Mission Operations

PLATO (PLAnetary Transits and Oscillations of stars), a candidate mission for the M3 slot  in ESA's Cosmic Vision programme, will characterise exoplanetary systems by detecting planetary transits and conducting asteroseismology of their parent stars.

Launch

The current mission scenario is to launch PLATO using a Soyuz-Fregat 2-1b vehicle (ST fairing), with direct insertion into an orbit around the second Lagrange point (L2) of the Sun-Earth system. For this type of orbit, the launcher has a capability of just over 2100 kg.

Orbit

PLATO will be located at L2. Credit: ESA/NASA

The selected orbit at L2 is a large-amplitude (500,000 × 400,000 km) free-insertion Lissajous type. L2 has been chosen for its stable ambient environment in terms of temperature and radiation and the possibility of eclipse-free orbits with an unobstructed view of large parts of the sky (the Sun, Earth and Moon are all located in a relatively small solid angle, viewed from the spacecraft). Once in orbit the PLATO spacecraft will be periodically rotated around its pointing axis in order to keep the sunshield facing towards the Sun. Orbit control manoeuvres will be performed once per month.

Science operations

The mission will have a nominal lifetime of six years, divided into three phases. The first two phases will be used for long-duration observations, with each observation focusing on a part of the sky that is expected to contain a high density of cool dwarf stars. One of these sky fields is likely to be around ecliptic longitude (λ) of 210° and latitude (β) of -60°, and the other around λ = 306° and β = 67°, which are close to the galactic plane. The duration of each of these observations will be several years – the first for 2-3 years, the second for two years - in order to repeatedly observe transits with orbital periods similar to that of Earth. This is necessary to reduce the likelihood of flagging false transits, arising from the detection of changes in a star’s brightness, for example, those occurring naturally in the star, in the stellar environment (for example, background objects) or artificially induced in the spacecraft payload. The last phase will be a ‘step-and-stare’ phase, where several different observation fields with interesting scientific targets will be monitored for a period of several months each. The step-and-stare phase will be at least one year long.

Ground segment

The ground segment of PLATO will be composed of three elements:

• a Science Operations Centre (SOC) - located at the European Space Astronomy Centre (ESAC), in Villanueva de la Cañada, Spain - with the responsibility for scheduling and preparing the observations, as well as performing the routine analysis of the data, producing and distributing the validated light curves. Most of the PLATO data will be made publicly available as soon as it is reduced. A small amount of data will be reserved for the payload and data centre principal investigators and co-investigators. This data will be subject to a proprietary period of 1 year (to be confirmed);
• a Mission Operations Centre (MOC) - located at the European Space Operations Centre (ESOC) in Darmstadt, Germany - which will look after the ground segment and operations infrastructure for the flight operations segment of the PLATO mission, including converting the schedule and the instrument configuration commands into spacecraft commands and receiving the telemetry stream from the spacecraft. The PLATO MOC will be based on an extension of the existing ground segment infrastructure, customised to meet the specific requirements of this mission.
• one or more nationally funded Science Data Centres, which will be responsible for the pipeline processing of the data leading to the final mission products (calibrated stellar light curves) and for archiving and distribution of the data.

Communication with the PLATO spacecraft will be performed in the X-band, using the 35-metre antenna at New Norcia, in Western Australia. The daily telecommanding and communications period is 4 hours. The rest of the day the spacecraft will operate autonomously, without ground contact.