Hohmann transfer time
= Hohmann transfer time
{c}
{title2=$t=\pi\sqrt{(r_1+r_2)^3/(8GM)}$}
A <Hohmann transfer orbit> between coplanar <circular Kepler orbits> of radii $r_1,r_2$ traverses half an <elliptic orbit> of <semi-major axis> $a=(r_1+r_2)/2$. <Kepler's third law> therefore gives $t=\pi\sqrt{a^3/(GM)}$. Relative to the initial <orbital period> $T_1$, $t=(T_1/2)[(r_1+r_2)/(2r_1)]^{3/2}$. Radii must be measured from the attracting centre, rather than from its surface.