Flight computer

RocketSenior — canard-guided high power rocket

Senior capstone project: demonstrate closed-loop lateral guidance of a high power rocket using forward canards, and handle the canard-wake-on-aft-fin interference problem correctly.

This repository currently holds the preliminary sizing tool. It exists to answer the questions you have to answer before you can draw anything in OpenRocket: how big is the tube, how big are the fins, which motor, and can the canards actually do anything.

Why a sizing tool instead of just using OpenRocket

OpenRocket is a verification tool. It answers "is this specific rocket stable, and how high does it go." It cannot answer "what should my rocket be," because that depends on constraints it knows nothing about:

• the internal diameter needed to house four canard servos (this sets your airframe size),
• the lateral acceleration you need for a visible manoeuvre,
• the static margin you are willing to trade away to get control authority,
• whether the canard wake reverses the sign of your roll moment.

This tool computes those, converges on a baseline, and then prints the numbers to type into OpenRocket for an independent cross-check. Use both. Disagreement between them is information.

Quick start

pip install -r requirements.txt

python scripts/packaging_report.py   # what diameter do the actuators force on you?
python scripts/fetch_motors.py --diameter 54 --classes J K   # real thrust curves
python scripts/motor_trade.py        # rank every real L2 motor against the airframe
python scripts/sweep.py              # which (tube, motor, fin) combos meet requirements?
python scripts/baseline.py --plot    # full analysis + OpenRocket entry values

Layout

out/
  RocketSenior.ork   GENERATED by scripts/make_ork.py -- do not hand-edit, see below

The .ork is a build artifact, not the design

out/RocketSenior.ork is written from the same DesignParams the Python tool uses, and scripts/openrocket_check.py regenerates it on every run. That is the point: the two models cannot drift apart.

It also means anything you change in the OpenRocket GUI and save back to that path is destroyed the next time you run the check. Open it to look, simulate, and cross-check freely. If you want to tinker, Save As somewhere outside out/ first. If a change is worth keeping, it belongs in design/configure.py or scripts/make_ork.py, so that the next regeneration carries it forward.

design/
  atmosphere.py   US Standard Atmosphere 1976, troposphere
  aero.py         Barrowman CNa & CP buildup, component drag buildup
  avionics.py     nav bay / nose packing, and the D7 flight computer trade
  bay.py          the printed canard bay: servo pockets, bearing seats, retainers
  configure.py    parameter set -> full vehicle -> requirement scoring, and the
                  frozen baseline airframe every script imports
  control.py      canard pitch authority, roll authority, wake interference, crossrange
  estimation.py   D8: observability per flight phase, attitude error budget, sensor specs
  flight_computer.py  the Stage 2 board: BOM, power budget, log budget, board envelope
  flutter.py      fin flutter margin
  geometry.py     nose / tube / fin set definitions, Barrowman CP geometry
  hinge.py        the hinge as a load path: shaft, bearing, coupling, root joint
  joints.py       all four tube joints -- a coupler costs bore, not length
  mass.py         geometric structural mass + editable subsystem budget, CG
  materials.py    material allowables, in one place
  motors.py       RASP .eng thrust curve parser + placeholder generic motors
  onshape.py      minimal Onshape REST API client
  onshape_build.py  emits Onshape Part Studio feature JSON
  packaging.py    actuator bay packaging + hinge moment + servo torque margin
  recovery.py     dual-deploy sizing, descent time, wind drift, soft-goods packing
  seal.py         the aft gas seal and the internal bulkhead, sized as pistons
  horizontal.py   horizontal-launch 3-DOF: fly the manoeuvre, then score the turn
  trajectory.py   3-DOF RK4 ascent to apogee

How this fits with OpenRocket and RocketPy

Three tools, each for what it is actually good at. Do not try to make one do everything.

The intended pipeline: size here → validate the passive airframe in OpenRocket → export the derivatives from here into a RocketPy LinearGenericSurface → close the loop in 6-DOF → fly, and replace the interference factors with measured values.

Model validity and what you must not trust

Read this before you quote any number from this tool in a report.

The interference model is the one to be honest about in your defense: it is a physically-motivated parameterisation, not a validated prediction. The project plan therefore makes measuring it a flight test objective rather than an assumption.

Baseline result

75 mm (3 in) fiberglass airframe, 79.4 mm OD, 1361 mm long, 4 canards interdigitated 45° from 4 aft fins, on a Cesaroni Pro54 J449 Blue Streak, actuated by four KST X08 Plus V6.0 servos on direct drive, with 100 g of nose ballast. 6.10 kg wet / 5.48 kg dry, apogee 1379 m (4525 ft), max Mach 0.531, static margin 2.03 cal at rail exit rising to 2.52 in coast, 1.96 g of lateral authority at 8° of canard deflection, giving 424 m of crossrange over an 11.4 second usable control window. Recovery is an 18 in drogue and 56 in main deployed at 200 m, landing at 5.0 m/s after a ~0.93 km walk in a 15 mph wind.

Both fin sets were sized together by a Monte Carlo on margin robustness rather than independently by nominal stability — canard semispan 0.85 cal, aft semispan 1.55 cal. They pull in opposite directions, and searching them jointly under a probabilistic margin constraint beats trading one against the other. See docs/00-requirements.md §7.

The nose ballast is part of the design, not a contingency. Real 9 g servos in place of the 55 g budget placeholder removed ~180 g from ahead of the CG, which took P(SM < 1.0) to 1.8% against R1's 1% limit. 75 g of ballast is the minimum that satisfies R1; 100 g is the design point and brings it to 0.6%. It is deliberately the last free parameter — a washer stack you set after weighing the built vehicle, rather than fin area you commit to when you cut the tube. See §7.1.

Every number above is an output of scripts/baseline.py. Regenerate them rather than editing them by hand; they will move as the mass budget is replaced with weighed parts.