LISA on a tabletop

First milestone towards a hardware-in-the-loop testbed of the space-based gravitational-wave detector

The Laser Interferometer Space Antenna (LISA) is the European Space Agency's planned space-based gravitational-wave detector, expected to launch in 2035. LISA will observe gravitational waves at frequencies between 0.1 mHz and 0.1 Hz, where strong sources of gravitational waves populate the Universe. Its central measurement principle involves taking laser-interferometric distance measurements between test masses, free-falling in satellites 2.5 million kilometers away from each other. These measurements will be divided into satellite-to-satellite and satellite-to-test mass measurements. The latter have been demonstrated by the LISA Pathfinder mission, and the former cannot be directly tested in optical laboratories. Now, a team of AEI researchers has successfully demonstrated hardware simulations of the LISA inter-satellite links. Their hardware testbed uses field-programmable gate arrays, high-speed computer memory, and signal converters to digitally simulate realistic delays, Doppler shifts, and the injection and recovery of gravitational-wave signals. In their publication in Classical and Quantum Gravity, the team also describes their next steps toward creating an integrated laboratory facility to study and validate the metrology at the heart of LISA.

Paper abstract

Time-Delay Interferometry (TDI) is essential for the Laser Interferometer Space Antenna (LISA) to suppress laser frequency noise and extract gravitational-wave signals from inter-satellite phase measurements. While most recent studies of TDI have relied on software simulations, we present here the development and first results of a new hardware testbed that simulates the LISA inter-satellite links using RFSoC FPGA-based delay lines. The system digitally applies LISA-like delays, Doppler shifts, and injected gravitational-wave signals to MHz carriers with clock sidebands, and provides phasemeter-compatible outputs for TDI analysis. We demonstrate baseline performance of the delay line, including correction of differential ADC/DAC jitter, and static tests of TDI X1 combinations with external signals. In addition, we show injection and recovery of massive black hole binary waveforms through the hardware-in-the-loop setup. These results establish a flexible platform for testing TDI, clock noise transfer, and ranging techniques in a controlled environment, and outline future steps toward a full laboratory-scale simulator of the LISA constellation.