Loki Booster

I got this Loki booster a while ago.  It's a little banged up (the fins are slightly bent) but overall it's in pretty good shape since it's probably around 60 years old.  This one was never fired or filled with propellant. The transition section doesn't have the roll pins installed and can be removed to revel the interior of the motor.  It is also possible to see the rubber liner that protects the thin aluminum motor casing from the heat of combustion.  The black spots seen at the base of the motor and on the nozzle retaining ring seem to be the same material as the liner.  I'm not sure what the pin on the top of the transition section is for; it's spring loaded and maybe it's meant to help ensure a clean dart separation. The pin on the side was, I believe, to keep the dart from spinning as the rocket was spin stabilized.  It's cool to think that this small booster was capable of getting a dart up to 34 miles...

Loki

Ben pointed me to this PDF in the comments section of an earlier post (Thanks Ben!)  I hadn't actually seen this before.  This is a description of the Super Loki system that uses a larger 4" diameter booster and 1.65" dart.  The earliest Loki system used a 3" booster and the dart seems to have varied from 1.375-1.5" in diameter.  Another interesting difference, from what I can tell, is that the earlier version of the dart didn't utilize a boat tail.  That must have resulted in significantly more drag, and yet the performance of the dart was impressive.  This is a photo of one of those early versions that shows the connector/coupler that presumably fits into a recess at the base of the dart.

 

In later versions of the booster (and as seen in the PDF) you can see that the connector/coupler was hollow to accommodate the boattail of the dart.

Boosted Darts

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.