JOINT EVALUATION OF SPACE MATERIALS BY CNES AND JAXA

JOINT EVALUATION OF SPACE MATERIALS BY CNES AND JAXA Hiroyuki SHIMAMURA (1)*1, Eiji MIYAZAKI (1), Junichiro ISHIZAWA (1), Riyo YAMANAKA (1), Yugo KIMOTO (1), Stéphanie REMAURY (2)*2, and Pascale NABARRA (2) (1) Space Materials Section, Electronic Devices and Materials Group, Aerospace Research and Development Directorate, Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan. *1 Phone: +81-29-868-2323, E-mail: shimamura.hiroyuki@jaxa.jp (2) Materials and Coatings Laboratory, Thermal Control Department, Centre National D Etudes Spatiales (CNES), 18 Av. Edouard Belin, 31401 Toulouse cedex 9, France. *2 Phone: 33 (0) 5 61 27 31 33, E-mail: stephanie.remaury@cnes.fr ABSTRACT The Centre National D Etudes Spatiales and Japan Aerospace Exploration Agency have mutually evaluated some thermal control materials used for each country s spacecraft and have compared the results. The evaluation included the following items: - Thermo-optical properties (solar absorptance α S and normal infrared emittance ε N ) - Outgassing properties - Durability against atomic oxygen (AO) (Erosion yield and changes of α S and ε N ) - Durability against ultraviolet (UV) radiation (Changes of α S ) These evaluation and irradiation tests were conducted using each agency s facilities and test methods. Although some materials showed slight discrepancies attributable to differences between the facilities or the test methods used, generally good agreement was obtained in each evaluation. 1. INTRODUCTION The Centre National D Etudes Spatiales (CNES) and Japan Aerospace Exploration Agency (JAXA) decided to create a new space-parts working group in 2003. The materials evaluation test program was added to the working group and started in 2006. In the program, the Materials and Coatings Laboratory of CNES and the Space Materials Section of JAXA have continually exchanged information related to advanced materials developed for space applications and test methods and facilities for space material evaluations in each country. In addition, a joint evaluation of space materials has been conducted in the program. CNES and JAXA have evaluated French and Japanese thermal-control materials by using each agency s experimental procedures and facilities. The information exchange and the joint evaluation are expected to promote better understanding of practical space materials and to improve evaluation techniques in the respective countries. In this paper, the results of the joint evaluation are reported. 2. EXPERIMENT 2.1 Materials French and Japanese thermal control materials, such as atomic oxygen (AO) resistance polyimide films, rigid solar reflectors, white paints, and black paints, were evaluated. The descriptions of the evaluated materials are presented in Table 1. 2.2 Evaluation of Thermo-Optical Properties Measurement equipment and conditions for solar absorptance (α S ) and normal infrared emittance (ε N ) used in each agency are shown in Tables 2 and 3. 2.3 Evaluation of Outgassing Properties CNES and JAXA conducted outgassing tests according to ECSS Q70-02A [1] and ASTM E595 [2], respectively. These two standard test methods for outgassing are fundamentally equivalent. First, samples were conditioned in a certain environment. Then, the samples were baked at 125 C under high vacuum for 24 hours. Metallic plates were mounted next to the samples and maintained at 25 C during the baking to collect gasses volatilized from the samples. The samples and the collector plates were weighed before and after the baking. Subsequently, the samples were stored in a given set of circumstances for 24 hours after the baking, and then reweighed to evaluate their mass increase by water absorption. The stored condition of samples differs slightly in the two standards: 22±3 C and 55±10% relative humidity (RH) in ECSS Q70-02A, and 23±1 C and 50±5% RH in ASTM E595. These standards have a major difference in the sample configuration. Thin films are cut into small pieces on the order of 1.5 to 3 mm in ASTM E595. Coatings and adhesives are applied to thick metal or glass substrates, and dried. Then, they are peeled off from the substrates and collected in a specimen boat. In ECSS Q70-02A, thin films are cut into strips approximately 10 mm wide and rolled up to fit a specimen cup. Coatings and adhesives are applied to a degreased and dried metal foil of known thickness, such as aluminum foil, and then cut into strips. The outgassing

