As part of the second phase of its Earth Explorer Opportunity Missions (EEOM) programme, the European Space Agency (ESA) has selected three new proposals for feasibility study.

In the first instance, the Atmospheric and Climate Explorer (ACE) project envisages the use of a constellation of four satellites orbiting the Earth at 650 x 850 km and employing intersatellite cross-link measurement.

The European contribution to the Global Precipitation Mission (EGPM) proposal would make use of a sun-synchronous, polar-orbiting craft, while a programme known as SWARM would see two constellations of two satellites each placed in two orbital planes at 400 to 500 km altitude to study the Earth's magnetic field.

At the time of going to press, ESA was expected to proceed with two of these projects, with an initial launch date of 2008 and a budget of €110 million ($108.4 M). EEOM phase one began during 1999 and will see the Cryosat satellite (designed to monitor the world's ice sheets and sea ice distribution) launched during 2004 and the Soil Moisture and Ocean Salinity (SMOS) mission lift-off two years later in 2006.