ESA astronaut Tim Peake using ESA's muscle measurement machine Mares on the International Space Station. Tim shared this image, commenting: "No, not testing a new rollercoaster ride - research into muscle atrophy and how this may help patient rehabilitation on Earth".
Tim's six-month mission to the ISS is named Principia, after Isaac Newton’s ground-breaking Naturalis Principia Mathematica, which describes the principal laws of motion and gravity.
He is performing more than 30 scientific experiments for ESA and taking part in numerous others from ESA’s international partners.
ESA and the UK Space Agency have partnered to develop many exciting educational activities around the Principia mission, aimed at sparking the interest of young children in science and space.
More about the Principia mission: http://www.esa.int/principia
More photos from Tim on his flickr photostream: https://www.flickr.com/photos/timpeake