Where Did They Come From, Where Did They Go: Grazing Fireballs

For centuries extremely long grazing fireball displays have fascinated observers and inspired people to ponder about their origins. The Desert Fireball Network is the largest single fireball network in the world, covering about one third of Australian skies. This expansive size has enabled us to capture a majority of the atmospheric trajectory of a spectacular grazing event that lasted over 90 s, penetrated as deep as ∼58.5 km, and traveled over 1300 km through the atmosphere before exiting back into interplanetary space. Based on our triangulation and dynamic analyses of the event, we have estimated the initial mass to be at least 60 kg, which would correspond to a 30 cm object given a chondritic density (3500 kg m-3). However, this initial mass estimate is likely a lower bound, considering the minimal deceleration observed in the luminous phase. The most intriguing quality of this close encounter is that the meteoroid originated from an Apollo-type orbit and was inserted into a Jupiter-family comet (JFC) orbit due to the net energy gained during the close encounter with Earth. Based on numerical simulations, the meteoroid will likely spend ∼200 kyr on a JFC orbit and have numerous encounters with Jupiter, the first of which will occur in 2025 January-March. Eventually the meteoroid will likely be ejected from the solar system or be flung into a trans-Neptunian orbit

Recreating the OSIRIS-REx Slingshot Manoeuvre from a Network of Ground-Based Sensors

Optical tracking systems typically trade-off between astrometric precision and field-of-view. In this work, we showcase a networked approach to optical tracking using very wide field-of-view imagers that have relatively low astrometric precision on the scheduled OSIRIS-REx slingshot manoeuvre around Earth on September 22nd, 2017. As part of a trajectory designed to get OSIRIS-REx to NEO 101955 Bennu, this flyby event was viewed from 13 remote sensors spread across Australia and New Zealand to promote triangulatable observations. Each observatory in this portable network was constructed to be as lightweight and portable as possible, with hardware based off the successful design of the Desert Fireball Network. Over a 4 hour collection window, we gathered 15,439 images of the night sky in the predicted direction of the OSIRIS-REx spacecraft. Using a specially developed streak detection and orbit determination data pipeline, we detected 2,090 line-of-sight observations. Our fitted orbit was determined to be within about 10~km of orbital telemetry along the observed 109,262~km length of OSIRIS-REx trajectory, and thus demonstrating the impressive capability of a networked approach to SSA

Autonomous Triangulation and Dynamic Modelling of Uncooperative Space Objects using a Distributed Network of Remote Sensors

This doctorate thesis describes improvements and novel approaches to triangulation, dynamic modelling, and orbit determination of observed meteoroids from fireball networks. Additionally, building on, and inspired by the distributed network approach utilised within the fireball community around the world, herein describes a new technique to space surveillance and tracking with the use of multiple, wide field-of-view, relatively low resolution, ground-based sensors

3D meteoroid trajectories

Meteoroid modelling of fireball data typically uses a one dimensional model along a straight line triangulated trajectory. The assumption of a straight line trajectory has been considered an acceptable simplification for fireballs, but it has not been rigorously tested. The unique capability of the Desert Fireball Network (DFN) to triangulate discrete observation times gives the opportunity to investigate the deviation of a meteoroid's position to different model fits. Here we assess the viability of a straight line assumption for fireball data in two meteorite-dropping test cases observed by the Desert Fireball Network (DFN) in Australia – one over 21 s (DN151212_03), one under 5 seconds (DN160410_03). We show that a straight line is not valid for these two meteorite dropping events and propose a three dimensional particle filter to model meteoroid positions without any straight line constraints. The single body equations in three dimensions, along with the luminosity equation, are applied to the particle filter methodology described by Sansom et al. (2017). Modelling fireball camera network data in three dimensions has not previously been attempted. This allows the raw astrometric, line-of-sight observations to be incorporated directly. In analysing these two DFN events, the triangulated positions based on a straight line assumption result in the modelled meteoroid positions diverging up to 3.09 km from the calculated observed point (for DN151212_03). Even for the more typical fireball event, DN160410_03, we see a divergence of up to 360 m. As DFN observations are typically precise to < 100 m, it is apparent that the assumption of a straight line is an oversimplification that will affect orbit calculations and meteorite search regions for a significant fraction of events