  In the first part of this paper, inspired by the geometric method of
Jean-Pierre Marec, we consider the two-impulse Hohmann transfer problem between
two coplanar circular orbits as a constrained nonlinear programming problem. By
using the Kuhn-Tucker theorem, we analytically prove the global optimality of
the Hohmann transfer. Two sets of feasible solutions are found, one of which
corresponding to the Hohmann transfer is the global minimum, and the other is a
local minimum. In the second part, we formulate the Hohmann transfer problem as
two-point and multi-point boundary-value problems by using the calculus of
variations. With the help of the Matlab solver bvp4c, two numerical examples
are solved successfully, which verifies that the Hohmann transfer is indeed the
solution of these boundary-value problems. Via static and dynamic constrained
optimization, the solution to the orbit transfer problem proposed by W. Hohmann
ninety-two years ago and its global optimality are re-discovered.
