초소형 큐브위성 3축 자기 토커(Magnetorquer) 지구 자기장 상호작용 및 1,000Hz 0-Alloc C# B-dot 모멘텀 디새추레이션 엔진

using System;
using System.Numerics;
using System.Runtime.CompilerServices;

namespace ZeliDesk.Education.StemSpace.CubeSatAcs
{
    public readonly record struct MagnetometerTelemetry(
        Vector3 MagneticFieldMicroTesla, // 3축 자력계 측정치
        Vector3 AngularRateRadPerSec,
        float BatteryVoltageVolts
    );

    public ref struct MagnetorquerCommand
    {
        public Vector3 CommandedMagneticMomentAm2; // 3축 자기 모멘트 (A*m^2)
        public Vector3 CoilPwmDutyPercent;
        public bool DetumblingConverged;
    }

    public static class CubeSatBdotControlCore
    {
        private const float MaxDipoleMomentAm2 = 0.25f; // 1U/3U 큐브위성 코일 한계
        private const float BdotGainK = 1.2e5f;

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static void ComputeBdotTorque(
            ref readonly MagnetometerTelemetry tel,
            ref Vector3 previousBField, // 스택 관리 이전 자기장 벡터
            float dtSec,
            ref MagnetorquerCommand cmd)
        {
            // 1. 자기장 시간 변화율 (B-dot) 계산
            Vector3 bDot = (tel.MagneticFieldMicroTesla - previousBField) / Math.Max(dtSec, 0.001f);
            previousBField = tel.MagneticFieldMicroTesla;

            float bNorm = tel.MagneticFieldMicroTesla.Length();
            if (bNorm < 1.0f)
            {
                cmd.CommandedMagneticMomentAm2 = Vector3.Zero;
                cmd.CoilPwmDutyPercent = Vector3.Zero;
                cmd.DetumblingConverged = false;
                return;
            }

            // 2. B-dot 피드백 법칙: m = -k * (B_dot / ||B||)
            Vector3 targetMoment = -BdotGainK * (bDot / bNorm) * 1e-6f;

            // 3. 코일 전자기 모멘트 클램핑
            targetMoment.X = Math.Clamp(targetMoment.X, -MaxDipoleMomentAm2, MaxDipoleMomentAm2);
            targetMoment.Y = Math.Clamp(targetMoment.Y, -MaxDipoleMomentAm2, MaxDipoleMomentAm2);
            targetMoment.Z = Math.Clamp(targetMoment.Z, -MaxDipoleMomentAm2, MaxDipoleMomentAm2);
            cmd.CommandedMagneticMomentAm2 = targetMoment;

            // 4. PWM 듀티비 환산 (-100% ~ +100%)
            cmd.CoilPwmDutyPercent = new Vector3(
                (targetMoment.X / MaxDipoleMomentAm2) * 100.0f,
                (targetMoment.Y / MaxDipoleMomentAm2) * 100.0f,
                (targetMoment.Z / MaxDipoleMomentAm2) * 100.0f
            );

            // 5. 각속도 0.5 deg/s 이하 수렴 확인
            cmd.DetumblingConverged = tel.AngularRateRadPerSec.Length() < 0.0087f;
        }
    }
}