You will need to acquire the 3 science weapons available in Eridanos.
The Needler:After escaping the building with Halcyon Helen v2 return to the Penthouse and talk to her. During the dialogue you will get the opportunity to persuade her to give you the Needler. If you have level 40 persuade the Needler is yours, otherwise pickpocket or kill her, take the Needler and then re-load a previous save. If you sided with Ludovico then you will encounter Helen v2 again and kill her for The Needler.
Udder Buddy:The easiest of these to acquire is Udder Buddy and you can get it as soon as you have access to the North Island. When you go up the elevator, ahead and to the left is "Legal Hunting Supplies". Standing at the counter is Mildred Lenox who will give you the quest "Lost Little Milk Mech". Complete the quest and return to her to receive the Udder Buddy.
Spectrum Gatling:Spectrum Gatling is located on the SW Island in the RR&DD lab behind Dr. Blossom. The access card to enter the lab is found at a picnic site nearby as part of the main quest "A Momentary Taste of Purpleberry". After entering the area behind Dr. Blossom you can access the terminal to get the Spectrum Gatling Gun using the 8 different types of Spectrum Vodka. The vodka types can be found in front of the bartender in the Rizzo Distillary in the NE island.
Credit to SilverFox for their
guide.