PARIS — The scheduled Feb. 25 launch of Europe’s Cryosat-2 polar ice monitoring satellite has been postponed for at least several weeks following an assessment by designers of the Russian-Ukrainian Dnepr rocket that the converted ballistic missile might not be able to place the craft into its intended orbit without modification, the European Space Agency (ESA) announced Feb. 19.

ESA officials are expected to arrive in Dnepropetrovsk, Ukraine, the week of Feb. 22 to hear firsthand from the Dnepr’s designer, the Yuzhnoye organization, what the proposed modifications are, what risks they might create and what flight modifications they would force on Cryosat-2.

In the meantime, Cryosat-2 will be removed from the Dnepr rocket to protect it from the subzero temperatures at Russia’s BaikonurCosmodrome in Kazakhstan. Dnepr is launched from an underground silo.

Richard Francis, ESA’s Cryosat-2 program manager, said Yuzhnoye and Moscow-based ISC Kosmotras, which markets the Dnepr rocket, had originally said a year ago that the planned 720-kilometer polar orbit intended for Cryosat-2 was beyond the capacity of Dnepr. Yuzhnoye and Kosmotras proposed, and ESA agreed, that the orbit be lowered by several kilometers.

ESA officials modified the early orbit profile of Cryosat-2 to accommodate the lower Dnepr drop-off point.

In December, Dnepr managers reversed their assessment, saying fresh analyses had shown that the rocket could carry Cryosat-2 into its intended orbit. The Cryosat-2 team then returned to their original post-separation flight plans, and the satellite was shipped to the Russian-run BaikonurCosmodrome.

But on Feb. 18, Yuzhnoye informed the Cryosat-2 team at Baikonur that the steering motors on Dnepr’s second stage may not have enough fuel to ensure mission success.

Francis said he remained unclear as of Feb. 19 about what new information caused the change of opinion. He said one option under review is a relatively simple change in the ratio of fuel to oxidizer fed into the steering motors, which Dnepr officials have said could provide the marginal performance increase needed for the launch. But that may force Cryosat-2 flight managers to refigure the flight trajectory, which likely cannot be done overnight.

“We would like them to explain to us what their thinking is,” Francis said. “I think they are aware that with Cryosat’s history, we are particularly concerned with launcher issues.”

Cryosat-2 was built following the October 2005 loss of Cryosat, which was destroyed when its Rockot vehicle — another converted ballistic missile — failed at launch because of a malfunction of its second stage. Cryosat and Rockot’s upper stages are believed to have fallen into the Lincoln Sea in the Arctic Circle.

Because of the importance of polar ice measurements to the assessment of climate change, ESA agreed to finance construction of a duplicate Cryosat.

Peter B. de Selding was the Paris bureau chief for SpaceNews.