test conditions and the sample configuration for each agency s evaluation are listed in Table 4. The difference of the sample configuration in RSR is presented in Fig. 1. For PSBN in CNES s evaluations, fragments removed from the substrate in a similar way to ASTM E595 were used. 2.4 Atomic Oxygen Bombardment Tests and Evaluations of Durability against Atomic Oxygen The AO tests were performed for all materials, except for the black paints, by using the ESA/ESTEC AO Facility [3] in CNES s evaluations and the Combined Space Effects Test Facility [4] in JAXA s evaluations. The facilities and conditions used for the AO tests in each agency s evaluation are listed in Table 5. The AO generation in these facilities is based on a laser detonation phenomenon. The facilities can expose materials to AO at 5 ev to simulate a low earth orbit (LEO) environment. The AO incidence is almost perpendicular to the samples. The mass loss of the samples caused by AO was measured, and then erosion yields were determined from the mass loss and the AO fluence by using the following equation [5]: m E = AρF where E: erosion yield, cm 3 /atom m: mass loss, g A: exposure area, cm 2 ρ: density of samples, g/cm 3 F: AO fluence, atoms/cm 2 Changes in α S and ε N caused by the AO tests were also evaluated in the conditions shown in Tables 2 and 3. 2.5 Ultraviolet Irradiation Tests and Evaluations of Durability against Ultraviolet Radiation The ultraviolet (UV) irradiation tests were performed for all materials, except for the black paints, by using SEMIRAMIS [6, 7] in CNES s evaluations and the JAXA UV Test Equipment [8] in JAXA s evaluations. The facilities and conditions used for the UV irradiation tests are listed in Table 6. These facilities can produce UV-ray matching solar light with a xenon lamp and irradiate the UV to materials under high vacuum. The wavelength region of the UV is approximately 200 400 nm in both facilities. The materials were irradiated by UV of approximately 1000 Equivalent Solar Hours (ESH) at 3.5 Solar Constants (SC) in CNES s evaluations, and 1112 ESH at 7 SC in JAXA s evaluations. The materials were kept at about 40 C and 20 C during the UV irradiation tests in CNES s and JAXA s evaluations, respectively. The α S of each sample was measured before and after the UV irradiation tests and the changes were compared between the two agencies results. In CNES s evaluations, α S measurements were conducted under vacuum at 40 C using the spectrophotometer equipped with SEMIRAMIS. By contrast, α S values were measured under atmospheric pressure in the conditions shown in Table 2 in JAXA s evaluations. 3. RESULTS AND DISCUSSION 3.1 Thermo-Optical Properties The α S and ε N measurement results for all materials are shown in Fig. 2. The α S results were almost equivalent in both agencies evaluations. Meanwhile, the ε N results in CNES s evaluations demonstrated a tendency to be slightly lower than those in JAXA s evaluations; the difference was 0.11 at maximum in SiO 2 /UPILEX-S/Al. The difference might be attributed to the difference of the equipment used. DB-100, used in CNES s evaluations, measures ε N relative to the reference materials (Gold and Black). In contrast, TESA 2000, used in JAXA s evaluations, can determine ε N absolutely. The comparable results have been confirmed among many other materials in the comparison of measured values between DB-100 and TESA 2000 [9]. 3.2 Outgassing Properties The outgassing test results, total mass loss (TML), recovered mass loss (RML), collected volatile condensable material (CVCM), and water vapor regained (WVR), are presented in Fig. 3. Both agencies results indicated good agreement in SiO 2 /UPILEX-S/Al, MAPATOX K/Kapton/Al, PSB, Astro White, and Astro Black; RSR and PSBN showed large differences between the two agencies results. The differences in the outgassing test results of RSR might be attributable to the difference of cure temperature in the manufacturing process of the samples. RSR is normally cured on a substrate at 200 C for one hour. The RSR used in CNES s evaluations was coated on 30-µm-thick aluminum foils, while that used in JAXA s evaluations was coated on 3-mm-thick glass plates. The RSR used in JAXA s evaluations is expected to be cured at less than 200 C because of the thick glass substrates with high heat capacity, resulting in inadequate reticulation. The inadequate reticulation can worsen the outgassing properties. The outgassing properties of RSR coated on 30-µm-thick aluminum foils were tested by JAXA to compare with those in CNES s evaluation. The samples were cut into 10-mm-wide strips, folded up and placed into a specimen boat. The RSR outgassing properties were as follows: TML=0.288%, RML=0.284%, CVCM=0.076%, and WVR=0.004%. These outgassing properties gave close agreement with those in CNES s evaluation. In the outgassing test results of each agency for PSBN, a large discrepancy was confirmed in WVR. As mentioned above, there is a slight difference in the stored

