2015 IR&D Annual Report

Stratospheric Compressor for Lighter-than-Air Vehicles, 15-R8575

Principal Investigators
James Noll
Grant Musgrove

Inclusive Dates: 07/13/15 – Current

Background — A vehicle with trajectory control and persistent operation capabilities up to 120,000 feet altitude does not currently exist and is a game-changing technology sought for military and scientific applications. The extremely low air density and steady winds at these altitudes make station-keeping with a single aircraft or lighter-than-air (LTA) vehicle impractical. However, a network of LTA vehicles with limited trajectory control can transit through an area of interest and achieve persistence over an area as a collective group. Low power directional control of the LTA vehicle can be achieved by exploiting wind differences at different altitudes. Technology that enables efficient movement of air into and out of an LTA vehicle’s ballonet allows repeatable altitude changes for long duration flights.

Approach — The objective of this research is to determine and characterize the best method to add air mass to an LTA vehicle for altitude and trajectory control applications in the stratosphere. A matrix of performance parameters for compressors that facilitate altitude control of LTA vehicles was generated. Preliminary design concepts for the compressor aerodynamic flow path were developed using a one-dimensional analysis. The results of this preliminary design were used to formulate initial requirements and size the supporting systems for the stratospheric compressor. A review of the overall system feasibility concluded that further study was warranted in a second phase of study.

In Phase II, the preliminary aerodynamic flow path developed will be simulated in three-dimensional space using computational fluid dynamics (CFD). The performance capabilities will be revised and the derived requirements for the supporting systems will be updated. An integrated modeling tool for sizing the compressor and its subsystems will be created, with particular emphasis on overall compressor system mass and power requirements as a function of altitude and desired air flow rate. In parallel, a preliminary design for test equipment and procedures to assess compressor performance characteristics will be generated.

Accomplishments — In Phase I of this project, preliminary compressor designs for buoyancy control at high altitudes were created. Feasibility of the designs was assessed based on mass and power of compressor systems. Findings in Phase I indicate there are viable compressor designs for achieving trajectory control of an LTA platform suited for small commercial and military payloads intending to fly over specific targets, as well as large scientific payloads with capability to steer away from population centers. Phase II is in progress and will validate assumptions made in the initial aerodynamic modeling, perform more rigorous study of heat management, and develop test methodology for performance evaluation of stratospheric compressor systems.

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