TR2019-125

On-Orbit Additive Manufacturing of Parabolic Reflector via Solar Photopolymerization



We consider an alternative solution for the conflicting requirements found in designing a spacecraft antennas, via on-orbit 3D printing. High gain and wide bandwidth depend upon large aperture, while economical orbital deployment dictates lightweight, sturdy, and small structures able to fit (or fold) inside the payload shroud of the launch vehicle. Finally, the antenna must function on orbit; a failed antenna deployment compromises the entire mission. Current solutions are to launch a final-shape unit (compromising on gain, and bandwidth), or to launch a folded antenna (compromising strength and reliability). An alternative solution is to 3D-print the antenna reflector on-orbit, using a photosensitive resin that polymerizes by crosslinking to a stable heat-resistant solid when exposed to UV. As the antenna is produced on orbit, in microgravity, it does not need to be any more robust than necessary to survive orbit correction maneuvers. Thus, it may be much thinner and lighter than a conventional antenna that must survive the stresses of launch and orbital insertion. After printing, the additional motors required for printing then become available for adjusting antenna focus, off-axis aiming, and beam pattern squint control, as well as aiming the antenna beam rapidly on orbit by using non-holonomic motions of the printed antenna against the main spacecraft bus.. As the antenna specifics are not determined until actual printing, it would be possible to pre-launch spare space vehicles and print the antenna with a specific (and possibly asymmetric) beam pattern on demand. To verify the feasibility of free-form 3D printing such structures with adequate shape control and surface smoothness to be used as spacecraft antennas, we built such a head-and-ram free-form 3D printer extruding several candidate resins. While bathing the printer in UV, and using an early candidate low-volatility resin, we successfully freeform-printed in air and earth gravity a 165mm (6.5”) parabolic antenna with an approximately f/1 focal ratio and a measured gain of 28 dB (vs a dipole) in the Ku band (13.5 GHz) with a simple dipole feed. Further resin candidates improved the strength-to-weight ratio by producing a desirable structural foam when extruded under vacuum of approximately 25 millibar.