First results of the ORGANIC experiment on EXPOSE-R on the ISS

Abstract

The ORGANIC experiment on EXPOSE-R spent 682 days outside the International Space Station, providing continuous exposure to the cosmic-, solar-and trapped-particle radiation background for fourteen samples: 11 polycyclic aromatic hydrocarbons (PAHs) and three fullerenes. The thin films of the ORGANIC experiment received, during space exposure, an irradiation dose of the order of 14 000 MJ m −2 over 2900 h of unshadowed solar illumination. Extensive analyses were performed on the returned samples and the results compared to ground control measurements. Analytical studies of the returned samples included spectral measurements from the vacuum ultraviolet to the infrared range and time-of-flight secondary ion mass spectrometry. Limited spectral changes were observed in most cases pointing to the stability of PAHs and fullerenes under space exposure conditions. Furthermore, the results of these experiments confirm the known trend in the stability of PAH species according to molecular structure: compact PAHs are more stable than non-compact PAHs, which are themselves more stable than PAHs containing heteroatoms, the last category being the most prone to degradation in the space environment. We estimate a depletion rate of the order of 85 ± 5% over the 17 equivalent weeks of continuous unshadowed solar exposure in the most extreme case tetracene (smallest, non-compact PAH sample). The insignificant spectral changes (below 10%) measured for solid films of large or compact PAHs and fullerenes indicate a high stability under the range of space exposure conditions investigated on EXPOSE-R.

The astrobiological mission EXPOSE-R on board of the International Space Station

“…The obtained results from EXPOSE-R, one of the longest international astrobiological exposure missions in LEO are collected in this issue (Berger et al 2014;Bertrand et al 2014;Bérces et al 2014;Bryce et al 2014;Bryson et al 2014;Carrasco et al 2014;Cottin et al 2014;Dachev et al 2014;Mancinelli et al 2014;Neuberger et al 2014;Novikova et al 2014;Panitz et al 2014;Vergne et al 2014).…”

“…The two chemical experiments of the EXPOSE-R mission were designed to use the environment of outer space, especially the highly energetic solar extreme UV radiation, to study processes of chemical evolution (Table 1). Emphasis was laid on the study of the photochemical stability of complex organic compounds, analogues to those detected in the interstellar medium and in circumstellar clouds (Bryson et al 2014), as well as in comets and the atmosphere of Saturn's moon Titan (Carrasco et al 2014; Cottin et al . 2014).…”

“…Due to various off-nominal events that interrupted the data acquisition (see above), and the consequent severe loss of environmental data, it was impossible to determine the total UV fluence received during the mission from the transmitted data. The only way out was model calculations to assess the total UV fluences at the sample sites, which were performed by the RedShift Design and Engineering BVBA, Belgium (Beuselinck & van Bavinchove 2011). Shadow maps were calculated for EXPOSE-R from available ISS mission flight data of the ISS position in its orbit, ISS attitude, joint angles defining positions of solar arrays and radiators, evolution of the ISS configuration, and information of visiting spacecrafts and their docking positions (Space Shuttle, Soyuz, Progress, Automated Transfer Vehicle (ATV)).…”

“…Reasons could be a typical loss of phase during simulated thermostat-controlled heater operation, inaccuracies in the solar irradiation simulation (caused by missing input data), changes in the EXPOSE-R power dissipation or changes in the environment (e.g. the Zvezda solar array position) (Beuselinck & van Bavinchove 2011). However, comparison between simulated temperatures and telemetry data generally confirmed the validity of the simulation.…”

“…Here, we present the technical and operational details of the EXPOSE-R mission. Results of the experiments participating in the EXPOSE-R mission are reported by the experimenters individually in this issue (Bérces et al 2014; Berger et al 2014; Bertrand et al 2014; Bryce et al 2014; Bryson et al 2014; Carrasco et al 2014; Cottin et al 2014; Dachev et al 2014; Mancinelli et al 2014; Neuberger et al 2014; Novikova et al 2014; Panitz et al . 2014; Vergne et al 2014).…”