Randomize radius

* Randomize radius to +/- 20% to give the bodies some difference in surface gravity.
* Set an absolute limit of 5 g for habitability.
* Advice on gravity.
* Always build an orbiting station on inhabited worlds with a larger gravity (large
  currently being defined as over 1.07 g.
* New Planet info posts: 'Escape velocity' and 'Mean density'.
* Search and Rescue - Flavour 4 has extra text on dialogue when target planet is more
  than 1.2 g.

data/lang/core/en.json

@@ -411,6 +411,10 @@
     "description": "",
     "message": "Equatorial to polar radius ratio"
   },
+  "ESCAPE_VELOCITY": {
+    "description": "",
+    "message": "Escape velocity"
+  },
   "EXACT_MATCH_X": {
     "description": "",
     "message": "Exact match: %system"
@@ -783,6 +787,10 @@
     "description": "",
     "message": "Mass: %{mass}t"
   },
+  "MEAN_DENSITY": {
+    "description": "",
+    "message": "Mean density"
+  },
   "MEDICINES": {
     "description": "",
     "message": "Medicines"

data/lang/module-advice/en.json

@@ -7,6 +7,14 @@
     "description": "",
     "message": "Know when to leave town"
   },
+  "ADVICE_11_BODYTEXT": {
+    "description": "",
+    "message": "Make sure you know the surface gravity of a planet before you even think of landing on it."
+  },
+  "ADVICE_11_HEADLINE": {
+    "description": "A reference to the song 'The Harder They Come', by Jimmy Cliff",
+    "message": "The harder the g, the harder the fall"
+  },
   "ADVICE_1_BODYTEXT": {
     "description": "Point made is: the real illegal goods traders are fixed to each station, but police's fake illegal goods traders will be random every time.",
     "message": "As you return to a station, be wary of those alternative market places you do not recognize, and you will stay out of trouble with the law."

data/lang/module-searchrescue/en.json

@@ -305,7 +305,7 @@
   },
   "FLAVOUR_4_TYPEOFHELPTEXT": {
     "description": "",
-    "message": "The pilot is asking for {unit} tons of {cargo}."
+    "message": "The pilot is asking for {unit} tons of {cargo}. {high_gravity}"
   },
   "FLAVOUR_5_ADTEXT": {
     "description": "",
@@ -427,6 +427,22 @@
     "description": "",
     "message": "All cabins full. No more space for more passengers."
   },
+  "HIGHGRAVITY_0": {
+    "description": "",
+    "message": "The surface gravity on {planet} is {gravity} g. Please take this into consideration."
+  },
+  "HIGHGRAVITY_1": {
+    "description": "",
+    "message": "You should know that {planet} is {gravity} g."
+  },
+  "HIGHGRAVITY_2": {
+    "description": "",
+    "message": "You will land and take off in {gravity} g."
+  },
+  "HIGHGRAVITY_3": {
+    "description": "",
+    "message": "{planet} is {gravity} g."
+  },
   "HOW_FAR": {
     "description": "",
     "message": "How far away is the target?"

data/modules/Advice/Advice.lua

@@ -32,6 +32,7 @@ local travellers_advice_indices = {481, -- tame black market
 								   23,  -- double trouble
 								   52,  -- service ship
 								   248, -- change faction
+								   171, -- the harder the g
 }
 
 -- Hold all different types of advice/rumours available:

data/modules/SearchRescue/SearchRescue.lua

@@ -862,7 +862,8 @@ local onChat = function (form, ref, option)
 			pass         = ad.pickup_pass,
 			deliver_crew = ad.deliver_crew,
 			unit         = unit,
-			cargo        = cargo
+			cargo        = cargo,
+			high_gravity = ad.high_gravity,
 		})
 		form:SetMessage(typeofhelptext)
 
@@ -1203,7 +1204,7 @@ end
 
 local makeAdvert = function (station, manualFlavour, closestplanets)
 	-- Make a single advertisement for the bulletin board of the supplied station.
-	local due, dist, client, entity, problem, location
+	local due, dist, client, entity, problem, location, high_gravity
 	local lat = 0
 	local long = 0
 
@@ -1270,6 +1271,15 @@ local makeAdvert = function (station, manualFlavour, closestplanets)
 		due = (5 * dist + 4) * Engine.rand:Integer(20,24) * 60 * 60     -- TODO: adjust due date based on urgency
 	end
 
