The purpose of the "L3 Study" is to understand how NASA might participate in ESA's L3 Gravitational Wave mission to inform our engagement through its earliest stages and to prepare for the 2020 decadal survey.
A link to the November 17, 2015 draft version of the charter is available here [PDF].
In November 2013, ESA selected the "Hot and Energetic Universe" as the theme of the second large mission (L2) in its Cosmic Vision program. The theme is to be addressed by an X-ray Observatory led by ESA, to be launched in 2028. On June 27, 2014, ESA announced that the Athena is the mission to concept to fulfill this theme (see http://sci.esa.int/cosmic-vision/54241-athena-to-study-the-hot-and-energetic-universe/). NASA is be working with ESA to define the possible NASA contribution to this ESA-led X-ray mission.
NASA's Physics of the Cosmos (PCOS) Program plans to establish a Science and Technology Definition Team (STDT) to study concepts for a potential reduced-scale strategic spectroscopy X-ray mission with total mission cost less than $1B in FY 2013 constant year dollars. The X-ray Probe (XAP) STDT is being constituted to assist the Astrophysics Division, through its PCOS Program Office, in developing a reference mission concept of high scientific, technical, and programmatic merit that would both address the X-ray science goals and program prioritizations of the Decadal Survey New World New Horizons (NWNH) for X-ray astrophysics and be executable within the Astrophysics Division's notional budget profile. For further details, see the Call for Letters of Application for Membership in the Science and Technology Definition Teams for Reduced Scale X-ray Mission Concepts.
NASA's Physics of the Cosmos (PCOS) Program is initiating two studies to develop mission concepts that could meet some or all of the objectives outlined in the New Worlds, New Horizons decadal report for the areas of X-ray astronomy and gravitational-wave science. The PCOS Program will work with these communities to define mission concepts that achieve these science objectives at multiple price points.
This begins with the release of a formal Request for Information (RFI) on each topic. In parallel, NASA will release an open solicitation inviting members of the science community to participate in a Community Science Team (CST) for the X-ray mission or the gravitational-wave mission. The Program Office will work with each CST to review the RFI responses. In the late Fall workshops, which will be open to the community, will be held to discuss the RFI responses and define the mission concepts that will be studied.
A PCOS Program study team, working with each CST, will identify the requirements relevant to each concept, define the mission configuration options, execute mission design runs at mission design laboratories, refine the mission concepts and draft a mission concept study report. The Program Office will integrate the mission reports in May 2012 for submission to the NRC's Committee on Astronomy and Astrophysics.
Details relevant to each of these architecting studies can be found by following the links below: