The Large Observatory for X-ray Timing (LOFT), a mission devoted to investigating the behaviour of matter under extreme conditions by means of X-ray timing, was proposed as a candidate M-class mission in response to the 2010 Call for Medium-size Missions for ESA's Cosmic Vision plan. In February 2011, LOFT was one of four missions selected by ESA for a study and assessment phase.
A Science Study Team has been appointed by the Director of Science and Robotic Exploration to support ESA with evaluation and advice during this study phase, with particular emphasis on issues of scientific performance. The team has been reviewing the critical scientific requirements, and developing a detailed science case to be presented at the end of 2013, in the form of a "Yellow Book". The case will be presented in a public meeting in Paris in January 2014.
A study at the ESA Concurrent Design Facility (CDF) was conducted in September 2011 to investigate a technical approach that is feasible within the cost and technical constraints of Cosmic Vision M-class missions. The results of the CDF study were used to prepare an open Invitation to Tender issued to Industry in Autumn 2011. Industrial activities will continue through summer 2013, providing more detailed design data for the mission feasibility.
In parallel, a consortium of institutes has been selected by ESA through an open call to carry out the nationally-funded assessment studies for the instruments and the development of critical technologies for the payload, including detectors, electronics, and collimator elements. These developments are progressing well towards a prototype demonstration module by early 2014.
On 21 January 2014, the five M3 candidate missions were presented to the scientific community, in Paris, France. The ESA Science Programme Committee selected PLATO as the third medium-class mission at their meeting on 19 February 2014.