Paper ID: 551 The 16th International Conference on Space Operations 2020

Guidance, Navigation, and Control (GNC) (7) GNC - 1 ”Flight Dynamics and Navigation - I” Oral Presentation (1)

Author: Mr. Erik Lessac-Chenen Kinetx, Inc., United States, [email protected]

Ms. Coralie Adam Kinetx, Inc., United States, [email protected] Mr. Derek Nelson Kinetx, Inc., United States, [email protected] Mr. John Pelgrift Kinetx, Inc., United States, [email protected] Mr. Sahr Eric Kinetx, Inc., United States, [email protected] Ms. Leilah McCarthy Kinetx, Inc., United States, [email protected]

OPTICAL NAVIGATION OPERATIONS PREPARATIONS FOR THE TROJAN-ASTEROID MISSION

Abstract The Lucy Jupiter-Trojan asteroid mission will launch in October of 2021, setting out for the first-ever exploration of the Trojan asteroid clusters at the Jupiter-Sun L4 and L5 points. Between June 2027 and November 2028 Lucy will the conduct five consecutive close flybys in the L4 cluster. In 2033, it will return to the Jupiter Trojans to conduct one more close flyby: the Patroclus/Meonetius binary asteroid system in the L5 cluster. In 2025, enroute to the Trojans, Lucy will perform a flyby of the main belt asteroid 52246 Donaldjohanson. Robust optical navigation (OpNav) capabilities, techniques, and planning will be essential to the navigation efforts of the Lucy mission, enabling precise and accurate navigation relative to the flyby targets. Due to the geometry of the flyby encounters, any improvement in B-plane targeting and time of flight (TOF) uncertainty must be obtained using optical navigation. Since most Trojans do not have known moons to provide parallax information, TOF information must be derived from single-body OpNav combined with a priori Hubble Space Telescope-based or ground-based information. To these ends, a concept of operations, and expanded OpNav planning and operations tools have been developed to meet the specific challenges the Lucy mission presents. Additionally, rigorous OpNav operations simulations are ongoing to verify these strategies and procedures. This paper will describe these efforts and results.

Optical Navigation, a sub-function of the Flight Dynamics System (FDS), uses information extracted from spacecraft images to assist in the orbit determination (OD) of the spacecraft. The primary tool for OpNav on the Lucy mission is the KinetX Star-Based Image Processing Suite (KXIMP)[1], which will be utilized for star-based instrument pointing and centroid-based navigation. The objective of centroid-based OpNav is to determine the position of the target body center relative to inertial star positions. The iner- tial camera pointing and observed location of the Trojan center of mass (CM) are derived using a variety of algorithms available in KXIMP[1]. The OD estimation filter minimizes the difference between observed and predicted (pixel, line) body centers, along with other radiometric tracking data measurements. These OpNav capabilities and tools maintain substantial mission heritage, having been employed successfully during the [2] and Ultima Thule[3] encounters in 2015 and 2018, and currently on the

1 OSIRIS-REx mission to Bennu[4].

The Lucy Trojan flybys present specific challenges to the OpNav process and planning. Because of the short timeframe of the four 2027 encounters, a shared, standard, and compact encounter timeline for all Lucy flyby OpNav campaigns was developed, as well as a combined overlapping timeline for the Eurybates and Polymele encounters which occur just one month apart. These encounter timelines ensure that navigation, maneuver, and scientific requirements are met for all encounters.

The trajectory that makes possible four consecutive flybys in fifteen months leaves little flexibility in the approach geometry and timing. High phase angle approaches and little-to-no a priori knowledge on the Trojan shapes will impact OpNav performance, requiring extensive simulation, analysis, and charac- terization. Additionally, the Lucy Trojan targets include one known binary system, as well as possible unknown binaries. These binary systems require OpNav procedures for the mitigation of reduced bright- ness, possible binary self-occlusion, and binary-orbit phasing issues such as strobing. Because an unknown binary might not become apparent until late in the approach, and uncertainties in mean anomaly of the known binary can remain, rigorous analysis of mission impact of binary systems on OpNav center-finding capabilities and OD effects must be done through simulations and Operational Readiness Tests (ORTs).

To meet these challenges, OpNav planning tools to be utilized during the pre-launch, cruise, and pre- approach phases have been developed. The OpNav Opportunity (OpOpp) and Fly-Point-Shoot (FPS) tools analyze imaging opportunities and coverage under trajectory, ephemeris, and pointing uncertainties; a Signal-To-Noise Ratio (SNR) calculator for the Trojan bodies determines the number and exposure- times of images needed at each epoch. Time-frames for in-flight planning of imaging parameters such as epoch and exposure-time have been established to ensure OpNav can safely and effectively respond to changing conditions from increased knowledge gained during the approach phase.

The Lucy OpNav team performs encounter simulations to better understand its capabilities for the six encounters. Patroclus/Meonetius binary encounter simulations are run to characterize OpNav and OD capabilities for a known binary system, and thread tests for unknown binary systems will be conducted. Detailed analysis of center-finding performance during all encounters is done to characterize OpNav cen- terfinding capabilities under varying a priori knowledge.

This paper will discuss the details of the Lucy OpNav ConOps and capabilities. Details of the plan- ning tools, encounter timelines, and simulation results will be presented. This material is based upon work supported by the National Aeronautics and Space Administration under Contract 80GSFC18C0070 through the Discovery Program.

[1] C. D. Jackman and P. J. Dumont, “Optical Navigation Capabilities for Deep Space Missions”, Proceedings of the AAS/AIAA Space Flight Mechanics Meeting, February 2013.

[2] C. D. Jackman, D. S. Nelson, W. M. Owen, M. W. Buie, S. A. Stern, H. A. Weaver, L. A. Young, K. Ennico, C. B. Olkin, “New Horizons Optical Navigation On Approach To Pluto”, American Astronautical Society 29th Guidance and Control Conference

[3] D. S. Nelson, E. J. Lessac-Chenen, J. Y. Pelgrift, C. D. Adam, F. J. Pelletier, J. A. Bauman, D. R. Stanbridge, J. T. Fischetti, M. J. Salinas, J. R. Spencer, S. B. Porter, M. W. Buie, M. E. Holdridge, H. A. Weaver, C. B. Olkin, S. A. Stern, “Optical Navigation for New Horizons’ Flyby of Kuiper Belt Object (486958) 2014 MU69”, AAS/AIAA Astrodynamics Specialist Conference

[4] P. G. Antreasian, M. C. Moreau, C. D. Adam, A. French, J. Geeraert, K. M. Getzandanner, D. E. High- smith, J. M. Leonard, E. Lessac-Chenen, A. Levine, J. McAdams, L. McCarthy, D. Nelson, B. Page, J. Pelgrift, S. Rieger, E. Sahr, D. Wibben, B. Williams, K. Williams, D. Lauretta, and T. O.-R. Team, “Early Navigation Performance of the OSIRIS-REx Approach to Bennu”, American Astronautical Society, 2019.

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