//////////
//////////
//////////   THE ONLY THINGS THAT NEED TO BE CHANGED

set isp to 287. 						//VACUUM Specific Impulse of the engine.
set minthrot to 0.29. 						//set to the minimum thrust of your engine(s). For stock, this is just 0.
set shipheight to 2.8.						//height of ship so engines know when to cut off.
set throttleupbuffer to 0. 					//set this to 1 if your engines take time to throttle up. it just adds an extra kilometer of bufferzone. set to 0 if not.
set la to 57.66.						//latitude of desired coordinates
set lo to 9.13.							//longitude of desired coordinates

//////////   THE ONLY THINGS THAT NEED TO BE CHANGED
//////////
//////////






set angleb to 0.

until round(angleb) = 91{
	set coorpos to latlng(la,lo):position.
	SET anArrow TO VECDRAW(
      		V(0,0,0),
      		//ship:body:position,
      		coorpos,
      		RGB(1,0,0),
      		"This is where you should be landing",
      		1.0,
      		TRUE,
      		0.2
  	).
	set uv to v(0,1,0).
	set ev to vcrs(ship:body:position,uv).
	set nv to vcrs(ev,ship:body:position).
	set vec1 to vcrs(ship:body:position,ship:velocity:surface).
	set dot1 to vdot(nv,vec1).
	set anglenorth to -1*(arccos(dot1/(nv:mag*vec1:mag))-90).
	set dot2 to vdot(ev,vec1).
	set angleeast to -1*(arccos(dot2/(ev:mag*vec1:mag))-90).
	if angleeast>0 and anglenorth<0 {
		set anglenorth to 360+anglenorth.
	}. else if angleeast<0 and anglenorth<0 {
		set anglenorth to 180-anglenorth.
	}. else if angleeast<0 and anglenorth>0 {
		set anglenorth to 180-anglenorth.
	}.

	set srfprohdg to anglenorth.

	set uv to v(0,1,0).
	set ev to vcrs(ship:body:position,uv).
	set nv to vcrs(ev,ship:body:position).
	set vec1 to vcrs(ship:body:position,latlng(la,lo):position).
	set dot1 to vdot(nv,vec1).
	set anglenorth to -1*(arccos(dot1/(nv:mag*vec1:mag))-90).
	set dot2 to vdot(ev,vec1).
	set angleeast to -1*(arccos(dot2/(ev:mag*vec1:mag))-90).
	if angleeast>0 and anglenorth<0 {
		set anglenorth to 360+anglenorth.
	}. else if angleeast<0 and anglenorth<0 {
		set anglenorth to 180-anglenorth.
	}. else if angleeast<0 and anglenorth>0 {
		set anglenorth to 180-anglenorth.
	}.

	set tgthead to anglenorth.

	set neg to 0.

	if tgthead<srfprohdg {
		set neg to -1.
	}. else if tgthead>srfprohdg {
		set neg to 1.
	}.
	set targpos to -1*ship:body:position+latlng(la,lo):position.
	set angleb to vang(targpos,-ship:body:position).
	set normal to neg*vcrs(ship:velocity:surface,ship:body:position).
	lock steering to normal.
	clearscreen.
	print "The current angle is: "+round(angleb)+" Degrees".
	wait 0.1.
}.


set ship:control:fore to 1.
print " ".
print "Firing RCS for Ullage".
wait 2.
lock throttle to 1.
set ship:control:neutralize to true.



