I found this at super trouper (English translation glossary) Idioms / Maxims / Sayings,
'As the ABBA Magazine described it in their December 1980 issue, “’Super Trouper’ is the name given by lighting crews to the biggest spotlight in the theatre or circus”. I don’t know the origin of this nickname, but I don’t think it actually comes from a brand name “Trouper”.'
A trooper is a mounted soldier or police officer and, in the United States, a state police officer; a trouper is a member of an acting company, especially an experienced, steady, dependable actor. The term is extended in that elevated sense: any solid performer (not just an actor) is a trouper.Source: trooper, trouper. The Columbia Guide to Standard American English. 1993
All the best.