condition of samples between ECSS Q70-02A and ASTM E595: 22±3 C and 55±10% RH in ECSS Q70-02A, and 23±1 C and 50±5% RH in ASTM E595. In particular, the difference in RH potentially influences WVR for high-hydroscopic materials such as inorganic paints. Then, the relation between RH and moisture absorption in PSBN was investigated. First, fragments of PSBN were completely dried at 125 C for 24 hours under vacuum, and then stored at different conditions of RH for 24 hours: 30, 50, and 70±3%RH. The temperature was kept at 23±1 C in each condition. The fragments were weighed before and after the conditioning, and the mass increase due to absorption was measured. The water adsorption isotherm for the PSBN at 23±1 C is shown in Fig. 4. The moisture absorption of the PSBN exhibited a large increase in more than 50% RH. The result means that WVR of PSBN can vary significantly according to RH of the stored condition. It is conceivable that the PSBN were stored at higher RH in CNES s evaluations than in JAXA s evaluations. 3.3 Durability against Atomic Oxygen Bombardment Erosion yields of each material are shown in Fig. 5. SiO 2 /UPILEX-S/Al, PSB, and Astro White indicated a good agreement; there were discrepancies in MAP ATOX K/Kapton/Al, RSR and PSBN between the two agencies evaluations. However, the erosion yields of these materials themselves were very small; their values were in the order of E-25 cm 3 /atoms. Therefore, the discrepancies are expected to be practically inconsequential. The α S and ε N changes by the AO tests are presented in Fig. 6. In the α S changes, slight differences were observed in the white paints, PSB, PSBN and Astro White. One of the possible causes for this result is the difference in intensity of the extreme ultraviolet (EUV), which is a by-product from the oxygen plasma generated by a laser detonation phenomenon [3]. No significant difference was observed in the ε N changes for all materials. 3.4 Durability against Ultraviolet Irradiation The α S changes by the UV irradiation tests are presented in Fig. 7. The white paints, PSB, PSBN and Astro White, indicated a small inconsistency between each agency s results. The result is attributable to the difference in the measurement environment of α S. As described above, α S was measured under vacuum in CNES s evaluations, while it was measured under atmospheric pressure in JAXA s evaluations. It is noted that recovery of α S, or a bleaching effect, occurs when the samples are transferred from vacuum to atmospheric pressure after irradiation tests [7]. In addition, white paints are more sensitive to the recovery phenomenon than polymers [7]. Consequently, the α S of PSB, PSBN, and Astro White in JAXA s evaluations were slightly lower than those in CNES s evaluations. 4. CONCLUSIONS The results of the joint evaluation by CNES and JAXA are as follows: - Thermo-optical properties The α S values measured by each agency were almost equivalent in all materials. The ε N values in CNES s evaluations were slight lower than those in JAXA s evaluations. The difference between the measuring equipment might be the cause of this result. - Outgassing properties All materials except RSR and PSBN had a good consistency between each agency s results. The inconsistency of the RSR outgassing properties is attributable to the difference of cure temperature in the manufacturing process. For PSBN, it is the RH of the stored condition which affects strongly the outgassing properties. - Durability against AO The erosion yields of MAPATOX K/Kapton/Al, RSR and PSBN mismatched slightly between each agency s results. However, the discrepancies were very small, being practically inconsequential. Only white paints showed a slight inconsistency in the α S changes due to the presence of EUV. All materials had a good agreement in the ε N changes. - Durability against UV radiation Only white paints showed a slight inconsistency in the α S changes. The recovery phenomenon might have occurred in JAXA s evaluations. The measurement environment was different between each agency s evaluations: vacuum in CNES s evaluations and atmospheric pressure in JAXA s evaluations. The joint evaluation indicated that the test methods and facilities of both agencies are in rather good agreement, although some materials showed a slight difference in the results, as mentioned above. In addition, noteworthy comparison points of the evaluation results of space materials were clarified. This joint evaluation enhanced the collaboration between CNES and JAXA on evaluations and developments of space materials.

