Milestone for climate research satellite mission

AEI developed engineering model of key instrument for ESA’s Next Generation Gravity Mission has been successfully tested

To the point

• Major Milestone: AEI researchers have developed the engineering model of the Instrument Control Unit (ICU) for the scientific payload of the European Space Agency’s Next Generation Gravity Mission (NGGM). Now, they have successfully completed the ICU's final performance verification campaign.
• Observing climate change from space: Scheduled for launch in 2032, NGGM will continue and extend the heritage of the GRACE satellite missions. From a low Earth orbit, it will observe critical indicators of climate change. Together with GRACE-C, NGGM will observe changes of the Earth’s gravity field much more rapidly and clearly.
• Expertise at the AEI: AEI researchers leverage their decades of experience to foster synergies between space-based gravitational-wave observation and Earth observation. They are contributing to three future satellite missions: GRACE-C, NGGM, and LISA.

After four years of technological development at the AEI and four months of rigorous testing, the engineering model of the Instrument Control Unit (ICU) for the European Space Agency’s (ESA) Next Generation Gravity Mission (NGGM) has passed its final technological review with flying colors. The ICU monitors and coordinates the measurement, control and data handling functions of the spaceborne laser instrument. With the successful completion of the performance verification campaign, the AEI team has demonstrated the ICU’s compliance to the most relevant requirements. 

“Our ICU is the first dedicated instrument control system for inter-satellite laser-interferometry developed entirely in Europe,” says Vitali Müller, a senior scientist responsible for NGGM at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute; AEI).

“This achievement demonstrates the unique expertise of AEI’s scientists and engineers to develop and validate complex laser-interferometric instruments for space missions,” adds Guido Müller, director of the Precision Interferometry and Fundamental Interactions department at the AEI, “The experience gained through NGGM strengthens the technological foundation for future missions such as LISA and further consolidates the leading role of the Max Planck Society and science in Germany in space-based interferometry.”

ESA’s Next Generation Gravity Mission

NGGM is a planned European satellite tandem scheduled for launch in 2032. Its goal is to globally monitor indicators of climate change. This includes detecting sinking groundwater levels, melting ice caps, and rising sea levels by observing changes in the Earth’s gravitational field.

NGGM will continue the long-term measurements of climate change indicators begun by earlier satellite missions such as GRACE, which mapped the Earth’s gravity field from 2002 to 2017, and GRACE Follow-On, which began its observations in 2018 and is expected to continue them until 2028. GRACE Follow-On’s successor, GRACE-C, is scheduled to launch in 2028.

Observing climate change from space with lasers

NGGM and GRACE-like missions send laser beams back and forth between two satellites to measure changes in their relative distance with nanometer precision. These tiny distance changes are caused by the varying gravitational pull of the part of the Earth below the satellites. Using this data, researchers can determine, for example, how much ice has melted in a specific region of Greenland or how groundwater levels have changed in a particular area of the world.

The Instrument Control Unit serves as the brain of NGGM’s Laser Tracking Instrument. It derives the inter-satellite distance measurements from the laser signals, controls the optical bench electronics and laser subsystems, and generates the telemetry that is sent to the spacecraft’s onboard computer.

Better maps with MAGIC

All GRACE-like satellite pairs circle the Earth 220 kilometers apart from each other in a low Earth orbit that takes them over the planet’s poles. The two NGGM satellites will have a similar distance, but their orbit will be inclined relative to the GRACE orbits.

The Mass-Change and Geosciences International Constellation (MAGIC) project will combine GRACE-C and NGGM measurements while the satellites simultaneously observe Earth. With MAGIC, researchers will be able to significantly improve how precisely they can monitor changes in the Earth’s gravitational field – both in time and in space.

“With MAGIC, we can see much more rapidly and clearly how and where our planet changes”, says Gerhard Heinzel, group leader at the AEI and the Instrument Scientist for German contributions to GRACE-C. “MAGIC will produce gravity maps of the Earth up to every three days instead of once a month with a resolution as good as 100 kilometers instead of several hundred.”

Expertise at the AEI

AEI researchers are involved in the design of the laser instruments used in both GRACE-C and NGGM because of their decades of expertise. They leverage their prior experience in designing and managing GRACE Follow-On technology to foster synergies between space-based gravitational-wave observation and Earth observation: The phasemeter developed at the AEI for the planned space-based gravitational-wave observatory LISA was adapted to the needs of the gravity field mapping missions. Additionally, an improved differential wavefront sensing algorithm was implemented as a joint venture between the development of NGGM’s ICU and LISA.

The ICU engineering model was realized under contract to SpaceTech GmbH together with industrial partners: Guizzo Space, for the electronics design and manufacturing, and Airbus Defence and Space GmbH supporting the firmware and software development.

The results from the engineering model development, design, and tests will guide the next steps towards further ICU development and the launch of NGGM. The industrial partners will now start building engineering-qualification and flight models of the ICU. This will be accompanied by further extensive tests of the hardware at the AEI.