Hi Enigma. I am pretty new as well. Only 4 days.
To kill the Atrax at our level you will need help. Go to Camp Icarus and ask if anyone has healing skills. If they do, ask if they would help you kill the Atrax to complete a mission.
If they say yes, they will go with you. Once you get close enough to shoot the Atrax, start shooting and DO NOT MOVE as you fire. Your friend will then heal you every time the Atrax attacks you. They will probably be able to heal you fast enough that you can kill the Atrax before he kills you.
That is what I did after some kind person named Luna offered to help me kill the Atrax. I killed it, finished the mission and made a new friend as well. A good day on Calypso.