On Thu, Aug 8, 2019 at 12:30 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Thu, 8 Aug 2019, Nels Anderson wrote:
and Electron's video embedded therein seem to show:
* No retro burn;
* Tail-first re-entry.
As to how a tail-first attitude is achieved in the first place, though,
the video obfuscates with confusing changes of perspective...
A high-mass-ratio liquid-fuel rocket will typically be aerodynamically
stable that way without help, because the front end is all very light
empty tanks, and the base is full of heavy engine. (There are obviously a
lot of assumptions hiding behind that statement, and exceptions would not
be hard to invent.) Mind you, that's static stability -- damping can be
very slight in thin air, so a reentry vehicle can oscillate a lot around
its nominally-stable position.
I wonder whether active attitude control, at least to set up a
tail-first attitude, might be the key difference from what SpaceX did.
It that's all it takes, though, I would then wonder why SpaceX didn't
try it.
I doubt very much that SpaceX could have made things work even as well as
they did without active attitude control. But there are potentially many
other differences between the designs... and remember that RocketLab
hasn't actually recovered successfully yet. SpaceX talked a good fight on
first-stage splashdown recovery, but couldn't make it work.
Henry
