From 986574a73a9478ddf31f33afdd80f1c9f545abe9 Mon Sep 17 00:00:00 2001
From: cinnaboot <cinnaboot@protonmail.com>
Date: Wed, 27 Jul 2022 07:47:35 -0400
Subject: [PATCH] add circularize impulse types

---
 src/game.cpp   | 25 +++++++++++++++++++------
 src/game.h     |  4 +++-
 src/main.cpp   | 19 +++++++++++--------
 src/orbits.cpp | 11 +++++++++++
 src/orbits.h   |  4 ++++
 5 files changed, 48 insertions(+), 15 deletions(-)

diff --git a/src/game.cpp b/src/game.cpp
index 6504f0e..5e7610d 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -139,7 +139,6 @@ getFreeManeuver(GameState* gs)
 	return nullptr;
 }
 
-// TODO: appendManeuver(orbit, node) would be better
 bool
 addManeuver(GameState* gs,
 			GameOrbit* orbit,
@@ -152,7 +151,10 @@ addManeuver(GameState* gs,
 		return false;
 	}
 
-	if (impulse_delta_v == 0.f) {
+	if (impulse_type != ImpulseType::CIRCULARIZE_RAISING
+		&& impulse_type != ImpulseType::CIRCULARIZE_LOWERING
+		&& impulse_delta_v == 0.f)
+	{
 		LOGF(Warning, "refusing to add maneuver with 0 dv\n");
 		return false;
 	}
@@ -172,9 +174,12 @@ addManeuver(GameState* gs,
 	node->impulse_type = impulse_type;
 	// TODO: thrust calculations
 	//double flight_path_angle = orbit->system.sat.gamma;
-	//node.impulse_vector.x = ...
+	//node->impulse_vector.x = ...
 
-	if (node->impulse_type == ImpulseType::PROGRADE) {
+	if (node->impulse_type == ImpulseType::PROGRADE
+		|| node->impulse_type == ImpulseType::CIRCULARIZE_RAISING
+		|| node->impulse_type == ImpulseType::CIRCULARIZE_LOWERING)
+	{
 		node->true_anomaly = true_anomaly;
 		node->impulse_delta_v = impulse_delta_v;
 		node->active = true;
@@ -222,8 +227,16 @@ applyManeuver(GameOrbit* orbit, ManeuverNode* maneuver)
 	TwoBodySystem& sys = orbit->system;
 
 	assert(maneuver);
-	// FIXME: assuming prograde impulse vector
-	assert(maneuver->impulse_type == ImpulseType::PROGRADE);
+	// TODO: other impulse types
+	assert(maneuver->impulse_type == ImpulseType::PROGRADE
+			|| maneuver->impulse_type != ImpulseType::CIRCULARIZE_RAISING
+			|| maneuver->impulse_type != ImpulseType::CIRCULARIZE_LOWERING);
+
+	if (maneuver->impulse_type == ImpulseType::CIRCULARIZE_RAISING) {
+		maneuver->impulse_delta_v = orbitGetCircVelocity(orbit->system);
+	} else if (maneuver->impulse_type == ImpulseType::CIRCULARIZE_LOWERING) {
+		maneuver->impulse_delta_v = orbitGetCircVelocity(orbit->system, false);
+	}
 
 	// re-calculate state vectors at the maneuver node
 	double theta = maneuver->true_anomaly;
diff --git a/src/game.h b/src/game.h
index f4d80af..10102d1 100644
--- a/src/game.h
+++ b/src/game.h
@@ -27,6 +27,8 @@ enum struct ImpulseType
 	NONE,
 	PROGRADE,
 	RETROGRADE,
+	CIRCULARIZE_RAISING,
+	CIRCULARIZE_LOWERING,
 	INCLINATION_CHANGE,
 	GENERAL_PLANE_CHANGE,
 	OTHER,
@@ -96,7 +98,7 @@ bool addManeuver(GameState* gs,
 		GameOrbit* orbit,
 		ImpulseType impulse_type,
 		double true_anomaly,
-		double impulse_delta_v);
+		double impulse_delta_v = 0.f);
 
 bool testManeuverStep(ManeuverNode* maneuver,
 		double previous_theta,
diff --git a/src/main.cpp b/src/main.cpp
index 34d1470..7020b1e 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -251,19 +251,22 @@ loadScene(GameState* gs, RenderState* rs)
 	gs->coord_overlay = addCoordinateOverlay(rs);
 
 	OrbitalElements el1 = orbitInit(8000, 0, 0, 0, 0, DEG2RAD(-90));
-	GameOrbit* go_1 = loadOrbit(gs, rs, body, el1, rg, "sat_01");
+	loadOrbit(gs, rs, body, el1, rg, "sat_01");
+	//GameOrbit* go_1 = loadOrbit(gs, rs, body, el1, rg, "sat_01");
 
 	OrbitalElements el2 = orbitInit(20000, 0, 0, 0, 0, 0);
-	loadOrbit(gs, rs, body, el2, rg, "sat_02");
-	//GameOrbit* go_2 = loadOrbit(gs, rs, body, el2, rg, "sat_02");
+	//loadOrbit(gs, rs, body, el2, rg, "sat_02");
+	GameOrbit* go_2 = loadOrbit(gs, rs, body, el2, rg, "sat_02");
 
+#if 0
 	double v_transfer = orbitGetTransferVelocity(go_1->system, el2);
 	addManeuver(gs, go_1, ImpulseType::PROGRADE, DEG2RAD(180), v_transfer);
-	// FIXME: can't get circularization here unless we simulate the transfer
-	// 	orbit ahead of time, eg) applyManeuver to a dummy orbit
-	// 	could also add a ImpulseType::CIRCULARIZE and calculate in
-	// 	applyManeuver()
-	addManeuver(gs, go_1, ImpulseType::PROGRADE, DEG2RAD(180), 0.500);
+	addManeuver(gs, go_1, ImpulseType::CIRCULARIZE_RAISING, DEG2RAD(180));
+#else
+	double v_transfer = orbitGetTransferVelocity(go_2->system, el1);
+	addManeuver(gs, go_2, ImpulseType::PROGRADE, DEG2RAD(180), v_transfer);
+	addManeuver(gs, go_2, ImpulseType::CIRCULARIZE_LOWERING, DEG2RAD(0));
+#endif
 
 	return true;
 }
diff --git a/src/orbits.cpp b/src/orbits.cpp
index f2c70ea..465080c 100644
--- a/src/orbits.cpp
+++ b/src/orbits.cpp
@@ -343,6 +343,17 @@ orbitGetTransferVelocity(const TwoBodySystem& sys,
 	return vt - v1;
 }
 
+double
+orbitGetCircVelocity(const TwoBodySystem& sys, bool raise_apoapse)
+{
+	double r = (raise_apoapse) ? sys.r_apoapsis : sys.r_periapsis;
+	double mu = sys.body.mu;
+	double epsilon_target = orbitGetSpecificEnergy(r, mu);
+	double v = orbitGetVelocity(epsilon_target, mu, r);
+
+	return v - sys.sat.v;
+}
+
 
 // internal
 
diff --git a/src/orbits.h b/src/orbits.h
index bbea848..1fab44c 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -258,3 +258,7 @@ orbitGetTimeOfFlight(TwoBodySystem sys, double theta_begin, double theta_end);
 // NOTE return impulse magnitute for Hohmann transfer orbit
 double orbitGetTransferVelocity(const TwoBodySystem& sys,
 	const OrbitalElements& target);
+
+// NOTE: return impulse magnitude for orbit circularization
+double
+orbitGetCircVelocity(const TwoBodySystem& sys, bool raise_apoapse = true);