> Hydraulics are usually closed, but that adds mass vs short acting open systems. F9 fins only work for 4 mins. We were ~10% off.
EDIT: never mind - I've learned that they have a steering function, as well as drag inducing function, and they ran out of hydraulic fluid required to induce more drag, which would thus slow the rocket down. Leaving my comment here in case anyone else is curious.
Basically, because they lost steering it came in too steep, and ended up falling onto the deck on its side because the engines couldn't compensate for that position.
If the rocket's trajectory is correct, all that is required is a final hard burn to negate all downward velocity a short distance above the barge deck.
Since the main propulsion isn't going, closed hydraulics would have to have an independent power supply. Probably batteries. Instead, they replace all that with some compressed air. They can run out of compressed air, but can also run out of whatever powers the pumps in a closed system.
The hydraulic fluid is probably RP-1 and is probably dumped into the fuel tank, where it's available for later burning. Another 2-for-1.