NASA has powered on the laser ranging interferometer or LRI instrument aboard the recently launched twin climate-monitoring satellites Gravity Recovery and Climate Experiment Follow-On or GRACE-FO.

The satellites were launched from the Vandenberg Air Force Base in California on May 22 aboard a SpaceX Falcon 9 rocket.

Working As Expected

The LRI, which was flown as a technology demonstration, already made its first measurements along with GRACE-FO's main microwave ranging instrument. Data from the two instruments reveal they agree as expected.

LRI's first light operation happened over a course of two days. On June 13, the twin GRACE-FO satellites started to sweep their lasers in a spiral pattern to search for each other.

Each of the two satellites will be able to detect the laser signal of the other but this is not an easy feat. Each of the lasers has power equivalent to about four laser pointers and needs to be detected from an average of 137 miles.

Despite the ultra-precise assembly of the satellites, NASA said that this does not provide enough guarantee that the laser from each spacecraft is aligned well enough to hit the other spacecraft.

"There are coin-sized holes on each satellite through which the laser has to be precisely pointed towards the holes in the other satellite over a distance of more than 200 kilometers [137 miles], while both spacecraft race around Earth at 27,000 kilometers an hour [16,000 miles per hour]," explained Gerhard Heinzel, the instrument manager at the Max Planck Institute. "It is truly mind-boggling."

It is for this reason that the first time the LRI is turned on, the components of LRI on each of the satellites have to perform a scan to send out signals and to capture the other satellite's signals in all possible configurations.

Downlinked data revealed that each of the spacecraft was able to see several flashes of light during the spiral scans, which indicate that both LRI instruments received light from the opposite spacecraft and were working as expected.

"We're trying something that is very hard -- the first-ever demonstration of laser interferometry in space between satellites," Heinzel said. "But it's very satisfying to puzzle over a problem and find something that works."

GRACE-FO Mission

The mission, a partnership between NASA and the German Research Center for Geosciences, will track the changing pull of gravity on the GRACE-FO satellites. This will provide the data needed to help scientists monitor and have a better understanding of the thinning of the ice sheets, the rising sea levels, the phenomena popularly associated with climate change, and the flow of magma underground.

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