In STII why was Reliant looking for a planet to test the Genesis device instead of an Obreth class vessel?
Well Khan couldn't have put up much of a fight with an Oberth...
What is the difference between an explorer class ship and a survey ship? Seems to me both classes do the same missions!
I would imagine a Survey ship is designed to do just that - perform surveys of large areas of space. They then send that data back to Star Fleet which reviews it and identifies areas that deserve exploration - at which point an Explorer would be sent to perform that more detailed mission.
So a survey ship would be small and fast with very good long-range sensors designed to quickly review large volumes of space. If it scanned our solar system, it would identify that there were eight major planets, of which one had a Class M environment and showed signs of not just life (based on spectra) but also advanced life (based on EM radiation like radio and TV). But it would not be able to know our planet as well as our own reconnaissance satellites do since it would likely be scanning us from light-years away.
So Star Fleet would send in the Explorer which would perform a full-boat analysis of Earth and it's civilization.
I always thought it was the other way around, with the big Explorers finding a new system or Nebula, etc. They'd take a few quick scans then go off and explore new things. After which a survey ship would come in and really explore it.
At least that's how i always thought it.