Taking advantage of a second chance rarelyafforded in the space business, a team of European scientists will launch theCryoSat 2 satellite Thursday to measure how fast Earth's polar ice sheets aremelting.
A Dnepr rocket will blast off from Kazakhstanat 1357 GMT (9:57 a.m. EDT) Thursday. Sixteen minutes later, the 112-foot-tallbooster will release the 1,587-pound satellite into a polar orbit designed toregularly carry CryoSat2 over the Arctic and Antarctic ice caps.
See our complete launch timelinefor more details.
CryoSat 2's operational orbit will be 445miles high with an inclination of 92 degrees, according to the European SpaceAgency.
The launch will come more than four yearsafter a similar spacecraft fell back to Earth during a launchmishap in 2005. Officials said the second stage engine on the Rockot launchvehicle did not turn off on schedule, causing the second and third stages toremain attached, dooming the mission.
"This time around, all of us will be alltoo familiar with the idea that launches can fail," said Duncan Wingham,CryoSat 2's lead investigator. "We should be less relaxed than last time.Space is a risky business. You spend many years building these things, then youstick them on a tube of high explosives and you put a match to it."
ESA and CryoSat's science team immediatelybegan lobbying to build a replacement satellite.
"In the early hours after the failure, Icame to recognize that my job description had changed," Wingham said."It wasn't to exploit the data, it was to rejustify the mission. Withinhours, I took that issue up with the space agency."
ESA's Ministerial Council, consisting ofrepresentatives from the agency's member states, considered the proposal duringa meeting a few months after the launch failure. Finalapproval for CryoSat 2 came about four months after its predecessor crashedinto the Arctic Ocean, according to Richard Francis, the mission projectmanager.
Scientists and politicians both recognizedthe importance of CryoSat and concluded a new mission should go ahead, Winghamsaid.
"We had this mission that was completelyjustified and deserving, so there was great goodwill among the upper echelonsof ESA to rebuild it," Francis said.
CryoSat 2's radar altimeter will map land andsea ice with enough precision to detect how much ice mass is being lost.The data will improve the understanding of how the ice sheets affect climateand rising sea levels, according to scientists.
"Although, on the day the failure, Ifeared that I had a mountain to climb, it turned out not to be that way,"Wingham said. "It proved a much less difficult task than I had imagined 90minutes after the failure."
The mission's cost is 140 million euros, or$187 million under current exchange rates, according to ESA.
Francis said engineers made 86 changes fromthe old satellite during the development of CryoSat 2.
The most visible change is the addition of asecond radar instrument named SIRAL to give the CryoSat 2 payload fullredundancy in case the primary sensor fails.
"The first one was completelynon-redundant and was susceptible to any single-point failure," Francissaid. "With a rebuild, we couldn't afford that."
Officials alsoupdated the spacecraft's software, added a new communications system, andincreased the size of the flight batteries, according to Francis.
ESA also selected a new rocket to launchCryoSat 2, turning to the Ukrainian Dnepr booster, a modified Soviet-era SS-18ballistic missile. The Dnepr is sold for international and commercial launchesby Kosmotras, a company chartered by the Russian and Ukrainian governments.
The Dnepr will spend the countdown inside ofan underground silo at the Baikonur Cosmodrome.
Controllers at the European Space OperationsCenter in Germany will start the countdown eight hours before launch at 0557GMT (1:57 a.m. EDT).
CryoSat 2 will be powered up six hours beforeblastoff to begin a series of health checks ensuring it is ready for launch.The primary control team will begin their shift at ESOC around 1157 GMT (7:57a.m. EDT).
The satellite will be placed in launch modeat 1217 GMT (8:17 a.m. EDT) and will be put on internal power at 1307 GMT (9:07a.m. EDT), according to ESA.
The Dnepr rocket team will evacuate thelaunch pad about a half-hour before liftoff, and the booster's automaticsequence will start at T-minus 15 minutes. ESA's last chance to call an abortis five minutes before launch.
An official inside the Dnepr launch controlcenter will push the "start" button at T-minus 2 minutes, 56 seconds.
When the countdown clock reaches zero, theDnepr rocket's guidance system will lock into its inertial navigation modewhile the launcher is still in its underground silo.
"The actual black powder ignition, whichshoots the missile out of the silo, happens about five seconds later,"Francis said. "That's the visible launch."
The Dnepr first stage's RD-264 engine willignite as the rocket is suspended nearly 100 feet above the ground, quicklyramping up to nearly 1 million pounds of thrust to propel the launcher skyward.
The first stage will be jettisoned at T+plus1 minute, 50 seconds and the payload fairing should be released at T+plus 5minutes, 9 seconds, according to ESA.
After completing its role in the launch, theDnepr's second stage will separate from the third stage nearly six minutesafter liftoff.
The Dnepr's third stage will make a180-degree turn a few moments later to drag CryoSat 2 into orbit in a backwardorientation. The rocket's designers conceived the unusual approach to improvethe missile's accuracy during wartime.
"If you look at the statistics for theRussian missiles, it's the one that has the highest accuracy," Francissaid.
CryoSat 2 will remain inside a protectivecanister during the third stage burn to prevent contamination from the engine'sexhaust cloud.
"With a satellite, that could cause someunpleasant thermal effects, not to mention pollution, so the spacecraft remainsin this gas dynamic shield right up until shortly before separation,"Francis said. "So there's no possibility of a signal from the spacecraftbecause it's inside a metallic enclosure."
The spacecraft will separate from the Dnepr thirdstage at T+plus 16 minutes, 28 seconds.
A communications site in Malindi, Kenya,should acquire the first radio signals from CryoSat 2 about 17 minutes afterlaunch. A Norwegian ground station named Troll in Antarctica will attempt tocontact the satellite a half-hour into the mission.
Francis said CryoSat 2's solar panel andradar antenna are fixed, eliminating risks posed by deployable appendages.
If all goes well, the control team will powerup Cryosat 2's SIRAL radar over the weekend and the first test results could beavailable by around Monday.
It will be six months before engineers finishcommissioning the satellite and hand it over for scientific use, Francis said.
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