Quite untested, but changed silos to be build-able only in certain areas. Also added loaders.

control.lua

@@ -197,6 +197,9 @@ script.on_event(defines.events.on_player_left_game, function(event)
     FindUnusedSpawns(game.players[event.player_index], true)
 end)
 
+----------------------------------------
+-- On BUILD entity. Don't forget on_robot_built_entity too!
+----------------------------------------
 script.on_event(defines.events.on_built_entity, function(event)
     if global.ocfg.enable_autofill then
         Autofill(event)
@@ -209,9 +212,14 @@ script.on_event(defines.events.on_built_entity, function(event)
     if ENABLE_ANTI_GRIEFING then
         SetItemBlueprintTimeToLive(event)
     end
+
+    if global.ocfg.frontier_rocket_silo then
+        BuildSiloAttempt(event)
+    end
 end)
 
 
+
 ----------------------------------------
 -- Shared vision, charts a small area around other players
 ----------------------------------------
@@ -248,7 +256,12 @@ script.on_event(defines.events.on_robot_built_entity, function (event)
     if global.ocfg.enable_regrowth then
         OarcRegrowthOffLimits(event.created_entity.position, 2)
     end
+
+    if global.ocfg.frontier_rocket_silo then
+        BuildSiloAttempt(event)
+    end
 end)
+
 -- I disabled this because it's too much overhead for too little gain!
 -- script.on_event(defines.events.on_player_mined_entity, function(event)
 --     if global.ocfg.enable_regrowth then
@@ -281,15 +294,19 @@ end)
 script.on_event(defines.events.on_research_finished, function(event)
     
     -- Never allows players to build rocket-silos in "frontier" mode.
-    if global.ocfg.frontier_rocket_silo then
-        RemoveRecipe(event.research.force, "rocket-silo")
-    end
+    -- if global.ocfg.frontier_rocket_silo then
+    --     RemoveRecipe(event.research.force, "rocket-silo")
+    -- end
 
     if LOCK_GOODIES_UNTIL_ROCKET_LAUNCH and 
         (not global.satellite_sent or not global.satellite_sent[event.research.force.name]) then
         RemoveRecipe(event.research.force, "productivity-module-3")
         RemoveRecipe(event.research.force, "speed-module-3")
     end
+
+    if ENABLE_LOADERS then
+        EnableLoaders(event)
+    end
 end)
 
 ----------------------------------------

lib/frontier_silo.lua

@@ -85,18 +85,22 @@ local function CreateRocketSilo(surface, siloPosition, force)
     -- Set tiles below the silo
     tiles = {}
     i = 1
-    for dx = -5,5 do
-        for dy = -5,5 do
-            tiles[i] = {name = "concrete", position = {siloPosition.x+dx, siloPosition.y+dy}}
+    for dx = -6,6 do
+        for dy = -6,6 do
+            if ((dx % 2 == 0) or (dx % 2 == 0)) then
+                tiles[i] = {name = "concrete", position = {siloPosition.x+dx, siloPosition.y+dy}}
+            else
+                tiles[i] = {name = "hazard-concrete-left", position = {siloPosition.x+dx, siloPosition.y+dy}}
+            end
             i=i+1
         end
     end
     surface.set_tiles(tiles, true)
 
     -- Create indestructible silo and assign to a force
-    local silo = surface.create_entity{name = "rocket-silo", position = {siloPosition.x+0.5, siloPosition.y}, force = force}
-    silo.destructible = false
-    silo.minable = false
+    -- local silo = surface.create_entity{name = "rocket-silo", position = {siloPosition.x+0.5, siloPosition.y}, force = force}
+    -- silo.destructible = false
+    -- silo.minable = false
 
     -- TAG it on the main force at least.
     game.forces[global.ocfg.main_force].add_chart_tag(game.surfaces[GAME_SURFACE_NAME],
@@ -128,6 +132,33 @@ function GenerateAllSilos(surface)
     end
 end
 
+-- Validates any attempt to build a silo.
+-- Should be call in on_built_entity and on_robot_built_entity
+function BuildSiloAttempt(event)
+
+    -- Validation
+    if (event.created_entity == nil) then return end
+    if (event.created_entity.name ~= "rocket-silo") then return end
+
+    -- Check if it's in the right area.
+    local epos = event.created_entity.position
+
+    for k,v in pairs(global.siloPosition) do
+        if (getDistance(epos, v) < 5) then
+            SendBroadcastMsg("Rocket silo has been built!")
+            return
+        end
+    end
+
+    -- If we get here, means it wasn't in a valid position. Need to remove it.
+    if (event.created_entity.last_user ~= nil) then
+        FlyingText("Can't build silo here! Check the map!", epos, my_color_red, event.created_entity.surface)
+        event.created_entity.last_user.mine_entity(event.created_entity, true)
+    else
+        log("ERROR! Rocket-silo had no valid last user?!?!")
+    end
+end
+
 -- Generate clean land and trees around silo area on chunk generate event
 function GenerateRocketSiloChunk(event)
 

lib/game_opts.lua

@@ -86,7 +86,7 @@ local function ExpandGameOptionsGui(player)
             game_info_str = game_info_str.."\n".."Everyone (all teams) have shared vision."
         end
         if (global.ocfg.frontier_rocket_silo) then
-            game_info_str = game_info_str.."\n".."Silos are NOT craftable. There is at least one already located on the map."
+            game_info_str = game_info_str.."\n".."Silos are only placeable in certain areas on the map!"
         end
         if (global.ocfg.enable_regrowth) then
             game_info_str = game_info_str.."\n".."Old parts of the map will slowly be deleted over time (chunks without any player buildings)."

lib/oarc_utils.lua

@@ -392,6 +392,7 @@ end
 function DisableTech(force, techName)
     if force.technologies[techName] then
         force.technologies[techName].enabled = false
+        force.technologies[techName].visible_when_disabled = true
     end
 end
 
@@ -1002,3 +1003,18 @@ function Autofill(event)
         AutoFillVehicle(player, eventEntity)
     end
 end
+
+-- Map loaders to logistics tech for unlocks.
+local loaders_technology_map = {
+    ['logistics'] = 'loader',
+    ['logistics-2'] = 'fast-loader',
+    ['logistics-3'] = 'express-loader'
+}
+
+function EnableLoaders(event)
+    local research = event.research
+    local recipe = loaders_technology_map[research.name]
+    if recipe then
+        research.force.recipes[recipe].enabled = true
+    end
+end