To get the Lost in Space medal you have to use the wear the space suit and leave the airlock after closing the interior door, activationg decompression, opening the exterior door, use the rope under the panel with the yellow triangle and find the second blue crystal in the debris field. Then continue and blow up the entire ship by combining the bomb with the second solution (detergent, acid and alcohol) and place it at the power core. Make sure that you detonate the bomb while you stand close to the core.
For the Hull Breach medal you have to blow up the isolation ward where the crystals are.
Do nothing at the begining or eject yourself for the Spaced medal.
Use the code on the key pad in the quarters. You can find it out by watching the security tapes at the murder scenes which you can only do after combining a datapad mark II processor with your data pad.