PARIS - The European Space Agency (ESA) is deferring a development go-ahead for its next Mars mission and considering a German-led lunar mission as it attempts to align exploration ambitions to budget realities.

Speaking at the International Space Exploration 2007 symposium in Berlin, Director General Jean-Jacques Dordain said the agency will kick off the detailed definition Phase B of the ExoMars lander mission, slated for launch in 2013, as planned at the end of this year. However, approval for Phase C/D full-scale development will have to await the next ESA ministerial summit on Nov 25-26, 2008.

In June, ESA approved an extensive redesign to the mission to enable it to accommodate a much bigger payload. The redesign, featuring a bigger lander/rover and use of a heavy-lift launch vehicle instead of the midsize Soyuz as initially envisioned, adds a further 350 million euros ($500 million) to the initial 650 million euro price tag. An optional telecommunications orbiter would boost the cost another 150 million euros.

Agency officials had indicated they hoped most of the major development items, except perhaps the orbiter, could be drawn from existing science and technology budget lines. However, Dordain said the magnitude of the changes was such that it implied an essentially new mission, requiring a ministerial-level greenlight.

ESA's manned space and microgravity director, Daniel Sacotte, minimized the importance of the move, saying it had been envisioned from the beginning and insisting financial commitments are already in hand to ensure the re-scoped mission is approved. But science program board members indicated several nations, including Italy and the U.K., had pushed for 2007 approval but had been rebuffed. Moreover, they said, the original reduced-scale mission continues to be pursued in the event the enhanced design is rejected.

Also postponed until next year's summit is a decision on whether to build a European orbiter for ExoMars, or go with a NASA or Russian Space Agency solution. NASA's Mars Reconnaissance Orbiter (MRO) is the baseline, but may not be available. Use of a Russian relay satellite planned for the Phobos-Grunt mission, in return for a science instrument exchange, is another potential alternative. Italy plans to propose a nationally funded orbiter to meet the requirement.

Sacotte said ESA will propose a European orbiter to minimize program risk, with the MRO and Phobos-Grunt as backups. The choice of launcher - Ariane 5 or Proton - remains open. He indicated work is underway at the European spaceport in Kourou, French Guiana, to permit handling of nuclear radioisotope heaters engineers want to use in the mission.