Who proposed the orbital transfer method now called a Hohmann transfer orbit?

Walter Hohmann proposed the orbital transfer method now called a Hohmann transfer orbit.

German engineer Walter Hohmann described the method in his 1925 book The Attainability of the Celestial Bodies. A Hohmann transfer uses an elliptical orbit to move between two approximately circular, coplanar orbits with two major engine burns.

For a transfer to a higher orbit, a spacecraft burns to enter the ellipse and later burns again to circularize at the destination. A transfer to a lower orbit reverses the arrangement. The method is fuel-efficient when the starting and destination orbits are suitably aligned.

Real missions may use faster or more complex trajectories because launch windows, gravity assists, inclination changes, and travel time matter. The term therefore describes an idealized two-impulse strategy, not every journey between planets.