Manuel Cegarra Polo, UNSW Canberra; Rasit Abay, UNSW Canberra; Steve Gehly, UNSW Canberra; Andrew Lambert, UNSW Canberra; Philippe Lorrain, UNSW Canberra; Sudantha Balage, UNSW Canberra; Melrose Brown, UNSW Canberra; Courtney Bright, UNSW Canberra
Keywords: CubeSat, attitude detection, light curve, BRDF
Abstract:
Identification and characterization of the growing population of resident space objects (RSO) in orbit around Earth is central to current and future Space Traffic Management and Space Situational Awareness activities. Research at UNSW Canberra Space seeks to assist this effort through combining optical measurements of selected RSO with numerical astrodynamics modelling techniques to extend the information that can be inferred about an RSO from its photometric light curve signature.
The initial phase of this research was completed in July 2018, where a collection of photometric light curves was obtained using different nodes of the Falcon Telescope Network (FTN) for the Buccaneer Risk Mitigation Mission (BRMM) 3U CubeSat. The material properties and dynamic attitude motion of BRMM during the FTN observations are known, with rotational body rates commanded from 0.2°/second to 5°/second about multiple combinations of body axes to build a comprehensive database of light curves for analysis. Further variation in the light curve database is obtained from a small number of observations obtained prior to solar panel and antenna deployment.
The Buccaneer Risk Mitigation CubeSat Mission (BRMM) was launched on 18th November 2017. It is a joint mission between University of New South Wales (UNSW) Canberra and Defence Science and Technology Group (DST Group). The BRMM is a risk mitigation mission for the future Buccaneer Main Mission (BMM). The key mission objectives of BRMM are to
1. Undertake and monitor the complex commissioning of a high frequency receiver and antenna to be used for the Jindalee Operational Radar Network (JORN) calibration
2. Acquire accurate flight dynamics data for Astrodynamics and Space Situational Awareness models
3. Further develop Australian expertise in small-satellite development and operations.
The work here reports on the initial analysis of the photometric light curves central to the Space Situational Awareness mission goals.
A set of 70 light curves was obtained during two observational campaigns corresponding to passes over different nodes of the Falcon Telescope Network. Each light curve signature contains a bulk change in intensity over time due to the change in range as BRMM approaches the FTN node on its Low Earth Orbit trajectory. Superimposed on the mean intensity change are characteristic peaks and troughs produced by reflections from individual facets of the spacecraft; the magnitude and frequency of which are highly dependent upon the spacecrafts attitude and body rate. Samples from the light curve database are presented with the attitude data downlinked from the spacecraft telemetry to demonstrate the variation in light curve characteristics with varying body rate and satellite configurations.
Supporting the optical data are numerically simulated light curves, generated by applying the Ashikhmin-Premoze Bidirectional Reflectance Distribution Function (BRDF) Model for the BRMM geometry using a high-fidelity 6DOF orbit propagator supported by the Orekit orbit propagation library for computations related to time systems, coordinate frames, and gravitational perturbations. The performance of the numerical simulation was evaluated by superimposing the attitude profile reported by the spacecraft telemetry on top of the propagated orbit to provide a one-to-one comparison between the measured and simulated light curves for select cases.
A preliminary investigation into the feasibility of using the simulation tool to infer attitude dynamics from a given light curve signature is also presented. A candidate set of simulated light curves was generated by numerically propagating a set of initial attitude states and constant body rates through the observation window. The results were searched to find the case that provided the best fit to the observed light curve. A further study was initiated to investigate the errors introduced by the assumption of a constant body rate throughout the observation for the simulated light data.
Date of Conference: September 11-14, 2018
Track: Non-Resolved Object Characterization