Ariane 6 (A64)
In June 2018, I was completing several long-standing projects for launching in Summer and thought about starting a new project. I'd come off a sequence of open-interstage projects (Aerobee, Iris and Boosted Arcas) and needed something different.
The Ariane 6 A64 is planned to have four strap-on boosters, something I had not yet undertaken, so that seemed perfect for a new challenge.
The first question with a scale model is always the scale. As usual, I try to come up with a scale that corresponds to available body tube sizes. This rocket also couldn't be too small because I needed space for the drop-away booster mechanism so I wanted to use a 5.5" or larger tube.
At 3% (2.85% to be precise), the main body could be 6" tubing and the boosters could be 3.9" tube couplers:
|Prototype (m)||Model (in)||Model (mm)|
|Main AF len||60.6||68.0||1721|
|Main AF Θ||5.4||6.1||154|
|Main nose len||8.3||9.3||237|
|Booster AF Θ||3.4||3.8||97|
|Booster body len||13.0||14.6||371|
|Booster nose len||13.0||14.6||371|
This also makes the rocket a manageable size at 5' 10" (1.8m). See the overall drawing for details.
The aft end is where all the complexity of this rocket is; the forward is just a standard dual-deployment setup with a mid AV bay. So the first thing to work out was how the drop-away boosters would work. Luckily, the design of the prototype could be used pretty much as-is. A side plate near the aft of the boosters would lock against the aft end of the sustainer and the forward strut would slot into the sustainer. Then the only trick was retaining/releasing the boosters.
I decided that the thrust would be transferred through the aft plate and the forward strut was needed only for retention and alignment. That means the only remaining tricky part is how to keep each booster in place until its motor burns out. I decided to use a solenoid, activated by electronics to pin it in place.
I decided to use clear plastic fins for stability (one new thing at a time). Because of the four outboards and needing space for the launch rail, they didn't fit evenly 120° apart, so they're not quite radially symetrical. See the aft detail in the overall drawing.
The most interesting part was the boosters and how to interfaced with the main rocket, so that's what I started on first. There's lots of great detail: the nose, ribbing along body and the tail.
After figuring out the design, I started printing the tail parts. The profiles were PLA, but the retainers (to suggest the nozzles) needed to be more heat-resistant so I had them printed by Sculpteo in Multijet Fusion PA12, which is heat-resistant to 700°C.
Above you can see the four tail end profiles and a PLA prototype of the retainer. And below you can see how the white profile fits around the MMT and the retainer caps it off.
Unusually for me, the prototype rocket is not yet in service. So "history" is a bit of a misnomer. There is good general information on French Wikipedia. There are also some nice 3D renderings for reference.
I also found the image above very useful for getting dimensions, even if not complete, thanks to "Crumb fire" on The Rocketry Forum.
The side view above (full size here) was very useful for markings and shapes. Although you will notice there is some variance in the different drawings, especially in the nose of the strap-on boosters.