Mary Nehls

Electron Radiation Effects on Candidate Solar Sail Material

Solar sailing is a unique form of propulsion in which a spacecraft gains momentum from incident photons. Solar sails are not limited by reaction mass and provide continual acceleration, reduced only by the lifetime of the lightweight film in the space environment and the distance to the Sun. Once thought to be difficult or impossible, solar sailing has come out of science fiction and into the realm of possibility. Any spacecraft using this propulsion method would need to deploy a thin sail that could be as large as many kilometres in extent. The availability of strong, ultra lightweight, and radiation-resistant materials will determine the future of solar sailing. The National Aeronautics and Space Administrations (NASA) Marshall Space Flight Center (MSFC) is concentrating research into the utilization of ultra lightweight materials for spacecraft propulsion. The Space Environmental Effects Team at MSFC is actively characterizing candidate solar sail material to evaluate the thermo-optical and mechanical properties after exposure to space environmental effects. This paper will describe the irradiation of candidate solar sail materials to energetic electrons, in vacuum, in an effort to determine the in-space operational survivability of several candidate sail materials. Results from this research indicate that the candidate sail materials can survive significant doses of electron radiation while under high uniaxial stress.

Survey of Beamed Energy Propulsion Concepts by the MSFC Space Environmental Effects Team

This is a survey paper of work that was performed by the Space Environmental Effects Team at NASA’s Marshall Space Flight Center in the area of laser energy propulsion concepts. Two techniques for laser energy propulsion were investigated. The first was ablative propulsion, which used a pulsed ruby laser impacting on single layer coatings and films. The purpose of this investigation was to determine the laser power density that produced an optimum coupling coefficient for each type of material tested. A commercial off‐the‐shelf multilayer film was also investigated for possible applications in ablative micro‐thrusters, and its optimum coupling coefficient was determined. The second technique measured the purely photonic force provided by a 300W CW YAG laser. In initial studies, the photon force resulting from the momentum of incident photons was measured directly using a vacuum compatible microbalance and these results were compared to theory. Follow‐on work used the same CW laser to excite a stable optic...

Ablative Laser Propulsion Using Multi-Layered Material Systems

Experimental investigations are ongoing to study the force imparted to materials when subjected to laser ablation. When a laser pulse of sufficient energy density impacts a material, a small amount of the material is ablated. A torsion balance is used to measure the momentum produced by the ablation process. The balance consists of a thin metal wire with a rotating pendulum suspended in the middle. The wire is fixed at both ends. Recently, multi-layered material systems were investigated. These multi-layered materials were composed of a transparent front surface and opaque sub surface. The laser pulse penetrates the transparent outer surface with minimum photon loss and vaporizes the underlying opaque layer.

Solar sail material performance property response to space environmental effects

The National Aeronautics and Space Administrations (NASA) Marshall Space Flight Center (MSFC) continues research into the utilization of photonic materials for spacecraft propulsion. Spacecraft propulsion, using photonic materials, will be achieved using a solar sail. A solar sail operates on the principle that photons, originating from the sun, impart pressure to the sail and therefore provide a source for spacecraft propulsion. The pressure imparted to a solar sail can be increased, up to a factor of two, if the sun-facing surface is perfectly reflective. Therefore, these solar sails are generally composed of a highly reflective metallic sun-facing layer, a thin polymeric substrate and occasionally a highly emissive back surface. Near term solar sail propelled science missions are targeting the Lagrange point 1 (L1) as well as locations sunward of L1 as destinations. These near term missions include the Solar Polar Imager and the L1 Diamond. The Environmental Effects Group at NASAs Marshall Space Flight Center (MSFC) continues to actively characterize solar sail material in preparation for these near term solar sail missions. Previous investigations indicated that space environmental effects on sail material thermo-optical properties were minimal and would not significantly affect the propulsion efficiency of the sail. These investigations also indicated that the sail material mechanical stability degrades with increasing radiation exposure. This paper will further quantify the effect of space environmental exposure on the mechanical properties of candidate sail materials. Candidate sail materials for these missions include Aluminum coated Mylar TM, TeonexTM, and CP1 (Colorless Polyimide). These materials were subjected to uniform radiation doses of electrons and protons in individual exposures sequences. Dose values ranged from 100 Mrads to over 5 Grads. The engineering performance property responses of thermo-optical and mechanical properties were characterized. The contribution of Near Ultraviolet (NUV) radiation combined with electron and proton radiation was also investigated.

Spectroscopic Investigations on the Effect of Proton Bombardment of Polyimide

The effect of the radiation component of the space environment on polyimide films is reviewed. Experimental data obtained by electron spin resonance and dynamical mechanical analysis proved that the ionizing radiation generates free radicals with a long lifetime through a dominant chain scission mechanism. The radiation-induced shift of the glass transition of polyimide towards lower values confirms the decrease of the average molecular mass of the polymer during irradiation. The importance of polyimide for space exploration is critically analyzed.