By Helen Briggs
BBC News science reporter, Frascati
Radar tracking stations are searching for Europe's missing Cryosat spacecraft, amid concerns it has broken up over the ocean.
The European Space Agency probe lifted off at 1902 local time (1602 BST) from the Plesetsk Cosmodrome in Russia.
Russian space officials said the flight broke up and crashed into the sea, but Esa has not yet confirmed it.
The £90m (135m euro) mission was designed to monitor how climate change was affecting the Earth's ice masses.
Early signs suggested the launch had been successful, but the satellite went missing some 90 minutes later.
Chief scientist Duncan Wingham of University College London said the mission was either lost or in an unknown orbit around the Earth.
He said: "Space is a risky business, it always has been.
"If we're lucky we might be in an orbit we could recover from. Until they locate it, we won't know."
The satellite was launched on a Rockot vehicle, a converted SS-19 intercontinental ballistic missile.
The rocket, which in the Cold War would have been armed with nuclear weapons, had been modified for peaceful space duties with the addition of a Breeze-KM upper stage.
Dr Matthias Oehm, chief executive officer of Eurockot, said they had not received the expected signals from either the spacecraft or the upper stage of the rocket that should have injected it into orbit.
"This is not a positive sign for the success of the mission," he told a news conference at Esa's European Space Research Institute, in Frascati, near Rome.
Mission scientists had gathered there to watch the launch via satellite link from Russia. They clapped and cheered as the rocket was seen clearing the launch pad in a cloud of smoke. But their jubilation was short-lived.
About 90 minutes after launch, when the spacecraft should have separated from the upper stage of its rocket, mission controllers failed to locate the satellite.
THE EARTH'S ICE COVER
Two types of polar ice: The ice that covers land and the ice that floats on the sea
The large Greenland and Antarctic ice sheets cover 10% of the Earth's land area
Surface measurements and overflights suggest Greenland's ice is undergoing melting
Data from the Antarctic points to melting at the edges and some growth in central regions
Considerable thinning of Arctic sea ice has been recorded by nuclear subs since the 1950s
Observations from space are more extensive, but overall there remains a paucity of data
Volker Liebig, director of Earth Observation Programmes at Esa, said he could not say for sure that the mission was lost, as there was still a chance that a signal from the spacecraft would be received.
"We just don't know what has happened," he said.
Ground-based radar and tracking stations are now searching for Cryosat.
One possibility is that the spacecraft has broken up in orbit and fallen into the ocean. In this scenario, the satellite would burn up in the Earth's atmosphere.
Mr Liebig said there was "no real danger" that it could cause damage on descent.
Cryosat was the first of Esa's so-called Earth Explorer missions. These are relatively low-cost projects that seek quick answers to some important environmental questions. In the case of Cryosat, the quest was for some definitive data on the behaviour of polar ice.
Previous satellite measurements, submarine and surface readings point to rapid melting in some areas, particularly in the Arctic Ocean where the extent of summer ice reached a record minimum this year.