Plasmonic Force Propulsion Revolutionizes Nano/PicoSatellite Capability

The results for plasmonic space propulsion are very exciting. Plasmonic force propulsion can significantly enhance the state-of-the-art in small spacecraft position and attitude control by 1-2 orders of magnitude. PFP thrusters are a promising new propulsion system for both cubeSats and other small satellites which can be used as both an RCS and ACS. They require no power, and are extremely low mass and volume. Their low thrust and short switching time makes them ideal for missions where exact distances between spacecraft must be maintained or missions which require extremely high pointing capabilities. A cubeSat employing PFP thrusters would be able to maintain at attitude which was only limited by its attitude sensing instruments. Our results have elucidated the design geometry and configuration for a plasmonic force propulsion thruster, and we have created a conceptual design. A single plasmonic force propulsion thruster should consist of many individual asymmetric nanostructures arranged in a multi-stage, layered, array. Nanostructures should be arranged end-to-end in series to form a multi-stage because a single nanostructure produces very small force and multiple stages are necessary to achieve useable thrust and exit velocity. Multi-stage nanostructures should be layered (i.e., stacked) on top of each other. Each layer should be designed to resonate at a different wavelength within the broadband solar spectrum. This will maximize use of the broadband solar spectrum as shorter wavelength light is absorbed/resonates with top layers, while longer wavelength light passes through to resonate with lower layers. Finally, the multi-stage layers of nanostructures should be repeated in an array to provide increased thrust. Results for a conceptual design of a plasmonic thruster that has 35 layers, 86 array columns, multi-stage length of 5 mm, a 5-cm-diameter light focusing lens, and uses 100 nm polystyrene nanoparticles expelled at a rate of 1x106 per sec would have a thrust of 250 nN, specific impulse of 10 sec, and minimum impulse bit of 50 pN-s. The thruster mass and volume are estimated at 100 g and 50 cm3, respectively. Plasmonic propulsion is ideally suited for proximity and attitude control maneuvers where the total spacecraft delta-V is relatively small (on the order of 1 m/s, compared with high delta-V orbit raising/maintenance maneuvers ~10-100 m/s). Because of its lower dry mass, plasmonic propulsion has a lower wet system mass for missions requiring delta-V of 3 m/s or less. This is ideal for proximity and attitude control where single maneuvers are mm/s, not main propulsion for orbit raising/maintenance. The ultra low thrust of PFP thrusters could also be used for attitude or proximity control on larger satellites. NASA's Laser Interferometer Space Antenna mission to detect gravitational waves requires that the satellites know their positions relative to each other and maintain precise orbits to with respect to each other. The LISA spacecraft will not be formation flying and the distance between them will be constantly changing but needs to be constantly known to within 20 pm over 5,000,000 km. As a result, this mission will require extremely precise reaction control thrusters with thrusts on the order of a micro-newton or less.[22-24] PFP thrusters can position a cubeSat accurately to within 3 pm, meaning they could position a larger satellite with greater precision making them a viable option for the LISA mission or future NASA missions which require greater precision. PFP thrusters are also a viable option for the NASA proposed Stellar Imager or SI mission†. This mission concept consists of 20-30 formation flying "mirror sats" each one a meter diameter mirror precisely placed to within 5 nm over several kilometers. Each mirror sat will also have to control its attitude to less than 0.76 milliarcseconds. The entire Interferometer telescope will allow 0.1 milliarcsecond resolution images of stellar surfaces and the universe in general to be taken.[26-28] It is estimated that PFP thrusters can provide pointing accuracy to within 2 ×10-9 degrees or 0.0072 milliarcseconds or 7.2 microarcseconds for a cubeSat. Each mirror sat will be a 1 m diameter mirror segment only a few times larger than a cubeSat so it is reasonable to expect a "mirror sat" employing PFP thrusters to have pointing accuracies comparable to those predicted for a cubeSat. As a result of our study, the TRL of plasmonic force propulsion has been raised from 1 to 2. We have invented a practical application for the technology: space propulsion. This application is speculative, and our analytical and numerical studies presented here required assumptions without proof or detailed analysis. However, these studies show that plasmonic force propulsion has the potential to provide a 1-2 order of magnitude benefit in the precision pointing and proximity control for small spacecraft.