diff --git a/src/main.cpp b/src/main.cpp
index df76f55..eba061b 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -79,12 +79,12 @@ updateSatellitePosition(entity& satellite)
 	entSetWorldPosition(satellite, xform * glm::vec4(v.x, v.y, v.z, 1));
 }
 
-// NOTE: use validateEllipse(orbit.ep) before calling to avoid failing
+// NOTE: use ellipseValidate(orbit.ep) before calling to avoid failing
 //	assertions
 void
 updateOrbit(orbital_elements& orbit, ellipse_3d& e3d, entity& ellipse_entity)
 {
-	orbit.ep = constructEllipseAE(orbit.ep.a, orbit.ep.e);
+	orbit.ep = ellipseInitAE(orbit.ep.a, orbit.ep.e);
 	ellipse3DUpdate(orbit.ep, e3d);
 
 	for (uint i = 0; i < e3d.vert_count; i++)
@@ -133,14 +133,15 @@ postFrameCallback(render_state* rs)
 	if (!ellipsesEqual(c_orb.ep, g_orbit.ep)) {
 		// NOTE: handle the case where semimajor axis lowered with low
 		//	eccentricity would fail validation
-		if (c_orb.ep.a < g_orbit.ep.a && c_orb.ep.a > 0
+		if (c_orb.ep.a < g_orbit.ep.a
+			&& c_orb.ep.a > 0
 			&& c_orb.ep.e == g_orbit.ep.e)
 		{
 			c_orb.ep.b = c_orb.ep.a * sqrt(1 - pow(c_orb.ep.e, 2.0));
 		}
 
-		if (validateEllipse(c_orb.ep)) {
-			c_orb.ep = constructEllipseAE(c_orb.ep.a, c_orb.ep.e);
+		if (ellipseValidate(c_orb.ep)) {
+			c_orb.ep = ellipseInitAE(c_orb.ep.a, c_orb.ep.e);
 			g_orbit.ep = c_orb.ep;
 			entity& ellipse_entity = rs->render_groups[0].entities[0];
 			updateOrbit(g_orbit, g_ellipse3d, ellipse_entity);
@@ -185,7 +186,7 @@ main()
 
 	// NOTE: semi-major axis in km, eccentricity, gravitational parameter
 	g_orbit = orbitInit(26564.5, 0.7411, 398601.68);
-	ellipse_parameters ep = constructEllipseAB(g_orbit.ep.a, g_orbit.ep.b);
+	ellipse_parameters ep = ellipseInitAB(g_orbit.ep.a, g_orbit.ep.b);
 
 	// TODO: (renderer) this needs to be more convenient
 	shader_wrapper sw = { SIMPLE_SHADER, nullptr, rs->simple_shader };
@@ -193,7 +194,7 @@ main()
 	rs->render_group_count = 1;
 
 	entity& ellipse_entity = rs->render_groups[0].entities[0];
-	g_ellipse3d = constructEllipse3D(ep, 256);
+	g_ellipse3d = ellipseInit3D(ep, 256);
 	simple_mesh* sm = constructEllipseMesh(g_ellipse3d, glm::vec3(255, 0, 255));
 	entInitMesh(ellipse_entity, sm, GL_LINE_LOOP);
 	entRotate(ellipse_entity, (float) M_PI_2, glm::vec3(1, 0, 0));
diff --git a/src/orbits.cpp b/src/orbits.cpp
index a55f522..cb45c2a 100644
--- a/src/orbits.cpp
+++ b/src/orbits.cpp
@@ -3,7 +3,7 @@
 
 
 ellipse_parameters
-constructEllipseAB(double a, double b)
+ellipseInitAB(double a, double b)
 {
 	assert(a > 0 && b > 0 && a >= b);
 	ellipse_parameters ep = { a, b };
@@ -16,15 +16,15 @@ constructEllipseAB(double a, double b)
 }
 
 ellipse_parameters
-constructEllipseAE(double a, double e)
+ellipseInitAE(double a, double e)
 {
 	assert(e >= 0 && e < 1);
 	double b = a * sqrt(1 - pow(e, 2.0));
-	return constructEllipseAB(a, b);
+	return ellipseInitAB(a, b);
 }
 
