I've been a fan of the boosted dart concept for a long time. My first introduction to the concept was the RRS's boosted dart project that was launched in 1996. I hadn't begun my journey into the world of amateur rocketry yet but just six years after that launch and a year or so of building my own motors, I found myself at the RRS site in the Mojave desert with what I thought was a big rocket, a scratch built rocket that was powered by my version of Chuck Knights J-class sugar motor fabricated from PVC pipe. That rocket flew and was recovered successfully. Later that same day I witnessed a firing of a motor that dwarfed anything I had done or even thought was in the realm of what an amateur could do. It was a slightly larger version of the booster that the RRS guys had launched at Blackrock. It was a spectacular firing that unfortunately cato'd. It made a HUGE impact on me never the less and as I began researching the old sounding rockets of the 50's and 60's I came across the Loki Dart and became even more intrigued by the boosted dart concept. The amazing thing about the boosted dart concept is that the dart typically coasts most of the way to apogee. In the case of the RRS, the booster reached an apogee of around 3 miles while the dart coasted to approximately 50 miles. It's kind of like hitting a baseball. Think about it, a baseball completely changes direction when the ball is hit by the bat and yet within those few milliseconds that it is contact with the bat it gets everything it needs to "coast" into the stands. I've been slowly getting back to rocketry lately and have been thinking about a high altitude attempt. The boosted dart concept seems like the way to go. I don't currently have the ability to build something the size of the RRS boosted dart project, but that's where the little Loki dart comes in. The Loki dart from the 50's had a max altitude around 34 miles. The booster for the Loki is a relatively tiny 3" in diameter and produced a bit over 2000lbs of thrust for a little under 2 seconds. Now those numbers seem much more doable. I should be able to fabricate a motor up to 7" in diameter, which is good since I'm working with a lower ISP propellant I'll need a larger booster than the Loki used to get similar performance. The TR-1 motor that Theo and I are currently constructing has the same total thrust as the Loki booster. That motor isn't currently geared towards being a booster but with some relatively minor design changes it could be a decent booster for a boosted dart. I'm planning to fly this motor as a boosted dart to get some experience. If that goes well, the plan is to build a larger 6" diameter optimized booster and see just how high we can go.
You can find a PDF of the RRS booster dart project on the RASAero site here.