Well, this is really built for fairly low altitude, but my older SM-S pack had some fairly high altitude stuff, but it was all black and shiny. it would be easy enough to make an engine designed for high altitude/speed flight, that worked poorly or not at all at low altitude. I'll put together a test pack of this in a bit for testing purposes if you people would be so kind as to give me some suggestions. I think the parts are a overpowered and too efficient currently, but the Isp drops off quickly with altitude.