They definitely are difficult and I completely sympathize. I had enough CC to buy the Grade 7 parts right off the bat. Yesterday, I did the missions on my main and they were tough. Thanium Disruption I barely made it through on the 3rd try with, and I kid you not, 25 HP left on my ship's hull out of 4000. Fourth time, 31. I think out of the 6 I completed 1 bonus mission in total.
Today, I got to clear all of the Space Combat missions on my Gunslinger alt with the Grade 7 parts as well. On her, I completed them all on the first try including every bonus mission, sans the one for the Thanium Disruption. Speaking of the Thanium Disruption, today, on that one after watching a video on where/when to hit certain abilities and when to attack and when to dodge, I came out with barely any damage to my hull at all versus yesterday's 25/4000HP.
In all, it is just a very, very steep learning curve. Once you learn the tricks, though, they are easy - they require you to pay much more attention and focus on survival as well as doing damage and completing objectives.
Now, if the actual Operation Weeklies for the Heroic Space Missions would pop up that would be nice too