I imagine that having assembled a top-notch engine development team, Musk would not want it to go idle. After the Merlin 1D and the Super Dracos, what engine developments do they have left?
That is what this thread is about.
Elon mentioned highly efficient staged combustion and "mostly methane". The airforce asked everyone for a specified engine and SpaceX asked, 'can it be methane?'. We're speculating on very little info here, wondering if those facts are all related, and what the plan might be, and potential implications.
Questions like these have arisen:
Is it methane for both stages? Will there be commonality?
Does cross-feed potential factor in (like a 4 engine 1st stage for full-cross-feed or a 5 engine for almost full cross-feed plus landing engine)?
1) Is methane the choice because of future Mars ISRU?
2) Is methane the choice because of reusability implications like these:
2a) Amenability to re-entry or re-ignition purposes: Perhaps a component of the ullage after separation can be flashed into compressed methane gas and oxygen gas within their respective systems by a light-weight, carefully controlled, exothermic reaction within the tanks to provide structural rigidity for re-entry (vapour pressure/fugacity), and force the ubiquitous presence of prop reagents through the plumbing as a gas for low initial thrust levels until the liquid component is forced back to the plumbing by acceleration of the stage (changing from gas propellants back to "the usual liquid burn") in a sputtering transient?
2b) low/no coking
2c) relative low cost and abundance of LNG?
2d) Improved performance?
3) Is methane the choice because of concerns about cumulative emmissions at very high future flight rates?
And other themes:
Is Merlin 2 pushed back forever? Or is this an intermediate step with better near-term commercial potential and reduced risk?
Is a crygenic raptor stage pushed back forever? Or is this an intermediate step with better near-term commercial potential and reduced risk?
If a new engine were announced tomorrow, when might it first see commercial use?
How might the new SpaceX engine stack up against previous development programs from decades ago?
Will the bells be retractable or extendible for protection during re-entry and efficiency maximization as the flight progresses?
What will the song be on the announcement video? Something by the band "30 seconds to Mars" perhaps?