Could upper stage engines be brought back to earth inside the Dragon?

[ArbitraryConstant]

Or would you be able to land the upper stage vertically with the vacuum nozzle attached/extended?

The reusability video shows it retracting. Flexible plumbing would be complicated so I suspect it's an entire outer sheath with the engine/propellant tanks as a movable unit inside.

[Joel]

OK, I give up. Thanks a lot for all the feedback!

[rst]

Or would you be able to land the upper stage vertically with the vacuum nozzle attached/extended?

The reusability video shows it retracting. Flexible plumbing would be complicated so I suspect it's an entire outer sheath with the engine/propellant tanks as a movable unit inside.

The reusability video shows something funky going on around the nozzle, but I can't clearly see what. 

If they're going to have a sheath around the nozzle, would it make sense to just retain the interstage (or some portion of it) to serve the purpose? You'd have to arrange it to both keep the rocket exhaust from impinging the sheath, and also keep the plasma on reentry from impinging the nozzle.  But if there's a geometric arrangement that does that (cutting off the interstage at the same cross-sectional level as the nozzle edge, perhaps?), it would save you the weight and potential reliability problems associated with actuators for a movable structure.

[meekGee]

Using the sheath might work, but you can't keep it around the nozzle when it fires, since the radiated heat from the nozzle will disintegrate it.  (and if not, will melt the nozzle)

Off all the things that SpaceX showed, this second stage recovery trick is the biggest head-scratcher for me.   

Options that I see are:
- Retracting engine assembly
- A sliding sheath (So basically a retracting "everything")
- Drop the nozzle extension
- Make the nozzle extension survive rentry (face up) and have a large landing gear.

This should be a new thread.

[hrissan]

Using the sheath might work, but you can't keep it around the nozzle when it fires, since the radiated heat from the nozzle will disintegrate it.  (and if not, will melt the nozzle)

Off all the things that SpaceX showed, this second stage recovery trick is the biggest head-scratcher for me.   

Options that I see are:
- Retracting engine assembly
- A sliding sheath (So basically a retracting "everything")
- Drop the nozzle extension
- Make the nozzle extension survive rentry (face up) and have a large landing gear.

This should be a new thread.

Second stage recovery depicted in video is possibly just a wild guess by SpaceX itself. There is lots of heavy hardware involved - 4 superdracos with tankage, long landing legs or retractable nozzle structures... And all this subtracts directly from the payload!

May be they will come up with better solution.

1. How about jetisson away most of the MVac nozzle to allow throttling to 3-5% of thrust without flow separation issues?

2. How about landing the stage without legs into special adapter which will lock onto hovering stage and "capture" onto special tabs built into engine-tank thrust structure?

With those ideas the only weight you need to add are the heat shield (it is lightweight) and small thrusters for attitude control and ullage (they are also lightweight).

[ArbitraryConstant]

If they're going to have a sheath around the nozzle, would it make sense to just retain the interstage (or some portion of it) to serve the purpose?

I mean the whole heat shield and fuselage might be a sheath around the fuel tank/engine.