地球质量为M，质量为m的飞船在地面所受重力mg=GMm/R^2 得：GM=gR^2 飞船在距离地面高度为h的运行轨道，GMm/(R+h)^2=m(4π^2/T^2)(R+h)T=√[4π^2(R+h)^3/(gR^2)]
GMm/(R+h)^2=m(R+h)4π^2/T^2GM/R^2=gT=2π/R√(R+h)^3/g
