Fibertek proposes to develop a spaceflight prototype 1940 nm, 100 W thulium (Tm) laser suitable for NASA spaceflight and long-duration unmanned aerial vehicle (UAV) missions. The proposal is innovative because it demonstrates 100 W of polarization maintaining (PM) performance at 1940 nm. We expect a 2x to 3x improvement in efficiency compared to available commercial off-the-shelf (COTS) unpolarized Tm fiber lasers, and the laser will be packaged for high reliability for spaceflight operation. This SBIR leverages commercial Tm laser technology, published scientific test data, available optical components, and Fibertek's validated Tm fiber laser model. A spaceflight 100 W PM Tm laser is enabling and provides a path to space for a pulsed, Q-switched 2 um Ho:YLF laser with up to 80 mJ/pulse at 100-200 Hz. Lidar performance design studies from a low earth orbit (LEO) satellite indicate that 80 mJ of pulsed 2 um energy enables the simultaneous measurements of CO2 and water vapor using Integrated Path Differential Absorption (IPDA) and global wind light detection and ranging (lidar). NASA laser experiments have shown the 100 W of 1940 nm peak pump power is needed to generate 80 mJ/pulse.