The Valkyrie humanoid robot was built at NASA Johnson Space Center with leadership from Nic Radford and Rob Ambrose. The Human Centered Robotics Lab at UT Austin provided expertise in the design of rotary series elastic actuators and inspiration for the design of the linear series elastic actuators based on the UT-SEA design of our student Nick Paine. UT Austin also provided expertise on developing robust force controllers of the series elastic actuators and thorough testing on torque tracking and joint position impedance control.