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Unique climate mission to end as an impressive shooting star

Posted December 22, 2017

The twin climate satellites GRACE 1 and GRACE 2 have completed their mission and will burn up like shooting stars on re-entering the Earth’s atmosphere.

Since the GRACE mission was launched into space by NASA in 2002, it has comprehensively mapped the Earth’s climate. Research from DTU Space based on data received from the GRACE satellites has helped to establish that Greenland is losing about 280 billion tonnes of ice sheet a year, corresponding to a global rise in sea levels of 0.8 millimetres a year.

DTU Space has made a big mark on the mission. In addition to extensive climate research based on data collected from the twin Gravity Recovery and Climate Experiment (GRACE) satellites, DTU Space has also delivered two star trackers for each satellite, which have ensured that they have navigated precisely in relation to each other and in their respective orbits around the Earth.

“The GRACE mission has been very special. The two satellites constituted a relatively inexpensive mission, but one which has contributed hugely to our scientific work. Hundreds of scientific articles have been published based on data delivered by the satellites. Danish researchers and DTU Space have contributed to many of them, both as lead authors and co-authors,” says Professor Per Knudsen from DTU Space.

“GRACE is regarded as being one of the most important climate missions so far to have been carried out in space. It forms the basis for much of the IPCC’s work and climate reporting.”

The GRACE mission has been joined by other missions along the way, and these are now continuing the work of monitoring the Earth’s climate from space by delivering data to researchers.

Precise mapping of Greenland’s ice sheet
The GRACE satellites have mapped the Earth’s magnetic field, the hydrological cycle and important aspects of the oceans’ movements.

“The mapping has been done with great precision, which has led to important research findings. Among other things, we have been able to use this data to map changes in the Greenland ice sheet very precisely. Data from the GRACE satellites is thus one of the reasons why today we know so much about the impact of climate change on the ice melting,” says Per Knudsen.

In principle, the GRACE satellites measure variations in the Earth’s gravitational field as water shifts around the Earth. For example when ice melts and runs into the oceans, when water moves from subterranean aquifers, and when sea water changes temperature. Based on this and other data, it is possible to calculate the changes in the ice masses.

“GRACE is one of the most highly honoured NASA satellite missions, and our contribution has worked perfectly, and we are naturally proud of this,” says Professor John Leif Jørgensen from DTU Space, who is behind the development of the star trackers for the GRACE satellites.

No risk of space debris on Earth
It is not possible to predict exactly when the satellites will enter the Earth’s atmosphere and burn up after using all their fuel and beginning their descent.

However, there is no risk of them crashing and destroying anything here on Earth,” says John Leif Jørgensen.

“It was a requirement that the GRACE satellites were built in such a way that nothing would be left of them by the time they hit the Earth’s surface, as they will have burnt up completely,” he says.

Source: DTU

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