The casting of spells generally assumes needing to use the spoken word.
Underseas initially introduced additional time requirements for doing this called Notes about Magic Underwater
Dimensional Outbreak page 98 Demons in Space "spell casting in space" appears to revisit this: it takes DOUBLE the time to cast a spell if you can't hear yourself saying it, instead you mouth it and focus hard on it. Even then there is an 11% chance of failure.
This apparently something only demons (including Dyvalians) can do now, perhaps due to their ability to survive in space without a vacuum (they can't breathe) and because of having cast spells "countless times" over thousands/millions of years. However that limit may only apply to a space vacuum and not underseas casting.