To be honest, you should not have trained investigation 1, by far the easiest way is to wait till you have 7-10k BH xp and train invest 1+2 at the same time. you will find when you use the droids with only invest 1 that 8/10 times the droid will be destroyed by a meteor or somethin to that effect before it reaches its target. which therefore makes it very difficult to complete the missions and can get very expensive when ur going through 10+ droids per mission. On top of the droids being destroyed you will also have to send more droids out when you get the Target lost message.
Well... hope this helps...
Good luck, its a hard grind on invest but worth it.
! final note... it might be worth you grinding all the weapons out and then working on investigation, not so boring and doesnt actually take that long.