The EarthCARE satellite will carry four instruments for observations of clouds and aerosols with four synergistic sensing methodologies.
The three-axis stabilised satellite platform was designed to accommodate the four instruments, which need unobstructed and very accurately collocated views of Earth as well as unobstructed views for solar calibration of the passive instruments.
The satellite design meets these challenges by employing a fully customised carbon fibre-based platform with the radar, lidar and startrackers (used for determining the satellite’s attitude) positioned as close together as possible, thereby minimising alignment errors.
The satellite is dominated by the large Cloud Profiling Radar (CPR) antenna, which is 2.5 m across. The long trailing solar panel at the rear gives the satellite an overall length of 19 m. The solar panel is made up of five sections and covers an area of 21 sq m and, at the satellite’s low orbital altitude, helps minimise atmospheric drag.
EarthCARE will orbit Earth at an altitude of around 393 km. The altitude needs to be as low as possible to optimise the use of the lidar and radar, but not too low where atmospheric drag would impact fuel consumption and the life of the mission.
Since global coverage is required, EarthCARE’s orbit is near-polar. It crosses the equator in the early afternoon, providing optimal illumination and minimal sun glint for the passive instruments.
The system’s power demand is significant. The two active instruments, the Atmospheric Lidar (ATLID) and the CPR, require 2500 W.
The size of the satellite (with solar panel and CPR antenna stowed for launch) and its mass of about 2000 kg plus fuel makes it compatible with both Soyuz and Zenit launchers.
The following table summarises the two orbits foreseen for routine operations and for the calibration and validation phase when a shorter revisit time is required.
|Mean solar local time||14:00 (descending node)||14:00 (descending node)|
|Mean spherical altitude||393.14 km||394.43 km|
|Repeat cycle||25 days/389 orbits||9 days/140 orbits|
|Orbital duration||5552.7 sec||5554.3 sec|
The satellite prime contractor is Astrium GmbH (DE) and the base platform is built by Astrium Ltd (UK).