Go to the place in Skytown when you have to get the first part of the bomb you have to make using your ship. Near the bottom there is some Phazite, shoot the switch inside to activate the satellite system. Go to the top and go around the walls using the spiderball tracks and bomb all the bomb slots to get markers on your map for where every expansion (missile,ship missile,and E tanks) is in every part of the game, except the items that are in the Valhalla