What is the period of a craft orbiting just above the Moon's surface? (Moon: $M = 7.35 \times 10^{22}\ \text{kg}$, $R = 1.74 \times 10^{6}\ \text{m}$; $G = 6.67 \times 10^{-11}\ \text{N m}^2/\text{kg}^2$.)