Improve maneuver node execution accuracy by basing time-to-burn on the

estimated burn duration of half of the delta-V instead of half of the
estimated duration of the entire burn to account for the acceleration
increasing over the course of the burn as the rocket uses fuel.

lib/node.ks

@@ -10,17 +10,20 @@ function estimated_burn_duration {
     // Based on:
     //  https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation
     //  https://space.stackexchange.com/questions/27375/how-do-i-calculate-a-rockets-burn-time-from-required-velocity
+    //  https://www.alternatewars.com/BBOW/Space/Rocket_Equations.htm
     //
     parameter burn.
     parameter isp is isp_sum().
-    parameter maxthrust is SHIP:maxthrust.
+    parameter thrust is SHIP:availablethrust.
 
     if burn:istype("Node") {
         set burn to burn:deltav.
     }
 
-    local exhaust_velocity is isp * (CONSTANT:G * KERBIN:mass).
+    local deltav is burn:mag.
-    return ((SHIP:mass * exhaust_velocity) / maxthrust) * (1 - CONSTANT:E^(-burn:mag/exhaust_velocity)).
+    local exhaust_velocity is isp * CONSTANT:g0.
+    local wet_mass is SHIP:mass.
+    return ((wet_mass * exhaust_velocity) / thrust) * (1 - CONSTANT:E^(-deltav/exhaust_velocity)).
 }
 
 
@@ -71,20 +74,20 @@ function execute_burn {
     lock STEERING to node.
     wait until vang(SHIP:facing:vector, node:burnvector) <= 0.5.
 
-    local warp_time is max(0, node:eta - (burn_duration/2) - 5).  // 5s before we need to start burn
+    // Start time is based on half of the delta-v instead of half the burn time to account for the acceleration increasing
-    if warp_time {
+    // over the course of the burn as the rocket uses fuel, and thus the 2nd half of the burn will take less time than the first.
-        print "Warping to maneuver node".
+    local burn_start_time is TIME:seconds + node:eta - estimated_burn_duration(node:deltav/2).
-        warp_for(warp_time).
+    warp_to(burn_start_time - 3).  // 3s before we need to start burn
 
-        print "Approaching maneuver node".
+    print "Approaching maneuver node".
-        wait until node:eta <= ceiling(burn_duration/2).  // ceiling since we'd rather start the burn too soon to have time for perfecting it
+    wait until TIME:seconds >= burn_start_time.
-    }
 
     print "Burn!".
-    // Decreasing throttle linearly with burn duration will only have an effect below 1s, otherwise it will be at max
+    // Decrease throttle linearly with burn duration when under 1 second, but ensure we always finish by burning with at least 1% power at all times.
-    lock THROTTLE to max(0.01, burn_duration).  // ensure we always finish the burn by burning with at least 1% power at all times
+    lock THROTTLE to max(0.01, min(1.0, burn_duration)).
     
-    // The burn vector will start to drift once we have very little left to burn. Therefore, save the burn vector as it is right now, and lock steering to it, instead of the dynamic vector
+    // The burn vector will start to drift once we have very little left to burn.
+    // Therefore, save the burn vector as it is right now, and lock steering to it, instead of the dynamic vector
     wait until burn_duration <= 1.
     local dv0 is node:burnvector.
     lock STEERING to dv0.

lib/rcs.ks

@@ -86,5 +86,6 @@ function rcs_translate {
         local z is pid_z:update(TIME:seconds, relative_velocity():z).
 
         set SHIP:CONTROL:TRANSLATION to ship_raw_to_ship_control(V(x,y,z)).
+        wait 0.  // wait one physics tick
     }
 }

lib/warp.ks

@@ -3,13 +3,16 @@
 function warp_to {
     parameter timestamp.
 
+    if timestamp <= TIME:seconds {
+        return.
+    }
+
+    print "Warping for " + round(timestamp - TIME:seconds, 1) + " seconds".
     KUNIVERSE:timewarp:warpto(timestamp).  // TODO: improve.
     wait until TIME:seconds >= timestamp. // TODO
 }
 
 function warp_for {
     parameter seconds.
-
-    print "Warping for " + round(seconds, 1) + " seconds".
     return warp_to(TIME:seconds + seconds).
 }