Mun to Kerbin Return Script by olex

--
--         Mun to Kerbin Return Script by olex
--                    Version 1.0
--
--                 for MechJeb 1.9.1
--
--------------------------------------------------------
-- Usage: * save to KSP/PluginData/mumechlib/GoHome.lua
--        * in game, open autom8
--        * enter: dofile("GoHome.lua")
--        * and follow the instructions.
--
-- Quicksave before using.
-- If an "coroutine out of sync" error pops up, load the save and try again.
--
-- No guarantees, but it should work :) Have fun!
--------------------------------------------------------

function KerbinReturnDriver(pe)
    if pe == nil then
        pe = 20.0
    end
    if pe > 70 then
        print "Final periapsis not in atmosphere, no automatic landing."
    end

    print "Lifting off..."
    mechjeb.attitudeTo("up", "SURFACE_NORTH") -- vertical ascent
    mechjeb.thrustActivate(100)
    while vessel.altitudeTrue < 300 do
        wait(0.25)
    end

    print "Escaping the Mun..."
    -- this needs to be optimized. figure out an escape vector
    -- that is as close as possible to the opposite of Mun's orbital velocity
    -- but not lower than 0° to the surface
    mechjeb.attitudeTo("right", "SURFACE_NORTH") -- heading east
    while vessel.orbitEccentricity < 1 do
        wait(0.25)
    end
    mechjeb.thrustDeactivate()

    print "Coasting to Mun escape, hang on."
    mechjeb.warpToEvent("soi")
    wait(mechjeb.free)

    print("Lowering Kerbin periapsis to "..pe.."km...")
    mechjeb.changePe(pe * 1000)
    wait(mechjeb.free)

    print "Coasting to Kerbin, stand by."
    mechjeb.warpToEvent("pe")
    while vessel.atmosphericDensity <= 0 and (not mechjeb.free()) do
        wait(0.25)
    end
    mechjeb.controlRelease()

    if vessel.atmosphericDensity > 0 then
        print "Re-entry... hold onto something."
        mechjeb.attitudeTo("back", "ORBIT")
        while vessel.speedSurface > 250 do
            wait(0.1)
        end
        print "Landing."
        mechjeb.autoStageActivate()
        mechjeb.land()
        wait(mechjeb.free)
        mechjeb.autoStageDeactivate()
        print "Welcome home!"
    else
        print "Not in atmosphere at periapsis. We're done here."
    end
end

function GoHome(pe)
    local co = coroutine.create(KerbinReturnDriver)
    coroutine.resume(co, pe)
end

print "Usage: GoHome(<desired Kerbin periapsis in km, default 20>)"