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.

GRACE-C Mission Performance SummaryGRACE Follow on Mission Summary

 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.

LRI OverviewIntersatellite Ranging Instrument Set-Up

 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