In the Mars Colony, shield generator area when you're on the lift, click to retun to last position and to get to the bomb. Use the maintanence key to open the hatch. Some warnings will go off and say that there are explosivesin the hatch. You will need to order the wire nodes to stop the bomb. the order of the color nodes is:

Level 1: Green, Red, Yellow
Level 2: Blue, Yellow, Red
Level 3: Yellow, Blue, Green

You can't waste much time. Your time left is on the top right of the lift panel.