Space leaves its mark on materials: exposure to such a harsh environment can darken, crack or crater their surfaces – or even erode them away entirely. The nothingness of hard vacuum can also provoke ‘outgassing’ vapours from materials that might degrade delicate mission systems. Accordingly ESA and the French space agency CNES are giving European researchers the chance to pit the latest aerospace materials directly against space.
“In-flight degradation can result in oxidation due to atomic oxygen – caused by standard oxygen molecules being broken apart by solar radiation, becoming very reactive single atoms of oxygen – or darkening from UV radiation,” explains Sebastien Vincent-Bonnieu of ESA’s SciSpacE team.
“In addition coatings can crack due to the extreme temperature shifts encountered in orbit, embrittlement can be triggered by radiation, while impacts from space debris or micro-meteoroids can create small craters.”
A total of 15 different materials will be exposed directly to space on the Euro Materials Ageing Experiment, part of the Bartolomeo ‘front porch’ attached to Europe’s Columbus module aboard the International Space Station. The materials were selected following an ESA-CNES announcement of opportunity for European researchers.
“A wide variety of materials will be tested, including polymers with atomic oxygen protection coatings, 3D printed metals and plastics and new carbon fibre reinforced composites,” adds Sebastien.
“We will also fly our own materials to characterise their response to the space environment and provide reference data for experimenters,” explains Adrian Tighe, Materials Engineer in ESA’s Materials' Physics and Chemistry Section. “For example we will fly Kapton foils to measure atomic oxygen fluence, a novel UV sensitive material to measure solar radiation and clean glass surfaces to measure in-orbit contamination.
“We will also fly a ceramic white coating, similar to that flown on BepiColombo, so we can directly study how it behaves in space. While it is not possible to get the materials back from a spacecraft cruising toward Mercury, it is possible to get them back from the ISS for detailed analysis back on Earth!”
All the materials will undergo detailed pre-flight examination and characterisation, using a suite of advanced surface analysis equipment and techniques. This will be performed by ESA's Materials’ Physics and Chemistry Section, in the Materials and Electrical Components Laboratory, which is based in the ESTEC technical centre in the Netherlands.
The team will for instance look at the materials’ surface structure and chemical composition using scanning electron microscopes, x-ray photoelectron spectroscopy, atomic force microscopy – using a nano-scale stylus that ‘feels’ individual atoms – plus laser-based ‘Raman’ spectroscopy and 3D laser confocal microscopy.
Riccardo Rampini, head of the Materials' Physics and Chemistry Section, explains: “It is important to characterise the materials before flight to be able to assess the in-flight degradation. We will also keep samples of the materials on-ground and monitor them regularly to check that there is no ground based degradation.”
Some materials could erode completely in orbit, so they are checked first in ground-based environmental test facilities, such as ESTEC’s LEOX atomic oxygen facility. This is also very useful to compare ground-based and flight data, helping to update our prediction models about how materials behave in the space environment. Vibration testing is also required to make sure the samples will survive the violence of their flight to orbit.
“All this analysis is performed only on reference samples, rather than the flight items,” notes Adrian. “These flight samples need to be handled extremely carefully to minimise contact and prevent contamination before flight,” notes Adrian.“Even trace contamination can cause degradation when exposed to intense UV in orbit – so any fingerprints would be clearly revealed, for instance.
“The flight samples will therefore be integrated into their holders very carefully, in full cleanroom conditions, and carefully checked using inspection lamps. Once all the samples are mounted they will be passed to CNES for integration onto the EMA payload.”
The detailed testing will subsequently be repeated when the samples are returned to Earth again – a relatively rare opportunity for the Materials’ Physics and Chemistry section team.
Riccardo says: “We did receive materials back from space from our Materials Exposure and Degradation Experiment (MEDET) – which we developed in conjunction with CNES and the French aerospace lab ONERA – as well as materials from the Long Duration Exposure Facility and the solar arrays of the Hubble Space Telescope – and we really learned a lot from the post-flight characterisation and analysis.
“This EMA payload is also a great opportunity for our section’s research fellows to get experience working with real spaceflight hardware and to learn how a space project works, especially working to a strict launch deadline, as well as with the universities and small companies putting forward the samples.”
The overall EMA payload is scheduled to fly to the ISS in 2022.