diff --git a/src/orbits.cpp b/src/orbits.cpp
index f3b21a0..05c7de0 100644
--- a/src/orbits.cpp
+++ b/src/orbits.cpp
@@ -14,8 +14,8 @@ systemInit(TwoBodySystem& system, GravBody gb, OrbitalElements el)
 	system.epsilon = orbitGetSpecificEnergy(system.ep.a, gb.mu);
 	system.h = orbitGetAngularMomentum(system.ep.p, gb.mu);
 	system.orbital_period = orbitGetPeriod(system.ep.a, gb.mu);
-	system.r_apoapsis = system.ep.a - system.ep.c;
-	system.r_periapsis = 2 * system.ep.a - system.r_apoapsis;
+	system.r_periapsis = system.ep.a - system.ep.c;
+	system.r_apoapsis = 2 * system.ep.a - system.r_periapsis;
 }
 
 GravBody