Mission requires a part that I cannot find.

[Kim Hanson]

I am a noob, been playing only a week.  1.8.1 with KER and Automated Science Sampler.

I grabbed what looked like an easy mission.  Satellite in equatorial orbit, antenna, power, and "materials bay".  It turns out a "service bay" (only thing I had at the time) is not the same as a "materials bay" so I looked through the tech tree and "materials bay" is nowhere to be found. 

Is this a class of containers and I just have to find one in that class?

[Vanamonde]

It's this part, wherever it might be on your modded tech tree. 

https://wiki.kerbalspaceprogram.com/wiki/SC-9001_Science_Jr.

[Kim Hanson]

The Science Junior!  In a million years I never would have guessed that.

[Zeiss Ikon]

Yeah, a little naming mismatch there.  Glad you found the right thing.