My recollection is that they were injecting both methane and helium at
various points in the burn - half-recalled, methane to help ignition and
helium for stability?
Don't know whether they're still doing that or not. But they were
having problems that caused the switch to nylon in the first place, so
they may well still be taking extraordinary measures to tame the beast
after switching back.
My take on the lesson to be learned is that large nitrous hybrids are
more trouble than they're worth. Three different sets of
fluid-injection plumbing (if still present, of course) negates any
simplicity advantage over a liquid biprop, I'd say.
But regardless, congrats to everyone involved in the successful flight,
and best of luck for safe ops from here on.
Henry
On 4/5/2018 4:02 PM, Paul Mueller wrote:
Congrats to Virgin Galactic for a successful powered flight of VSS Unity today.
Interesting that they switched back to an HTPB-based fuel after switching to a nylon-based one for their last powered flights over 3 years ago (IIRC). As I recall, they had some issues with combustion stability with the nylon fuel grain so they had added some other systems (methane?) to help with that. Hopefully that complexity is gone if they've switched back to HTPB.
My recollections may be wrong on all this--wondering if any arocket folks can comment...
Anyway, good to see them flying again!
Paul M