Twin sportscar-sized satellites to chase water changes on Earth

Olive Hawkins
May 26, 2018

When the rocket's second stage has completed its ascent to the injection orbit altitude, it will pitch down (its nose points down) 30 degrees and roll so that one of the twin GRACE-FO satellites is facing down, toward Earth, and the other is facing up, toward space.

SpaceX is continuing its rapid-fire schedule of rocket launches today with a dual-purpose mission to deliver satellites for both NASA and its communications client Iridium. The two Gravity Recovery and Climate Experiment Follow-On mission (GRACE-FO) spacecraft will join five Iridium NEXT communications satellites as the payload on a SpaceX Falcon 9 rocket.

This is an unusual launch - the rocket will be making some complicated maneuvers 300 miles up to make sure NASA's satellites are deployed correctly, then it travels the rest of the way to the targeted orbit for the communication satellites.

SpaceX's recovery ship, Mr Steven is heading out into the ocean to attempt to catch at least one half of the expensive shell used to protect spacecraft during the early phases of launch.

The Iridium Next communications satellites that SpaceX is launching with GRACE-FO are the latest in a series for Iridium Communications to build up that company's satellite constellation.

According to the laws of physics, the slightest variation in mass on Earth modifies the pull of gravity on satellites.

The GPS III satellites are expected to provide improved security against cyberthreats, as well as more accuracy for navigation. Two of those included new Earth-observing satellites from NASA. They are the replacement for the original GRACE mission, which ended operations in 2017, fifteen years after it first began.

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The fairings landing in the Pacific Ocean after deploying parachutes to slow their descent.

The McLean, Virginia, company now has 55 Iridium NEXT satellites in orbit. This launch makes the Iridium NEXT satellite constellation a conglomeration of 75 satellites (nine of which are spares).

"GRACE was really a revolutionary mission for us understanding the water cycle and how the climate behaves and the trends that are taking place", said Frank Webb, GRACE-FO project scientist at NASA's Jet Propulsion Laboratory.

Watch the live launch of GRACE-FO right here! The pair measure Earth's gravity field by detecting minute changes (down to a micron level) in the distance between the spacecraft caused by anomalies in gravity.

In addition to the microwave ranging system also used by the original GRACE satellite, the GRACE-FO satellites will use a laser rangefinder to measure their separation.

The GRACE-FO satellites were assembled by Airbus Defence and Space in Germany.

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