The Japan Aerospace Exploration Agency (JAXA) and Nihon Dempa Kogyo Co., Ltd. (NDK) have developed a unique QCM sensor system, the Twin-QCM, for ground use that operates under a wide temperature range. It was developed in 2015 and marketed in 2017. The Twin-QCM series has one model with a built-in heater and one with a built-in Peltier element. The current operational temperature limits of the Twin-QCM are -80 and +125 degrees C (Twin-TQCM) and -196 and +125 degrees C (Twin-CQCM). The lower minimum temperature limit of the Twin-TQCM is due to the presence of a Peltier element. We initiated the development of an advanced Twin-QCM intended for flight and exploration in 2021. Then, we began work on the "cryo-use" Twin-TQCM module, an engineering model (EM) of the update to the Twin-TQCM, which could be used under cryogenic temperatures below -80 degrees C. The EM was verified to operate at cryogenic temperatures during development. Next was a performance evaluation in deposition sensing. We built an experimental chamber to measure deposition rates using an EM for testing. This paper reports our experimental results of cryo-use Twin-TQCM EM performance.

In this study, the outgassing properties of bamboo-derived cellulose nanofibers (CNFs) for space applications were investigated. Outgassing rate tests based on ASTM E1559 were conducted on bamboo, bamboo-derived CNF, and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized CNF (T-CNF). The results showed that CNF emitted only water, while bamboo and T-CNF emitted outgas that is not water and had the peaks at -40( degrees)C and 55( degrees)C, respectively, in quartz crystal microbalance thermogravimetric gas analysis. These findings reveal that CNFs are promising materials for low-outgassing applications. Moreover, the results indicate that the TEMPO treatment produces outgassing sources into the CNF.

Expectations for high-resolution observations by very low Earth orbit (VLEO, below 300 km) satellites are growing. However, the density of atomic oxygen (AO) is much higher in VLEO than in LEO (300 km or higher), so severe degradation of materials is a concern due to high-flux AO collisions. To clarify the degradation, we developed and deployed the material degradation monitor (MDM) mission onboard the super-low altitude test satellite (SLATS). In the MDM, several materials were exposed to the environment at 160-560 km from 23 December 2017 to 1 October 2019 and observed optically by a CCD camera. In general, AO fluence is evaluated by measuring the volume or mass loss of a polyimide, but this was difficult to do because the samples could not be returned to the ground in this mission. This study evaluated AO fluences using the CCD images of a polyimide, Vespel. The sample had nine non-penetrating holes with different bottom-plate thicknesses and was monitored by the CCD while being illuminated by LED light from the back. The CCD images reveal the intensity of the light transmitted through the holes in the bottom plate. The erosion depths of the polyimide, corresponding to the AO fluences, can be evaluated from the pixel values at the hole positions on the images. Here, the correlation between the pixel values and thickness was investigated for pristine and AO-exposed Vespel samples using the MDM engineering models. The total green pixel values followed the Beer-Lambert law for the bottom-plate thicknesses, regardless of AO exposure. Applying the correlation to the MDM flight images, we found that the AO fluence increased significantly after the end of March 2019, finally reaching (6.5-9.8) x 1021 atoms/cm2. This optical imaging method would be useful for evaluating the AO effects on the other MDM samples and high AO fluences in future VLEO missions.

Atomic oxygen (AO) is the dominant constituent of the residual atmosphere in low Earth orbit (LEO). AO collides with spacecraft at a velocity of 8 km/s, causing oxidation and erosion of polymeric materials. Particularly in very low Earth orbit (VLEO) at altitudes below 300 km, the AO density is at least ten times that at 500-700 km, and the concentration of molecular nitrogen (N2) is 10% or more. Such high-flux AO and N2 can cause nonlinear processes and mass losses for polymers. This study aims to clarify the optical property changes for polymeric materials exposed to LEO and VLEO in the Material Degradation Monitor (MDM) mission onboard the SuperLow-Altitude Test Satellite (SLATS). The AO and N2 fluences and the UV irradiances were estimated using the NRLMSISE-00 atmospheric and solar radiation models. The relationships were investigated between the changes in CCD images and the estimated fluences of the samples. For silsesquioxane (SQ)-coated polyimide film, the diffuse reflection of visible light increased noticeably with an AO fluence above 1 x 1021 atoms/cm2. The formation of a silica layer on the coating induces cracks. For silver-coated FEP films, the diffuse reflection increased entirely at AO fluences above 3 x 1021 atoms/cm2. The AO and N2 collisions would erode and roughen the FEP surfaces. Visible transmission through silver-coated FEP films also increased locally with increasing AO fluence, indicating that some AO oxidized the silver layer despite the presence of an Inconel (Ni alloy) layer. The visible reflection from Beta Cloth was decreased by its reaction with UV. Further, the competitive reactions with UV and AO resulted in two-step changes in the visible reflection from the ETFE polymer (cable covering).

