// Landing Burn



// Configuration

set radarOffset to 26.850.                                  // Measure "alt:radar" of the vehicle when landed 27.977



// Physics

lock trueRadar to alt:radar - radarOffset.                  // Distance from the bottom of vehicle to the ground

lock g to constant:g * body:mass / body:radius^2.           // Gravitational acceleration

lock maxDecel to (ship:availablethrust / ship:mass) - g.    // Maximum achievable deceleration of the vehicle

lock stopDist to ship:verticalspeed^2 / (2 * maxDecel).     // Distance to kill all the velocity

lock idealThrottle to stopDist / trueRadar.                 // Hoverslam throttling setting

lock impactTime to trueRadar / abs(ship:verticalspeed).     // Time to impact with the current velocity



// State variables

set burnStarted to 0.                                       // 1 if landing burn has started



clearscreen.



wait until ship:verticalspeed < -1.

    print "Preparing for landing burn...".

    rcs on.

	print "RCS Online...".

    brakes on.

    lock steering to srfretrograde.

	list engines in elist.

		for eng in elist

		{

			if eng:hasgimbal

			{

				set maxrange to eng:gimbal:range.

				set eng:gimbal:limit to maxrange/2. // this will limit engine gimbal

			}

		}



	print "Engine gimbal limited...".





wait until trueRadar < stopDist.

    print "Landing burn has begun!".

    set burnStarted to 1.

    lock throttle to idealThrottle.



wait until burnStarted = 1.

    until impactTime < 4.

        print "Deploying landing legs...".

        gear on.



wait until ship:verticalspeed > -0.01.

    print "Falcon 9 first stage has landed at LZ-1!".

    set ship:control:pilotmainthrottle to 0.

    wait 5.

    rcs off.

    sas off.

    brakes off.