How do we get robots to take self-portraits on Mars? - Perseverance-Ingenuity and Curiosity selfies

The Perseverance rover landed in Jezero crater, Mars, on 18 February 2021. It carried with it a technology demonstration, the Ingenuity helicopter, which has demonstrated the first controlled, powered flight on another planet. This paper describes how an iconic, April 2021 image of the Perseverance rover with the Ingenuity helicopter was designed and executed as the rover was getting ready to deploy the helicopter. WATSON is a camera mounted at the end of the rover's robotic arm and was used to acquire the self-portrait. WATSON is designed to take close up pictures of rocks and regolith on Mars but can also provide views of the terrain. A single image covers a small portion of the scene. In order to a create a mosaic covering the full rover and helicopter, 62 WATSON images were acquired. To allow the images to be mosaicked together, the camera needs to be kept in the same spot. The robotic arm has five degrees of freedom for motion; small changes in orientation can require significant repositioning of the robotic arm joints. To document this, a movie of the arm motion was acquired by the rover's mast-mounted left navigation camera pointed at the WATSON and robotic arm while it was simultaneously moving to acquire the selfie. For the first time, we also captured the sound of the arm motion as it was acquiring the selfie. In the case of the Perseverance selfie with the Ingenuity helicopter, we also had to think about how to position the rover with respect to the helicopter and fit the selfie acquisition into the helicopter prime mission timeline. This paper also describes the history of NASA Mars rover selfies.