REFERENCES [1] European Cooperation for Space Standardization (ECSS) Q70-02A, Thermal Vacuum Outgassing test for the Screening of Space Materials. [2] American Society for Testing and Materials (ASTM) Standard E595, Standard Test Method for Total Mass Loss and Collected Volatile Condensable Materials from Outgassing in a Vacuum Environment. [3] Bruno Weihs and Marc Van Eesbeek, Secondary VUV Erosion Effects on Polymers in the Atomic Oxygen Exposure Facility, ESA SP-368, November, 1994. [4] Hiroyuki Shimamura and Eiji Miyazaki, Investigations into Synergistic Effects of Atomic Oxygen and Vacuum Ultraviolet, Journal of Spacecrafts and Rockets, Vol. 46, No. 2, March April, 2009, pp. 241 247. [5] Kim K. de Groh and Bruce A. Banks, MISSE PEACE Polymers Atomic Oxygen Erosion Results, NASA TM-214482, 2006. [6] J. Marco and S. Remaury, Simulation Conditions Impact on Space Degradation Evaluation of Thermo-Optical Materials Properties, ESA SP-616, September, 2006. [7] J. Marco and S. Remaury, Evaluation of Thermal Control Coatings Degradation in Simulated Geo-Space Environment, High Performance Polymers, 16, 2004, pp. 177 196. [8] Youichi Nakayama, et al., Evaluation and Analysis of Thermal Control Materials under Ground Simulation Test for Space Environment Effects, High Performance Polymers, Vol. 13, No. 3, 2001, pp. S433 S451. [9] Kazuyuki Mori and Hiroyuki Shimamura, Comparison of Thermo-Optical Properties in Different Equipments, Proceedings of the 29th Japan Symposium on Thermophysical Properties, Oct. 8 10, 2008, pp. 205 207. (in Japanese)

AO Resistance Polyimide Film Material SiO 2 /UPILEX-25S/Al MAP ATOX K/Kapton/Al Table 1 Evaluated materials list. Details 25-µm-thick UPILEX-S coated with SiO 2 (front side) and aluminum (back side) 25-µm-thick Kapton coated with polydimethylsiloxane varnish (front side) and aluminum (back side) Supplier, Country UBE Industries Ltd., Japan MAP, France Rigid Solar Reflector RSR polydimethylsiloxane varnish on aluminum substrate MAP, France PSB Binder: potassium silicate, Pigment: Zn 2 TiO 4, on aluminum substrate MAP, France White Paint PSBN Binder: potassium silicate, Pigment: ZnO, on aluminum substrate MAP, France NOVA500 Astro White Binder: silicone, Pigment: ZnO, on aluminum substrate Nippon Paint Co. Ltd., Japan Black Paint NOVA500 Astro Black Binder: polyurethane, Pigment: C, on aluminum substrate Nippon Paint Co. Ltd., Japan Equipment, Manufacturer Table 2 Measurement equipment and conditions for solar absorptance (α S ). CNES evaluations Portable reflectometer EL510, Elan Informatique JAXA evaluations Spectrophotometer U-4100, Hitachi High-Technologies Corp. Wavelength, nm 300-2500 250 2500 Reference sample Depends on the coating to be measured Spectraron (SRS-99) Integrating sphere, diameter/material Detector Φ70 mm/ Barium sulfate paint Thermopile Φ200 mm/spectraron UV-VIS: Photomultiplier NIR: Water cooling PbS Solar spectrum Xenon flash ASTM E 490-73a Measurement temperature, C Ambient temperature Ambient temperature Equipment, Manufacturer Table 3 Measurement equipment and conditions for normal infrared emittance (ε N ). CNES evaluations Portable reflectometer DB-100, Gier Dunkle JAXA evaluations Portable reflectometer TESA 2000, AZ Technology, Inc. Wavelength, µm 5-25 3 35 Measurement method Relative Absolute Reference sample Gold and Black Measurement temperature, C Ambient temperature Ambient temperature

