Feather moment considerations, abort scenario
Thanks for that AWST article, a wealth of information!
By deduction and combination from the various sources:
Feather unlock (and actual feathering?) nominally at Mach 1.4 (says NTSB Hart)
Engine burn of 3rd powered flight had been 20 sec to Mach 1.4 71kft
Engine burn planned 4th (this) powered flight approx 20 sec to approx Mach 1.4
(my assumption, not to change fuel and durn-time/Mach in one step)
Operational goal 2 minute burn Mach 3.4, 370 kft
Feather unlock lever, I wonder, is this:
- A safety lever securing the actual movement of the feather lever?
Or
- A lever disengaging physical locking pins allowing subsequent feathering by the pneumatic actuators
(or inadvertantly allowing uncommanded feathering by aerodynamic forces overpowering pneumatics-only)
Feather unlock c.q. actual feathering at Mach 1.4
- After motor burn-out around Mach 1.4 in third test
- Aerodynamic forces at that altitude/speed acceptable for coasting flight
- Aerodynamic forces at that altitude/speed also acceptable if still powered?
If yes on the latter, then it makes sence to unlock and/or feather after Mach 1.4 in the procedure for longer-burn flights, in order to discover anomaly in the essential feathering function for safe re-entry, and allow early motor-stop, in stead of continuing to push energy into the vehicle.
Hypothesis: Mach 1.4 and associated altitude and weight may be the limit for safe unfeathered re-entry?
Of course the unburned fuel mass after premature motor-stop is an additional weight/energy burden for reentry, the loaded SS2 is 30kLB (AWST), how much of that is the fuel mass? And can the oxidiser be dumped (through the extinguished engine) without re-lighting it?
A jettisonable rocket motor in case of feather failure comes to mind. Although that would also add complexity.
Any thoughts, additional information, corrections on that?