In article ,
says...

On 2020-05-23 16:46, David Spain wrote:

https://i.stack.imgur.com/H4RtH.png

Which doesn't really show the pressurization plumbing as far as I can
see.


Nor does it show a dome to terminate the lower end of the O2 tank above
engines.

I was told here quite forcefully here that the Starship/SuperHeavy won't
have helium pressurization.

Starship won't have helium tanks.

I was also told here that there may be smaller tanks to run the
thrusters. And those round tanks might be those instead of fuel for landing.

The header tanks serve both purposes.

Cite:

https://space.stackexchange.com/ques...the-spherical-
tank-in-this-drawing-of-the-bfs/18769#18769

From above:

Question
--------
ITS Spaceship design question II.: The ITS Spaceship has two
mystical spherical tanks, marked green in this slightly edited
image. The whole tank design looks very exciting, and there's
rampant speculation on this sub about the purpose of those
spherical tanks:

are they for landing fuel?
... or are they storing 'hot' gaseous propellants as part of
the autogenous propellant pressurization system?
... or are they used for on-orbit propellant densification to
store vapor before it's liquefied again?

All of the above perhaps?

Answer by Elon Musk
-------------------
Those are the header tanks that contain the landing
propellant. They are separate in order to have greater
insulation and minimize boil-off, avoid sloshing on entry
and not have to press up the whole main tank.

Especially for Super Heavy, one would think you'd want as large a single
tank as you could to add versatility (more fuel for launch in a
disposable launcher mode vs use some of that fuel to land after
launching lesser load).

I really don't think SpaceX will ever intentionally dispose of a Super
Booster. They might do so with a Starship-like upper stage. But, I
suppose like Falcon, if the customer wants to pay for a disposable
launch, SpaceX would oblige, charging them for the disposed parts, of
course.

That said, Starship/Super Booster is optimized to be a fully reusable
TSTO. Any use as an expendable would be a compromise, not an optimal
thing to do.

If you dedicate a tank to landing, it's fixed size removes some of that
flexibility.

That's what they appear to be doing though.

In the case of super heavy, would it be correct to state that thrusters
would only be used after MECO to turn the rocket around to orient it for
re-entry ? During re-entry per say, are they used or does it rely solely
on the fins for orientation ?

I'm sure it will be very Falcon 9 first stage like.

Just curiuous to on why thsoe round tanks would be so big.

Landing propellant.

You could have a small tank that is replenished from big tank via a
small pump and heaters to make it gaseous since thrusters wouldn't
typically be use continously for long periods, you'd have time to refill
the small tanks by moving some liquid from big tanks, heat it into gas
into small tank.

I don't know the details of how SpaceX will handle pressurization in the
header tanks, but it won't involve helium, according to Musk.

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.