There are only 25 parts that are needed to complete the game. The other parts are optional.

Main Engine
Positron Generator
Eternal Fuel Dynamo
Whimsical Radar
Extraordinary Bolt
Nova Blaster (optional)
Shock Absorber
Radiation Canopy
Geiger Counter
Sagittarius
#1 Ionium Jet
Automatic Gear
Gravity Jumper
Space Float (optional)
Non-Dixion
Guard Satellite
Libra
Analog Computer
Omega Stabilizer
Repair-Type Bolt
Massage Machine (optional)
Interstellar Radio
Gluon Drive
UV Lamp (optional)
Zirconium Roter
Pilot's Seat
Bowsprit
Chronos Reactor
#2 Ionuim Jet
Secret Safe (optional)