I have figured out what is going on with this accolade. As suggested, I went to shooter mode. This is what you need to do IN ADDITION to a few other things (unless you can get your elevation higher; I will explain below; shooter mode allows you to jump AND shoot, RPG does not).
What is happening in this mission is Cryptic has put up "see-thru" walls, or invisible walls to prevent anyone from jumping down from the high areas of the map (leaving the set environment)... The invisible wall facing the Romulans and scorpion fighter is just a hair taller than you can shoot, UNLESS:
You have a Catian (cat) on the team or an engineer places a cover shield on one of the taller structures on the platform you are standing on.
If the catian (cat) jumps while in shooter mode they can get the fighter targeted and killed. I personally think standing on a cover shield is the easier way.
Anywho, I hope this helps....
Confirmed. Sadly you do need an engineer, but, I just completed this Accolade. Facing the Ship & Romulans you get on the Right Pillar, using one of the poles to the right of it. Then you jump onto the top section of the pillar, stand on the edge of that an place your cover shield, so that it lands on the bottom step. Then you jump onto the top of the Shield. Go into shooter mode, aim down from the ship a little bit, then press and hold your fire button while spamming your jump. >> Screen Shot Link <<
Currently it is possible to get this accolade with a quantum mortar only.
I am wondering as well, when sector defense accolades get fixed. Same for the "Detective" accolade, which is still not retro-obtainable for characters, who have finished the corresponding mission prior to the introduction of the mentioned accolade.