EXPOSE is a facility dedicated to exobiology, developed by ESA for medium- and long-term flights and installed outside the International Space Station (ISS) (Figure 1). It is designed to enable several simultaneous experiments involving the exposure of chemical and biological samples, while recording temperature and effective exposure time. LISA is involved in EXPOSE-E through the PROCESS experiment, in EXPOSE-R through the AMINO experiment and in EXPOSE-R2 through the PSS (Photochemistry on the Space Station) experiment.

 

 

 Figure 1 : En haut, EXPOSE avant son départ ; en bas, EXPOSE sur l'ISS (International Space Station)

The EXPOSE platform houses hundreds of samples of various kinds. In the case of the PSS experiment, they are arranged at a rate of 25 cells per sample holder. The cells are arranged to optimize space. To prevent leakage, which would distort all experiments by modifying the cell contents independently of the phenomenon observed, cells and sample holders are sealed with joints and screws (Figure 2), but are also brazed (welded). These preventive measures require lengthy preparation of the installation, as well as careful opening at the end of the experiment.

Figure 2 : une plateforme EXPOSE. Les portes échantillons ont des côtés de 86mm

On a sample holder, there are two layers of cells: the top layer, containing exposed cells, and the bottom layer, containing unexposed cells (Figure 3). Both sets of samples are identical, but the unexposed cells will serve as in-flight control samples: they will undergo the same temperature fluctuations as the exposed cells, but will not be affected by space radiation. Similarly, other control samples are kept in the laboratory, under different temperature and radiation conditions.

 

Figure 3 : organisation d'un porte échantillon pour les expériences du LISA, avec une couche de cellules exposées, et une couche de cellules non exposées. Les cellules font 9mm de diamètre, pour 12mm de profondeur

 

During their stay in orbit, the cells are not continuously exposed to solar radiation, due to the orientation of the space station. To be able to interpret the results accurately, we need to know the actual exposure time. To this end, EXPOSE is fitted with sensors to measure this time. Temperature is also measured.

These experiments exposing molecules to solar UV are the first long-term experiments (1 to 2 years) to be carried out in space. PROCESS samples returned to Earth in September 2009, AMINO samples in March 2011, and PSS samples in March 2016.