NGGM Concept Consolidation
In the frame of ESA's “Consolidation of the system concept for the next generation gravity mission”, Thales Alenia Space sub-contracted STI for the Laser Metrology Instrument (LMI). The LMIs concepts investigated find their basis in the Laser Ranging Interferometer development for GRACE FO as well as former ESA studies.
Investigated NGGM concepts
The SpaceTech LMI concepts include two possible off-axis “Racetrack” instrument schemes:
- Optical transponder scheme with two active S/C instrument parts, based on the racetrack design applied on GRACE Follow-On.
- Retroreflector scheme with one active one passive S/C instrument part, from former NGGM studies
The figures below illustrate the two schemes. An abstract with more details can be found in the SPIE Digital Library.
Optical transponder scheme for NGGM
Optical retroreflector scheme for NGGM
The two viable advantageous options for NGGM
- Both, the optical transponder as well as the retroreflector scheme, are considered capable to provide the required performance, with:
The transponder scheme is a “safe” option, with the LRI configuration from GRACE FO being fully qualified. The US contribution, mainly reference cavity and phasemeter, would need to be developed further for an all European instrument.
- The retroreflector scheme offering the possibility to implement two identical spacecrafts and a less complex optical link acquisition. The low received power and the resulting high requirement on straylight, multipath suppression and potential cycle slipping is currently investigated further in a breadboarding activity to enable final instrument scheme selection.