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The Ice, Cloud and Land Elevation Satellite, or ICESat-2, is to date NASA's most advanced ice-monitoring spacecraft. Able to measure changes in ice thickness, forest growth and cloud height up to 0.02 inch (0.4 millimeter) each year, according to NASA ICESat-2 offers scientists an unprecedented view of Earth's changing systems. especially at its poles.
"Watch and understand how [ice] This change helps us understand why it is changing, "said Waleed Abdalati, a geographer at the University of Colorado at Boulder and designer of ICESat-2, which in turn will refine environmental prediction models and help better levels and climate change due to melting ice.
ICESat-2 was manufactured by Northrop Grumman Innovation Systems in Dulles, Virginia, and built at NASA's Goddard Space Center in Washington at a height of 3.81 meters and a base of 2.5 feet by 6.2 feet. . According to Donya Douglas-Bradshaw, Director of Instruments at Goddard, ICESat-2 is one of the largest satellites built at Goddard.
After 10 years and multiple launch dates, the satellite is expected to take off on a Delta II rocket on September 15, 2018, from Vandenberg Air Force Base in California.
Scientific objectives and justifications
ICESat-2 will start with four main objectives:
- Measure the changing mass on ice caps and glaciers around the world.
- Measure how much melting ice from Greenland and Antarctica contributes to the rise in sea level. Ice melting in Antarctica, for example, has accelerated in the past five years. "We know there is going to be a rise in sea level," said Peter Neff, a glaciologist at the University of Washington in Seattle, but scientists do not know how much or how long.
- Estimate the thickness of sea ice in the Arctic and watch for any changes. Scientists know how much sea ice region in the Arctic has changed since 1980. But satellites like ICESat-2 help determine changes in sea ice thickness. A decrease in the thickness of sea ice could exacerbate ocean warming by allowing more light to reach the surface of the ocean and increase the temperature of the ocean. ;water.
- Measure the height of the forest to calculate the amount of carbon stored in the plants. Plants store carbon as food and use it to grow. This stored carbon can not help warm the climate or acidify the oceans.
The data collected by ICESat-2 builds on 15 years of data initiated by its predecessor, ICESat, which was in space from 2003 to 2010. ICESat-2 was first proposed in 2008, but its construction began in 2010. launch date in 2015. Between ice satellites, NASA has used its IceBridge airborne operation to continue monitoring critical ice areas from 2009 until now.
ATLAS – the scientific engine of ICESat-2
ICESat-2 was a $ 1.056 billion project, said Richard Slonaker, director of the ICESat-2 program in Washington, DC, on a conference call. Much of this money has been spent on developing a single high-tech instrument called the Advanced Laser Altimetry System, or ATLAS. The instrument basically works as a stopwatch: it sends a laser to Earth and the time it takes for the light to reach the surface and come back. The shorter the time, the higher the light rise is important.
But this simple explanation belies the sophistication of the instrument. ATLAS draws a single green laser beam (532 nanometers) in a diffractor that divides the beam into six beams, coupled in three pairs. On the surface of the Earth, these lasers form a line. Each laser of a pair is at 295 feet (90 meters) from each other and each pair of lasers is located 2.1 miles (3.3 kilometers) one way. on the other.
This design allows ICESat-2 to calculate the tilt of a surface, which, if it is not taken into account, could appear as a change in elevation – a problem that the NASA discovered with the unique ICESat laser system, GLAS. ATLAS is also equipped with a backup laser in case of malfunction.
ATLAS draws 10,000 laser pulses per second, each pulse containing about 300 trillion photons. Only a dozen photons return to the satellite, where they bounce off a reflective beryllium mirror of 2.6 feet (0.8 meters). The sensor stops the "stopwatch" and measures the travel time of photons to 1 billionth of a second. This timing is adapted to the position of the satellite – determined by an on-board GPS system and a Star Tracker that observes the nearby constellations to determine the spacecraft's orientation – and determines which object on Earth was measured
"To put this into perspective, ICESat-2 is a half-second to collect 5,000 measurements of altitude in each of its six beams," said Tom Wagner, ICESat-2 Program Manager at NASA Headquarters. in Washington. DC And each of these measurements is spaced 28 inches (71 centimeters) apart.
Moving in a pole-to-pole orbit, ICESat-2 travels 1,387 different orbital paths every 91 days. Therefore, the spacecraft will provide data for each season of the year.
At launch, the satellite was to operate for three years, but much of its 3,482 pounds. (1,580 kilograms) is a fuel that, if desired, can extend the mission of ICESat-2 to seven years.
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