Disadvantages
Relative to their mass, traditional hypergolic propellants are less energetic than some cryogenic propellant combinations, such as liquid hydrogen / liquid oxygen or liquid methane / liquid oxygen. That is to say that for a given payload to be put into orbit, a launch vehicle using hypergolic propellant would be more massive than one using these cryogenic fuels due to the greater mass of hypergolic propellant required.
Traditional hypergolics are also corrosive, toxic and carcinogenic, requiring expensive safety precautions on the ground.
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