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This fascinating question and answer covers how Insight's seismometer was deployed by its robot arm, and how a subsequent robot arm maneuver covered it with a wind and thermal shield.

What parts of the InSight lander are missing between these two photos?

Why could the wind and thermal shield not be pre-integrated into the seismometer, removing the need for a second robotics maneuver?

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Lognonné et al. "SEIS: Insight’s Seismic Experiment for Internal Structure of Mars" 2019 is the definitive telling of the SEIS instrument, yet it does not fully explain why the two units must be mechanically separate, going only so far as to say:

SEIS and WTS must not touch (for noise reasons)

Additional factors that benefit from the physical separation include the leveling requirement and the required thermal time constant.

The seismometer parts of SEIS (VBBs) must be leveled (presumably w.r.t. the "local down" direction) very accurately:

VBBs must therefore be levelled and can operate in nominal configuration without saturation up to about 0.25° and 0.02° degrees of tilt in their lowest and highest sensitivity mode

But the unpredictable Martian terrain upon landing necessitated planning for ground angles up to 15°:

SEIS extreme tilt

(From Lognonné et al.)

This independent leveling of the SEIS box and wind & thermal shield seems difficult were they to be mechanically attached. Also consider the risks from the swing dynamics of a hypothetical tether attachment.

The precise seismic measurements require thermal stability (hence wind and thermal shield). The required time constant between the evacuated sphere with the seismic sensors and the wind & thermal shield is:

between the sphere crown and WTS: this time constant shall be higher than 5.5 hours.

The thermal environment is depicted below:

thermal sources

(From Lognonné et al.)

The detailed thermal model predicted a lower (worse) time constant for WTS to sphere of 4.6 hours. The added conduction from a mechanical linkage between the wind and thermal shield and SEIS would have negatively impacted this value.

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