High Stability Laser (HSL)

ESAs next generation gravity mission (NGGM) is a successor to GOCE. The launch date towards the end of this decade shall provide significantly improved measurement resolution.
Similar to the GRACE mission (launched 2002) a satellite-satellite-tracking (SST) scheme is planned, with a laser interferometer instead of a Ka-Band link providing much higher measurement accuracy.

High Stability Laser key importance

Of key importance for the laser interferometer is a laser source with sufficient power and extremely high frequency stability down to several Hz (from 281 THz laser frequency).

In the scope of the “High Stability Laser (HSL)” activity funded by ESA (2012 to 2015), an elegant bread board (EBB) of a master oscillator – fiber power amplifier stabilized to a Fabry-Perot reference cavity has been developed.

Key characteristics of HSL

  • Modular
  • Fibre-based
  • Light
  • High stability of laser frequency and output power

HSL ConceptHSL concept

 Key and driving instrument requirements for High Stability Laser

  • Laser frequency stability of  40 Hz/√Hz (for 0.1 mHz -1 Hz)
  • Laser power stability of 1x10-3  1/√Hz (for 0.1 mHz -1 Hz)

SpaceTech's role in the HSL project

SpaceTech as the prime contractor with the project partners National Physical laboratory (NPL), Fraunhofer Institute for Laser technology (ILT) and Airbus DS was responsible for:

  • Project coordination and system engineering
  • Thermal and structural modeling of the laser head (being developed by ILT) and the laser stabilization unit (being developed by NPL)
  • Design of space compatible electronics
  • Performance modeling
  • AIT planning

The HSL EBB has been set-up and successfully met all requirements.
In 2016, the consortium of SpaceTech, Fraunhofer ILT, the National Physical Laboratory (NPL) and Airbus DS has been selected for the development for the high stability laser (HSL) for a potential 'Next Generation Gravity Mission' (NGGM) to further proceed the successful development and testing of the HSL EBB performed between 2012 and 2015.

Activity objective of HSL

The objective of this activity is to raise the maturity of the laser system to TRL 5 on subunit level and TRL 7 on component level. SpaceTech as prime contractor signs responsible for project management, system engineering, electrical, structural and thermal design. Fraunhofer ILT is responsible for the laser head and the environmental test campaign of laser head components. The National Physical Laboratory is responsible for the reference cavity. Airbus DS performs the environmental test campaign of the laser system. This activity will end 2018.


The project work is/was carried out under a programme of and funded by the European Space Agency (ESA). The view expressed herein can in no way be taken to reflect the official opinion of the European Space Agency.

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