Very nice, overall. The concept is refreshingly original in this, the Great Age of Tower Defense and Puzzle Platformers. There's something strangely satisfying about flinging an object into an intricate, semi-stable orbit around multiple celestial bodies.
I liked the minimalist aesthetic, with the gray static background and simple, geometric planets and stars. Adding too much detail would, I feel, distract from the essential puzzle aspect of the game, not to mention making it unnecessarily harder. That said, I feel it could have benefited from some simple, subtle background music. Nothing flashy, just something to fill the ear-space besides flat, hissing static.
If I have one semi-serious gripe, it's that the difficulty tends to yo-yo between levels. Specifically, those levels that just have one body, such as a star, tend to be too easy: just use the pathfinder to trace a line roughly in line with that of your orbit, and launch. Comparatively, the earlier levels with planets orbiting a star are quite a bit harder. I feel that the game would benefit from having single-body levels serve as an introduction to the orbiting mechanic, the level timer, and varying gravitational fields, among other things. That said, I also think you could scrap them entirely, and the game wouldn't suffer unduly as a result.
All in all, a very solid offering that could prove truly exceptional with a bit more polish. Keep up the good work.