A deep$-$space probe moves away from Earth with a speed of $0\mathrm{.}86$ c$.$ An antenna on the probe requires $3\mathrm{.}9$ s $($probe time$)$ to rotate through $1\mathrm{.}2$ rev. How much time is required for $1\mathrm{.}2$ rev according to an observer on Earth? Answer in units of s$.$