NOAA's Geostationary Operational Environmental Satellites (GOES) monitor the solar X-ray activity that enable the NWS Space Environment Center to perform operational specification and forecast of the space environment. The disk-integrated solar X-ray flux has been recorded for more than two decades by the GOES X-ray Sensor (XRS). Since 2003, GOES Solar X-ray Imager (SXI) has provided real-time images of the Sun and lower corona. On 2004 October 15, a sounding rocket launched from White Sands Missile Range marked an important milestone in the first-ever attempt at on-orbit response calibration of GOES X-ray instrumentation. This paper provides an overview of this effort, which includes participation of NOAA, NASA, University of Alaska, and University of Colorado. In addition, results of initial data reduction and analysis for the XRS, SXI, and the sounding rocket are presented.