Exploration of the outer planets can be taxing on the ion optics of ion propulsion systems because of the higher power and propellant throughput than the present state-of-the art. Carbon-carbon composite ion optics are an enabling technology extending the life of ion optics operated at high specific impulse, power, and propellant throughput because of their low erosion rates compared to molybdenum ion optics. Large 57cm carbon-carbon composite ion optics have been designed, built, and demonstrated for this purpose. Experience and lessons learned from previous developments have led to the successful development of the NEXIS Ion Optics in one design cycle. Ultrasonic inspection of the first set of accelerator grid laminates uncovered intraply delaminations which were resolved in the second set by using an improved laminate cure cycle to liberate more volatiles from the phenolic laminate. Improved control of carbon-carbon manufacturing processes has resulted in grids with open area fraction control to within ±0.6% of design.
Carbon-carbon composite optics have recently been flown on the Hayabusa mission9. The Carbon-Based Ion Optics (CBIO) project10-12 demonstrated that 30cm CC ion optics can be built at a reasonable cost, operated with good performance, and survive launch loads. The larger size of the NEXIS Ion engine challenged us to take the CC production process to an entirely new scale. The NEXIS Optics have an overall size of 77cm with a 57cm diameter beam, roughly twice the size of the CBIO optics. The lessons learned from CBIO provided a very valuable starting point, but many challenges had to be overcome in order to successfully demonstrate the NEXIS 57cm ion optics. These lessons, combined with special attention to design improvements, have enabled us to build launch-survivable ion optics with long life and good performance.