High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) will be a medium sized jet aircraft capable of operating in the upper troposphere to lower stratosphere, highly modified to carry a substantial scientific research payload. It will be capable of transporting observational scientists over greater rantes and for longer duration than has previously been possible. HIAPER will be designed to serve a broad cross-section of the geosciences community and will fill a major gap in the current U.S. airborne research fleet.