I am not sure a percussion type primer would work in a vacuum.
I am not sure a percussion type primer would work in a vacuum.
Why would you think that?
Priming materials are made to detonate (not deflagrate [burn]) when mechanically crushed. Like black and smokeless powders,they contain a stoichiometric fraction of their own oxidizers, so they definitely do not depend on atmospheric air for reaction.
The only thing that might desensitize primers is the near absolute zero temperatures available in space. (The "Arrhenius relationship" dictates that reaction rates approximately halve with every 10K drop in temperature.) Even then, the instantaneous temperature spike generated by the crushing forces of the striker might well negate ambient temperatures.
I would be more concerned that those temperatures might degrade the deflagration rate of the propellant powder, rather than the sensitivity of the primer.
OTOH, what is most commonly used to effect separation of objects (rocket stages, etc...) in space? Explosive bolts... (But I understand that most of them are electrically initiated -- which could overcome any low temperature quenching effects...)