Environmental assessment in the prelaunch phase of Hayabusa2 for safety declaration of returned samples from the asteroid (162173) Ryugu: background monitoring and risk management during development of the sampler system
Earth, Planets and Space volume 74, Article number: 90 (2022)
We report ground-based environmental assessments performed during development of the sampler system until the launch of the Hayabusa2 spacecraft. We conducted static monitoring of potential contaminants to assess the environmental cleanliness during (1) laboratory work performed throughout the development and manufacturing processes of the sampler devices, (2) installation of the sampler system on the spacecraft, and (3) transportation to the launch site at the Japan Aerospace Exploration Agency’s (JAXA’s) Tanegashima Space Center. Major elements and ions detected in our inorganic analyses were sodium (Na), potassium (K), and ionized chloride (Cl–); those elements and ions were positively correlated with the total organic content and with exposure duration in the range from 101 to 103 nanograms per monitor coupon within an ~ 30-mm diameter scale. We confirmed that total deposits on the coupon were below the microgram-scale order during manufacturing, installation, and transportation in the prelaunch phase. The present assessment yields a nominal safety declaration for analysis of the pristine sample (> 5.4 g) returned from asteroid (162173) Ryugu combined with a highly clean environmental background level. We expect that the sample returned from Ryugu by Hayabusa2 will be free of severe and/or unknown contamination and will allow us to provide native profiles recorded for the carbonaceous asteroid history.
The re-entry capsule of the Hayabusa2 spacecraft was successfully retrieved from Woomera, South Australia, on December 6, 2020 (Tachibana et al. 2021; Yada et al. 2021a). Hayabusa2 made comprehensive surveys of C-type near-Earth asteroid (162173) Ryugu (e.g., Watanabe et al. 2019; Sugita et al. 2019; Kitazato et al. 2019, 2021; Grott et al. 2019; Jaumann et al. 2019; Arakawa et al. 2020; Morota et al. 2020; Okada et al. 2020; Tatsumi et al. 2021a, 2021b; Sakatani et al. 2021) with two touchdown operations for sampling. The Hayabusa2 sampler system worked as expected in the two landing operations (e.g., Tachibana et al. 2014, 2021, 2022; Sawada et al. 2017; Okazaki et al. 2017; Appendix). The sample container, which contained the Ryugu sample, was sealed using the metal-seal system developed to maximize the scientific value of the sample, especially with regard to retention of volatile gases from samples and prevention of terrestrial air contamination (e.g., Sawada et al. 2017; Okazaki et al. 2017). If there is no severe and/or unknown contamination on samples, detailed sample analyses will provide us with crucial information on the primordial native condition of organics, water, and mineral interactions regarding key issues in the molecular evolution of the asteroid.
To assess the entire sampling process aimed at safeguarding the scientific value and preventing unknown contamination, the Hayabusa2 sampler team conducted (i) off-nominal operational assessments (e.g., projector operation: Takano et al. 2020; small carry-on impactor: Ito et al. 2021) and (ii) a laboratory-based environmental assessment aimed at monitoring the background cleanliness at each stage of the development of the Hayabusa2 spacecraft (e.g., see the assessment policy by Sawada et al. 2017). Focusing on the latter issues, this technical report describes the assessment results during the prelaunch phase (Table 1). Based on both quantitative and qualitative assessments, we can evaluate potential contaminants that could have been artificially introduced, and this can be performed seamlessly during implementation, engineering development, launch, or capsule re-entry into the Earth’s atmosphere. We can thus provide a robust final safety declaration for analyses of samples from the pristine C-type asteroid Ryugu.
Overview of the Hayabusa2 sampler status for quality assurance
We designed a seamless monitoring procedure with an efficient workflow up to the time of initial sample processing (Tachibana et al. 2014; Okazaki et al. 2017; Sawada et al. 2017) to formulate a safety-declaration protocol for the Ryugu sample (i.e., Tachibana et al. 2021, 2022; Yada et al. 2021a, 2021b; Pilorget et al. 2021). Table 1 provides an overview of sample processes through initial implementation, engineering development, and assessment on the Hayabusa2 sampler team axis. To date, we have a range of knowledge from lessons learned during assessments of contaminants in the previous Hayabusa mission (e.g., category-3 particles; Uesugi et al. 2019 and references therein), potential contaminants from off-nominal operations of the Hayabusa2 (e.g., Takano et al. 2020; Ito et al. 2021), the curation procedure and cleanliness level at the Japan Aerospace Exploration Agency (JAXA) Extraterrestrial Sample Curation Center (e.g., Sugahara et al. 2018; Yoshitake et al. 2021; Yoshikawa et al. 2021), and sample transportation containers for Hayabusa2 samples (e.g., Ito et al. 2020; Shirai et al. 2020; Uesugi et al. 2020). We also highlight literature sources for quality control and assurance for other sample-return projects (e.g., Dworkin et al. 2018; McCubbin et al. 2019; Chan et al. 2020; and references therein). As a practical assessment based on that of Sawada et al. (2017), we deployed a contamination monitor coupon set near the sampler flight model to assess how much Earth-derived terrestrial material was present until the launch of the Hayabusa2 spacecraft (Fig. 1a).