until 5=4 {
	set normal to neg*vcrs(ship:velocity:surface,ship:body:position).
	lock steering to normal.
	set targpos to -ship:body:position+latlng(la,lo):position.
	set angleb to vang(targpos,-ship:body:position).
	set futureshippos to (-1*ship:body:position)+positionat(ship,time:seconds+(ship:orbit:period*(angleb/360))).
	set futuretargpos to targpos+(latlng(la,lo):velocity:orbit*ship:orbit:period*(angleb/360)).
	set futureangle to vang(futuretargpos,futureshippos).
	clearscreen.
	print " ".
	print "Predicted angle: "+futureangle.
	print "Current angle:   "+angleb.
	wait 0.1.
	set targpos to -ship:body:position+latlng(la,lo):position.
	set angleb to vang(targpos,-ship:body:position).
	set futureshippos to (-1*ship:body:position)+positionat(ship,time:seconds+(ship:orbit:period*(angleb/360))).
	set secondangle to vang(futuretargpos,futureshippos).
	if secondangle>futureangle {
		break.
	}.
}.
lock throttle to 0.
clearvecdraws().
clearscreen.
lock steering to -ship:velocity:surface.
set m0 to ship:mass*1000. 								//ships mass in kg
set localacc to body:mass*constant:g/ship:body:position:mag^2. 	  			//surface level acceleration on whatever body. The change in acceleration over altitude should be negligible
set T to ship:maxthrust*1000.	  									//Thrust of the engine
set W to (m0*localacc).   								//Weight of the spacecraft pre-burn on whatever body
set g to 9.81.										//1 earth/kerbin g
set e to 2.7182818284590452353602874713527.						//I know i probably don't have to set e, but whatever
set pi to 3.141592654.







set massflow to (T/(isp*g)).			//massflow of engine in terms of thrust and isp
set veq to isp*g.



set a0 to ship:maxthrust/ship:mass.
set s to ship:velocity:surface:mag^2/(2*a0).


until 5=4 {
	set a0 to ship:maxthrust/ship:mass.
	set s to ship:velocity:surface:mag^2/(2*a0).
	set coorpos to latlng(la,lo):position.
	SET anArrow TO VECDRAW(
      		V(0,0,0),
      		//ship:body:position,
      		coorpos,
      		RGB(1,0,0),
      		"This is where you should be landing",
      		1.0,
      		TRUE,
     		0.2
    	).
	clearscreen.
	set targpos to -ship:body:position+latlng(la,lo):position.
	set angleb to vang(targpos,-ship:body:position).
	set radians to (pi/180)*angleb.
	set distance to ship:body:position:mag*radians.
	print " ".
	print "The burn distance is:		" + round(s) + " meters".
	print "The current distance is:		" + round(distance) + " meters".
	if distance-s < ship:velocity:surface:mag*0.25 {
		set ship:control:fore to 1.
		print " ".
		print "Firing RCS for Ullage".
	}.
	wait 0.1.
	if abs(distance-s) < ship:velocity:surface:mag*0.15 {
		break.
	}.

}.
clearvecdraws().
sas off.
rcs on.
lock steering to -ship:velocity:surface.
lock throttle to 1.
set ship:control:neutralize to true.
set T to ship:maxthrust.
set a0 to ship:maxthrust/ship:mass.
set throt to 1.

until ship:velocity:surface:mag < 15 {
	set currentthrust to ((T-(minthrot*T))*throt)+(minthrot*T).
	set a1 to ship:velocity:orbit:mag^2/ship:body:position:mag.
	set a2 to body:mass*constant:g/ship:body:position:mag^2.
	set adiff to a2-a1.
	set aup to arcsin(adiff/(currentthrust/ship:mass)).
	if ship:verticalspeed > 0.1 {
		set aup to aup-0.1.
	}. else if ship:verticalspeed < 0.1 {
		set aup to aup+0.1.
	}. else {
		set aup to aup.
	}.
	set uv to v(0,1,0).
	set ev to vcrs(ship:body:position,uv).
	set nv to vcrs(ev,ship:body:position).
	set vec1 to vcrs(ship:body:position,ship:velocity:surface).
	set dot1 to vdot(nv,vec1).
	set anglenorth to -1*(arccos(dot1/(nv:mag*vec1:mag))-90).
	set dot2 to vdot(ev,vec1).
	set angleeast to -1*(arccos(dot2/(ev:mag*vec1:mag))-90).
	if angleeast>0 and anglenorth<0 {
		set anglenorth to 360+anglenorth.
	}. else if angleeast<0 and anglenorth<0 {
		set anglenorth to 180-anglenorth.
	}. else if angleeast<0 and anglenorth>0 {
		set anglenorth to 180-anglenorth.
	}.

