The SEIS seismometer is now set down on Mars, 19 December 2018 | INSTITUT DE PHYSIQUE DU GLOBE DE PARIS


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  The SEIS seismometer is now set down on Mars, 19 December 2018

NASA has just successfully placed the SEIS seismometer from the InSight probe on Mars. This is the first time in the history of space exploration that an instrument has been deployed by a robotic arm on the surface of another planet. The success of this critical step for the rest of the mission is the result of years of unceasing technical efforts by the American, French and European teams.


The SEIS seismometer of the InSight probe seen by the robotic arm IDC camera after its deployment in sol 22. (© NASA/JPL)


The complex sequence of instructions ordering the deployment had been sent on 18 December 2018 (at 17:11 in California) to the Red Planet. On 19 December 2018 at 18:40 local time (Mars), the InSight arm activated to place the 9.5 kg SEIS seismometer on the ground. For this high-risk operation, the instrument had been completely shut down and many tests had previously been carried out on Earth to confirm the commands, as the landing site had been faithfully reproduced for the occasion.


To place SEIS on the ground, the robotic arm performed a fairly complex series of movements. But the duration of the deployment sequence itself is quite short: only 10 minutes. However, the need to acquire images via the probe cameras increased the duration of the operation to about 20 minutes, spread over the course of 45 minutes. It is estimated that the SEIS seismometer planted its three feet in the sand at 7:05 (California), or 18:54 Martian time.


SEIS is now situated straight ahead of the robotic arm (to ensure that the tether connecting the instrument to the landing gear rests flat on the ground), and as far as possible (1.65 metres) from the probe, to minimise disturbances.


However, the operations are far from over for SEIS. Engineers will first have to align the seismometer with the horizontal surface using the motorised levelling cradle. Once this step is completed, the very broad band (VBB) sensors, which are currently inactive unlike the short-period (SP) sensors, will be refocused and calibrated. All the data transmitted by the six seismic sensors will then be used to characterise the noise level of the placement site, as well as the level of disturbances induced by the cable connecting the instrument to the landing gear.


When the performance is deemed acceptable, the cable still located in the TSB casing will be completely unwound, which will then allow the final placement, over the instrument, of the imposing wind and thermal shield (WTS).


There is still a lot of work to be done before the first Martian geophysical station is fully operational, but the installation of the first seismometer on Mars is already a great success —which the team members will celebrate properly by probably taking a few days off for the Christmas holidays!