Environmental assessment based on static monitoring
Figure 1b, c presents the schematic design and appearance of the monitor coupon, which contains a Pyrex container, an aluminium container, and carbon adhesive tapes for inorganic and organic assessments and microscopic observations, respectively (see Sawada et al. 2017 for more details). The timeline and assessment plans for quality control, monitoring, collection, and storage during development of the Hayabusa2 sampler are summarized in Fig. 1d. To evaluate both the inorganic and organic background levels of the ambient environment, we deployed the monitor coupon during assembly of the sampler system (Figs. 2 and 3). For comparison with the static cleanliness test described above, we also performed air-filter sampling (Multistage Andersen Cascade Impactor, Tokyo Dylec Corp.) and swab sampling using reference sources involving a quartz filter (8 cm diameter × 4 mm thickness) and glass wool (~ 0.3 g), respectively. The artefacts precipitated during the thermal vacuum test of the spacecraft (Sawada et al. 2017) were also analysed for identification of volatile compounds (Additional file 1).
The analytical methods used for inorganic and organic assessments and quantitative and qualitative evaluations have been reported previously (e.g., Takano et al. 2020; Ito et al. 2021). All glassware and aluminium materials were washed with organic solvent and flushed with ultrapure water, as described by Karouji et al. (2014). All glassware and aluminium parts used in the assessment were cleaned by heating (450 °C for 5 h) in air to remove any artefacts of organic contaminants (e.g., Takano et al. 2020).
Results and summary
Inorganic and organic assessments
The concentrations of total organics, major elements, and major ions monitored by the coupons at different locations, occasions, and/or durations (coupon set code; CPS-1 to CPS-12) are summarized in Fig. 4. Concentrations of elements, ions, and total organics were less than or on the order of 103 nanograms (i.e., 1 μg or less) for all coupons (~ 30 mm in diameter). The raw concentrations of the elements (Fe, Cu, Ni, Cr, Zn, Na, K, Ca, Mn, Al, Ti, Mg, Co, Sn, Pb, V, and P), ions (including Cl−, NO2−, Br−, NO3−, SO42−, PO43−, and F−), and organics are shown in Tables 2, 3, and 4, respectively. The concentrations normalized to surface area (i.e., ng cm−2) were obtained from the monitor coupon size (Fig. 1b). The quantitative values for static monitoring per unit time are shown in Fig. 4b and Table 4. Although there were some difficulties in specifying the exact compound source within the ultrasmall-scale analyses, this coupon was stored at JAXA for future secondary analysis (detailed analysis) if necessary.
The major inorganic elements and ions detected were sodium (Na), calcium (Ca), potassium (K), chloride (Cl−), sulfate (SO42−), and nitrate (NO3−). Their profiles were positively correlated with the total organic content in the range 101–103 ng per monitor coupon. This result indicates a profile different from the chemical compositions of oceanic salt and anthropogenic biological fluids (e.g., a seawater and sweat composition; Terasawa et al. 2001). Figure 5 shows time-dependent static accumulation of ambient aerial deposits onto the monitor coupons throughout the procedure (CPS-1–12, including STA1, SFA2, and VAB). There were clear positive correlations between total sodium, potassium, and chloride and total organic contents, which closely approximated the 1:1 line. Both major inorganic ions and total organic fluxes converged in the range 101–103 ng per monitor coupon, resulting in static deposition of < 1 μg overall within ~ 7.0 and ~ 5.3 cm2 for aluminium schale and Pyrex schale, respectively. Representative compositions of organic deposits were obtained by the gas chromatography (Fig. 6). This result is a static monitoring method and may depend on the environmental gradient to determine whether the dust flux had reached equilibrium or not, especially for volatile components. A wide range of aliphatic hydrocarbons comprising straight-chain alkanes (< n-C19H40) was detected (e.g., m/z = 57 for the extracted ion chromatogram). The total amounts of other miscellaneous organics were quantified based on the corresponding responses with the internal standard method (e.g., Takano et al. 2020). The exposure time-dependent accumulation profiles were similar to the results for cleanliness tests run in the clean-room chamber at the Institute of Space and Aeronautical Science (ISAS)/JAXA (i.e., the nitrogen-circulation clean chamber; Sugahara et al. 2018).
