Fall 2020 Seminar Series: Jason Benkoski
Johns Hopkins Applied Physics Laboratory
Host: Jim Spicer
The feasibility of an interstellar mission hinges on the ability to achieve a high escape velocity. 20 AU/yr would be required to reach 500 AU approximately 25 years after launch. Such speeds may be possible by performing a powered gravity assist around the Sun. We propose unconventional approach that simultaneously addresses the need for high specific impulse and close proximity to the Sun–convert the heat of the Sun into usable thrust by passing a propellant through the heat shield. Factoring in both improvements, the escape velocity is predicted to more than double relative to a conventional heat shield with a hydrazine kick stage.
To demonstrate that this technology is compatible with state-of-the-art heat shields, we designed and fabricated a 20 x 20 cm prototype on an additive manufacturing process. It was coated with a yttria-stabilized zirconia coating that can survive 2863 K (versus 2345 K for alumina). The system was tested in a custom-built outdoor test facility. At an illumination equivalent to 20 Suns, the white coating remained below 130°C. Helium propellant flowing at a rate of 1.2 g/s further reduced the temperature to 66°C. A specific impulse on the order of 200 s at 243°C was consistent with expectations. Agreement between experiment and model implies that predictions at higher temperatures hold true and that the coating could survive a perihelion of 2.5 solar radii with a hydrogen flow rate of 15 g/m2-s.