+	-- Create message string for the cases where the target landed on a planet that is higher gravity (> 1.2 g)
+	high_gravity = ""
+	if planet_target:GetSystemBody().gravity / 9.8066 > 1.2 and flavour.id == 4 then -- flavour id 4 is landed on a planet
+		high_gravity = string.interp(l["HIGHGRAVITY_" .. Engine.rand:Integer(0, getNumberOfFlavours("HIGHGRAVITY"))], {
+			planet       = planet_target:GetSystemBody().name,
+			gravity      = string.format("%.2f", planet_target:GetSystemBody().gravity / 9.8066),
+		})
+	end
+
 	--double the time if return to original station is required
 	if flavour.reward_immediate == false then due = 2 * due end
 	due = Game.time + due
@@ -1358,6 +1368,7 @@ local makeAdvert = function (station, manualFlavour, closestplanets)
 		system_local   = system_local,
 		station_target = station_target,
 		planet_target  = planet_target,
+		high_gravity   = high_gravity,
 		system_target  = system_target,
 		flavour	       = flavour,
 		client	       = client,

data/pigui/modules/system-view-ui.lua

@@ -808,6 +808,10 @@ function Windows.objectInfo:Show()
 					value = (not starport) and ui.Format.Distance(body.radius) or nil },
 				{ name = lc.SURFACE_GRAVITY, icon = icons.body_radius,
 					value = (not starport) and ui.Format.Speed(body.gravity, true).." ("..ui.Format.Gravity(body.gravity / 9.8066)..")" or nil },
+				{ name = lc.ESCAPE_VELOCITY, icon = icons.body_radius,
+					value = (not starport) and ui.Format.Speed(body.escapeVelocity , true) or nil },
+				{ name = lc.MEAN_DENSITY, icon = icons.body_radius,
+					value = (not starport) and ui.Format.Mass(body.meanDensity).."/m3" or nil },
 				{ name = lc.ORBITAL_PERIOD, icon = icons.body_orbit_period,
 					value = op and op > 0 and ui.Format.Duration(op, 2) or nil },
 				{ name = lc.DAY_LENGTH, icon = icons.body_day_length,

src/LangStrings.inc.h

@@ -304,6 +304,8 @@ DECLARE_STRING(N_EARTH_RADII)
 DECLARE_STRING(N_SOLAR_RADII)
 DECLARE_STRING(SURFACE_TEMPERATURE)
 DECLARE_STRING(SURFACE_GRAVITY)
+DECLARE_STRING(ESCAPE_VELOCITY)
+DECLARE_STRING(MEAN_DENSITY)
 DECLARE_STRING(N_CELSIUS)
 DECLARE_STRING(N_YEARS)
 DECLARE_STRING(N_DAYS)

src/galaxy/StarSystemGenerator.cpp

@@ -29,6 +29,9 @@ static const fixed AU_EARTH_RADIUS = fixed(3, 65536); // XXX Duplication from St
 static const fixed FIXED_PI = fixed(103993, 33102);	  // XXX Duplication from StarSystem.cpp
 static const double CELSIUS = 273.15;
 
+// max surface gravity for a permanent human settlement
+static const double MAX_SETTLEMENT_SURFACE_GRAVITY = 50; // m/s2 .. roughly 5 g
+
 static const Uint32 POLIT_SEED = 0x1234abcd;
 static const Uint32 POLIT_SALT = 0x8732abdf;
 
@@ -655,7 +658,7 @@ void StarSystemRandomGenerator::PickPlanetType(SystemBody *sbody, Random &rand)
 	// We get some more fractional bits for small bodies otherwise we can easily end up with 0 radius which breaks stuff elsewhere
 	//
 	// AndyC - Updated to use the empirically gathered data from this site:
-	// http://phl.upr.edu/library/notes/standardmass-radiusrelationforexoplanets
+	// https://phl.upr.edu/library/labnotes/standard-mass-radius-relation-for-exoplanets
 	// but we still limit at the lowest end
 	if (sbody->GetMassAsFixed() <= fixed(1, 1)) {
 		sbody->m_radius = fixed(fixedf<48>::CubeRootOf(fixedf<48>(sbody->GetMassAsFixed())));
@@ -669,6 +672,9 @@ void StarSystemRandomGenerator::PickPlanetType(SystemBody *sbody, Random &rand)
 		// Anything bigger than 200 EU masses is a Gas Giant or bigger but the density changes to decrease from here on up...
 		sbody->m_radius = fixed::FromDouble(22.6 * (1.0 / pow(sbody->GetMassAsFixed().ToDouble(), double(0.0886))));
 	}
+	// randomize radius or the surface gravity will be consistently 1.0 g for planets in the 1 - 200 EU range.
+	sbody->m_radius = fixed::FromDouble(sbody->GetRadiusAsFixed().ToDouble() * ( 1.2 - (0.4 * rand.Double()))); // +/-20% radius
+
 	// enforce minimum size of 10km
 	sbody->m_radius = std::max(sbody->GetRadiusAsFixed(), fixed(1, 630));
 
@@ -1447,7 +1453,7 @@ void PopulateStarSystemGenerator::PopulateStage1(SystemBody *sbody, StarSystem::
 	sbody->m_population = fixed();
 
