Launch readiness of Athena is planned for 2031. The mission could be launched by an Ariane 5 or another launch vehicle with equivalent lift capability and fairing size. It will operate at L2, the second Lagrange point of the Sun-Earth system, in a large amplitude halo orbit. The operational orbit will be reached with a direct transfer trajectory towards L2, with limited ∆V demands. The L2 orbit is preferred to alternative scenarios (for example, low inclination Low Earth Orbit, or Highly Elliptical Orbit) as it provides a very stable thermal environment as well as good instantaneous sky visibility and high observing efficiency.
Athena will predominantly perform pointed observations of celestial targets. There will be around 300 such observations per year, with durations ranging from 103 to 106 seconds, with a typical duration 105 seconds per pointing. This routine observing plan will be interrupted by target of opportunity observations (for example, gamma ray bursts and other transient events) at an expected rate of twice per month.
The telemetry and telecommands data rates will not present significant drivers for the ground system design and will be able to be met with existing systems. Automated responses to contingency situations such as high levels of solar radiation will be able to place the instruments into a safe configuration and to resume operations efficiently as soon as the alert has passed. Athena will require only standard ground station coverage during launch, activation, cruise, and orbit injection at L2. Station keeping and other L2 orbital operations will not require special coverage.
The baseline mission duration for Athena will be four years, with consumables sized to allow a six-year extension to maximise the return from this ambitious mission. With a conservative observing efficiency of 85%, Athena will be able to achieve the science goals of the Hot and Energetic Universe theme during the baseline mission, while preserving around 20% of the available time for observatory science.
Athena's operational ground system requirements will be able to be satisfied with a standard ESA ground segment approach for commanding, controlling and monitoring the spacecraft and instruments, and for the downlink of housekeeping and scientific data. The baseline is to locate the Athena Mission Operations Centre (MOC) at the European Space Operations Centre (ESOC) and the Science Operations Centre (SOC) at the European Space Astronomy Centre (ESAC), with additional contributions funded by Member States.