The Seismic Instrument for Asteroids (SIA) for the RAMSES mission to asteroid Apophis

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The Seismic Instrument for Asteroids (SIA) will be deployed to the surface of asteroid 99942 Apophis by the ESA–JAXA RAMSES mission prior to the asteroid’s closest approach to Earth to measure its seismic response to tidal forces [1,2]. SIA will monitor the seismic activity continuously from three hours before to six hours after perigee - this is the critical window when peak tidal-induced seismic activity is expected [1]. Before and after this critical window, periodic SIA measurements will support seismic background noise assessment and allow for monitoring other natural sources such as micrometeoroid impacts and thermal cracking [3–5]. The SIA measurements will be used to constrain the seismicity of Apophis and probe the asteroid’s subsurface and internal structure. SIA is a compact seismometer (Fig. 1) specifically designed to be integrated into a small asteroid surface package (the Ramses CubeSat-2) and to operate under the harsh conditions at the surface of Apophis without requiring leveling. The instrument includes a three-axis accelerometer and three single-axis geophones along with dedicated custom-built low-noise electronics and is designed to achieve an instrument noise level below 1.0 × 10⁻⁹ m/s/√Hz over the 5 - 200 Hz band. Both the sensor assembly and the electronic stack (Fig. 1) are integrated into a common mechanical assembly with outer dimensions of 190 x 98 x 54 mm. At the instrument level, SIA has successfully passed a vacuum thermal balance test, qualification-temperature burn-in thermal cycles, and Electromagnetic Compatibility (EMC) tests. The performance tests have demonstrated that the electronic, sensor and integrated instrument noise levels meet the science requirements. The Engineering Model is expected to be delivered mid-2026 with the Flight Model delivery early 2027.This presentation will provide an update on the SIA science objectives, planned operations and the instrument development in preparation for the 2028 RAMSES launch.Figure 1: A photo of the electronic stack and the sensor assembly of the SIA instrument. Both parts are integrated into a common mechanical assembly.AcknowledgementsSIA is being developed at ISAE-SUPAERO with support from the French Space Agency (CNES) and the European Space Agency (ESA), in collaboration with IPGP.References[1] DeMartini, J. et al. (2025) Planetary Science Journal, 6:263.[2] Ballouz et al., (2025) Planetary Science Journal, 5:251.[3] Murdoch, N. et al., (2017) Planetary and Space Science, 144, 89-105.,[4] Murdoch, N. et al., (2015) Asteroids IV, University of Arizona Press Space Science Series.[5] Compaire, N., et al. (2022). Geophysical Journal International, 229(2), 776-799.

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