The recent expedition for the Mars Rover “Perseverance” used an optical interference filter installed by the Fraunhofer Institute for Surface Engineering and Thin Films (IST).

It assisted NASA's Rover in the investigation of the dust in the planet's atmosphere – and it does so under the most extreme conditions.

After more than half a year and a journey of 472 million km, the Mars Rover “Perseverance” successfully landed on Mars and delivered spectacular images of the planet.

A special optical filter from the Fraunhofer IST in Braunschweig has been integrated and was located in an optical sensor for dust characterisation in the “Mars Environmental Dynamics Analyser”, or MEDA for short.

“The MEDA performs weather measurements, including wind speed and direction, temperature and humidity, as well as radiation and the quantity and size of dust particles in Mars atmosphere,” said Dr. Michael Vergöhl, Head of the department of Low-Pressure Plasma Processes at the Fraunhofer IST in Braunschweig, outlining the system.

His department uses a special coating system, the EOSS sputtering system, to develop, amongst other items, high-precision optical filter systems.

“Our developments are always custom-made products – in this case, the Rover is fitted with a bandpass filter manufactured specifically for this particular application.”

Mars dust provides an insight into climate history

Over the course of the mission, the Mars Environmental Dynamics Analyser was intended to make a significant contribution towards preparing for human exploration of Mars.

In this context, data provided was regarding daily weather reports, information on radiation and wind patterns, and insights into the dusty surface which dominates the planet.

Project Manager Stefan Bruns explained the special challenges which are associated with the project.

He said: “The so-called 'angular shift', i.e., the distortion of the measurement through obliquely incident near-infrared light to be detected, must be as minimal as possible, whilst the filter must simultaneously withstand the extreme gamma, proton and ionising radiation present locally.

“In addition, a fundamental aspect is temperature stability: Even at very low temperatures of down to -120 degrees Celsius, the transmitted wavelength range of 950 nm, known as the passband, must not shift significantly.”

Stable performance under extraordinary environmental conditions

MEDA’s sensors are integrated into the Rover at various positions, including the “neck” of the instrument, the front panel and the interior.

Sensors for radiation exposure and dust are located on the top of the Rover, where the filter was deployed.

“The task of the filter is to let through light solely in the 'near' infrared range. The aim is to hereby identify the dust in the Mars atmosphere,” explained Stefan Bruns.

The filter was requested by the Spanish space organization INTA.

The IST scientists manufactured the so-called bandpass filter on the EOSS coating system by means of magnetron sputtering.

In order to ensure that the extremely thin individual layers of the filter are deposited with high precision and homogeneity, the optical monitoring system MOCCA+, also developed at the IST, was used.

Bandpass filters are, of course, not only for interstellar use.

Michael Vergöhl, Head of the department, said: “Bandpass filters are regularly used for applications on Earth.

“The special feature of these filters is that they remain very stable, even under extraordinary environmental influences.”