Satellite flown into space to monitor Earth's oceans
BY STEPHEN CLARK
Posted: June 20, 2008
NASA partnered with European scientists to launch an ocean research satellite from California early Friday, giving forecasters a new tool to make more accurate predictions of weather patterns and climate change.
The 125-foot-tall rocket, boosted by three solid-fueled motors, ignited with a brilliant flash of light and arced south from the launch pad into a moonlit night sky. The rocket dropped the three solid boosters into a safe zone in the Pacific Ocean, then used the main engine to steer around offshore oil rigs and reach the proper trajectory.
The first stage engine shut down a few moments earlier than planned, but the rocket's second stage compensated for the shortfall by burning a few seconds longer, said Omar Baez, NASA launch director for the mission.
The Delta 2 completed its pinpoint space delivery mission 55 minutes after liftoff by releasing the 1,113-pound spacecraft in an orbit approximately 823 miles high with an inclination of about 66 degrees to the equator. The orbit will take Jason 2 over 95 percent of the world's ice-free oceans.
A camera mounted on the rocket's upper stage showed live footage of the satellite flying away from the Delta 2.
"All indications are that Jason 2 is operating," Baez said after the launch.
Engineers in France will spend the next few weeks verifying the spacecraft's science instruments are in good shape.
Jason 2 carries a suite of instruments built by U.S. and French scientists to measure the distance between the orbiting spacecraft and the ocean surface. Scientists expect a precision of between one and two inches.
"Measuring sea level from 830 miles in space with errors of a few inches is not just cool science, it's a really critical application for everybody on the planet," said Eric Lindstrom, Jason 2 program scientist at NASA Headquarters.
Lindstrom likened the feat to measuring the thickness of paper lying on the ground from the top of a skyscraper.
The satellite, also called the Ocean Surface Topography Mission by NASA, is expected to last at least three years. Thales Alenia Space of France was the spacecraft's prime industrial contractor.
Other partners in the mission include the National Oceanic and Atmospheric Administration, the French space agency, and EUMETSAT, the operator of Europe's weather satellites.
U.S. government agencies provided $176 million of the mission's cost, or about 40 percent of the total funding, said Steve Neek, program executive at NASA's Science Mission Directorate.
European partners spent $256 million on Jason 2, Neek said.
The world's oceans vary in height by up to six-and-a-half feet, and the sea-surface terrain can be used to chart currents, water temperatures, tides, and ocean eddies, according to Neek.
"The ocean really behaves like a natural thermostat regulating our climate," said Lee-Leung Fu, Jason 2 project scientist at the Jet Propulsion Laboratory in Pasadena, Calif.
Sea water helps cool the atmosphere, but sea levels rise when ocean temperatures warm or ice melts, Fu said.
Researchers will incorporate real-time data from Jason 2 into their computer models to improve weather and ocean forecasts on scales ranging from a few days to more than a year.
The improvements will also be important for predicting the development of hurricanes, said Laury Miller, chief scientist at the NOAA Lab for Satellite Altimetry.
Jason 2 will not only supply up-to-date ocean information to sailors and weather forecasters, but also keep tabs on the global mean sea level to track the melting of the polar ice caps.
The average sea level has risen at a rate of about one-tenth of an inch per year, according to data from Jason 2's predecessors.
"That sounds like a very small number to you, but this is in fact twice the rate of sea level change estimated from sparsely located tidal gauges over the preceding 100 years," Fu said.
The satellite's Poseidon 3 instrument is the mission's primary experiment. Developed by CNES, the French space agency, Poseidon 3 will bounce radar beams off the ocean surface and measure the distance by determining the time it takes for the reflected radio waves to be received by a sensor on the spacecraft, said Parag Vaze, Jason 2 project manager at JPL.
Poseidon 3 can also gauge ocean currents, wave characteristics and wind speed, scientists said.
The third-generation instrument is based on other payloads flown on two previous U.S.-French satellites, beginning with the experimental TOPEX/Poseidon mission launched in 1992.
TOPEX/Poseidon revolutionized the field of oceanography, which had before relied on scattered reports from ships and weather buoys.
"The availability of these measurements has meant a breakthrough in physical oceanography," said Mikael Rattenborg, EUMETSAT director of operations.
The observation of oceans from space gave scientists the first clear insight into El Nino and La Nina climate patterns characterized by the warming and cooling of waters in the eastern Pacific Ocean.
The partnership continued with a subsequent operational satellite called Jason 1, which was sent into space in 2001. Jason 1 is still providing researchers a daily dose of data on the world's oceans, and the precursor satellite will be part of a tandem mission with Jason 2.
Scientists will closely monitor the two satellites' instruments over the next six months, making sure they operate identically to provide uniform data. After the calibration phase is completed, Jason 1 will move to an orbit parallel to Jason 2, effectively doubling the mission's global coverage, Fu said.
Although Jason 1 is beyond its projected life span, scientists expect it to continue working despite the loss of several key backup systems.
Fu said engineers project there is an 80 percent chance Jason 1 will work for at least two more years, giving scientists an opportunity to conduct dual operations with Jason 2.
Jason 2's charter is to extend the 15-year legacy of TOPEX/Poseidon and Jason 1 into the next decade.
The legacy's continuation is crucial to answering some of the key questions scientists are facing about global warming, according to Fu.
"We really don't know the answer. That's why we need continuing satellite measurements like Jason 2 to extend the data record into the future," Fu said.
Jason 2's science instruments include several improvements to allow the radar system to analyze sea levels near coasts and in icy regions, Vaze said.
"We anticipate much improved observations in the coastal zones, which are home to more than half of the world's population," Fu said.
A network of 60 radio beacons positioned around the world will track the spacecraft as it flies overhead, determining its exact position in space to make sure the data gathered by the Poseidon 3 instrument is accurate.
Vaze said ground controllers will also use navigation data provided by a laser ranging system and receivers linking the spacecraft with the Air Force's GPS satellites.
A microwave instrument assembled by NASA's Jet Propulsion Laboratory will measure water vapor in the atmosphere. Water can interfere with radar signals transmitted by Poseidon 3, causing errors of up to 20 inches in humid conditions.
NOAA and EUMETSAT are already planning a follow-on satellite for launch in the next decade. The spacecraft, called Jason 3, would likely continue the string of constant sea level monitoring through 2020, forecasters said.
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