 bool
-validateEllipse(const ellipse_parameters& ep)
+ellipseValidate(const ellipse_parameters& ep)
 {
 	// TODO: find out why satellite position gets wonky with orbit
 	// 	eccentricity > 0.995 while passing through true anom = 0.
@@ -45,7 +45,7 @@ ellipsesEqual(ellipse_parameters& e1, ellipse_parameters& e2)
 }
 
 ellipse_3d
-constructEllipse3D(ellipse_parameters ep, uint vert_count)
+ellipseInit3D(ellipse_parameters ep, uint vert_count)
 {
 	assert(ep.a > 0 && ep.b > 0 &&
 		ep.a >= ep.b &&
@@ -70,7 +70,7 @@ orbitInit(double a, double e, double mu)
 void
 orbitUpdate(orbital_elements& o, double a, double e)
 {
-	o.ep = constructEllipseAE(a, e);
+	o.ep = ellipseInitAE(a, e);
 	o.epsilon = orbitGetSpecificEnergy(o.ep.a, o.mu);
 	o.h = orbitGetAngularMomentum(o.ep.p, o.mu);
 }
diff --git a/src/orbits.h b/src/orbits.h
index 3dc2a8e..5ce8d77 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -34,24 +34,59 @@ struct orbital_elements
 	glm::vec3 pos;	// NOTE: true anomaly in 3d with ep.f2 at origin
 	double v;		// NOTE: velocity magnitute
 	double gamma;	// NOTE: (γ) flight path angle
+#endif
 };
 
 struct ellipse_3d
 {
+	// TODO: would be better to have a higher level composite object so we
+	// 	don't have to store this twice
 	ellipse_parameters ep;
 	glm::vec3* vertices;
 	uint vert_count;
 };
 
+struct gravitational_body
+{
+	double mu;		// NOTE: (μ) gravitational parameter
+	double radius;	// NOTE: radius of ideal sphere representing the body
+	// double r_atmos;	// TODO: bodies w/ atmosphere
+};
+
+struct satellite
+{
+	glm::vec3 position;
+	glm::vec3 velocity;
+	// double theta;	// NOTE: true anomaly
+	// double r;		// NOTE: radius magnitude
+	// double gamma;	// NOTE: (γ) flight path angle
+	// double v;		// NOTE: velocity magnitute
+};
+
+// NOTE: top level composite for 2 body system
+struct system
+{
+	gravitational_body grav_body;
+	satellite sat;
+	//ellipse_parameters ep;
+	ellipse_3d e3d;
+	orbital_elements elements;
+
+	double epsilon;		// NOTE: (ε) specific orbital energy, MJ/kg
+	double h;			// NOTE: angular momentum
+	double r_apoapsis;	// NOTE: apoapse distance from body center
+	double r_periapsis;	// NOTE: periapsis distance from body center
+};
+
 
 ellipse_parameters
-constructEllipseAB(double a, double b);
+ellipseInitAB(double a, double b);
 
 ellipse_parameters
-constructEllipseAE(double a, double e);
+ellipseInitAE(double a, double e);
 
 bool
-validateEllipse(const ellipse_parameters& ep);
+ellipseValidate(const ellipse_parameters& ep);
 
 bool
 ellipsesEqual(ellipse_parameters& e1, ellipse_parameters& e2);
@@ -59,7 +94,7 @@ ellipsesEqual(ellipse_parameters& e1, ellipse_parameters& e2);
 // NOTE: create vertices for a 3d ellipse
 // NOTE: all vertices are in the x/y plane with z = 0
 ellipse_3d
-constructEllipse3D(ellipse_parameters ep, uint vert_count);
+ellipseInit3D(ellipse_parameters ep, uint vert_count);
 
 void
 ellipse3DUpdate(ellipse_parameters ep, ellipse_3d& e3d);
diff --git a/tests/orbit_test.cpp b/tests/orbit_test.cpp
index 1963fd4..21df5a4 100644
--- a/tests/orbit_test.cpp
+++ b/tests/orbit_test.cpp
@@ -22,7 +22,7 @@ TEST_CASE("orbit propagation", "[orbits]")
 	orbital_elements orbit = {};
 	double a = 26564.5; // kilometers
 	double e = 0.7411;
-	ellipse_parameters ep = constructEllipseAE(a, e);
+	ellipse_parameters ep = ellipseInitAE(a, e);
 	orbit.ep = ep;
 	double initial_anom = 260 * M_PI / 180; // radians
 	unsigned int time_step = 60 * 50; // seconds