To ensure the continuation of the gravity field measurements, the Grace Follow-On (GRACE-FO) mission is under development in a US–German cooperation. To allow a cost efficient development and a launch in 2017, the GRACE Follow-On satellites are very similar to the original GRACE satellites with some improvements and a technology demonstrator for further gravity missions. Therefore, in addition to the K-Band an experimental laser ranging instrument (LRI) will fly, based on a laser interferometer. The goal of the LRI is to improve the distance measurement accuracy significantly from some micrometers to some ten nanometers at 0.1 Hz frequency.
Challenging key instrument requirements are:
- Ranging measurement accuracy of 80nm/√Hz (for 10-100 mHz)
- Laser beam co-alignment of less than 50 µrad
The instrument consists of a frequency stabilized laser, a triple mirror assembly (retroreflector), an optical bench and an electronics board to evaluate the interference signal.
The main tasks for SpaceTech are
- Industrial responsibility for german LRI contribution
- Development of the triple mirror assembly, a light weight retroreflector providing the beam routing with 600 mm beam offset and 50 µrad coalignment accuracy
- Development of the optical bench including beam steering mechanism, signal detection and electronics
- In house assembly, integration and Test of the EMs and PFMs on unit- and instrument-level and support at spacecraft-level