Tank Pressurization on Starship

On 6/9/2020 10:07 AM, David Spain wrote:
On 6/8/2020 6:24 PM, JF Mezei wrote:
How can they run only the pre-burners? Wouldn't that run turbopumps that
would push a lot of unburned methane and oxygen out of the engine bell ,
risking ignotion when it sees a spark or a falme at the landing site?

Yes I would assume so. There is a risk of ignition outside the engine
until the methane gas dissipates to below about a 6% methane/air ratio.
Below that it isn't methane rich enough to ignite.

Or can they adjust mixes so that they have full burn of methane in both
the pre-burners so the the exchaust no longer contains combustible gases?


Another thought, all the test firings I've seen so far of SN4 have been
very very short. So if they did run a preburner only test, it was for so
short a period of time there was very little volume of gas ejected from
the engine to be that hazardous. Pressure can also be controlled by
limited tank venting as well. Stay below 6% ambient mix and nothing will
happen.

Dave