High-Altitude Long-Endurance (HALE) unmanned air vehicles have been the focus of significant research and development efforts for decades. The state of the art has been advanced to enable higher operational altitudes, longer durations with greater payloads, and increased autonomy. The desire to extend the endurance of these vehicles has led to research in solar-regenerative propulsion systems, which rely on a solar photovoltaic array coupled to an energy storage system. Solar-regenerative propulsion systems could theoretically propel air vehicles for many months.
An intercenter NASA study was performed to benchmark the performance potential of solar regenerative propulsion for operationally useful HALE missions and to quantify the technology improvements required, if any, to enable these missions. The secondary purpose, given a near-term technology-level assumption, was to examine several nonregenerative propulsion options to identify a preferred system concept for the study missions. The NASA Langley Research Center led the team, with participation from the NASA Ames Research Center, the NASA Dryden Flight Research Center, and the NASA Glenn Research Center.
HALE configurations considered in the analysis of alternatives. LH2, liquid hydrogen.
Long description of figure.
An analysis of alternatives and a technology requirements study were conducted for two mission areas utilizing various types of HALE unmanned air vehicles. A hurricane science mission and a communications relay mission provided a set of vehicle requirements that were used to derive 16 potential HALE configurations, including heavier-than-air (HTA) and lighter-than-air (LTA) concepts with both consumable fuel and solar-regenerative propulsion systems.
Analysis proceeded in two phases. During phase I, the 16 potential solutions were analyzed, and the two leading consumable fuel configurations (one each from the HTA and LTA alternatives) were selected for the second phase of the study. One of the HTA solar-regenerative power system configurations was also chosen for additional analysis. Phase II consisted of an operational analysis of the two consumable fuel configurations to derive the required fleet sizes and a life-cycle cost estimate for each potential fleet. An HTA diesel-fueled wing-body-tail configuration emerged as the preferred concept given near-term technology constraints. The cost-effectiveness analysis showed that simply maximizing vehicle endurance can be a suboptimum system solution. In addition, the solar-regenerative power system configuration was utilized to perform both a missions requirements study and a technology development study. Given near-term technology constraints, the solar-regenerative-powered vehicle was limited to operations during the long days and short nights found at higher latitudes during the summer months. Technology improvements are required in the energy-storage-system specific energy and the solar cell efficiency, along with airframe drag and mass reductions, to enable the solar-regenerative vehicle to meet the full mission requirements.
Glenn contact: Lisa L. Kohout, 216-433-8004, Lisa.L.Kohout@nasa.govLast updated: December 14, 2007
Responsible NASA Official:
Gynelle.C.Steele@nasa.gov
216-433-8258
Point of contact for NASA Glenn's Research & Technology reports:
Cynthia.L.Dreibelbis@nasa.gov
216-433-2912
SGT, Inc.
Web page curator:
Nancy.L.Obryan@nasa.gov
216-433-5793
Wyle Information Systems, LLC
