United Launch Alliance is preparing the company's Delta 2 rocket for take-off on Saturday on a flight to put in orbit a $ 1 billion NASA satellite – ICESat-2. The satellite will take 10,000 laser pulses per second on the Earth below to measure the height, thickness and extension of theand glaciers.
The goal is to replace a previous, less powerful satellite – – ICESsat – and to extend the measurements of the "IceBridge" aircraft, allowing for more accurate predictions ofdue to climate change and other factors. The instruments also measure the height of forests, lakes and .
"One of the most important things for us as scientists trying to bindto changes in the earth system is the duration of the recording," said Tom Wagner, a senior scientist at the NASA.
"With ICESat, IceBridge and ICESat 2, we will be able to look at the decadal time scale and look at how the biggest variations in terrestrial systems are affecting ice, so we can do better work with forecasts and also understand the changes that are taking place now. "
Takeoff from the Vandenberg Air Force Base in Northwest Los Angeles is targeted for 5: 46 am PDT (GMT-7; 8:46 am EDT), & # 39; opening a two and a half hour window. Meteorologists predicted a 1
As the take-off will mark the start of a critical environmental research mission, it will mark the end of an era for Delta 2 while the nostalgic rocket engineers take the final flight of the work booster.
Taking the inaugural flight 1989, the mid-range Delta 2 missile, originally built by McDonnell Douglas, then Boeing and now the United Launch Alliance, placed the first of more than two dozen Global Positioning System navigation satellites, changing the way transport operates in America and around the world.
Since then, Delta 2s has launched dozens of satellite telephone repeaters, seven missions to Mars, including Pathfinder, Spirit and Opportunity rovers and numerous Earth observation satellites and scientific spacecraft, including the telescope Spitzer space and the Kepler telescope for planet hunting.
In all, 154 Delta 2 missiles were launched between the first flight of the booster in February 1989 and its most recent flight in November 2017. The program suffered only one failure, caused by the breaking of a strap-on repeater in the 1997, and since then, 99 Delta 2 in a row have been successfully launched. If all goes well, ICESat-2 will score 100.
"I'm a little bit sad about that," said NASA's launch director Tim Dunn. "Delta 2 occupies a very special place in the heart of so many people, has been around for 30 years and has carried on the legacy of Delta 1, which arrives until May 1960. This will be the 381 th launch of any kind of Delta, the 155th launch of a Delta 2. "
Scott Messer, head of NASA programs for United Launch Alliance, said the Delta 2 missiles launched" everything from GPS missions to Earth observers like ICESat- 2 and meteorological satellites and missions to Mars. "
" If you think about it, the Delta 2 vehicle has touched the lives of probably every single person in America in the technology it has enabled in its 30s – a very important part of the story of space. "
The ICESat-2 mission is a final load suitable for the Delta 2.
The 3,340-lb. solar-powered satellite is one of the most technologically sophisticated environmental research space vehicles ever built. It is designed to measure the height, thickness and extension of land and sea ice with an accuracy of less than one inch.
It will do so from a polar 300-mile orbit inclined at 88 degrees to the equator using a single tool known as the Advanced Topographic Laser Altimeter System, or ATLAS, which includes a laser and a & # 39; advanced electronics that can activate it thousands of times per second. If problems develop, a backup is on board.
By measuring the time taken by a telescope in the ATLAS instrument to detect photons reflected in space, scientists can calculate how far a frozen surface is, compare it with the surrounding areas and determine the relative height and thickness. As time passes, researchers can see how these levels are changing.
"When the beam exits the instrument, it is divided into six beams," said Donya Douglas-Bradshaw, director of ATLAS instruments at NASA's Goddard Space Flight Center. "ATLAS essentially acts as a stopwatch. The ATLAS laser emits 10,000 pulses per second with one trillion photons in each shot. Each time the laser turns on, a stopwatch is started."
It will take about 3.3 milliseconds for the green rays to leave the laser, reach the earth's surface and recover. Only about a dozen photons in each beam will return it to the telescope, but each will reflect a specific longitude, latitude and elevation.
"ATLAS has the ability to label a single photon up to one millionth of a second of accuracy," This precision allows the instrument to detect annual changes in raising the ice by an order of half a centimeter. "
Tom Neumann, deputy director of the ICESat-2 project, said that the billionth of a second accuracy is crucial.
"Sea ice is often only a few centimeters higher than the water that it floats, "he said." And because the speed of our laser light is so fast, the timing must be incredibly accurate. ATLAS will be able to measure height differences of a few centimeters from its orbit to 300 miles above the Earth. It is truly an incredible engineering undertaking, but it is one of those on which science depends critically. "
The original ICESat presented a single laser beam and measured the elevation at about 100 yards along its ground track, the new satellite measuring the elevation every two feet with each of its six rays as the satellite moves through space at about 16,000 miles per hour
"To put this in perspective, in the second half it takes a person to blink, ICESat-2 will collect 5,000 elevation measurements in each of its you're beams, every minute of every hour of every day for the next three years, "he said." And that incredible timing accuracy will allow us to measure elevation changes across the entire ice sheet to less than a centimeter. "
This is important, he said, because the changes in height of one centimeter, or less than half an inch, on an ice cap the size of Antarctica" represent an enormous amount of water, or gains or losses from the ice sheet – 140 gigatons of value, "said Neumann
The ICESat-2 orbit is designed to allow repeated observations of the same areas in which the mission advances.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 are looking at, "said Neumann.
ICESat-2 is designed to work for at least three years, but the spacecraft has enough propellant on board to last from seven to 10 years if it stays healthy. [1 9659034]