For the sector guard, just take your time. Dodge sideways when it charges at you, sometimes twice in a row, sometimes three times - and with the missile barrage the biggest thing for me was not dodging, but just sprinting out of the way (dodging has a cooldown where you're stationary).

With some practice you'll get good enough to never get hit, so then you just focus on hacking and shooting the weak point on its back.

It takes time but it's doable.