	set srfretrohdg to anglenorth-180.

	lock steering to heading(srfretrohdg,aup).
	set laterala to currentthrust*cos(aup)/ship:mass.
	clearscreen.
	print " ".
	print "Lateral Deceleration: "+laterala+" m/s^2".
	print "Desired Deceleration: "+a0+" m/s^2".
	print "Up angle:             "+aup+" degrees".

	set tdesired to a0*ship:mass/cos(aup).
	set throt to (tdesired-(minthrot*T))/(T*(1-minthrot)).
	lock throttle to throt.


	wait 0.1.

}.

lock steering to -ship:velocity:surface.
wait until ship:groundspeed<0.2.


lock throttle to 0.
clearscreen.
set ship:control:pilotmainthrottle to 0.
sas off.
print " ".
print "Preparing for Suicide Burn".
print "May God have mercy on your soul".
lock steering to heading(0,90).
set m0 to ship:mass*1000. 					//ships mass in kg
set localacc to body:mass*constant:g/(body:radius^2).  		//surface level acceleration on whatever body. The change in acceleration over altitude should be negligible
set T to ship:maxthrust*1000*0.95.	  				//Thrust of the engine
set W to (m0*localacc).   					//Weight of the spacecraft pre-burn on whatever body


set g to 9.81.							//1 earth/kerbin g
set e to 2.7182818284590452353602874713527.			//I know i probably don't have to set e, but whatever
set throttleupbuffer to 1000*throttleupbuffer.

set r to body:radius+ship:altitude.
set gm to body:mass*constant:G.



set massflow to (T/(isp*g)).			//massflow of engine in terms of thrust and isp
set twmc to ((T-W)/massflow).			//a constant I found in calculations. I did this to avoid writing it over and over again
set t2 to 2.
set t1 to 1.




set burnalt to 0.
//set decel to (T/m0)-localacc.

set altdiff to 0.
set difference to 1.
set radaralt to ship:altitude.
wait 5.
until difference < altdiff  {
	wait 0.1.

	set r to body:radius+ship:altitude.
	set gm to body:mass*constant:G.
	set localacc to (gm/((body:radius+ship:altitude)-(body:radius+ship:geoposition:terrainheight)))*((1/(body:radius+ship:geoposition:terrainheight))-(1/(body:radius+ship:altitude))).
	set m0 to ship:mass*1000.
	set W to m0*localacc.
	set T to ship:maxthrust.
	set twmc to ((T-W)/massflow).

	set radaralt to ship:altitude-ship:geoposition:terrainheight.
	set tb to ((m0 - e^((ln(m0))-((massflow*ship:verticalspeed*-1)/(T-W))))/massflow).
	set mf to (m0-(massflow*tb)).
	set burnalt to twmc*((tb*ln(m0))-(((mf*ln(mf))-mf-(m0*ln(m0))+m0)/-massflow)).
	set difference to (-burnalt+radaralt).

	clearscreen.
	print " ".
	print "Burn Altitude:   "+round(burnalt)+" meters".
	print "Radar Altitude:  "+round(radaralt)+" meters".
	print "Difference:      "+round(difference)+" meters".
	if difference < ship:verticalspeed*10*-1 {
		set ship:control:fore to 1.
		print " ".
		print "Firing RCS for Ullage".
	}.

	set altdiff to (ship:verticalspeed*-1)*0.15+throttleupbuffer.

