April 22, 2019

InSight lander completes seismometer deployment on Mars


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NASA’s InSight lander has placed a protective enclosure over a French-developed seismometer designed to detect tremors on Mars, completing the deployment of the first of two science instruments delivered to the Red Planet in November.

Using its nearly 8-foot-long (2.4-meter) robotic arm, InSight followed commands beamed up from Earth to cover the seismometer package with a dome-shaped wind and thermal shield Saturday.

The milestone follows weeks of leveling and cable adjustments since InSight’s robot arm picked up the seismometer itself from the lander’s deck and placed it on a rock-free portion of the Martian surface that was within reach of the stationary lander.

The shield will ensure winds and temperature swings do not affect the sensors inside the seismometer instrument. Without the added protection, winds could add “noise” to the instrument’s measurements, making it harder to discern when it registers a quake on Mars, scientists said.

Ringed with a thermal barrier and chain mail around the bottom, the wind and thermal shield will also moderate temperatures inside the instrument. Scientists were concerned warming and cooling trends might expand and contract metal springs and other parts inside the instrument, according to NASA.

“Temperature is one of our biggest bugaboos,” said Bruce Banerdt of NASA’s Jet Propulsion Laboratory in Pasadena, California, principal investigator for the InSight mission. “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.”

Diagram of InSight’s seismometer package. Credit: NASA/JPL-Caltech

Temperatures measured by InSight since its Nov. 26 landing on Mars fluctuate by about 170 degrees Fahrenheit, or 94 degrees Celsius, over the course of a Martian day, or sol, NASA said in a statement.

InSight braked to a rocket-assisted landing at Elysium Planitia, a broad equatorial plain.

The seismometer instrument was provided by the French space agency, CNES, and its development was led by the Institut de Physique du Globe de Paris. JPL built the wind and thermal shield, and leads the overall InSight mission.

The seismometer package was designed with several layers of insulation against temperature changes on Mars. When some parts inside expand and contract, others are designed to do so in the opposite direction to counteract the effects of the changes, according to NASA. The seismic sensors themselves are encased within a vacuum-sealed titanium sphere, which is then overlaid with a hexagonal copper container with honeycomb cells that trap air and keep it from moving.

“Mars provides an excellent gas for this insulation: Its thin atmosphere is primarily composed of carbon dioxide, which at low pressure is especially slow to conduct heat,” NASA said in a statement.

The instrument contains three sets of seismic sensors at its core, which was placed on the surface Dec. 19.

Scientists will also monitor weather conditions, including winds and temperatures, with a meteorological station carried aboard inSight. The weather information can be applied to seismic measurements to filter out data that might have been corrupted by environmental conditions.

A camera on the elbow of InSight’s robotic arm captured 11 images stitched together to create this self-portrait in December. Credit: NASA/JPL-Caltech

Next up for InSight will be the deployment of the mission’s other main instrument: the Heat Flow and Physical Properties Package, or HP3.

HP3 was developed by DLR, the German space agency, and is scheduled to be transferred from InSight’s instrument deck to the Martian surface with the robot arm next week.

The heat probe consists of a mechanized mole that will dig into the Martian crust to a depth of up to 16 feet, or 5 meters, deeper than any previous Mars mission has reached.

The mole is expected to take around six weeks to reach that depth with roughly 10,000 individual mechanical hammer blows, accounting for several planned pauses to allow the instrument to record thermal conductivity measurements.

The underground probe will measure the heat coming from Mars’s interior, providing information for scientists to study the planet’s internal structure.

Combining the heat probe and the seismic results — which will also tell scientists about layers inside Mars — Banerdt’s team seeks to examine how the rocky planets formed in the ancient solar system, providing a comparison for what geologists already know about Earth.

The procedures to place the instruments on the Martian surface represent a first in the exploration of Mars. While previous NASA missions have used rovers to drive around the Red Planet, none before InSight have physically placed payloads into permanent positions directly on the surface.

The seismometer and heat probe will transmit their readings back to InSight through umbilical cables. The lander will then beam the data back to Earth through communications relay orbiters flying overhead.

“I liken it to … playing that “Claw” game at a carnival, but you’re doing it with a really, really valuable prize, and you’re doing it blindfolded, where you can only take occasional pictures, and then you’re doing it via remote control on another planet,” said Elizabeth Barrett, InSight instrument operations lead at JPL, describing the carefully-choreographed procedure to move the instruments to the Martian surface.

“It takes a little bit longer,” she said. “You need take more pauses to make sure you actually have the grapple of the payload before you lift it up, and it’s actually on the ground before you let it go.”

Engineers created a mock-up of the lander, the instruments and the surrounding environment in a lab at JPL to simulate the instrument deployment procedures before executing them on Mars.

“Sensitive is really an understatement,” Banerdt said of the seismometer. “It’s an exquisitely sensitive device for measuring the motion of the ground. And when we talk about motion, we’re talking about vibrations that have an amplitude comparable to the size of an atom.

“These are waves that were generated, maybe, by a marsquake on the other side of the planet, have traveled all the way through the planet, getting their waveform modified as they go through the planet and picking up information about the deep interior structure, and then we are able to pick it up when it comes back up to the surface under the seismometer,” Banerdt said before InSight’s launch last May.

The seismic sensors aboard InSight evolved from mission concepts in the 1990s and 2000s that would have dispatched multiple small probes to Mars, creating a global geophysical network. InSight will give scientists just one seismic station, but experts have developed techniques to glean information about the interior of Mars, even with a single seismometer.

Researchers have attempted seismic detections on Mars before, but seismometers on NASA’s Viking landers in the 1970s provided inconclusive results. The instruments were mounted the decks of the landers, making them susceptible from interference from spacecraft vibrations and winds.

That’s where the wind and thermal enclosure deployed Saturday comes in.

“Not only do you have to have a very sensitive device for measuring those motions but you have to protect it from everything else that might affect it,” Banerdt said. “We have several different layers of protection, it’s sort of like a Russian doll.”

Once the instruments are deployed and operational, the InSight science mission is planned to last one Martian year, or roughly two Earth years.

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Follow Stephen Clark on Twitter: @StephenClark1.


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