A method an apparatus for selecting a forward link and return link data rate for a constant power, variable data rate two-way, mobile satellite communications link. The forward link and return link signal strength (in the form of carrier power to noise power spectral density ratio) is measured, cataloged, and the values are used for the data rate selection. In addition, a ping can be sent by the network operation center to the mobile unit and the response to the ping is used for updating the information of both forward link and return link signal strength, so the chance of wrong data rate selection can be reduced. Multiple re-transmission attempts combined with gradually increased re-transmission margin ensures the proper data rate decision can be eventually achieved even with occasionally inaccurate signal strength information.