High stability laser for interferometric Earth Gravity measurements in the context of a Next Generation Gravity Mission (NGGM)
Programme
GSTP
Programme Reference
G611-017MM
Prime Contractor
SPACETECH GMBH
Start Date
End Date
Status
Contracted
Country
Germany
Objectives
The high-stability laser for interferometric measurements is one of the key elements of European non-dependence regarding enabling technologies for Earth Gravity missions of type GRACE FO and beyond. The goal of the follow-on activity is to increase the TRL of the laser head from TRL3/4 to TRL5/6 on subsystem/component level respectively. The main focus lies on raising the TRL of the individual fibre components to TLR6, as the next important development step to a later full qualification, followed by the development of a TRL 5 design on the laser head.
Description
Potential concepts and their related technologies for a Next Generation Gravity Mission (NGGM) as a follow-up to the GOCE mission are currently being studied. The mission will be designed to monitor the variations of the Earth?s gravity field to a level that allows the study of mass transport processes not only in solid Earth but also at the Earth surface layer and in the lower atmosphere. In order to achieve the challenging set of objectives it is necessary to significantly improve the measurement resolution and accuracy far beyond the current level of GOCE or its predecessor mission GRACE. Previous studies and validation experiments conclude that the best measurement concept is spacecraft-to-spacecraft tracking of two satellites flying an in-line formation tandem of 100 ? 250 km distance in a low Earth orbit at around 300 km height. The concept to infer local/instantaneous gravitational acceleration anomalies with ultimate precision from sophisticated laser interferometry between the satellites is similar to the designated GRACE follow-up EX-5. In this context the laser system with its key performance parameters stability / noise of the laser frequency (and output power) is a core element of such mission driving the ultimate measurement precision.
;
The proposed activity is based on the technology developed in the frame of TRP contract 'High-Stability Laser with Fibre Amplifier + Laser Stabilisation Unit for Interferometric Earth Gravity Measurements' (Elegant Breadboard). The laser specifications are compatible with a displacement measurement performance of 10 nm/ Hz1/2 on system level over the full measurement bandwidth, i.e. aiming beyond GRACE FO capabilities.
;
The scope of this follow-on activity comprises three consecutive major work
activities:
;
- Perform environmental tests with the laser head of the High-Stability Laser Elegant Breadboard, developed in the current activity 'High-Stability Laser Elegant Breadboard. These tests are focused on the fibre amplifier (FCB) an consist of thermal vacuum tests (operational and nonoperational), vibration and shock tests.
- Assess and verify the development status of the fibre amplifier components (such as inline optical Isolators, bandpasses, pump diodes and photodiodes) in detail.
- Investigation on the space qualification status of the required components.
- Discussion with the manufactures on used processes and ;materials.
- Environmental test programme (thermal vacuum, radiation, vibration and shock) for the components where the qualification ;tatus is not sufficient to meet the HSL requirements (based on ;GOCE mission environment).
- The goal is to achieve TRL6 on component level. Up to 10 samples of each component will be tested. The results of environmental testing will be measured data on the space worthiness of the tested components.
- Laser Head design refinement to TRL5 design on Laser Head subsystem level including breadboard testing on component level to verify critical design details (e.g. fiber fixation technology).
;
It is proposed to develop the Laser Stabilisation Unit (LSU) to TRL 6 at the sub-system level. In particular, the ;following additional tasks are proposed:
- Based on the input from environmental testing from the ORCS activity (GSTP AO06-28MM - Optical Reference Cavity for Space (ORCS)), and further environmental testing of HSL1-EBB (High Stability Laser Elegant Bread Board) including the optics arm, to assess the baseline TRL close to project start.
- The Laser Stabilisation Electronics will be redesigned as a digital electronics package satisfying NGGM requirements.
- The design of the LSU will be refined in order to meet TRL 6.
- Relevant sub-components for further development shall be identified and ? where necessary and feasible ? selected components investigated for flight compatibility.
;
In addition, the current consortium is proposed to include NPL (UK). NPL will be responsible to implement the additional tasks proposed in this update of the activity. ;
NPL has been part of the HSL1 consortium and designed and built the Laser Stabilisation Unit for the High Stability Laser, which successfully passed all performance and environmental testing.
;
It is proposed to change the scope, budget and duration of the activity.
;
Under the previous activity change, a first optics arm was designed for the Laser Stabilization Unit (LSU). The objectives of the proposed activity change are to update the design based on new requirements and to manufacture and test an Optics Coupling Arm (OCA) by integrating it with an existing and functioning optical system. The choice of this optical system, currently at TRL 6, is the Optical Stabilising Reference Cavity (OSRC), which is being developed under another GSTP activity, G617-189MM - Development of an acceleration insensitive, thermal noise mitigated, Optical Stabilising Reference Cavity (OSRC) Engineering Model.
;
In order to verify the optics arm, a test will be performed, using a structural Ground Support Equipment (GSE), representing the structural thermal cavity model. The result will be a verified TRL6 on the OCA. The activity change also aims at achieving a more compact optics arm including the relevant analysis.
;
The procurement policy of these additional tasks remains DN with the consortium responsible for the implementation of the original activity led by Spacetech (DE).
;
The additional work will be co-funded by FUTURE-EO programme. GSTP funding is limited to 233K?. Any further work related to this activity will not be funded by GSTP.
Application Domain
Earth Observation
Technology Domain
17 - Optoelectronics
Competence Domain
5-Radiofrequency & Optical Systems and Products
Initial TRL
TRL 3
Target TRL
TRL 5
Achieved TRL
TRL 5