NASA puts a lid on InSight's Mars seismometer
NASA's InSight lander continues to set up house on Mars and has now placed a domed shield over the Seismic Experiment for Interior Structure (SEIS) instrument package that its robotic arm placed on the surface on December 19, 2018. After weeks of calibration and adjustment to the advanced seismometer, adding the Wind and Thermal Shield will both protect the instrument and greatly enhance its sensitivity and accuracy.
According to NASA, the SEIS seismometer is a key instrument in the unmanned lander's mission to better understand the deep structure and dynamics of the Red Planet. However, the very sensitivity that makes device so valuable also makes it vulnerable. The Martian winds can shake the seismometer, blanking out its data with noise, as can the temperature variations that can vary as much as 170° F (94° C) per day, causing the components to stretch and contract and produce more noise.
Normally, seismometers are protected against temperature and errant vibrations by making them very large and burying them in deep vaults several feet underground. The space agency says that this is impossible for the InSight mission, so a workaround was needed.
"Temperature is one of our biggest bugaboos," says InSight Principal Investigator Bruce Banerdt of NASA's Jet Propulsion Laboratory in Pasadena, California. "Think of the shield as putting a cozy over your food on a table. It keeps SEIS from warming up too much during the day or cooling off too much at night. In general, we want to keep the temperature as steady as possible."
The shield has an aerodynamic profile to make the Martian winds force it down on the ground, while it's made up of chain mail and thermal blankets to provide a tight seal on uneven surfaces. In addition to this, the seismometer is built with components that are designed to expand and contract in opposite directions to cancel one another out, much like the pendulum on a grandfather clock.
Along with these precautions, the instrument package is sealed in a titanium sphere that, in turn, is set inside another hexagonal box with a honeycomb structure that traps the Martian air, which NASA says has excellent insulating properties at low pressures. And if this wasn't enough, InSight is designed to keep tabs on the local weather, so mission control can make allowances and clean up any corrupted data.
With the SEIS now fully deployed, InSight's next task will be to set the Heat Flow and Physical Properties Package (HP3) on the surface of Mars.