"data-medium-file =" http://www.clarksvilleonline.com/wp-content/uploads/2011/08/NASA.jpg "data-large-file =" http://www.clarksvilleonline.com/wp -content / uploads / 2011/08 / NASA.jpg "class =" alignleft size-full wp-image-85503 "title =" NASA – National Aerospace Authority "src =" http://www.clarksvilleonline.com/ wp-content / uploads / 2011/08 / NASA.jpg "alt =" NASA – National Aerospace Authority "width =" 200 "height =" 165 "/> Pasadena, CA – Imagine standing in front of the roof of a building in Los Angeles and trying to aim a laser so accurately that it could hit a certain building in San Diego, more than 100 miles (160 kilometers) away.
This accuracy is for the performance The technology demonstration on board the GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) mission will soon be successful.
For the first time, a promising technology is emerging called laser distance interferometry between two satellites tested lites
GRACE-FO will demonstrate the effectiveness of using lasers instead of microwaves to more accurately measure fluctuations in the separation distance between the two spacecraft, potentially reducing the precision of Ranged range measurement on future GRACE-type missions by a factor of at least 10 (NASA / JPL-Caltech)
GRACE-FO, scheduled for launch on May 19, is continuing the rich legacy of the original GRACE mission, which launched in 2002 on a planned five-year mission and completed operations in the October 2017.
Under these findings, GRACE transformed our understanding of the global water cycle by showing how the masses of liquid water and ice change each month.
The mission also contributed to our knowledge of large-scale changes in the solid earth. GRACE-FO will ensure continuity of GRACE measurements for at least another five years and further enhance the scientific understanding of Earth system processes and the accuracy of environmental monitoring and forecasting.
How does GRACE work?
GRACE has obtained its data on the Earth's mass movement by accurately measuring minute changes in the distance between two spacecraft flying around the Earth in succession. As the satellites experienced a change in the distribution of Earth's mass – like a mountain range or a mass of underground water – Earth's gravitational force on the spacecraft changed the distance between them.
For example, the Himalayas changed the separation distance by about three hundredths of an inch (80 microns). By accurately calculating each month how the distance of the satellites changed during each orbit and over time, it was possible to detect changes in the earth mass distribution with high precision.
Measuring the change in separation between the spacecraft was too high a degree of precision because each spacecraft sent microwaves to the other. The way the waves changed with each other – how they disturbed each other – created a microwave interferometer in space.
This process essentially transformed the two spacecraft into a single instrument that could very accurately measure the change in distance between them, and in turn could be linked to changes in mass distribution on Earth.
What's new about GRACE-FO?
GRACE-FO works according to the same principles. Each spacecraft again carries a microwave instrument to track changes in the separation distance. But GRACE-FO also carries something new: a technology demonstration of a Laser Distance Interferometer (LRI), jointly led by NASA's Jet Propulsion Laboratory in Pasadena, California, and the Max Planck Institute for Gravitational Physics (Albert-Einstein Institute) in Hanover becomes. Germany. In addition to the transmission of microwaves, the GRACE-FO satellites will allow each other to emit laser radiation.
Since the wavelengths in a laser beam are much shorter than microwave wavelengths, the laser range interferometer will improve the tracking accuracy of separation changes – just as the measurement would be more accurate in millimeters rather than centimeters. The GRACE-FO interferometer detects changes in distance that are more than ten times smaller than what the microwave detects – changes as much as 100 times smaller than a human hair.
"With GRACE-FO, we're taking something out of the lab and getting it ready for space," said Kirk McKenzie, the LRI instrument manager at JPL. "The reason why we work decades in the lab is because our technology enables a new way of measuring and leading to scientific discoveries."
Each GRACE-FO satellite will be able to detect the laser signal of the other. But that is not an easy task. Each laser has the power of about four laser pointers and must be detected by a spacecraft on average 137 miles (220 kilometers) away. Even the ultra-precise positioning of the satellites is not enough to ensure that the laser transmitted by each spacecraft is well enough aligned to hit the other spacecraft.
McKenzie explains that for the first time the laser range interferometer is turned on, the LRI components on each spacecraft must scan to send out the instrument's signals and try to "catch" the other's signals in all possible configurations. The spacecraft has so many possible configurations that it takes nine hours
GRACE-FO will measure monthly changes in gravitational force resulting from changes in the Earth's mass among the orbiting satellites. As the satellites orbit the Earth in succession, these moving masses alter the gravitational force beneath them change the distance between them very easily. (NASA / JPL-Caltech)
For one millisecond of d There will be a flash of lightning every nine hours. Both spacecraft show that they are talking to each other. Once this signal detection has taken place, the optical connection of the interferometer is formed and then the instrument is operated continuously and autonomously.
"We are trying something that is very difficult – the very first demonstration of laser interferometry in space between satellites," said Gerhard Heinzel, the instrument manager at the Max Planck Institute. "But it's very satisfying to puzzle over a problem and find something that works."
The difficulty of the task required the development of various subjects. JPL monitored the laser on the interferometer, the measurement electronics and the optical cavity. The Max Planck Institute was responsible for the optics, detectors, mirrors and beam splitters. The GRACE-FO laser range interferometer also took advantage of the 15-year history of the two groups working on the technology of the ESA / NASA Laser Interferometer in Space Antenna (LISA) mission launched in the early 2030s.  Why try something so difficult?
"The GRACE-FO laser range interferometer may be a fundamental technology for future missions on Earth or even for the universe," said Frank Webb, project scientist at GRACE-FO at JPL. "This new, higher precision measurement should enable more efficient missions with lower mass, performance, and cost in the future, and we're curious to see how it works and what new signals we can get out of the data."
If this new technology is successful, promises Improving the resolution of future GRACEFO-like missions with a diameter of more than 200 miles (300 kilometers), together with an improved accelerometer, will allow future missions to track and pinpoint changes in smaller bodies of water, ice, and solid earth.
GRACE-FO is a partnership between NASA and the German Research Center for Geosciences (GFZ) in Potsdam, Germany
JPL heads the mission of the NASA Directorate for Scientific Missions. Additional contributions to the laser range interferometer include SpaceTech in Immenstaad; Tesat-Spacecom in Backnang, Germany; Ball Aerospace in Boulder, Colorado; iXblue in Saint-Germain-en-Laye, France; German Aerospace Center (DLR), Institute of Robotics and Mechatronics in Adlershof and Institute of Space Systems in Bremen; Hensoldt Optronik in Oberkochen; Apcon AeroSpace and Defense in Neubiberg / Munich; Diamond USA, Inc. and Diamond SA in Losone, Switzerland; and Airbus Defense and Space at Friedrichshafen
For more information on GRACE-FO, see:
https: //www.nasa. gov / gracefo
Earth, Gravity, Jia-Rui Cook, NASA, NASA's GRACE-FO satellite, NASA's Jet Propulsion Laboratory, NASA's Mission Directorate, National Aeronautics and Space Administration, Pasadena CA