ATHENA is planned to be launched by 2022 from Europe's Spaceport at Kourou, French Guiana, on an Ariane 5 vehicle, which has been selected for the size of its launcher fairing, a critical factor in maximising the telescope focal length without requiring an extendable optical bench.

ATHENA will operate at L2, the second Lagrangian point of the Sun-Earth system, in a halo orbit with a semi-major axis of about 700 000 km and a period of approximately 180 days. This orbit is preferred to alternative scenarios (for example, low inclination Low Earth Orbit, Highly Elliptical Orbit) as it provides a very stable thermal environment as well as a good instantaneous sky visibility.

The operational orbit will be reached with a direct transfer trajectory towards L2. Only two correction manoeuvres will be performed after launch, on day 2 (main launcher dispersion correction manoeuvre) and on day 10 (final correction manoeuvre). The spacecraft and instrument commissioning will take place in parallel with the transfer to L2. The operational orbit will be reached about 100 days after launch. Monthly station keeping manoeuvres will allow the nominal halo orbit to be maintained with a total ∆V of only 2 ms^-1yr^-1. The total ∆V budget over a 10-year mission is about 120 ms^-1.

The nominal lifetime is five years, with a possible extension for another five years enabled by an appropriate consumables budget. By proper choice of the launch date and time, it is possible to avoid eclipses during both the cruise to L2 and the operational phase.

The design of the spacecraft will allow a large pointing excursion around the average spacecraft-Earth-Sun direction (X axis, yaw, ± 180°) and considerable rotations about the transverse (Y) axis (pitch, ± 30°) and about the longitudinal (Z, telescope line-of-sight) axis (roll, ± 10°).

Ground segment

The ATHENA ground segment will comprise the ATHENA Mission Operations Centre (MOC), based at ESA's European Space Operations Centre (ESOC), and the ATHENA Science Ground Segment (ASGS), the latter comprising the ATHENA Science Operations Centre (operating from ESA's European Space Astronomy Centre, ESAC), the Instrument Team Centres and the ATHENA Science Data Processing Centre.

ATHENA will require only standard ground-station coverage during launch, cruise and injection to L2. For the science operations phase, a daily 3.5-hour X-band contact with ESA's New Norcia ground station is foreseen; this will allow an average of around 90 Gb of science data to be downlinked each day.

(For more detailed information about ATHENA mission operations, please consult the ATHENA assessment study report (Yellow Book) - see link in right-hand menu.)