Rendezvous with ISS

set T to vessel("Iss").
lock steering to prograde.
rcs on.
b1().

function b1 {
    wait 0.
    set TargetAp to ship:apoapsis + body:radius.
    lock ap to ship:apoapsis + body:radius.
    set smja to (ap + TargetAp) / 2.
    set targetvel to sqrt(body:mu*((2/ap)-(1/smja))).
    print targetvel.
    set maneuvertime to time + eta:apoapsis.
    set apvel to velocityat(ship, maneuvertime):orbit:mag.
    print apvel.
    set needvel to targetvel - apvel.
    print needvel.
    set nd to node(maneuvertime, 0, 0, needvel).
    add nd.
    set max_acc to 8/ship:mass.
    set burn_duration to nd:deltav:mag/max_acc.
    print "Crude Estimated burn duration: " + round(burn_duration) + "s".
    lock steering to prograde.
    wait until nd:eta <= (burn_duration/2 + 60).
    set np to nd:deltav. //points to node, don't care about the roll direction.
    lock steering to np.

    //now we need to wait until the burn vector and ship's facing are aligned
    wait until vang(np, ship:facing:vector) < 0.25.

    //the ship is facing the right direction, let's wait for our burn time
    wait until nd:eta <= (burn_duration/2).
    //we only need to lock throttle once to a certain variable in the beginning of the loop, and adjust only the variable itself inside it
    set ship:control:fore to 0.

    set done to False.
    //initial deltav
    set dv0 to nd:deltav.
    until done
    {
        set max_acc to 8/ship:mass.
        //throttle is 100% until there is less than 1 second of time left to burn
        //when there is less than 1 second - decrease the throttle linearly
        set ship:control:fore to min(nd:deltav:mag/max_acc, 1).

        //here's the tricky part, we need to cut the throttle as soon as our nd:deltav and initial deltav start facing opposite directions
        //this check is done via checking the dot product of those 2 vectors
        if vdot(dv0, nd:deltav) < 0
        {
            print "End burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            set ship:control:fore to 0.
            break.
        }

        //we have very little left to burn, less then 0.1m/s
        if nd:deltav:mag < 0.1
        {
            print "Finalizing burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            //we burn slowly until our node vector starts to drift significantly from initial vector
            //this usually means we are on point
            wait until vdot(dv0, nd:deltav) < 0.5.

            set ship:control:fore to 0.
            print "End burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            set done to True.
        }
    }
    unlock steering.
    unlock throttle.
    wait 1.

    //we no longer need the maneuver node
    remove nd.

    //set throttle to 0 just in case.
    SET SHIP:CONTROL:PILOTMAINTHROTTLE TO 0.
}

function b2 {
    wait 0.
    set TargetAp to T:apoapsis + body:radius.
    set ap to ship:apoapsis + body:radius.
    set smja to (ap + TargetAp) / 2.
    set targetvel to sqrt(body:mu*((2/ap)-(1/smja))).
    print targetvel.
    set now to time:seconds + 30.
    set maneuvertime to now.
    set apvel to velocityat(ship, maneuvertime):orbit:mag.
    print apvel.
    set needvel to targetvel - apvel.
    print needvel.
    set nd to node(maneuvertime, 0, 0, needvel).
    add nd.
    set max_acc to 8/ship:mass.
    set burn_duration to nd:deltav:mag/max_acc.
    print "Crude Estimated burn duration: " + round(burn_duration) + "s".
    lock steering to prograde.
    wait until nd:eta <= (burn_duration/2 + 60).
    set np to nd:deltav. //points to node, don't care about the roll direction.
    lock steering to np.

    //now we need to wait until the burn vector and ship's facing are aligned
    wait until vang(np, ship:facing:vector) < 0.25.

    //the ship is facing the right direction, let's wait for our burn time
    wait until nd:eta <= (burn_duration/2).
    //we only need to lock throttle once to a certain variable in the beginning of the loop, and adjust only the variable itself inside it
    set ship:control:fore to 0.

    set done to False.
    //initial deltav
    set dv0 to nd:deltav.
    until done
    {
        set max_acc to 8/ship:mass.
        //throttle is 100% until there is less than 1 second of time left to burn
        //when there is less than 1 second - decrease the throttle linearly
        set ship:control:fore to min(nd:deltav:mag/max_acc, 1).

        //here's the tricky part, we need to cut the throttle as soon as our nd:deltav and initial deltav start facing opposite directions
        //this check is done via checking the dot product of those 2 vectors
        if vdot(dv0, nd:deltav) < 0
        {
            print "End burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            set ship:control:fore to 0.
            break.
        }

        //we have very little left to burn, less then 0.1m/s
        if nd:deltav:mag < 0.1
        {
            print "Finalizing burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            //we burn slowly until our node vector starts to drift significantly from initial vector
            //this usually means we are on point
            wait until vdot(dv0, nd:deltav) < 0.5.

            set ship:control:fore to 0.
            print "End burn, remain dv " + round(nd:deltav:mag,1) + "m/s, vdot: " + round(vdot(dv0, nd:deltav),1).
            set done to True.
        }
    }
    unlock steering.
    unlock throttle.
    wait 1.

    //we no longer need the maneuver node
    remove nd.

    //set throttle to 0 just in case.
    SET SHIP:CONTROL:PILOTMAINTHROTTLE TO 0.
}

function calcangle {
    set sa to (2*body("Kerbin"):radius + T:altitude + ship:altitude)/2.
    set ta to body("Kerbin"):radius + T:altitude.
    print sa.
    print ta.
    return 180*(1-(sa/ta)^1.5).
}

function checkang {
    set VecS to ship:position - body("Kerbin"):position.
    set VecT to T:position - body("Kerbin"):position.
    set VecHV to vxcl(ship:up:vector, ship:velocity:orbit).
    set VecST to T:position - ship:position.
    set t_angle to calcangle.
    set cur_angle to vang(VecT, VecS).
    if vang(Vect, VecS)>90 {
        set cur_angle to -cur_angle.
    }

    print cur_angle - t_angle.
    return abs(cur_angle - t_angle) < 6.
}

until checkang {
    lock steering to prograde.
    print checkang.
    wait 1.
    clearscreen.
}

b2().
LOCK TargetVector TO Target:ORBIT:POSITION-SHIP:ORBIT:POSITION.
wait until TargetVector:mag < 5000.
run approach.
run dock.