Valve from the Ptolemy instrument aboard the Rosetta unmanned spacecraft. Rosetta, a European Space Agency (ESA) mission, launched on 2 March 2004. Its mission is to study the comet Churyumov-Gerasimenko from orbit and to drop the lander Philae onto the surface. Rosetta is scheduled to encounter the comet in November 2014.
© Science Museum / Science & Society Picture Library