 	/* Bad type of planet for settlement */
-	if ((sbody->GetAverageTemp() > CELSIUS + 100) || (sbody->GetAverageTemp() < 100) ||
+	if ((sbody->GetAverageTemp() > CELSIUS + 100) || (sbody->GetAverageTemp() < 100) || (sbody->CalcSurfaceGravity() > MAX_SETTLEMENT_SURFACE_GRAVITY) ||
 		(sbody->GetType() != SystemBody::TYPE_PLANET_TERRESTRIAL && sbody->GetType() != SystemBody::TYPE_PLANET_ASTEROID)) {
 		Random starportPopRand;
 		starportPopRand.seed(_init, 6);
@@ -1458,9 +1464,14 @@ void PopulateStarSystemGenerator::PopulateStage1(SystemBody *sbody, StarSystem::
 			sbody->m_population = fixed(1, 100000) + fixed(starportPopRand.Int32(-1000, 20000), 1000000000);
 			outTotalPop += sbody->m_population;
 		} else if (sbody->GetType() == SystemBody::TYPE_STARPORT_SURFACE) {
-			// give surface spaceports a population between 80000 and 250000
-			sbody->m_population = fixed(1, 10000) + fixed(starportPopRand.Int32(-2000, 15000), 100000000);
-			outTotalPop += sbody->m_population;
+			// No permanent population on gravities larger than defined in MAX_SETTLEMENT_SURFACE_GRAVITY
+			if (sbody->CalcSurfaceGravity() > MAX_SETTLEMENT_SURFACE_GRAVITY) {
+				outTotalPop = fixed();
+			} else {
+				// give surface spaceports a population between 80000 and 250000
+				sbody->m_population = fixed(1, 10000) + fixed(starportPopRand.Int32(-2000, 15000), 100000000);
+				outTotalPop += sbody->m_population;
+			}
 		}
 
 		return;
@@ -1623,6 +1634,9 @@ void PopulateStarSystemGenerator::PopulateAddStations(SystemBody *sbody, StarSys
 			++NumToMake;
 			pop -= rand.Fixed();
 		}
+		if ((NumToMake == 0) and (sbody->CalcSurfaceGravity() > 10.5)) {  // 10.5 m/s2 = 1,07 g
+			NumToMake = 1;
+		}
 
 		// Any to position?
 		if (NumToMake > 0) {

src/galaxy/SystemBody.cpp

@@ -805,6 +805,26 @@ double SystemBody::CalcSurfaceGravity() const
 	}
 }
 
+double SystemBody::CalcEscapeVelocity() const
+{
+	double r = GetRadius();
+	if (r > 0.0) {
+		return pow((2 * CalcSurfaceGravity() * r) , 0.5);
+	} else {
+		return 0.0;
+	}
+}
+
+double SystemBody::CalcMeanDensity() const
+{
+	double r = GetRadius();
+	if (r > 0.0) {
+		return GetMass()  / (4.0 / 3.0 * M_PI * pow(r, 3)); // Density = Mass / Volume
+	} else {
+		return 0.0;
+	}
+}
+
 void SystemBody::Dump(FILE *file, const char *indent) const
 {
 	fprintf(file, "%sSystemBody(%d,%d,%d,%u,%u) : %s/%s %s{\n", indent, m_path.sectorX, m_path.sectorY, m_path.sectorZ, m_path.systemIndex,

src/galaxy/SystemBody.h

@@ -253,6 +253,8 @@ class SystemBody : public RefCounted, public SystemBodyType, protected SystemBod
 	double GetPopulation() const { return m_population.ToDouble(); }
 
 	double CalcSurfaceGravity() const;
+	double CalcEscapeVelocity() const;
+	double CalcMeanDensity() const;
 
 	double GetMaxChildOrbitalDistance() const;
 

src/lua/LuaSystemBody.cpp

@@ -260,6 +260,47 @@ static int l_sbody_attr_gravity(lua_State *l)
 	return 1;
 }
 
+/*
+ * Attribute: escapeVelocity
+ *
+ * The speed an object need to break free from the gravitational influence
+ * of a body and leave it behind with no further acceleration.
+ *
+ * Availability:
+ *
+ *   July 2023
+ *
+ * Status:
+ *
+ *   experimental
+ */
+static int l_sbody_attr_escape_velocity(lua_State *l)
+{
+	SystemBody *sbody = LuaObject<SystemBody>::CheckFromLua(1);
+	lua_pushnumber(l, sbody->CalcEscapeVelocity());
+	return 1;
+}
+
+/*
+ * Attribute: meanDensity
+ *
+ * The mean density of a body (kg/m3).
+ *
+ * Availability:
+ *
+ *   July 2023
+ *
+ * Status:
+ *
+ *   experimental
+ */
+static int l_sbody_attr_mean_density(lua_State *l)
+{
+	SystemBody *sbody = LuaObject<SystemBody>::CheckFromLua(1);
+	lua_pushnumber(l, sbody->CalcMeanDensity());
+	return 1;
+}
+
 /*
  * Attribute: periapsis
  *
@@ -758,6 +799,8 @@ void LuaObject<SystemBody>::RegisterClass()
 		{ "radius", l_sbody_attr_radius },
 		{ "mass", l_sbody_attr_mass },
 		{ "gravity", l_sbody_attr_gravity },
+		{ "escapeVelocity", l_sbody_attr_escape_velocity },
+		{ "meanDensity", l_sbody_attr_mean_density },
 		{ "periapsis", l_sbody_attr_periapsis },
 		{ "apoapsis", l_sbody_attr_apoapsis },
 		{ "orbitPeriod", l_sbody_attr_orbital_period },