Researchers from the Sector of Neutron Activation Analysis and Applied Research of the JINR Frank Laboratory of Neutron Physics analyzed fragments of a roll of cotton cloth placed on the outer surface of the International Space Station more than 10 years ago.

With increasing service life of spacecraft, the problem of contamination of their outer surfaces by precipitates of unknown origin has arisen. This problem is particularly acute for the ISS. It should be noted that in space, the surfaces of the ISS are exposed to precipitation only from a certain side. The dust seems to be moving in a stream directed relative to the station. Such dust deposition does not create problems in terrestrial conditions, but in space, surfaces that get polluted may overheat, causing thermal deformation and many other possible problems, which may result in loss of airtightness and breakdown of the spacecraft. Fine particles moving at cosmic speeds are capable of interacting with the aluminum housings of the station modules and other structural elements. In aluminum alloys, under the influence of high-energy particles, the processes of crystallization and redistribution of alloying additives along the crystal faces occur, which leads to the deterioration of strength characteristics of materials. In addition, dispersed high-energy particles can penetrate the surface layers of metals, which further alters the characteristics of spacecraft materials. Thus, detailed information about the origin of dust pollution is necessary for planning future space missions. The possible influence of dust pollution on the mechanical properties of structural materials should be taken into account when developing new modules of space stations.

In the framework of the space experiment “Test”, aiming to study the sorption of cosmosol forming a finely dispersed depositional environment on the surface of the ISS, it was proposed to remove and deliver to the Earth the roll of cotton cloth placed by astronauts on the outer surface of the ISS. The studied roll of cloth was attached by Yury Lonchakov and American astronaut Michael Fincke to bracket 2312 during an extravehicular activity (EVA) session. It was placed on March 10, 2009, removed by astronauts on May 15, 2019, put into a zip-lock bag in the atmosphere of the space station and delivered to the Earth in September 2019 (Fig. 1). Thus, the time of exposure in outer space was more than 10 years.

To determine the elemental composition of the rolled cotton cloth, two fragments (one without visible traces of contamination and one contaminated) were handed over to the Frank Laboratory of Neutron Physics. The content of elements in fragment was determined using neutron activation analysis (NAA) at the REGATA facility of the IBR-2 reactor. Using NAA, 39 elements were determined in the contaminated fragment of the cloth and 19 elements – in the clean one.

There are several possible sources of elements deposited on the cloth. Dust particles shed by meteorites, asteroids or comets can be considered one of the important sources. To determine the origin of the elements, the ratios of elements established for chondrites were compared with the respective ratios obtained for the contaminated fragment of the cloth. Thus, the cosmic nature of magnesium, silicium, iron, uranium and thorium was confirmed.

Fig.1 Direction of movement of the station and the rolled cotton cloth attached to bracket 2312 on the outer surface of the ISS.

Since the ISS is mainly built of aluminum, and the pipelines are made of corrosion-resistant steels and titanium alloys, the station can be considered the main source of these elements.

In addition to cosmic bodies and the ISS itself, particles released from the Earth, for example, volcanic ash plumes, can be considered another source of element deposition on the cloth. Volcanic ash may be regarded as a possible source of Ba, Zr, Re, Sr, Rb and rare earth elements on the cloth. Ionized particles from gas and dust emissions from fumarole fields of volcanoes can enter the upper part of the ionosphere at the altitude of the ISS orbit with the ascending branch of the global electric circuit. This peculiar kind of ionospheric vertical conveyor provides an upward drift of aerosols in the field of the “Earth-ionosphere capacitor” due to a number of coupled mechanisms of turbulent electrothermal diffusion, accompanied by mass transfer of dispersed material above the Kármán line.

The leader of the project Dr. Inga Zinicovscaia, head of the Sector of Neutron Activation Analysis and Applied Research of the Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research, commented on the research results: “The main direction of research in the Sector is investigations in the field of ecology, but our team has always been interested in analyzing some unusual, unique samples. First of all, this is due to the fact that the neutron activation analysis technique offers wide application possibilities. And in 2019, a colleague from the A.N.Frumkin Institute of Physical Chemistry and Electrochemistry of the Russian Academy of Sciences provided us with such an opportunity by handing over to our Sector an interesting sample received from the Federal State Unitary Enterprise “Russian Metrological Institute of Technical Physics and Radio Engineering” (FSUE «VNIIFTRI») – a fragment of the roll of cotton cloth that had been on the outer surface of the International Space Station for more than 10 years.

At that time, the fragments of the roll of cotton cloth had already been analyzed in several scientific laboratories in order to determine the elemental composition and the presence of microorganisms. The methods that are usually used for this purpose are not very sensitive, and therefore not many elements were identified. Our colleagues decided that it would be interesting to try to apply the neutron activation analysis technique.

In 2020, for comparison, the second fragment of the roll was handed over – a clean one. This piece of cloth has never been in contact with cosmic dust. Despite the difficulties of that year caused by the pandemic, the samples were successfully irradiated. The results obtained showed that for such an object of study, neutron activation analysis is out of competition. We identified about 40 elements in the contaminated fragment of the roll and 20 elements in the clean one. Next, the task was to determine the sources of these elements. We identified three main sources of deposition of elements on the roll – these are cosmic bodies, the station itself, and particles released from the Earth.

The results of the study have already been published and we hope that they will interest our colleagues from Roscosmos and allow us to participate in other experiments carried out on the ISS. It is worth noting that immediately after analyzing the fragments of the roll, we received about 50 meteorites for analysis, including the Chelyabinsk meteorite. Therefore, it may be considered that this sample has given a start to the development of a new scientific direction in our Sector”.

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The results of the study are presented in the paper: Inga Zinicovscaia, Dmitrii Grozdov, Nikita Yushin, Alexey Safonov, Igor Proshin, Mikhail Volkov, Alexey Pryadka, Vladimir Belyaev, Elena Shubralova, OlegTsygankov. Analysis of the rolled cotton cloth fixed on the outer surface of the International Space Station using neutron activation analysis and complementary techniques. Acta Astronautica 189 (2021) 278–282, https://doi.org/10.1016/j.actaastro.2021.08.052