A conversation with Elon Musk

On Thursday, October 3, 2019 at 6:49:33 AM UTC-7, David Spain wrote:

Nozzle design helps to. It would appear to have sea level *and* vacuum
optimized nozzles is the win over aerospikes at least for a TSTO
vehicle. Though Elon remains open to any "gifts", in this regard.

Dave


What happened to nozzle extensions?

"For first stage rocket engines, the engine works with nozzle extension in
disposed position during the first minutes of flight and expands it at some
predefined level of air pressure. This scheme assumes the outer skirt of the
bell is extended while the engine is functioning and its installation to working
position happens in the upper layers of the atmosphere. It excludes problems
with flow separation at sea level and increases efficiency of the engine in
vacuum."

See:

https://en.wikipedia.org/wiki/Nozzle_extension