Early in the mission, the spacecraft will spend most of their time flying on the side of the Earth that faces away from the Sun.
Two satellites of the Cluster II programme were sent into orbit onboard a Russian Soyuz-Fregat rocket.
They went up a day late after a technical problem at the space port.
Cluster II is a "recovery" mission. The first attempt was destroyed at launch when the Ariane-5 heavy-lift rocket blew up 40 seconds into its maiden flight in 1996.
The programme actually comprises four identical satellites that will fly in a close, tetrahedral (triangular pyramid) formation - a first for a group of spacecraft.
The two satellites launched on Sunday will be followed by another pair on 9 August.
Magnetic shield
The Cluster quartet will investigate most of the major boundaries and regions of interest within the Earth's magnetic environment - the magnetosphere.
Cluster's role will be to look at how the magnetosphere interacts with this solar wind, and the high-energy particles from more violent solar events such as flares and so-called coronal mass ejections (CMEs).
There is currently a great deal of interest in these space weather phenomena. The charged particles, which move at hundreds of kilometres a second, can knock out electronics onboard satellites and in extreme cases interfere with power grids on the Earth's surface.
Weak points
Armed with data from Cluster II, scientists hope that they will be able to predict such threats to satellites with more certainty.
Early in the mission, the spacecraft will spend most of their time flying on the side of the Earth that faces away from the Sun.
After six months, they will move in front of the planet to investigate the polar cusps.
These are weak points in the Earth's magnetic shield, where charged particles penetrate the upper atmosphere and generate the spectacular Northern and Southern Lights.
From the end of December, data will be coming down from the four satellites at a rate of one gigabyte (two compact disks) every day.