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Project Progress

Authors: Ehrenfreund, Salama, Ricco, Bryson, et al.

EXPOSE-R was launched to the International Space Station ISS (Russian module) in November 2008. On 23 December 2008, the first space walk to attach EXPOSE-R to the external URM-D unit of the ISS failed due to technical problems. Another EVA on March 10, 2009 was successful and activated EXPOSE-R and sample exposure. Space exposure is planned for a period of at least 12-18 months.

1) Ground-based monitoring of EXPOSE-R samples in simulated space environment:

January 2009: A newly purchased Ocean Optics HR4000 spectrometer was installed in the laboratory of Dr. Farid Salama with a fiber optic interface that uses Ocean Optics Spectrasuite software for data collection. This spectrometer shares many of the optical design features, as well as much of the software, with the O/OREOS (organism/organic exposure to orbital stressors) flight spectrometer presently under development for a nanosatellite launch in February 2010 (see additional details in section 3 below).

February 2009: Postdoctoral associate Kathryn Bryson was hired to work on this DDF project at NASA/ARC.

March 2009: Transmission/absorption spectra were recorded by Dr. Bryson at approximately 11 months after original sample deposition for 9 of the 16 sample cells in the closed-bottom ground witness sample carrier of the EXPOSE-R Organics experiment. The cells contained thin films of C₆₀, C₇₀ (both buckminsterfullerenes), dibenzo[jk,a’b’]octacene, tetracene, ovalene, 2 samples of coronene, diphenanthro[9,10- b;9’10’-d]thiophene, and chrysene.

May 2009: The above 9 samples were remeasured by Dr. Bryson, and all the other cells in the closed-bottom ground witness sample carrier were also measured, in May at approximately 13 months after original sample deposition. The entire sample set included 2 samples of coronene, chrysene, triphenylene, tetracene, perylene, diphenanthro[9,10-b;9’10’-d]thiophene, ovalene, tetrabenzo[de,no,st,c’d’]heptacene, dicoronylene, C₆₀, C₇₀, C₆₀/C₇₀/ C84 mixture, circobiphenyl, dibenzo[jk,a’b’]octacene, and dinaphtho[8,1,2-abc:2’1’,8’-klm]coronene (as an example, the spectrum of ovalene is shown in Figure1). The measurements confirm that no alterations have occurred in the spectra of the ground sample. These preliminary measurements and studies were reported at the AAS 214th Conference.

Access to all the samples in the EXPOSE-R carrier was made possible in May by the implementation of a high-precision x-y-z slide assembly (Velmex) that allows for positioning the sample carrier relative to the spectrometer input over hundredths of millimeters (see Figure 2).
This allows multiple measurements of precisely the same location to be made on each cell window at any time desired. This is a crucial improvement since the thin films are not in general absolutely homogeneous.

2) Development of a laboratory prototype UV-Visible spectrometer for in-situ measurements of organic materials on future free-flyers and lunar surface exposure facilities

In addition to the measurements on the EXPOSE-R samples, Dr. Bryson also collected preliminary spectra of samples of materials under consideration for the O/OREOS Nanosatellite mission mentioned above. These samples included thin films of anthrarufin, phenylalanine, porphyrin (tetraphenylprphyrin), and ovalene.

Additional measurements in the coming months by Dr. Bryson will provide information than can help with the final downselect of materials for the O/OREOS mission, in addition to providing spectroscopic information that will help in optimizing the film thickness for this mission. In addition, degradation of these and similar films by UV irradiation may also be measured in Dr. Salama’s laboratory using the spectrometer described above, providing further data relevant to the measurements to be made during the O/OREOS mission.

3) Detailed characterization of the prototype’s performance via in-situ spectral measurements of control EXPOSE-R samples versus time in a simulated space environment, in direct comparison with a reference laboratory spectrometer.

A key goal of this DDF is to explore the potential scientific return using small-satellitecompatible spectrometer technology to study space environment-related effects on materials of astrobiological relevance. There is a close synergy between measurements made to date, as well as those planned for the next several months, using the laboratory UVvisible spectrometer purchased for this project, and measurements to be made on the same organic thin-film materials using an engineering test unit (ETU) spaceflight UV-vis spectrometer under development for the O/OREOS mission. In particular, the electronics and software are essentially identical between the DDF laboratory and the O/OREOS flight spectrometer and, based on specifications, the laboratory spectrometer’s optical bench should provide marginally better performance (spectroscopic parameters, dark levels), while the spaceflight prototype should provide significantly better measurement temperature stability (a requirement of the O/OREOS mission scenario) and better performance at spaceflight levels of shock and vibration. By comparing spectral changes in a number of astrobiologically relevant organic materials for these two spectrometers, we will understand whether the constraints on size and power placed on the flight unit result in any probable decrease in its ability to provide scientifically informative return for such materials.

Such information will guide the development of the next-generation small-satellite- compatible UV-visible spectrometer, which in all probability will be based on the O/OREOS flight instrument with modifications according to the results of this DDF funded study of performance vis a vis key science measurements. Because of this close coupling and relevance of the O/OREOS flight project, together with its tight budgetary constraints, we decided to support $25 k of the total cost of the O/OREOS engineering test unit development and fabrication using funds from this project. Future space missions will take advantage of the spectrometer technology developed for O/OREOS using science measurement results from this DDF project.