Tables 5 and 6 summarize the basic statistics and the correlation matrix for the concentrations of major components in the static samples (i.e., CPS1–12 and CAS1–12; n = 10). Most profiles of the major components (e.g., Na, K, Cl−, F−, NO3−, Zn, SO42−, Mg, and P) were positively correlated with each other, except for the profile of aluminium (Fig. 5e and Additional file 1: Figure S2). We note that we used clean room-type aluminium foil to store and carry the monitor coupons, which could potentially introduce a certain amount of aluminium onto the coupon. We also conducted microscopic observations of the solid contaminants to evaluate their morphological characteristics (Fig. 7) and found that globular particles were more common (70%) than fibrous particles (13%). Further non-destructive analyses using microRaman and infrared spectroscopy (e.g., Kitajima et al. 2015) can be performed at ISAS/JAXA upon request.
We stored the potential Earth-derived artefacts obtained from each procedure (Table 1) (i.e., the category-3 particles; Uesugi et al. 2019). Therefore, if necessary, we can provide a careful description, upon request, as suggested by the lessons learned from the previous Hayabusa mission (the asteroid Itokawa) with regard to high-resolution small-scale mass spectrometry (e.g., NanoSIMS: Ito et al. 2014; ToF–SIMS: Naraoka et al. 2015) and spectroscopy (e.g., X-ray absorption: Yabuta et al. 2014). Interestingly, Chan et al. (2021) and Parker et al. (2022) reported a detailed description of exogenous carbonaceous organic matter derived from the Itokawa sample.
Safety declaration of the Ryugu sample processes
The Hayabusa2 mission succeeded in delivering its re-entry capsule to Earth in December 2020, and the total sample amount was confirmed to exceed 5 g (Tachibana et al. 2021, 2022; Yada et al. 2021a, 2021b; Pilorget et al. 2021), including millimeter-sized grains to centimeter-sized pebbles. This study reports the prelaunch phase environmental assessment performed during manufacturing of the sampler devices, their installation onto the spacecraft, and their transportation. We conclude that the exposure-time-dependent deposition profiles of potential contaminants were firmly underscored and similar to the profiles obtained from the clean-room facility assessment (Sugahara et al. 2018). All potential contaminants have been stored at the JAXA Extraterrestrial Sample Curation Center in a nitrogen-purged storage area and are available for future analysis upon request.
The total amount of potential contaminants in the sampler system is estimated to be less than 100 ng cm−2, which is much smaller than the total amount of returned samples. Along with the fact that there was no off-nominal situation from spacecraft launch to the capsule’s re-entry to Earth, we conclude that ambient background artefacts have been characterized and will not affect detailed sample analyses.
We expect that the lessons learned in the process from implementation to practical knowledge during the last 8 years will also provide a valuable baseline for future sample-return missions (e.g., Dworkin et al. 2018; Usui et al. 2020; Anand et al. 2020; Chan et al. 2020; Neveu et al. 2020; Farley et al. 2020; Fujiya et al. 2021) and microspacecraft missions with a launch vehicle secondary payload (e.g., Ito et al. 2018; Hernando-Ayuso et al. 2019; Campagnola et al. 2019).
Availability of data and materials
The Hayabusa2 project is releasing raw data on the properties of the asteroid Ryugu from the following database in the Hayabusa2 Science Data Archives (DARTS, https://www.darts.isas.jaxa.jp/planet/project/hayabusa2/) with regard to the ONC (Optical Navigation Camera), TIR (Thermal InfraRed Imager), NIRS3 (Near InfraRed Spectrometer), LIDAR (LIght Detection And Ranging), SPICE (SPICE kernels) and PDS4 (PDS4 bundles). In addition, the catalogue of the Ryugu samples is also available in the database titled “Hayabusa2, Ryugu Sample Curatorial Dataset, (https://doi.org/10.17597/ISAS. DARTS/CUR-Ryugu-description) after Yamamoto et al. (2016) and Abe (2021)”. All of these database publications are compliant with ISAS data policies (https://www.isas.jaxa.jp/en/researchers/data-policy/). Please see also the Additional file 1.
