Design of an Gravitational Lens Point Probe Utilizing Self-Guided Beamed Propulsion

Authors: Rohan Jillapalli, MEng, Trent Collins, BS, Chris Limbach, PhD, and Hayden Morgan, MS

Background: A new beam propulsion concept utilizing overlapped laser and particle beams has been proposed with potential for long-range self-guiding and high momentum transfer efficiency. However, compatibility with the propulsion architecture requires a spacecraft that can survive the bombardment of neutral atoms and a high intensity laser. It is, therefore, necessary to develop methods for shielding the spacecraft while efficiently harnessing the momentum transfer. The work presented here describes the design of a spacecraft tailored for a solar gravitational lens mission which is propelled by the self-guided beam concept. 

Objective: The objective of this work is to evaluate a spacecraft design for a solar gravity lens mission in which the spacecraft is propelled by the concept beam propulsion method. 

Methods: A magnetic shielding approach is proposed whereby neutral particles are ionized through a two-step photo-ionization process consisting of excitation by an on-board laser and subsequent ionization by the overlapped self-guiding laser. The ionization of the particles produces a plasma beam which is shielded in similar fashion to the mini-magnetosphere concept. A superconducting coil configuration was designed to generate magnetic field strength sufficient to avoid direct impingement of the plasma beam on surfaces. To protect the craft from the co-propagating laser, high reflectivity mirrors and thermal management systems were designed. 

Results: For this mission, design tools were used to determine a science spacecraft mass budget of 100 kg and an on-board power budget of 250 W. The acceleration and final velocity of the craft are 21.4 m/s^2 and 200 km/s, respectively. Using calculated input values for incident mass and heat fluxes, thermal analysis revealed the spacecraft chassis temperature remained below 395 K. Utilizing the proposed ionization scheme along with the allocated power budget, the ionization model yielded over 90% ionization of the neutral beam. 

Conclusion: The proposed spacecraft design, which utilizes the self-guided particle and laser beam propulsion method, shows promise for withstanding the atomic beam and laser power influx during the acceleration phase of the mission. The lessons learned during the design process also provides value in informing future interstellar missions with a focus on critical areas for mass reduction which include the magnetic shielding and heat rejection subsystems.