CubeSats leaving the vicinity of Earth would not have access to GPS or other forms of terrestrial navigation. The Low Mass Radio Science Transponder (LMRST) is a bare-bones, two-way Doppler and ranging transponder, based on well established navigation techniques in use by the Deep Space Network. The proposed LMRST-Sat would be a TRL-raising demonstration mission for a developmental model of the X-Band LMRST exciter. Ka-Band and higher power versions of the instrument are also in development.
In addition to navigation throughout the solar system, LMRST would enable radiometric science such as gravity field determination and planetary atmosphere profiling via radio occultation.