}.

set ship:control:neutralize to true.
lock throttle to 0.95.


set W to m0*localacc.
set twmc to ((T-W)/massflow).



set throt to 0.95.
set zer to 0.

until ship:verticalspeed>-2 {

	wait 0.1.


	set radaralt to ship:altitude-ship:geoposition:terrainheight.

	set uv to v(0,1,0).
	set ev to vcrs(ship:body:position,uv).
	set nv to vcrs(ev,ship:body:position).
	set vec1 to vcrs(ship:body:position,ship:velocity:surface).
	set dot1 to vdot(nv,vec1).
	set anglenorth to -1*(arccos(dot1/(nv:mag*vec1:mag))-90).
	set dot2 to vdot(ev,vec1).
	set angleeast to -1*(arccos(dot2/(ev:mag*vec1:mag))-90).
	if angleeast>0 and anglenorth<0 {
		set anglenorth to 360+anglenorth.
	}. else if angleeast<0 and anglenorth<0 {
		set anglenorth to 180-anglenorth.
	}. else if angleeast<0 and anglenorth>0 {
		set anglenorth to 180-anglenorth.
	}.

	set srfretrohdg to anglenorth-180.

	set aup to 90.
	if ship:groundspeed>0.5 {
		set aup to 87.
	}. else {
		set srfretrohdg to 0.
	}.

	lock steering to heading(srfretrohdg,aup).

	set localacc to (gm/((body:radius+ship:altitude)-(body:radius+ship:geoposition:terrainheight)))*((1/(body:radius+ship:geoposition:terrainheight))-(1/(body:radius+ship:altitude))).
	set m0 to ship:mass*1000.
	set W to m0*localacc.
	set T to ship:maxthrust.
	set twmc to ((T-W)/massflow).

	set radaralt to ship:altitude-ship:geoposition:terrainheight.
	set tb to ((m0 - e^((ln(m0))-((massflow*ship:verticalspeed*-1)/(T-W))))/massflow).
	set mf to (m0-(massflow*tb)).
	set updatedburnalt to twmc*((tb*ln(m0))-(((mf*ln(mf))-mf-(m0*ln(m0))+m0)/-massflow)).
	set difference to (-burnalt+radaralt).
	set newdif to (radaralt-updatedburnalt).

	clearscreen.
	print " ".
	print "Burnalt: "+round(updatedburnalt)+" meters".
	print "Radar Altitude:  "+round(radaralt)+" 	meters".
	print "Updated Diff:    "+round(newdif)+" meters".




	if newdif>(shipheight+2) and newdif < 100 {
		set throt to 0.90.
		print " ".
		print "Throttle at "+round(throt*100)+"%".
	}. else if newdif >100 {
		set throt to .85.
		print " ".
		print "Throttle at "+round(throt*100)+"%".
	}. else if newdif < (shipheight+1) {
		set throt to 1.
		print " ".
		print "Throttle at "+round(throt*100)+"%".
	}. else {
		set throt to 0.95.
		print " ".
		print "Throttle at "+round(throt*100)+"%".
	}.

	lock throttle to throt.

	when radaralt-zer < 100 then {
		toggle gear.
		set zer to -100000.
	}.


}.

//toggle gear.

if ship:maxthrust*minthrot > ship:mass*localacc {
	toggle ag1.
}.


until ship:verticalspeed > - 1 {
	lock throttle to throt+0.1.
	wait 0.1.
}.

until alt:radar < shipheight+0.2 {
	set r to body:radius+ship:altitude.
	set gm to body:mass*constant:G.
	set localacc to gm/r^2.
	set w to localacc*ship:mass.
	set T to ship:maxthrust.
	set throt to (w-(minthrot*T))/(T*(1-minthrot)).
	if ship:verticalspeed < -0.75 {
		set throt to throt+0.05.
	}. else if ship:verticalspeed > -0.5 {
		set throt to throt-0.05.
	}. else {
		set throt to throt.
	}.
	lock throttle to throt.
	wait 0.1.
}.
lock throttle to 0.
rcs off.
unlock steering.
set ship:control:pilotmainthrottle to 0.


set coorpos to latlng(la,lo):position.
clearscreen.
print " ".
print "You landed "+round(coorpos:mag)+" meters".
print "from the intended landinge site".

wait until alt:radar<shipheight+0.1.