A shape model – what’s that?

Today, a new shape model of Rosetta’s comet is released by ESA. Some of you might immediately know what this is and how you might use it, and others will wonder ‘what’s that?’  This blog post, which has been prepared with the help of experts from the Rosetta Flight Dynamics team, explains what a shape model is, how it is created, and what you could use it for. At the most basic level, a shape model is a geometrical representation of an object. Shape models are commonly used in computer programmes where the motion or change of shape of a complex object needs to be represented. Applications can vary from medical imaging of organs, creating characters in cartoons and computer games, or — closer to home (at least for the Rosetta team) — modelling how the surface of a comet changes as it rotates. Back in the summer of 2014, the Rosetta mission operations and flight dynamics teams were faced with the mammoth task of figuring out how to approach and navigate around Comet 67P/Churyumov-Gerasimenko. After a year of marvellous close-up views of this comet it’s easy to forget that early models of the comet bore very little resemblance to the reality. The first hints that the comet might not have a simple shape came in July 2014, when images taken by the scientific camera, OSIRIS, revealed a double-lobed object. It was soon clear that navigation would be a challenge, and an important factor in successful navigation would be a robust shape model. The first, crude shape models were constructed by the flight dynamics team, using a method called silhouette carving. For this, software is used to map the silhouette of the comet, as seen in NavCam images, onto a large ‘virtual’ body and the parts of the body that […]

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