From e1c96579184f3c0baa9a801231facc4ce4f5309d Mon Sep 17 00:00:00 2001
From: cinnaboot <cinnaboot@protonmail.com>
Date: Fri, 22 Jul 2022 08:39:18 -0400
Subject: [PATCH] add orbitGetTransferVelocity()

---
 src/game.cpp   |  9 ---------
 src/main.cpp   | 12 +++++++++---
 src/orbits.cpp | 19 ++++++++++++++++++-
 src/orbits.h   |  4 ++++
 4 files changed, 31 insertions(+), 13 deletions(-)

diff --git a/src/game.cpp b/src/game.cpp
index fbd2292..66942a8 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -155,15 +155,6 @@ addManeuver(GameOrbit* orbit,
 
 
 	if (node.impulse_type == ImpulseType::PROGRADE) {
-		double clamped_theta = orbitClampAngle(true_anomaly) + 2 * M_PI;
-		LOGF(Debug, "adding prograde maneuver\n,"
-			"theta: %f,\n"
-			"clamped theta: %f,\n"
-			"dv: %f\n",
-			true_anomaly,
-			clamped_theta,
-			impulse_delta_v);
-
 		node.true_anomaly = true_anomaly;
 		node.impulse_delta_v = impulse_delta_v;
 		node.active = true;
diff --git a/src/main.cpp b/src/main.cpp
index e513e65..dd55a08 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -250,9 +250,15 @@ loadScene(GameState* gs, RenderState* rs)
 
 	gs->coord_overlay = addCoordinateOverlay(rs);
 
-	OrbitalElements el = orbitInit(8000, 0, 0, 0, 0, DEG2RAD(-90));
-	GameOrbit* go_1 = loadOrbit(gs, rs, body, el, rg, "sat_01");
-	addManeuver(go_1, ImpulseType::PROGRADE, DEG2RAD(180), 1);
+	OrbitalElements el1 = orbitInit(8000, 0, 0, 0, 0, DEG2RAD(-90));
+	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");
+
+	double v_transfer = orbitGetTransferVelocity(go_1->system, el2);
+	addManeuver(go_1, ImpulseType::PROGRADE, DEG2RAD(180), v_transfer);
 
 	return true;
 }
diff --git a/src/orbits.cpp b/src/orbits.cpp
index d5be426..f2c70ea 100644
--- a/src/orbits.cpp
+++ b/src/orbits.cpp
@@ -60,7 +60,6 @@ ellipseInitAE(double a, double e)
 OrbitalElements
 orbitInit(double a, double e, double iota, double ohm, double omega, double nu)
 {
-	// TODO: remaining elements: iota, ohm, omega, nu
 	OrbitalElements o = {0};
 	o.a = a;
 	o.e = e;
@@ -326,6 +325,24 @@ orbitGetTimeOfFlight(TwoBodySystem sys, double theta_begin, double theta_end)
 	return tof_end - tof_begin;
 }
 
+double
+orbitGetTransferVelocity(const TwoBodySystem& sys,
+	const OrbitalElements& target)
+{
+	const OrbitalElements& el1 = sys.elements;
+	assert(el1.iota == target.iota);
+	assert(el1.e == 0 && target.e == 0);
+
+	const double mu = sys.body.mu;
+	double a_t = (el1.a + target.a) / 2;
+	double transfer_energy = orbitGetSpecificEnergy(a_t, mu);
+	double r_periapse = el1.a; // NOTE: circular orbit
+
+	double v1 = orbitGetVelocity(orbitGetSpecificEnergy(el1.a, mu), mu, el1.a);
+	double vt = orbitGetVelocity(transfer_energy, mu, r_periapse);
+	return vt - v1;
+}
+
 
 // internal
 
diff --git a/src/orbits.h b/src/orbits.h
index 15625b0..bbea848 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -254,3 +254,7 @@ orbitGetPropagatedTrueAnomaly(TwoBodySystem sys,
 
 double
 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);