|Adjacent rooms||Ice Beam Gate Room
To get this missile, the easiest method is to shinespark from the previous room. You can attempt a 2-tap short charge, and if you run into one of the enemies you can continue holding Dash and Left, and use your i-frames to get through the rest of the enemies. Then charge the shinespark, open the door, and spark through. After you crash against the wall, hold Left and Angle Down and fire a shot, and you'll pick up the item.
After the item fanfare, continue falling down while holding jump, and you can press Right after touching the Sova to Damage Boost to the right side wall. Then aim down and fire to open the door, and run through.
The shinespark crash animation does cost time, so it would be faster to Space Jump across the room, as long as you're confident in not falling down.
One thing to watch out for is that the missile pack takes about 10 frames to spawn after the shot block gets destroyed, so in order for Samus' hitbox to touch the missile pack without falling past it, you will generally need to fire your shot at the peak of a jump, or while rising.
Fire a shot as you crest the third small hill, and release dash at the same time. This will open the door with enough time that you can run through. Start holding another shot before you hit the door, and release shot during the door transition. Once the next room loads, the shot should fire automatically, and you can jump to the other side.
The window on this jump is very small before you hit the crumble blocks, so you'll need to be precise. If the second Dessgeega jumps low, you'll need to fire the shot while Samus is inside its hitbox, where you can fire it earlier if the Dessgeega jumps high.
In order to check this item without falling down the shaft, the easiest way is to hold an angle button during the door transition, so you will Stop on a Dime as soon as you enter the room. If you use a mockball in the Ice Beam Gate Room, you only need Morph Ball, Super Missiles, and Power Bombs to check this item location.
Just be careful about the Dessgeega when going back in the room, since suitless they do 80 damage.