We propose to develop compact absolute wavelength references to weak molecular transitions, which is a challenge characteristic to space-based active sensing. The ASCENDS mission (Active Sensing of CO2 over Nights, Days, and Seasons) will be the first satellite-based mission employing precision laser spectroscopy for active sensing of molecules in space. Although ASCENDS will be first, it is expected that future NASA missions for planetary sensing or Venture class missions will also use active sensing. In Phase I, Vescent will demonstrate the technology to lock seed lasers to weak molecular transitions in a compact form factor. The final Phase II deliverable will be a complete laser system including a master laser and a slave laser locked to the master laser with a tunable frequency offset. The system will be designed so the slave laser can be used to tune across an O2 transition in a compact instrument designed for flight testing. The phase I effort will bring the technology readiness level to TRL 4. In Phase II we will work with NASA to bring the technology to TRL 6 with fully packaged prototypes and environmental testing.