Masking and Tracklet Building for Space Debris and NEO Observations: The Slovak Image Processing Pipeline

Introduction

Comenius University in Bratislava has acquired a 70 cm Newton telescope (see Figure 1) to set up in its Astronomical and Geophysical Observatory in Modra, Slovakia (further AGO), to observe space debris and other near-Earth objects. The set-up of this observational device consisted of many critical steps such as transportation of the telescope, installation in the cupola, installation of the telescope, acquisition of the necessary computing hardware, such as control unit, encoders, and other equipment, and the development of software (Šilha et al., 2018). As of writing of this chapter, it contains 9 Image Processing Elements (further IPEs):

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  star field identification,

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  image reduction,

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  background estimation and subtraction,

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  objects search and centroiding,

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  astrometric reduction,

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  masking,

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  tracklet building,

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  object identification and

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  data transformation.

The focus of this chapter will be on the description of two specific IPEs – masking and tracklet building.

Figure 1.

AGO70 telescope set up in its dome at Astronomical and Geophysical Observatory in Modra, Slovakia, belonging to the Comenius University Bratislava

Background

The term space debris encompasses all man-made objects which no longer serve any purpose on the Earth’s orbit (Klinkrad, 2006). Large objects orbiting around the Earth belong to this category, such as defunct satellites, rocket bodies used as heavy duty propellers, gloves lost by astronauts during planned spacewalks and other; small objects such as paint flakes, Westford needles, fuel slag, or other (Klinkrad, 2006).

The risk of space debris has risen the moment humanity has become active in space exploration.

The spacecrafts rarely returned back to the Earth. It was more cost-effective to provide fuel only for the outbound journey and leave the unmanned satellites on their former orbit or move them to farther orbits at the end of its life (such as the graveyard orbit). In the same manner, rocket bodies decoupled at higher altitudes are not being actively “cleaned up.” As a result, this led to the increase of space debris population which poses risk to the currently ran missions (ISS manoeuvres to move it out of the trajectory of incoming space debris) as well as for the future missions. Likewise, in the event of re-entry, a sufficiently large object which does not burn up in the atmosphere poses a danger to human lives – should it impact a populated area. Even though many objects are designed to burn up in the atmosphere or re-enter it at the end of their mission due to new regulations, the first step in understanding of the existing space debris is knowing where it comes from.

The biggest contributor of the space debris are fragmentation events which produce debris of various sizes (millimetres to metres). Reasons for fragmentation might be explosions of a satellite because of leftover fuel, damaged pressure tanks, collision with other satellite/debris or even deliberate destruction (Klinkrad, 2006). On the other side of the spectrum, each taking around 10% of the whole population, there is mission-related debris (such as the aforementioned gloves, a screwdriver, and other equipment) and the rocket bodies. An interesting, however small, subset of space debris population is anomalous debris – objects which usually have high area to mass ratio and their origin is not yet known.