After finishing the Ark Equipment job, talk to Portman to start this one. Head out to the Wasteland and follow your mini-map. Blow the door open and continue through in your vehicle, this is a good time to get the Roadkill achievement. Take your vehicle up the large elevator, take out the enemies up top and plant the two charges. Once they go off you'll be able to drive back to the Resistance Base and talk to Portman to finish the job. Talk to Captain Marshall for the Assault Capital Prime job.