diff --git a/src/orbits.h b/src/orbits.h
index 0ca1e86..8c03227 100644
--- a/src/orbits.h
+++ b/src/orbits.h
@@ -163,3 +163,5 @@ orbitGetSpecificEnergy(double a, double mu);
 glm::vec2
 polarToRect(double true_anom, double r);
 
+double
+orbitGetTimeOfFlight(system_2body sys, double theta_begin, double theta_end);