What did Poland build for NASA’s InSight Mars lander – and why did the “mole” stop?

A lander to look inside Mars

InSight – short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport – was launched on 5 May 2018 and landed on 26 November 2018 on a flat plain about 4.5 degrees north of the Martian equator. DLR describes it as the first purely geophysical observatory on another celestial body. It did not drive anywhere: its job was to listen to marsquakes with a French seismometer, use a radio experiment to find out whether its core is liquid or solid, and measure how much heat flows out of the interior.

The mission was managed by JPL, with the spacecraft built by Lockheed Martin Space and instruments from several European countries. Among the partners NASA lists two from Poland: the Space Research Centre of the Polish Academy of Sciences and the company Astronika.

A nail that hammers itself into the ground

HP3 – the Heat Flow and Physical Properties Package – was designed and integrated by DLR. Its key part was a probe about 40 centimetres long, connected to the lander by a tether full of temperature sensors. The probe was meant to hammer itself as much as 5 metres below the surface, dragging the tether behind it. Its sensors had to be buried at least 3 metres deep to measure the heat flow, away from the daily and seasonal swings of temperature at the surface.

According to the Polish Academy of Sciences, the probe was 25 millimetres wide, weighed about 500 grams and was made of titanium, steel and tungsten alloys. Inside, a hammering mechanism with internal spring-and-mass systems struck the tip again and again. That mechanism – the drive, which Astronika called the “mechanical heart” of the mole – was designed and integrated by Astronika, which also coordinated the mole’s development. The company describes it as a complete hammering mechanism made entirely in Poland, with contributions from the Space Research Centre PAS, the Institute of Aviation, the Welding Institute, Łódź University of Technology and Warsaw University of Technology.

Astronika’s Jerzy Grygorczuk was named a co-investigator on the InSight science team – according to the company, the first representative of a Polish company in that role on a NASA mission. He had earlier designed the mechanism of the MUPUS penetrator on the European Rosetta mission, which landed on a comet in 2014.

Why it stopped

The mole began hammering on 28 February 2019 and soon stalled at about 30 centimetres. A self-hammering probe depends on the ground around it: loose soil flowing around its body creates friction that holds it in place against the recoil of each stroke. Without enough friction, the probe simply bounces where it is. In June 2019 the team concluded that the most likely cause was an unexpected lack of friction in the soil at InSight’s site, which differed from soil seen elsewhere on Mars.

For almost two years engineers at JPL and DLR improvised. They used InSight’s robotic arm in ways it had not been designed for: lifting away the mole’s support structure, pressing against the probe and, finally, scraping soil onto it and packing it down. On 9 January 2021, sol 754 of the mission, the mole received 500 more hammer strokes without making progress, and the team ended the effort. Its top was then about 2–3 centimetres below the surface. The soil had clumped rather than flowing around the probe – very different from what earlier missions had led designers to expect. “We’ve given it everything we’ve got, but Mars and our heroic mole remain incompatible,” said Tilman Spohn of DLR, the instrument’s principal investigator.

Did the Polish mechanism fail?

No. The hammering mechanism kept working throughout; what was missing was grip from the soil. NASA attributes the problem to the unexpected properties of the ground at the landing site, and its account of the end of the attempt names the Space Research Centre and Astronika among the contributors to HP3 without suggesting a fault in the drive.

The effort was not wasted. NASA notes that engineers gained experience in operating a robotic arm on Mars, that the soil’s properties would be studied for years and that future missions which need to dig – for science or, one day, for astronauts looking for water ice – would benefit. The arm, freed from the mole, was then used to bury the tether connecting the lander to the seismometer, to reduce temperature-driven noise in the seismic data.

What InSight found anyway

The seismometer, supplied by France’s space agency CNES, recorded 1,319 marsquakes, including some caused by meteoroid impacts. Analysing about 35 of them, scientists reported in three papers in Science on 22 July 2021 that the Martian crust is thinner than expected – about 20 or 37 kilometres thick, depending on the model – that the mantle extends about 1,560 kilometres down and that the core has a radius of about 1,830 kilometres and is molten.

Dust gradually covered InSight’s solar panels. The lander last communicated with Earth on 15 December 2022, and NASA announced the end of the mission on 21 December 2022.

What it means for Poland

InSight showed that Polish teams can deliver a critical mechanism for a NASA planetary mission, and that a Polish engineer can sit on the science team that runs it. The data, like those of other NASA missions, are public. The story is also a reminder that Mars rewards caution: the planet’s soil was a bigger unknown than the machine. How missions like InSight are proposed and built is explained in From proposal to launch, the other Mars landers and rovers in Mars, one rover at a time, and the laboratory that ran InSight in Is JPL part of NASA?