diff --git a/src/orbits.h b/src/orbits.h
index 5ce8d77..22cdc12 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -15,18 +15,28 @@ struct ellipse_parameters
 	double e;	// NOTE: eccentricity
 	double c;	// NOTE: linear eccentricity
 	double p;	// NOTE: semilatus rectum
+	// FIXME: these should be swapped so f1 is primary focus
 	glm::vec2 f1;	// NOTE: 'vacant' focus
 	glm::vec2 f2;	// NOTE: 'primary' focus
 };
 
 struct orbital_elements
 {
+	// NOTE: classical orbital elements
+	// TODO: would be better to have a higher level composite object so we
+	// 	don't have to store this twice
 	ellipse_parameters ep;
+	// semimajor axis, a
+	// eccentricity, e
 	double iota;	// NOTE: (ι) inclination
 	double omega;	// NOTE: (ω) argument of periapsis
-	double mu;		// NOTE: (μ) gravitational parameter
 	double nu;		// NOTE: (ν) true anomaly
+	// longitude of the ascending node, Ω
+	// argument of periapsis, ω
+	// true anomaly at epoch, θ0
 
+#if 1
+	double mu;		// NOTE: (μ) gravitational parameter
 	double epsilon;	// NOTE: (ε) specific orbital energy, MJ/kg
 	double h;		// NOTE: angular momentum