(Adds dropped word "been", para 4)

By Tim Hepher

PARIS (Reuters) -The European Space Agency on Friday welcomed a deal for Britain to resume full membership of Europe's Copernicus programme, easing doubts over the next batch of climate-tracking satellites and the completion of development work by European space firms.

Britain said on Thursday it would re-join both Copernicus and the European Union's Horizon science research programme, ending a two-year post-Brexit standoff over funding.

Copernicus is a set of six families of Sentinel satellites designed to read the planet's "vital signs" including carbon dioxide.

Plans for six more "Sentinel Expansion" missions starting from 2026 have been left in suspense because of a funding gap of 721 million euros stemming mainly from Britain's exit from the EU.

In an interview with Reuters last month, the head of the European Space Agency - which co-leads the world's largest Earth observation project with the EU - warned that work would have to be suspended if there were no funding deal by next June.

But following Thursday's agreement, Director General Josef Aschbacher said the deal would allow UK scientists and industry to benefit fully from one of Europe's leading space programmes.

"The UK's full participation in the programme is a major boost to the climate-change agenda, which relies on space-based observations of our planet every single day,", Aschbacher told Reuters by email.

The agreement is a boost for satellite manufacturers including Europe's Airbus, France' Thales and Germany's OHB that had been awarded contracts to build the new set of satellites subject in part to an EU funding deal.

But while the political agreement signals a further improvement in bilateral relations between Britain and the EU, sources said details of funding were being finalised.

Neither Britain nor the European Commision gave a financial breakdown on Copernicus, or said whether the 721-million-euro funding gap had been fully closed.

Britain's direct but smaller contribution to Copernicus via ESA, which is not part of the EU, had been unaffected.

Prior to the deal, Aschbacher had been among the most senior climate-monitoring officials to voice concerns over wavering support for measures to combat climate change.

Leaving a hole in the Copernicus budget would have sent the wrong signal on Europe's commitment to combating climate change, he told Reuters last month.

Thursday's agreement came as ArianeGroup, owned by Airbus and Safran, said it had successfully run a hot-firing test on the main stage of the delayed Ariane 6 space launcher.

(Reporting by Tim Hepher; editing by David Evans)