NASA launches ICESat-2 satellite with laser pulses to measure the sea ice, glaciers and oceans of the Earth

United Launch Alliance is currently preparing the launch of the company's latest Delta 2 rocket for a flight to orbit a $ 1 billion NASA satellite, ICESat-2. The satellite will launch 10,000 laser pulses per second on Earth to measure the altitude, thickness and extent of the polar ice patches and glaciers.

The goal is to replace an older, less powerful satellite – ICESsat – and expand current IceBridge aircraft measurements, allowing for more accurate predictions of ice loss and sea level rise because of climate change and other factors. The instruments also measure the height of forest cover, lakes and levels of the ocean.

"One of the most important things for us as scientists trying to changes in the ice The length of the recordings is due to changes in the Earth system, "said Tom Wagner, chief scientist at NASA headquarters.

"By having ICESat, IceBridge and ICESat 2, we will be able to look at the ten-day time scale and see how variations of terrestrial systems affect the ice, so that we can do a better job with the forecasts and also understand the changes that are taking place. currently produce. "

Take-off from Vandenberg Air Force Base, northwest of Los Angeles, is scheduled for 5:46 am local time (GMT-7, 8:46 am EDT), opening a two-and-a-half hour window. Forecasters have predicted a 100 percent probability of acceptable weather, although ground fog should reduce visibility near the skate.

While the takeoff will mark the beginning of a crucial environmental search mission, it will mark the end of an era for the Delta 2 while the nostalgic rocket engineers will participate in the last flight of the propeller.

Making its first flight in 1989, the medium-sized Delta 2 rocket, originally built by McDonnell Douglas, then Boeing and now United Launch Alliance, put into orbit the first of more than two navigation satellites in the system. global positioning. America and around the world.

Since then, Delta 2 has launched dozens of satellite relay stations, seven Mars missions, including the Pathfinder, Spirit and Opportunity rovers, as well as numerous Earth observation satellites and scientific satellites, including the Spitzer Space Telescope. and the Kepler telescope.

A total of 154 Delta 2 rockets were launched between the first flight of the propeller in February 1989 and its last flight in November 2017. The program suffered only one failure, caused by the failure of the aircraft. a strap booster in 1997 and since then 99 Delta 2 in a row have been successfully launched. If all goes well, ICESat-2 will mark the hundredth.

"I'm a bit melancholy about this," said NASA's launch director Tim Dunn. "The Delta 2 has a very special place in the hearts of many people, it's been around for 30 years, and it's really a legacy of Delta 1, which dates back to May 1960. It's going to be the 381st launch of any type of Delta vehicle. , the 155th launch of a Delta 2. "

Scott Messer, NASA's program director for the United Launch Alliance, said Delta 2 rockets launched "everything from GPS missions to Earth observers such as ICESat-2 and weather satellites, as well as Mars missions". .

"If you think about it, the Delta 2 has probably touched the lives of everyone in America with the technology it has made possible in its 30s, so it's a very important part of it. of the history of space. "

The ICESat-2 mission is a final cargo adapted to the Delta 2.

The 3,340-pound solar satellite is one of the most technologically sophisticated environmental research spacecraft. It is designed to measure the height, thickness and extent of bottom ice and ground to an accuracy of less than one inch.

This will be done from a 300-mile-high polar orbit inclined 88 degrees from the equator using a single instrument called advanced laser altimetry system, or ATLAS, including a laser and advanced electronics capable of firing thousands of times. second. If problems develop, a backup is integrated.

By measuring the time required for a telescope in the ATLAS instrument to detect photons reflected back in space, scientists can calculate the distance between ice surfaces, compare them to surrounding areas and determine their height and their relative thickness. Over time, researchers can see how these levels evolve.

"By the time the beam is coming out of the instrument, it is divided into six beams," said Donya Douglas-Bradshaw, head of ATLAS instruments at NASA's Goddard Space Flight Center. "ATLAS essentially acts as a stopwatch, the ATLAS laser triggers 10,000 pulses per second with a trillion photons per shot, and every time the laser goes off, it triggers a stopwatch."

It will take about 3.3 milliseconds for the green beams to leave the laser, reach the earth's surface and bounce back. Only a dozen photons in each beam will travel to the telescope, but each will reflect a specific longitude, latitude, and elevation.

"Douglas ATLAS has the ability to label a single photon at one-billionth of a second," Douglas-Bradshaw said. "This accuracy allows the instrument to detect annual changes in ice elevation in the order of half a centimeter.

Tom Neumann, Assistant Project Director ICESat-2, said that precision to the billionth of a second is essential.

"Sea ice is often only a few centimeters higher than the water in which it floats," he said. "And as the speed of our laser light is so fast, the timing must be incredibly accurate.ATLAS will be able to measure elevation differences of just a few inches from its orbit 300 miles above the Earth." but science depends critically on it. "

The first ICES presented a single laser beam and elevation measured at approximately 100 meters along the ground track. Neumann said the new satellite's ATLAS instrument will measure the elevation every two feet with each of its six beams when the satellite moves in space at around 16,000 mph.

"To put this in perspective, in half a second, you need a person to blink, ICESat-2 will collect 5,000 elevation measurements in each of its six beams, every minute of every hour every day for the next three years. " I said. "And this incredible timing accuracy will allow us to measure elevation changes across the entire ice surface to within one centimeter."

That's important, he said, because the changes in altitude from one centimeter, or less than half an inch, on an ice sheet the size of the Antarctica represent a huge amount of water, either gains or losses from the ice sheet – 140 gigatonnes. "Neumann said.

The ICESat-2 orbit is designed to allow repeated observations of the same areas as the mission progresses. Every 91 days – 1,387 orbits – ICESat-2 will return to its starting point and begin to repeat its initial observations.

"This allows the mission to look at the same piece of land in each of the four seasons, allowing scientists to use this data to characterize the changes they observe," Neumann said.

ICESat-2 is designed to operate for at least three years, but the spacecraft has enough propulsion to last seven to ten years while it stays healthy.