Heavy.

Wasn't it originally 37 or 39 ?

Assuming payload goals are maintained, the ability to drop from 37 down
to 33 would be excellent news in terms of performance of engines as well
as weight of the steel ship.

On the other hand, if 33 is the maximum number they can physically fit
inside the fuselage, this could mean reduced payload at launch. (Once
launched fewer engines can run for longer time, but at launch, you need
that extra "oumph!" to lift all the fuel, the steel rocket and the payload.

Also, it is mention only the engines in the middle will gimbal. (Makes
sense for landing since only those will fire up). But just trying to
understand the torque aspect. Wouldn't engines on periphery have more
influence on direction of thrust?

(asking only on theoretical, I realise that costs would be higher to get
all those engines to gimbal instead of a few in the core ect)

Or is the distance betwween periphery and core engines relative to total
length of Super Heavy + Starship make any difference in torque too small
to be of consideration?

In article <MHHII.17161$7H7.1656@fx42.iad>,
jfmezei.spamnot@vaxination.ca says...
>
> Apparently, it has now been decided to have 33 engines on Super Heavy.

Initial tests will use 29 engines on Super Booster. Later they'll bump
that up to 33. The Raptors they are going to use are an improved
version with more thrust than initially planned. I'm sure that's part
of the reason for the reduction in engines.

https://www.teslarati.com/spacex-starship-super-heavy-booster-extra-
engine/

Tweet from Elon Musk:

Elon Musk @elonmusk - May 29
29 Raptors on Booster initially, rising to 32 later this year,
along with thrust increase per engine. Aiming for >7500 ton
thrust long-term. T/W ~1.5.

https://techstory.in/spacex-plans-to-boost-starship-raptor-engine-
performance/#:~:text=As%20SpaceX%20managed%20to%20boost,only%20rocket%
20improves%20its%20acceleration.

From above:

As SpaceX managed to boost Raptor 2 performance, the weight is
230 tons of thrust. With a peak lift off at 7600 tons the Super
Heavy Booster with 33 engines is reasonable.

> Also, it is mention only the engines in the middle will gimbal. (Makes
> sense for landing since only those will fire up). But just trying to
> understand the torque aspect. Wouldn't engines on periphery have more
> influence on direction of thrust?

Yes, but you really don't need the outer engines to gimbal. The inner
engines have more than enough control authority.
Jeff
--
All opinions posted by me on Usenet News are mine, and mine alone.
These posts do not reflect the opinions of my family, friends,
employer, or any organization that I am a member of.

On 2021-07-18 0:33, Jeff Findley wrote:
> In article <MHHII.17161$7H7.1656@fx42.iad>,
> jfmezei.spamnot@vaxination.ca says...

...

> https://techstory.in/spacex-plans-to-boost-starship-raptor-engine-
> performance/#:~:text=As%20SpaceX%20managed%20to%20boost,only%20rocket%
> 20improves%20its%20acceleration.

...

>> Also, it is mention only the engines in the middle will gimbal. (Makes
>> sense for landing since only those will fire up). But just trying to
>> understand the torque aspect. Wouldn't engines on periphery have more
>> influence on direction of thrust?
>
> Yes, but you really don't need the outer engines to gimbal. The inner
> engines have more than enough control authority.

Also, differential throttling of the outer engines could be used to
control pitch and yaw. But I don't know if SpaceX plans to do that. For
roll control one needs the attitude-control thrusters or off-center
gimballing engines.

JF Mezei was thinking very hard :
> Apparently, it has now been decided to have 33 engines on Super Heavy.
>
> Wasn't it originally 37 or 39 ?

Don't know what it was in the BFR renderings, but it was *29* earlier
this year.

> Assuming payload goals are maintained, the ability to drop from 37 down
> to 33 would be excellent news in terms of performance of engines as well
> as weight of the steel ship.
>
> On the other hand, if 33 is the maximum number they can physically fit
> inside the fuselage, this could mean reduced payload at launch. (Once
> launched fewer engines can run for longer time, but at launch, you need
> that extra "oumph!" to lift all the fuel, the steel rocket and the payload.

The Raptor they are putting in has more oomph than the Raptor on SN5
and SN6.

> Also, it is mention only the engines in the middle will gimbal. (Makes
> sense for landing since only those will fire up). But just trying to
> understand the torque aspect. Wouldn't engines on periphery have more
> influence on direction of thrust?
>
> (asking only on theoretical, I realise that costs would be higher to get
> all those engines to gimbal instead of a few in the core ect)
>
>
> Or is the distance betwween periphery and core engines relative to total
> length of Super Heavy + Starship make any difference in torque too small
> to be of consideration?

I don't think there's *room* to gimbal when you have 29-33 engines on
the periphery.

/dps

--
"What do you think of my cart, Miss Morland? A neat one, is not it?
Well hung: curricle-hung in fact. Come sit by me and we'll test the
springs."
(Speculative fiction by H.Lacedaemonian.)

Niklas Holsti used thar keyboard to writen:
> On 2021-07-18 0:33, Jeff Findley wrote:
>> In article <MHHII.17161$7H7.1656@fx42.iad>,
>> jfmezei.spamnot@vaxination.ca says...
>
>
> ...
>
>
>> https://techstory.in/spacex-plans-to-boost-starship-raptor-engine-
>> performance/#:~:text=As%20SpaceX%20managed%20to%20boost,only%20rocket%
>> 20improves%20its%20acceleration.
>
>
> ...
>
>
>>> Also, it is mention only the engines in the middle will gimbal. (Makes
>>> sense for landing since only those will fire up). But just trying to
>>> understand the torque aspect. Wouldn't engines on periphery have more
>>> influence on direction of thrust?
>>
>> Yes, but you really don't need the outer engines to gimbal. The inner
>> engines have more than enough control authority.
>
>
> Also, differential throttling of the outer engines could be used to control
> pitch and yaw. But I don't know if SpaceX plans to do that.

It seems there have been mixed messages on RB throttling, but the
latest seems to include that feature.

> For roll control
> one needs the attitude-control thrusters or off-center gimballing engines.

/dps

--
Maybe C282Y is simply one of the hangers-on, a groupie following a
future guitar god of the human genome: an allele with undiscovered
virtuosity, currently soloing in obscurity in Mom's garage.
Bradley Wertheim, theAtlantic.com, Jan 10 2013

JF Mezei wrote on 7/17/2021 :
> Apparently, it has now been decided to have 33 engines on Super Heavy.
>
> Wasn't it originally 37 or 39 ?

FWIW, 3 RCs have now been fired in a plumbed-in configuration. At
least one appears to have been in the "middle ring".

/dps

--
"That's a good sort of hectic, innit?"

" Very much so, and I'd recommend the haggis wontons."
-njm