Where is the Missile Expansion in Phazon Processing Center (Metroid Prime Origins)?

The Missile Expansion is in Phazon Processing Center, Phazon Mines. To get there you need Missile Expansion, Space Jump, Morph Ball, Power Bomb Expansion, Morph Ball Bomb, Varia Suit, Charge Beam, Wave Beam, Boost Ball, Super Missile, Spider Ball, Ice Beam first (starting a new game).

What you need first

Starting a new game from Landing Site, get these first, in this order, then go to Phazon Processing Center (161 rooms in all):

1. Missile Expansion in Landing Site (0 rooms; needed for Missile Expansion (Missile))
2. Space Jump in Alcove (1 room; needed for Missile Expansion (Space Jump Boots))
3. Morph Ball in Ruined Shrine (10 rooms; needed for Missile Expansion (Morph Ball))
4. Power Bomb Expansion in Magma Pool (6 rooms; needed for Missile Expansion (Power Bomb))
5. Morph Ball Bomb in Burn Dome (11 rooms; needed for Varia Suit (Morph Ball Bomb))
6. Varia Suit in Sunchamber (10 rooms; needed for Missile Expansion (Varia Suit))
7. Charge Beam in Watery Hall (7 rooms; needed for Wave Beam (Charge Beam))
8. Wave Beam in Chapel of the Elders (27 rooms; needed for Ice Beam (Wave Beam))
9. Boost Ball in Phendrana Canyon (8 rooms; needed for Ice Beam (Boost Ball))
10. Super Missile in Observatory (10 rooms; needed for Spider Ball (Super Missile))
11. Spider Ball in Quarantine Cave (9 rooms; needed for Ice Beam (Spider Ball))
12. Ice Beam in Antechamber (39 rooms; needed for Missile Expansion (Ice Beam))

Last stretch

From Antechamber, door by door:

1. Antechamber: go through the door to Reflecting Pool → Reflecting Pool (Ice Door; needs Ice Beam)
2. Reflecting Pool: go through the door to Transport Access South → Transport Access South (Ice Door; needs Ice Beam)
3. Transport Access South: go through the door to Transport to Tallon Overworld South → Transport to Tallon Overworld South
4. Transport to Tallon Overworld South: take the elevator → Transport to Chozo Ruins South assumed
5. Transport to Chozo Ruins South: go through the door to Transport Tunnel D → Transport Tunnel D (Ice Door; needs Ice Beam)
6. Transport Tunnel D: go through the door to Great Tree Hall → Great Tree Hall (Ice Door; needs Ice Beam)
7. Great Tree Hall: go through the door to Transport Tunnel E → Transport Tunnel E (Ice Door; needs Ice Beam)
8. Transport Tunnel E: go through the door to Transport to Phazon Mines East → Transport to Phazon Mines East (Ice Door; needs Ice Beam)
9. Transport to Phazon Mines East: take the elevator → Transport to Tallon Overworld South assumed
10. Transport to Tallon Overworld South: go through the door to Quarry Access → Quarry Access (Wave Door; needs Wave Beam)
11. Quarry Access: go through the door to Main Quarry → Main Quarry (Wave Door; needs Wave Beam)
12. Main Quarry: go through the door to Security Access A → Security Access A (Ice Door; needs Ice Beam)
13. Security Access A: go through the door to Mine Security Station → Mine Security Station (Ice Door; needs Ice Beam)
14. Mine Security Station: go through the door to Security Access B → Security Access B (Wave Door; needs Wave Beam)
15. Security Access B: go through the door to Elite Research → Elite Research (Ice Door; needs Ice Beam)
16. Elite Research: go through the door to Research Access → Research Access (Ice Door; needs Ice Beam)
17. Research Access: go through the door to Ore Processing → Ore Processing (Ice Door; needs Ice Beam)
18. Ore Processing: go through the door to Elevator Access A → Elevator Access A (Ice Door; needs Ice Beam)
19. Elevator Access A: go through the door to Elevator A → Elevator A (Ice Door; needs Ice Beam)
20. Elevator A: go through the door to Elite Control Access → Elite Control Access (Ice Door; needs Ice Beam)
21. Elite Control Access: go through the door to Elite Control → Elite Control (Wave Door; needs Wave Beam)
22. Elite Control: go through the door to Maintenance Tunnel → Maintenance Tunnel (Ice Door; needs Ice Beam)
23. Maintenance Tunnel: go through the door to Phazon Processing Center → Phazon Processing Center (Ice Door; needs Ice Beam)

More Missile Expansions

• Missile Expansion (Burn Dome)
• Missile Expansion (Crossway)
• Missile Expansion (Dynamo)
• Missile Expansion (Dynamo)
• Missile Expansion (Furnace)
• Missile Expansion (Gathering Hall)
• Missile Expansion (Hive Totem)
• Missile Expansion (Main Plaza)
• Missile Expansion (Main Plaza)
• Missile Expansion (Main Plaza)
• Missile Expansion (Ruined Fountain)
• Missile Expansion (Ruined Gallery)
• Missile Expansion (Ruined Gallery)
• Missile Expansion (Ruined Nursery)
• Missile Expansion (Ruined Shrine)
• Missile Expansion (Ruined Shrine)
• Missile Expansion (Training Chamber Access)
• Missile Expansion (Vault)
• Missile Expansion (Watery Hall)
• Missile Expansion (Watery Hall Access)
• Missile Expansion (Fiery Shores)
• Missile Expansion (Storage Cavern)
• Missile Expansion (Triclops Pit)
• Missile Expansion (Elite Control Access)
• Missile Expansion (Elite Research)
• Missile Expansion (Fungal Hall Access)
• Missile Expansion (Fungal Hall B)
• Missile Expansion (Main Quarry)
• Missile Expansion (Metroid Quarantine A)
• Missile Expansion (Metroid Quarantine B)
• Missile Expansion (Security Access A)
• Missile Expansion (Frost Cave)
• Missile Expansion (Gravity Chamber)
• Missile Expansion (Ice Ruins East)
• Missile Expansion (Ice Ruins East)
• Missile Expansion (Phendrana Shorelines)
• Missile Expansion (Phendrana Shorelines)
• Missile Expansion (Quarantine Monitor)
• Missile Expansion (Research Lab Aether)
• Missile Expansion (Research Lab Hydra)