The life cycle of a new science mission begins with an assessment study. During the assessment phase, of typically one year, we analyse the complete mission, including the launcher, mission profile, the spacecraft, the science payload, and the ground segment. We establish the science requirements and derive from that a payload suite to achieve these requirements. This process includes the following:

• Feasibility of achieving the science objectives
• Engineering risk and cost assessment
• Engineering trade-offs in view of maximising the scientific return for a given mission budget
• Identification of technological drivers and needs to be addressed

The phase includes internal as well as industrial activities. The later are usually in the form of two parallel competitive studies, leading to the definition of a mission baseline.

The assessment phase is concluded with the final results of the industrial studies, together with the definition of a reference payload complement, of a technology plan and of a complete risk and programmatic assessment.

The Cosmic Vision 2015-2025 assessment studies presently being conducted under SRE-FA responsibility are the following:

• The International X-ray Observatory (IXO), formerly known as XEUS, an L-class candidate in cooperation with JAXA and NASA, representing the potential follow on mission to XMM-Newton.
• EUCLID, a dark universe observatory proposed as an M-class candidate.
• PLATO, Planetary Transit and Oscillations of Stars, also an M-class candidate.
• SPICA, Space IR Telescope for Cosmology and Astrophysics, a JAXA-led mission to which ESA would contribute within an M-class envelope.

Euclid spacecraft. Credit: ESA	Euclid optical design. Credit: ESA
PLATO. Credit: ESA	SPICA telescope assembly. Credit: ESA

Following the selection of the mission candidates carried out by the Advisory Structure of the Science Directorate in October 2007, the study activities have been started, leading to the following main steps:

• Identification of the science requirements by the Science study team and study scientist (Q4/07, Q1/08).
• Identification of a reference payload (also referred to as a model payload) to be used in the preliminary system level studies (and to be later replaced by the actual mission payload, following the release of the related Announcement of Opportunity) (Q4/07, Q1/08).
• Internal ESA assessment study (phase-0 study, mainly in the form of a dedicated CDF run), covering all mission aspects (launcher, mission analysis, payload and spacecraft) and providing a first feasibility verification (Q1-Q3/08).
• Parallel competitive industrial studies (phase-A), with a duration of 1 year and covering again all mission aspects, with in-depth analysis of the requirements and associated design trade-offs and mission baseline selection (Q3/08 – Q3/09).
• Assessment studies of the instruments proposed for the missions (conducted by associated instrument consortia).
• Mission technology readiness review and compilation of associated Technology development Plan (Q3/09).
• Preparation of programmatic estimates for the future mission phases (Q3/09).

Before the release of the Cosmic Vision 2015-2025 call for new missions, SRE-FA has been working on a number of assessment studies. The main examples are listed below.

Darwin

SRE-FA was responsible (since July 2006) for the Darwin pre-assessment activities in close collaboration with the Advanced Technologies section, SRE-FT, who took care of the corresponding technology development activities. In addition, SRE-FA was also responsible for the Darwin-GENIE feasibility study, completed at the end of 2005. Darwin-related activities were stopped following the results of the Cosmic Vision 2015-2025 proposal selection process.

Artist's impression of a Darwin telescope (left) and the XEUS spacecraft (right) Credit: ESA

XEUS - (X-ray Evolving Universe Spectroscopy)

SRE-FA was responsible (since May 2005) for the XEUS pre-assessment activities in close collaboration with SRE-FT for the corresponding technology development activities. XEUS was selected as an L-class candidate for Cosmic Vision 2015-2025 in October 2007 and additional XEUS assessment activities were conducted by SRE-FA until June 2008. Since July 2008 the XEUS mission concept has been superseded by IXO – the International X-ray Observatory.

Solar Orbiter

In 2004 SRE-FA commenced the Assessment phase for the Solar Orbiter mission. This began with an internal ESA study using the Concurrent Design Facility (CDF) and continued with two parallel industrial contracts with the aims of:

1. Assessing the scientific payload including technical feasibility, and adhering to the constraints of mass, power and telemetry
2. Assessing the overall mission profile, and the spacecraft design and operations, taking account of the advances made for the BepiColombo project which, like Solar Orbiter, has operational periods very close to the Sun
3. Providing a cost assessment for the complete mission, plus the expected costs of payload development

The results of the industrial activities were summarised in a dedicated report at the end of Q4 2005, thus concluding the assessment phase of this mission. The Project Department, SRE-P, takes responsibility for the subsequent phases of the project. A Letter Of Intent for the Solar Orbiter payload procurement was issued by ESA in October 2007.

BepiColombo

In 2003 SRE-FP managed the final BepiColombo assessment study for the challenging mission to Mercury SRE-FA provided support on programmatic aspects and specific payload elements (dedicated Laser Altimeter study).