... Why did the parachute come off straight away?
I've been looking for clues on how the parachutes were attached to the earlier (version of this? ... ) rocket used in the prior launch and how they may have been positioned / attached in this latest version.
On the earlier version, there were two large bags (my guess = the parachutes per se) side by side on a sort of tray in the rear of the dorsal side of the rocket. This tray-thing spanned the dorsal quarter of the rear nozzle area, and it was therefore adjacent to the main exhaust nozzle. The nozzle ran slightly "beneath", and was aimed so as to miss, this tray-thing.
There were also 2 cylindrical canisters tethered to these bags (1 canister per bag). The canisters were separately mounted to either side of the nozzle (seen from a dorsal view) and slightly "above" and "outboard" relative to the bags on the tray-thing. My guess is that these canisters held the coiled lines attaching the parachutes to the rocket vehicle's rear.
After reviewing the previous flight video and this fatal one, I think something went wrong from the very beginning. The rocket rolls (rotates around its long axis) immediately upon leaving the launching platform and begins to turn away from a straight flight path. Neither this rolling nor so much turning is apparent in the previous flight.
The exhaust plume also seems significantly more violent and voluminous on this latest launch.
My first guess is that something broke or was breached in or around the main rocket exhaust nozzle upon launch, taking the flight out of control and blowing away one or both parachutes packs. If the same joint tray-mount was used for both chutes, the whole set may have been blown off at cone (though I can't see the additional debris I would expect).
On the previous flight one of these chutes deployed, with the other opening a bit later. AFAIK both chutes were manually activated by Hughes himself.
If my guess is right, Hughes may not have had any chutes available to deploy when this most recent flight turned back toward the ground.
Given what appears to be the greater violence and twisting of this last launch, there's a chance Hughes was injured or incapacitated early on.