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Grace Follow-on Could Arrive Too Late To Prevent Data Gap

Joint U.S.-German Grace satellites. Credit: NASA artist's concept

PARIS — A successor mission to the U.S.-German Grace satellites, which have measured Earth’s gravity field for a decade and found broader application in drought monitoring and water resource assessment, may not arrive in time to provide uninterrupted data, according to current program projections.

NASA and the German Aerospace Center, DLR, with the German Research Center for Geosciences, GFZ, appear to have secured sufficient funding to build and launch two Grace Follow-On (Grace FO) satellites. The follow-on mission will include a U.S.-German laser-interferometry instrument and an accelerometer provided by France’s Onera aerospace research facility.

The satellites will be manufactured by Astrium Satellites of Germany, which built the original Grace spacecraft.

The Grace spacecraft, launched in March 2002, are separated by 220 kilometers in their 500-kilometer orbit. Changes in mass in different areas of the Earth are measured by detecting small changes in the satellites’ separation.

The Grace satellites were originally scheduled to operate for five years. But they have remained in sufficiently good health for NASA and DLR to agree to successive mission extensions, the latest to 2015.

The satellites are flown in such a way as to maximize their mission life by putting as little stress on the satellites’ batteries as possible.

NASA’s Jet Propulsion Laboratory, DLR and GFZ originally hoped to have the Grace FO satellites in orbit by early 2016. But in recent presentations to Grace workshops, they say a launcher selection will not be made until next spring, with a launch in 2017.

“I cannot promise that” the current Grace satellites will be able to survive until the Grace FO spacecraft are launched, said Frank Flechtner, Grace FO project manager at GFZ, in a Nov. 16 response to SpaceNews inquiries. “We are doing our best and are optimistic that we will continue the mission’s duration as long as possible.”

DLR will select the launcher and has received bids from Arianespace of Europe, proposing Europe’s new Vega small-satellite launcher; from Eurockot of Germany, offering the German-Russian Rokot; and from Kosmotras of Moscow, which commercializes the Dnepr rocket.

Europe, proposing Europe’s new Vega small-satellite launcher; from Eurockot of Germany, offering the German-Russian Rokot; and from Kosmotras of Moscow, which commercializes the Dnepr rocket.

 

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