A lunar lander autopilot for lunar.unnecessarymodification.com

gistfile1.txt

// A lunar lander autopilot for https://lunar.unnecessarymodification.com/

function clamp(x, a, b) {
    return Math.min(Math.max(x, a), b);
}

function threshold(x, th) {
    return Math.abs(x) >= th ? x : 0;
}

function spow(x, p) {
    return Math.sign(x) * Math.pow(Math.abs(x), p);
}

function nangle(a) {
    if (a > 180) {
        return 360 - a;
    } else if (a <= -180) {
        return 360 + a;
    }
    return a;
}

class Vec {
    constructor(x, y) {
        this.x = x;
        this.y = y;
    }

    static fromAngle(a) {
        let arad = a / 180 * Math.PI;
        return new Vec(
            -Math.sin(arad),
            -Math.cos(arad),
        );
    }

    norm() {
        let len = this.abs();
        return new Vec(
            this.x / len,
            this.y / len,
        );
    }

    dot(v) {
        return this.x * v.x + this.y * v.y;
    }

    angle() {
        // The reference direction is towards the ground, same as the lander orientation.
        return nangle(-Math.atan2(this.y, this.x) * 180 / Math.PI - 90);
    }

    abs() {
        return Math.sqrt(this.x * this.x + this.y * this.y)
    }

    neg() {
        return new Vec(
            -this.x,
            -this.y,
        );
    }

    add(v) {
        return new Vec(
            this.x + v.x,
            this.y + v.y,
        );
    }

    sub(v) {
        return new Vec(
            this.x - v.x,
            this.y - v.y,
        );
    }

    mul(k) {
        return new Vec(
            this.x * k,
            this.y * k,
        );
    }
}

let {
    x_position,
    altitude,
    angle,
    userStore,
    log,
    plot
} = arguments[0];

let pos = new Vec(x_position, altitude);
let a = angle;

if (!("pos" in userStore)) {
    userStore.pos = pos;
    userStore.a = a;
    return {
        rotThrust: 0,
        aftThrust: 0,
        userStore: userStore,
    };
}

let v = pos.sub(userStore.pos);
let w = a - userStore.a;

let vset = new Vec(
    threshold(v.x * 0.8, 0.5),
    Math.max(v.y, spow(-pos.y / 70, 1.2)),
);
let verr = vset.sub(v);

let aset = clamp(v.add(verr.mul(0.8)).angle(), -90, 90);
let aerr = aset - a - spow(w, 1) * 4;
let wset = clamp(spow(threshold(aerr / 20, 0.1), 0.5), -4, 4);
let werr = wset - w;

let thrust = clamp(Vec.fromAngle(a).dot(verr.neg().norm()) * verr.abs() * 2.5, 0, 1);

thrust_rot = clamp(werr, -1, 1);

plot({
    vset: vset.abs(),
    v: v.abs(),
    thrust: thrust * 10,
});

userStore.pos = pos;
userStore.a = a;

return {
    rotThrust: thrust_rot,
    aftThrust: thrust,
    userStore: userStore,
};