Laser link acquisition demonstration for the GRACE Follow-On mission

Area of Science:

• Space Science
• Optical Engineering
• Satellite Technology

Background:

• Inter-satellite laser communication is crucial for modern space missions.
• The GRACE Follow-On mission requires robust laser link acquisition for its science operations.
• Existing acquisition schemes often necessitate dedicated, complex hardware.

Purpose of the Study:

• To demonstrate a cost-effective and efficient laser link acquisition scheme for the GRACE Follow-On mission.
• To validate the use of existing science operation hardware for laser link acquisition.
• To reduce the complexity and resource requirements for establishing inter-satellite laser links.

Main Methods:

• Experimental demonstration of a laser link acquisition strategy utilizing existing photodetectors and signal processing hardware.
• Implementation of a five-degree-of-freedom search (± 3 mrad pitch/yaw, ± 1 GHz frequency difference).
• Application of a Fast Fourier Transform (FFT)-based peak detection algorithm to identify the heterodyne beat note.

Main Results:

• Successful experimental demonstration of both commissioning (± 3 mrad) and reacquisition (± 300 μrad) scans.
• Achieved beam pointing accuracy within 142 μrad and laser frequency difference below 20 MHz during commissioning.
• Commissioning sequence completed in 6.3 hours, with reacquisition taking only 7 seconds.

Conclusions:

• The proposed scheme effectively acquires inter-satellite laser links without dedicated sensors, leveraging existing GRACE Follow-On hardware.
• The demonstrated method significantly reduces hardware complexity and cost for satellite laser communication.
• The acquisition strategy enables a seamless transition to differential wavefront sensing for auto-alignment, crucial for mission success.