I don't think they do the same job. Liquid hydrogen is likely a higher performance fuel, so it is often used in the second or third stages of a high performance launch rocket. But liquid hydrogen is not storeable, and must be manufactured right before use. So it really can't be used as the fuel for the on-board engines on the space craft that will spend weeks or month in space.
Acetylene-ammonia can be stored. So it can be used as the onboard fuel for a space craft that will spend quite a bit of time in space. The advantage of Acetylene-ammonia compare to existing storable fuel is it is not very toxic. Traditional storable fuel used on spacecraft is highly toxic, and require very careful handling. So Acetylene-ammonia fuel might be safer and easier to handle.
Another thing, Some of the major Russian and Chinese launch rockets were originally designed as ballistic missiles that can be stored for a long time and launch within minutes of a command, so they do use highly toxic storable fuel rather than more efficient liquid oxygen / hydrogen or LOX / Kerosin fuel. So the Russians and Chinese have a major incentive to replace these dangerous launch vehicles with vehicles using safer, but still compatible fuels. Western launch rockets probably have less incentive to use acetylene-ammonia fuel.
Acetylene-ammonia can be stored. So it can be used as the onboard fuel for a space craft that will spend quite a bit of time in space. The advantage of Acetylene-ammonia compare to existing storable fuel is it is not very toxic. Traditional storable fuel used on spacecraft is highly toxic, and require very careful handling. So Acetylene-ammonia fuel might be safer and easier to handle.
Another thing, Some of the major Russian and Chinese launch rockets were originally designed as ballistic missiles that can be stored for a long time and launch within minutes of a command, so they do use highly toxic storable fuel rather than more efficient liquid oxygen / hydrogen or LOX / Kerosin fuel. So the Russians and Chinese have a major incentive to replace these dangerous launch vehicles with vehicles using safer, but still compatible fuels. Western launch rockets probably have less incentive to use acetylene-ammonia fuel.
