Launch scenario and transfer |

PLATO is foreseen to be launched in 2026 from Kourou by a Soyuz 2-1b rocket with Fregat upper stage and injected onto a transfer trajectory to L2. The Fregat stage will inject the spacecraft either directly to L2, similarly to Euclid, or via a low Earth-bounded circular parking orbit, similarly to Gaia.

Soyuz launch from Kourou (Credit: ESA)

PLATO features a 40 degree half-cone zone, so-called prohibited zone, around the payload line of sight in which the Sun must never enter to prevent degradations of the telescope optics. If the spacecraft configuration is such that the payload line of sight is up-oriented towards zenith, it cannot be launched directly to L2 due to the required launch around noon local time of the perigee. A later lift-off time must be adopted which then requires an intermediate parking orbit keeping the prohibited zone safe, before the injection to L2 can take place at the next perigee pass.

Both launch strategies are designed so that launch is possible all year round with some exclusion windows to avoid Moon and Earth eclipses during transfer. The daily launch window lasts between 30 minutes up to 2 hours depending on the launch date.

Soyuz ascent trajectory for a direct transfer to L2.

The transfer will last approximately 30 days during which the spacecraft commissioning also takes place. Trajectory correction manoeuvres shall be performed by the spacecraft the latest 2, 5 and 20 days after the separation from Fregat (occurring about 2400 s and 6800 s after lift-off, respectively in the direct ascent and parking orbit scenario) in order to remove the launcher dispersions and correct the perigee velocity. A total delta-V of about 40 m/s is budgeted before margins for the transfer phase.