Mission background

Artists View of Swarm

Swarm is the fifth mission in ESA’s fleet of Earth Explorers. The Earth Explorers are specialised missions dedicated to observing different aspects of the planet and our environment. A secondary aim of the programme is to understand how these aspects interact with one another.

Swarm is studying the magnetic field, but its data can also help understand ocean currents and interactions in the atmosphere.

Swarm is a constellation of three satellites. While other Earth Explorers only use one satellite, three satellites are used for Swarm to help obtain better and more varied measurements as the three satellites are identical but fly in different orbits.

Satellite design

The three Swarm satellites have a rather unusual shape: trapezoidal with a long boom that was deployed once they reached orbit. The design was necessary to overcome challenges in accommodating the instrument package, and, because the satellites needed to fit into a single payload aboard the rocket.

Each satellite is about 9 m long, including the boom, with the surface at the front only measuring about 1 m2. This is to reduce the effect of air drag and to cut down on the amount of propellant needed to stay at the correct altitude. Below around 500 km, air drag tends to slow satellites down and lower the orbit.

The boom, which accounts for almost half the length of the satellite at 4 m, trails at the back. This is because the front surface is needed for the electric field instrument so that it can collect and measure the speed and direction of incident ions along the orbital path.

The satellite has no moving parts. This ensures that there are no vibrations that could influence the measurements made by the accelerometer, which is fixed at the very centre of the satellite. Likewise, the solar panels are fixed, forming the satellite 'roof'.

Magnetic cleanliness is of paramount importance to the mission, so the sensitive scalar magnetometers are mounted at the end of the boom, far away from any magnetic disturbance that the electrical units on the body may cause. The optical bench holding the vector field magnetometer and the three star trackers is mounted halfway along the boom. Throughout the design and manufacturing phases, magnetic cleanliness was a priority, with many tests carried out on almost every unit and final testing of the assembled satellite took place in a special facility.

At the beginning of the mission the satellites had a mass of 472 kg, with an additional 106 kg propellant at launch.

System budgets
Power GaAs triple junction cells with maximum power point tracker, 446 Wh EOL; battery 200 Wh
TM S-band @6 Mbit/s (in mode 2) TC: S-band @4 kbit/s
On-board storage 16 Gbit solid state recorder; up to 72 hours of data

Mission Operations

The final constellation of the mission was achieved on 17 April 2014. Swarm A and C form the lower pair of satellites flying side-by-side (1.4° separation in longitude) at an altitude of 462 km (initial altitude) and at 87.35° inclination angle, whereas Swarm B is cruising at a higher orbit of 511 km (initial altitude) and at 87.75° inclination angle.

Due to the natural orbit driftevaluation, the orbit of the satellites changes over time. The following is the current status and future status of the constellation:

  • In 2018: B was perpendicular to the lower A/C pair
  • In 2021: B will be counter-rotating to the lower A/C pair every 47 minutes

Flight operations are conducted at ESOC; post-launch support management from ESTEC; payload data ground processing at UK-PAC (Guildford), mission performance and user services at ESRIN; distributed higher level data processing and field modelling by scientific consortium; mission management at ESRIN.

There are two ground stations for Swarm located at ESA's facility in Kiruna, Sweden, 15 m (single station mission baseline); and a second facility at KSAT in Svalbard, Norway.

Discover more about the Swarm operations and track the mission in real-time with the ESTRACKnow tool.