And maybe all that electronic crap is just way over complex for what this is. You are a clever person. It seems complex to initiate the task required and prevent a late light or maybe I'm stupid at this.
Andrew, I don't think you're stupid at this. I think you're bright and eager and young. The first two aren't sins and the third is self-correcting with a modicum of patience.
Now, I do think that you're latching on to words and overreading/overthinking - jumping to conclusions about what I'm trying to accomplish . So let's just lay it out there to look at in the soft backlighting of the screen, shall we?
My first goal is to make a 1/100 sport scale full shuttle stack, without breaking the bank. I want to use the parts and skills I have. So I'm not going to 3D print a 1/100 space shuttle and use it to make vacuum formed upscales of the Estes #1284 1/184 space shuttle. Thought about it, though. I want to use other people's solutions where I can. So first - read all the George G. STS threads and website - and STS threads he's commented on here.
Then - parts. Tubing - 3.44" tubing from my 1/35 Atlas cloning project - good enough for the ET. BT58 from erockets - close enough for the SRBs. Shuttle - Guillow's foamy looks great, if not quite scale. Tweak design to be off scale in similar ways for rest of parts. Nothing is quite 1/100. All looks good together. Nosecones and ET aft dome - Sandman, check. Electronics for flight - Eggtimer Quantum and Quarks handy. Electronics for RC - Specktrum microbrick on hand from a Tercel upscale I haven't finished.
Design - flight goals first.
Full stack with RC glider.
Ground lit main motor in ET
Duck feet fins from ET or SRBs okay.
Separating SRBs nice to have.
Separating SRBs with motors - stretch goal.
For either case, SRBs should separate before ET apogee, during main burn is nice to have.
If possible, build for stretch goal, even if I don't fly it that way.
Safety considerations (remember, the hierarchy is design to avoid hazards, then engineer to control/mitigate, then procedure/education to manage remainder)
Overall stack stability - hands off RC boost. Forward weight and aft fins. Watch Cg/Cp, thrust to weight and speed off rail. Duck foot fin choice makes this easier than clear fins on the SRBs, or no fins. (Which have been done by others.)
Recovery deployment (ET and SRB both) - should be at low speeds, either by delay or flight computer. Quantum and quarks give me lots of flexibility.
- leaving the SRBs on and recovering with ET - easy, but not aesthetically pleasing.
- using an ET deployment event to separate SRBs. If I'm going to do it, I still want the separation during boost look.
- using SRB deployment events to separate - would need to be dual deploy in BT58 - possible, but heavy, or uses motor deploy - either at apogee or at burnout, not preferred.
- use a Flight Computer (in the ET) event during boost. Superficially like an airstart (same time in profile). Quantum can do this - for a pyro, not a servo. Also, means I'm not forced to fly with motors in boosters to provide motor deploy.
- by RC - required second RC that I don't have.
So, use the Quantum airstart ability to do -something- to cut the SRBs loose during ET boost.
Stretch goal - motors in SRBs - 'cause it's awesome.
More motors mean more failure modes.
For cluster with separable pods, worst failure is to lift core and leave behind a pod on the pad. Drag separation on the pad, as it were. So design to avoid possibility entirely. If SRB motor doesn't light, then core has to loft the booster with it. Solution known and practiced.
This would also allow me to airstart the SRBs - except I'm planning on using that channel for SRB separation.
Next failure mode is failure to light/late light/uneven thrust causing uneven thrust. Well, the STS stack has the SRB motors way out there compared to the length to the Cg. Lots of moment arm. So I'm going to cant the SRB motor mounts. And use good ignition practice. That, along with a stable design (helped by the aft fins) is about as good as I can do. Since I'm only doing SRBs for show, if at all, I'll start with A3s and see how it goes.
And I think that gets me to the current design ideas. I've got a couple plans to have a pyro event from the ET separate the SRBs - I just need to pick one to build. Other than that, build light and stable and simple. Pad light everything. Use devices I'm familiar with (like using Quarks as hotwire cutters.) Try to make the grim faced TWA RSO smile when he sees this beast.