Japan Aerospace Exploration Agency
Institute of Space and Astronautical Sciences/JAXA
Extraterrestrial Sample Curation Center
Tanegashima Space Center
Tsukuba Space Center
Spacecraft Test and Assembly Building
Vehicle Assembly Building
Spacecraft and Fairing Assembly Building
National Aeronautics and Space Administration
Thermal desorption system
GC coupled with mass spectrometry
Extracted ion chromatogram
Fourier transform infrared (spectroscopy)
Nanoscale secondary ion mass spectrometry
GAs extraction and analyses system
National Institute of Standards and Technology
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We express our sincere thanks to Associate Editor Dr. Yoko Kebukawa (Yokohama National University) and two anonymous reviewers for constructive comments that improved the initial version of the manuscript. We thank Dr. Keiko Nakamura-Messenger (Johnson Space Center/NASA), Dr. Chisato Okamoto (Kobe University), Dr. Satoru Nakazawa (ISAS/JAXA), Dr. Yuzuru Karouji (ISAS/JAXA), Dr. Hikaru Yabuta (Hiroshima University), Dr. Motoo Ito (JAMSTEC), Prof. Hiroshi Naraoka (Kyushu University), and the members of the Extraterrestrial Samples Curation Center (ESCuC), including the Astromaterials Science Research Group (ASRG), for discussions of the assessment procedure. We appreciate Sumitomo Heavy Industries, Ltd. and NEC Corporation, Ltd. for collaborating during the development of the Hayabusa2 sampling system. We also thank Renesas Semiconductor Manufacturing Co. Ltd. for their support of the chemical assessment. Preliminary reports based on these technical data were presented at the 2020 Solar System Symposium in Sapporo, Japan.
This work was supported in part by a Grant-in-Aid for Scientific Research in Innovative Areas (Research Project on the Evolution of Molecules in Space; No. 25108006) and No. 21KK0062 from the Japan Society for the Promotion of Science (JSPS).
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Sample assessment of the potential risk between the worst-assumption lines versus the actual native sample weight. ‘Worst case (off-nominal adverse case ~ 100%)’ plot of the potential assumption line (e.g., unrealistic artifacts in the range of 0.1 and 1.0 μg up to the launch of the spacecraft; e.g., Fig. 4) versus the native sample weight (5.4 g; actual sample achievement: Tachibana et al. 2021, 2022; Yada et al. 2021a, 2021b). See the minimum mission requirement (100 mg) in a nominal situation (Tachibana et al. 2014). Figure S2. a Scheme of the screening and cleanliness test for air-filter sampling (Multi-stage Andersen Cascade Impactor, Tokyo Dylec Corp.) using a quartz filter (8 cm diameter × 4 mm thickness). b Screening and cleanliness test for swab sampling using 0.3 g of glass wool and a 20 × 20 cm square. Photos were taken at Tanegashima Space Center before the launch of the Hayabusa2 spacecraft. Figure S3. Identification of volatile compounds in the precipitate material during the spacecraft’s thermal vacuum test. For the general protocol adopted for a thermal vacuum test of a spacecraft, see JAXA document JERG-2-130-HB005B and Sawada et al. (2017). Small amounts of phenol (C6H6O; molecular weight: 94.1), triethylphosphate (C6H15O4P; molecular weight: 182.1) and benzoic acid (C7H6O2; molecular weight: 122.1) were confirmed based on the TD–GC/MS method and a standard library database (method after Takano et al. 2020). Figure S4. a–d Other locations for collections of potential contaminants before and after launch of the Hayabusa2 spacecraft. Collected samples are in storage at ISAS/JAXA, but the data are not shown in this report. Please see also the Additional file 2: Movies S1 for the launch. Figure S5. Hayabusa2 sample capsule entering the Earth’s atmosphere (photo taken in Australia). Please see also the fireball movie captures taken near Coober Pedy, Australia, in the Additional file 3: Movie S2, Additional file 4: Movie S3, Additional file 5: Movie S4 (credit: JAXA). Figure S6. Hayabusa2 spacecraft just before launch in 2014 at Tanegashima Space Center (TNSC) with the Hayabusa2 sampler team members (credit: JAXA).
See Fig. 8.
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Sakamoto, K., Takano, Y., Sawada, H. et al. Environmental assessment in the prelaunch phase of Hayabusa2 for safety declaration of returned samples from the asteroid (162173) Ryugu: background monitoring and risk management during development of the sampler system. Earth Planets Space 74, 90 (2022). https://doi.org/10.1186/s40623-022-01628-z
- Hayabusa2 spacecraft
- Carbonaceous-type asteroid Ryugu
- Environmental assessment
- Static monitor coupon
- Inorganic and organic background
- Safety declaration