France's space agency on Thursday unveiled a revised proposal for an Ariane rocket ahead of a tough decision on launchers by the European Space Agency (ESA).

Ministers must decide whether they can afford to fund the development of two projects for Europe's next rocket.

These are an Ariane 6, promoted by France, that would be operational from the next decade and an intermediate launcher, the Ariane 5 ME, backed by Germany.

At a press conference in Paris, France's National Centre for Space Study (CNES) said the overhauled plans for the Ariane 6 resulted in a "simple design with great payload capacity," able to take between five and 10 tonnes into orbit.

It could be ready for launch in 2020, said CNES boss Jean-Yve Le Gall, a date that is a year or two earlier than was expected in July 2013.

"We are looking at a two-booster version, with costs of around 65 million euros [$83.85 million] per launch, and a four-booster version, at around 85 million euros per launch," said Le Gall.

"The per-kilo cost will be around 10,000 euros, roughly half that of Ariane 5 today," he said, referring to ESA's current workhorse.

CNES' previous design for the Ariane 6 had promised a 30-percent gain on Ariane 5 per-kilo launch costs.

"The industrial and institutional organisation of the project will be simplified, with the goal being to save costs," Le Gall pledged.

He admitted there would have to be "compromises" in Luxembourg, adding that around eight billion euros will be earmarked for launchers for the next decade.

"We tend to want everything, but the means to do so aren't always there," he said.

The presentation came a day after a preparatory meeting at ESA where the revised plans were approved by other figures in the space industry, including the head of launch operator Arianespace, Stephane Israel.

The December 2 meeting in Luxembourg will determine the outcome of a difficult political compromise in 2013 between ESA's major partners as nimble US firms such as SpaceX eye the market for satellite launches.

The German-backed Ariane 5 ME, standing for Midlife Evolution, would be a tweaked version of the Ariane 5.

It would in theory be ready by 2017 and yield operational costs over the existing ECA and ES models, which are highly reliable but need hefty subsidies.

In February, France's national auditor disclosed that French policymakers favoured dropping the ME to keep down development costs and prevent a feared delay to the Ariane 6.