Extra modes for Commercial crew utilization

[kch]

Could FH fly a single J2X second stage? Fact sheet says it's 120" wide and FH is ~144".

That should physically fit (with about a foot of clearance all around).

[Ben the Space Brit]

I've always thought that commercial crew could easily have far more than 2 flights a year.  Just off the top of my head, the three mission types are:

* NASA/ESA crew swap at mid-expedition duration;
* Expedition launch and lifeboat duty (whole crew rotation);
* Short duration Extended Operation Capability (EOC) with the extra personnel staging off the crew taxi rather than the station itself.

If you had a two-phase swap out, one by commercial and one by Soyuz at mid-expedition (changing all the science personnel but leaving the flight engineers), then that would total four Soyuz and three commercial crew flights to the ISS per year.  The EOC missions would be additional to that figure and would depend on a particular mission (maybe maintenance spacewalks that require training that the expedition crew does not have).

Could FH fly a single J2X second stage? Fact sheet says it's 120" wide and FH is ~144".

Propellent would be an issue.  J-2X is both hydrolox and fuel-hungry, so it's even money whether the FH core could lift an upper stage with great enough volume without over-balancing or something.

An EELV-scaled engine like RL-60 would probably be a better choice.


[edit]
Added thoughts on mission types and flight rate

[docmordrid]

Thought the SpaceX cores were built with a 40% margin vs ULA's 20% and 25%. If so why couldn't they use up 10 points or so of margin to spec a heavier stage? Maybe for cargo only?

Edit re balancing: perhaps, but I'd love to see it modeled.

[oldAtlas_Eguy]

The one thing I always wondered at was is the 40% loads margin for its original design loads of the F9H (32MT) configuration or just the F9 (10.5MT) design loads.