Preliminary asteroid deflection mission design for 2017 PDC using neutral beam propulsion

摘要

The surprise Chelyabinsk air burst event in 2013 that caused significant building damage and injuries demonstrated to the public that there is a near-term pressing need to develop a robust portfolio of asteroid deflection techniques that can be applied to asteroids with varying size, spectral type, and time until impact. The neutral beam for asteroid control (NBAC) technology is a globally neutral plasma thruster that seeks to fill the operational gap between high impulse and slow push asteroid deflection methods. It is unlike other propulsive methods in that it does not tether to the asteroid or expel charged ion beams. Additionally, NBAC can be used to modify both the spin state and trajectory of an asteroid. In this work, NBAC's performance is discussed for a range of asteroid sizes and spectral types for de-spin and deflection using the orbit of the hypothetical asteroid 2017 PDC. The analysis assumes that several NBAC-equipped spacecraft are deployed, each with 10 keV neutral beam emitter. The achieved deflection and the applicability of NBAC to a deflection campaign is presented. Calculations for achieved deflection are done using the General Mission Analysis Tool with gravitational perturbations from major bodies included. Loss of a spacecraft during deflection and its effect on mission success is also investigated. One major requirement in this work is adaptability of the NBAC-based concept to deflection campaigns where the asteroid has not been fully characterized. This work demonstrates how uncertainty in asteroid composition is factored into propellant and deflection time requirements for NBAC. Assuming one perihelion passage, NBAC can successfully deflect 2017 PDC given a size range of 100-150 m for S, C, B, and Xc-type asteroids. Failure of a one or two NBAC-carrying spacecraft during deflection does not preclude successful deflection for a set of sizes and densities. NBAC can be used to arrest asteroid rotations through hovering spacecraft that track the asteroid in its rotating frame. We present a general formulation for angular momentum of a monolithic, single boulder asteroid considering both its rotational and orbital angular momentum. We find that while arresting the rotation for this type of asteroid, it is likely to change its orbit as well. A variety of stable and unstable asteroid rotation states for the asteroid size are used. Propellant usage and time required to fully de-spin representative asteroids will be presented. Additionally, the time required for total de-spin will be compared to the time required for partial arrest. Partial arrest of unstable spinners is possible under mission constraints for a set of asteroid sizes and densities. Additionally, total arrest can be achieved for less than 60 kg per spacecraft for a four-spacecraft NBAC system.