SEIS seis­mome­ter

The Seismic Experiment for Interior Structure (SEIS) seismometer consisted of a total of six seismic sensors that recorded the vibrations of the Martian soil in three directions in space and at two different frequency ranges (Very Broad Band [VBB], covering 0.01–10 Hertz and Short Period [SP] covering 0.1–50 Hertz). The overlap of the two frequency ranges allows them to be mathematically combined into a single extremely broadband seismometer.

The three sensors that are sensitive to low frequencies were housed in an evacuated container, as the air resistance of even the thin Martian atmosphere would dampen the movement of the sensors too much. This container rested on a levelling system (LVL) with three telescopic legs to ensure that the casing was precisely horizontally aligned, as the VBB sensors would not work otherwise. The three sensors for the higher frequency range were mounted on the outside of the LVL. In order to protect the seismometer against wind and strong temperature fluctuations, a protective dome (Wind and Thermal Shield, WTS) was placed over it.

After arrival, the lander’s immediate surroundings were precisely mapped and surveyed to find the ideal location for the two instruments – SEIS and HP³. The robotic arm then lifted out and installed the seismometer, with the location checked and recorded once more before the WTS was placed on top of it.

Institutions from several countries provided the SEIS components. The low-frequency VBB sensors came from the Institute du Physique du Globe in France, the high-frequency SP sensors from Imperial College in the United Kingdom, and the control electronics were made at the Swiss Federal Institute of Technology in Zurich (Eidgenössische Technische Hochschule; ETH). The vacuum container, the WTS and the connecting cable, with almost 300 wires for electrical supply and data transmission to the lander, came from the NASA Jet Propulsion Laboratory (JPL) in the USA. Finally, the levelling system was developed and built by the Max Planck Institute for Solar System Research in Göttingen, Germany.