This proposal would develop pneumatic propulsion for a launch assist system. The Closed-End Launch Tube (CELT) system uses an elevated air pressure to push a moving piston down a cylinder. The piston is coupled to a low-friction sled riding directly above the cylinder, with the sled carrying the payload Reusable Launch Vehicle (RLV). The CELT system would be propelled by medium-pressure (150 pounds per square inch gage [psig]) air storage chambers, both stationary and on the moving piston, to raise air pressure directly behind the piston. Commercially available compressors can fill the air storage chambers in less than 2 hours. We would propose to start the RLV’s engines to gain additional thrust and confirm proper engine operation prior to activating the launch assist system.

The system is attractive because of its highly efficient energy utilization employing existing technology and materials. The technique can be scaled to much larger payloads by simply increasing the diameter of the cylinder. The design incorporates fail-safe low-g abort by venting the gas supply behind the piston, combined with a preset closed chamber ahead of the piston to develop gas pressure and brake the vehicle without excessive g loading. The CELT can reduce operational costs and complexity and can provide significant payload increases on RLV’s without the long, expensive development of other launch assist projects.

The rates of gas introduction, along with the rarefaction produced behind the moving piston and the compression wave in front of it, are challenges to the concept. The current project will advance the technology by modeling the system fluid dynamics and forces and testing the model against a laboratory-scale pneumatic tube.

A 3-inch-diameter, 1000-foot system is being designed and constructed to allow direct experimental verification of the tradeoffs for evacuation of the tube ahead of the piston, the effects of gas injection from the piston, and gas composition and temperature effects on terminal velocity in a practical pneumatic drive system. Telemetry from the piston will record acceleration and cylinder pressures near the piston, while pressure transducers and optical sensors on the pneumatic tube provide far-field pressure, position, time, and velocity information.

The acceleration tube is constructed from commercial sanitary tubing, with the inside surface polished to a 20-microinch finish. The acceleration and braking gas storage containers are standard ASME 200-psig compressed-air vessels. The controls are pneumatic with electronic initiation via a LabView data acquisition and control system. During the expected 2-second experiments, the 16 pressure transducers and 14 optical sensors will provide continuous pressure data and discrete position and velocity data versus time.

Results will be used to verify and upgrade the model, benchmark the numerical solutions, and predict the performance of the 1-percent demonstrator and the full-scale system. Selection would be made for the best terminal velocity design for a practical, scalable system.