Europe's Cryosat-2 spacecraft has launched from Baikonur in Kazakhstan on a mission to map the Earth's ice cover.
The spacecraft's Dnepr rocket climbed away from its silo at 1357 GMT (1557 CEST). The satellite was put in orbit 16.5 minutes later.
Cryosat's data should help scientists understand better how melting polar ice could affect ocean circulation patterns, sea level and global climate.
It is a copy of a spacecraft that was destroyed on launch in 2005.
Cryosat's controllers knew they had a successful flight this time when an alert tone sounded in the European Space Agency's operations centre in Darmstadt, Germany.
The tone indicated that a tracking station in Africa had picked up a signal from the satellite.
"Congratulations to all the teams involved," said Pier-Paolo Emanuelli, the flight operations director.
"We have a perfect acquisition of signal in Malinidi. The satellite looks in good shape."
Although built mainly in Germany and France, CryoSat-2 is led scientifically from the UK by its proposer and principal investigator, Professor Duncan Wingham from University College London.
He watched the launch from Darmstadt, and was thrilled to see the mission finally get into space.
"Today, it's just a real pleasure; and I speak on behalf of all the scientists who will use the data to just thank all of those many people who contributed to this mission. Personally, it's been a fabulous ride for me," he told the assembled guests at the German centre.
Cryosat-2 will measure very precisely the rates of change of sea and land ice in the Arctic and the Antarctic.
A key quest for the satellite will be to assess the volume of sea ice in the Arctic - something that has been hard to do from space.
Satellites have long been used to track ice extent (area), but calculating the thickness of the marine floes requires the overflying spacecraft to gauge the difference between the top of the ice surface and the top of the water - a relatively simple calculation then gives the overall volume.
Radar altimeters flown on missions previous to Cryosat have not had the resolution to do this as precisely as researchers would like, and have not flown far enough to the north to get a full view of the Arctic basin.
Cryosat, however, will see finer detail, and its "vision" will cover virtually all of the Arctic. Its orbit will leave just a 400km-wide circle at the pole that is out of sight of its instrument.
The radar has not one, but two antennas. By listening to the radar echoes with an additional device offset from the first by about a metre, the instrument can sense much better the shape of the ice below, returning more reliable information on slopes and ridges.
This is important for the study of Greenland and Antarctica where past missions have struggled to discern events at the edges of the ice sheets - the very locations where some of the biggest, fastest changes have been taking place.
Current assessments of Antarctic ice show some areas thickening and some areas thinning, with zones of rapid ice loss apparent in the West of the continent.
During the satellite era, Arctic ice extent has declined at a rate of 11.2% per decade as measured during the warmest summer month, September; and at 2.6% per decade in the coldest winter month, March.
Surveys of sea-ice thickness undertaken by submarines suggest ice draft may have reduced by about 40% compared with the 1960s and 1970s.
Interestingly, cold temperatures and strong winds saw the area of Arctic Ocean covered in ice this winter reach near-"normal" levels.
Cryosat-2 will now go into a commissioning phase in which its systems will be checked over. The current plan is to turn on the radar for the first time on Sunday.
"Very early on we will put data into the hands of the calibration, validation and retrievals team," explained Cryosat mission scientist Dr Mark Drinkwater.
"They will check out the quality of the measurements and advise us on how best to tune the instrument. We need that feedback so we can set up the instrument to provide the very best science," he told BBC News.
Cryosat becomes the only dedicated ice-monitoring satellite in space following the failure last year of the US space agency's (Nasa's) Icesat platform. The Americans are promising to build a follow-on satellite and have it ready for launch late in 2015.
Given Cryosat's expected longevity of perhaps 10 years or more, the two missions should enjoy a period of operation when they can compare and cross-calibrate their data.
Cryosat-2 is part of Esa's Earth Explorer programme - seven missions that will do innovative science obtaining data on issues of pressing environmental concern.
The first in the series, Goce (Gravity Field and Steady-State Ocean Circulation), was launched in March last year. The second, the Soil Moisture and Ocean Salinity (Smos) spacecraft, was launched last November.
Europe has doubled its spend on Earth observation in the past five years. It expects to launch more than 20 EO missions in the coming decade.