Table 4 Outgassing test conditions and sample configuration. CNES evaluations JAXA evaluations Test method ECSS Q70-02A ASTM E595 Condition before initial measurement and after baking 22±3 C and 55±10% RH for 24 h 23±1 C and 50±5% RH for 24 h Baking temperature Samples: 125 C, Collector plates: 25 C Samples: 125 C, Collector plates: 25 C SiO 2 /UPILEX-25S/Al strips ca. 10 mm wide small pieces on the order of 1.5 to 3 mm MAP ATOX K/Kapton/Al strips ca. 10 mm wide small pieces on the order of 1.5 to 3 mm Sample configuration RSR strips ca. 10 mm wide fragments PSB strips ca. 10 mm wide fragments PSBN fragments fragments NOVA500 Astro White strips ca. 10 mm wide fragments NOVA500 Astro Black strips ca. 10 mm wide fragments (a) (b) 20mm 5mm Fig. 1 Photographs of RSR for outgassing tests. (a) The sample prepared according to ECSS Q70-02A and (b) the sample prepared according to ASTM E595. 5mm Table 5 Facilities and conditions for the AO tests. CNES evaluations JAXA evaluations Facility ESA/ESTEC AO facility Combined Space Effects Test Facility AO generation principle Laser detonation phenomenon Laser detonation phenomenon AO energy, ev ca. 5 ca. 5 AO flux, atoms/cm 2 s 1.4 1.8 E+15 ca. 5 E+15 SiO 2 /UPILEX-25S/Al 5.7E+20 3.4E+20 MAP ATOX K/Kapton/Al 5.7E+20 3.4E+20 AO fluence, atoms/cm 2 RSR 5.7E+20 3.1E+20 PSB 3.0E+20 3.2E+20 PSBN 3.8E+20 3.2E+20 NOVA500 Astro White 5.7E+20 3.4E+20

Table 6 Facilities and conditions for the UV irradiation tests. CNES evaluations JAXA evaluations Facility SEMIRAMIS JAXA UV Test Equipment UV source Xenon lamp Xenon lamp UV wavelength region, nm ca. 200 400 ca. 200 400 UV flux, SC 3.5 7 Sample temperature, C ca. 40 ca. 20 SiO 2 /UPILEX-25S/Al 1001 1112 MAP ATOX K/Kapton/Al 1000 1112 UV fluence, ESH RSR 1000 1112 PSB 1001 1112 PSBN 1001 1112 NOVA500 Astro White 1001 1112 (a) (b) Fig. 2 Thermo-optical properties of each material. (a) Solar absorptance (α S ) and (b) normal infrared emittance (ε N ).

(a) (b) (c) (d) Fig. 3 Outgassing properties of each material. (a) TML, (b) RML, (c) CVCM, and (d) WVR.

Fig. 4 Water adsorption isotherm for PSBN at 23±1 C. Fig. 5 Erosion yields of each material in CNES s and JAXA s evaluations.

(a) (b) Fig. 6 Thermo-optical property changes of each material by AO tests. (a) Solar absorptance (α S ) changes and (b) normal infrared emittance (ε N ) changes. Fig. 7 Solar absorptance (α S ) changes of each material by UV irradiation tests.