Journey to Pluto

Someone on Discord suggested that I compose a piece about space and stars. Coincidentally, I decided I wanted to try composing something for Concert Band instead of just a hodgepodge of random instruments. I didn't yet feel ready for full orchestra; I wanted to experiment with a larger amount of instruments than I was before, but I needed to figure out how the Concert Band instruments would sound playing the melodies that I had in mind. So I went into Musescore, and it had a Small Concert Band template. I took away the Euphonium because I figured the Tuba was enough. I added in marimba, glockenspiel, etc, because I wanted them to compliment the other instruments and also to add twinkle like the stars. I have about two minutes of the piece so far, and I'm currently trying to figure out where to go with it next. I know that I want the beginning eight notes to reappear later on. I tried a few soundfonts, and decided that the GeneralUser soundfont sounded the best to me.

Couple general notes: Use metric modulation notation between 4/4 and 12/8 (i.e. triplet = eighth in 12). Easier to read than doing math mid-sight-read.
Good use of horn pedal in the beginning. Consider a stagger between parts or an offbeat rearticulation to sustain the tone.
Going from 60 to 100 was a bit awkward. Maybe an accel?
The first trip to 12/8 was way more awkward than the other ones, because you have the snare switching times in the middle of a roll. It takes away from the seamlessness of such a transition. On that note, you cannot use half notes in 12/8. Use ties to sustain the beat.
My next personal step would be to elaborate on this one idea a bit more by transferring melodies and registers to feel like a cohesive section. Don't feel limited by the eighth notes as part of a melody; using the same thing in augmentation with suspensions in the normal figure against it can sound really cool especially with harmony changes happening under. You can use prime form (013) to create inversions on the theme you have. Use a refrain from the beginning for another slow section (ABAB kind of) then finish with a more driving similar idea to the first B section. 
 

I quite liked it. Harmonically fairly basic it's unpredictable, the abruptness of the ending that I particularly liked, leaving it just hanging. The rocking between subdominant and dominant worked because it's a pretty lively piece and short enough not and you did vary the tonal centre part way through. It had hints of Nyman's "Think Slow Act Fast" to me but only just. I looked at the score. Perhaps I'd have done some of the doubling differently but what you've done would work. Not sure about all the tuned percussion being necessary but that's just my opinion and it may be just what you want.

Some of the balance was lost with this particular rendition. If performed, a conductor should sort out any problems there. 

Edit. Maybe I should add, given the section in which you've posted the work, that I see it as a piece complete in its own right, not part finished. It could be one of a suite of movements.