JAXA has proposed an innovative idea for satellites in Low Earth Orbit (LEO). The Super-Low Altitude Test Satellite (SLATS), also known as TSUBAME, is the first Earth observation satellite to occupy a Super-Low Orbit (S-LEO) or Very Low Earth Orbit (VLEO), below 300 km. The purposes of SLATS are 1) testing the maintenance of the satellite’s altitude with its ion engine against high atmospheric drag at a super-low altitude, 2) acquiring data on atmospheric density and atomic oxygen (AO), and 3) testing optical Earth observation. SLATS was successfully launched on 23 December 2017. SLATS was then altitude-controlled for 636 days to 271.7 km using chemical thrusters, aerodynamic drag, and ion engine propulsion. SLATS finally maintained its orbit of 167.4 km for 7 days and finished its operation on 1 October 2019. All the SLATS and Atomic oxygen MOnitor (AMO) data was acquired during these operations. The AMO is one of the mission sensors that monitor AO and its effects on spacecraft materials. The data from the AMO contributes to the choice of materials in future S-LEO satellite design. The data obtained by the AMO are valuable in that they provide considerable knowledge on AO fluence and its effects on space materials. A precise atmospheric density model and atmospheric composition model are indispensable for predicting the trajectory or re-entry of debris in orbit. Atmospheric models such as NRLMSISE-00, JB 2008, and DTM2013 have been developed, but few studies compare these models and the actual atmospheric environment in LEO. The average atmospheric density obtained from SLATS is lower than the value predicted by the atmospheric models (NRLMSISE-00, JB 2008, and DTM 2013). Understanding the model’s accuracy will contribute to the orbit control of future S-LEO satellites and the orbit prediction and control of debris in LEO.

Despite a number of studies comparing laparoscopic inguinal hernia repair (LH) and open herniorrhaphy (OH), the putative advantage of LH remains controversial due to a paucity of firm evidence. We hypothesized that LH has both advantages and disadvantages compared to OH and sought to clarify them by comprehensively analyzing the retrospective data using the combination of multiple statistical methods. Operative data for inguinal hernia during the period from February 1999 to December 2019 were examined. The patients were assigned into two groups according to the surgical procedure: laparoscopic percutaneous extraperitoneal closure (LPEC, n = 2410) and OH (n = 2038). Operative and anesthesia times and incidence of postoperative complications were evaluated using the propensity score methods and log-rank test. In comparison with OH, operative time of LPEC was longer for unilateral repair (21.59 ± 8.1 min vs 18.01 ± 8.0 min; p < 0.001) and shorter for bilateral repairs (28.55 ± 10.1 min vs 33.23 ± 11.7 min; p < 0.001), while anesthesia times were longer for both unilateral repair (57.67 ± 10.1 min vs 40.62 ± 11.9 min; p < 0.001) and bilateral repairs (65.95 ± 12.5 min vs 56.35 ± 15.1 min; p < 0.001). LPEC significantly reduced the risk of metachronous contralateral hernia (MCLH) (0.52% vs 9.29%; p < 0.001), but the recurrence rate was higher (0.21% vs 0.04%; p = 0.002) than OH. Orchiectomy due to testicular atrophy or torsion was required in 3 cases of OH (0.19%), whereas it was not seen in LPEC. LPEC had a less risk of MCLH and testicular complications but was associated with a higher recurrence rate and longer anesthesia time. Propensity scoring techniques can enhance the robustness of retrospective comparisons between groups over several years of data collection, which is frequently required in pediatric surgery studies.

Contamination is always troublesome in spacecraft development, but it has yet to be investigated because outgassing, transportation, deposition, and re-emission largely depend on spacecraft design. Designing spacecraft requires an accurate estimate of contaminant emission and deposition. Particularly for today's sophisticated spacecraft, analytical tools would be indispensable-but current simulations need to be improved. Our study addresses the first phase in the occurrence of contamination: improving the outgassing model. We focused on diffusion-limited phenomena because the diffusion rate of outgassing molecules in materials is thought to be much slower than their desorption rate at the surface. A new outgassing test method and analytical procedure was originally devised for extracting the parameters of the diffusion model. In comparing the desorption and diffusion models, we developed a model for the emission of outgassing molecules based on the diffusion theory and updated some functions of Japan's Spacecraft Induced Contamination Environment analysis software (J-SPICE). From this, we developed J-SPICE2 and installed the diffusion model to the software for calculating outgassing behavior. (C) 2021 Society of Photo-Optical Instrumentation Engineers (SPIE)

The role of N 2 in the upper atmosphere on the atomic oxygen (AO)-induced erosion of polyimide in low Earth orbit (LEO) and sub-LEO is investigated through ground-based experiments and flight data. The experiment is performed by adding an Ar beam at the same collision energy as an undecomposed O 2 component in the AO beam formed by laser detonation to simulate the physical effect of simultaneous N 2 collision in sub-LEO. The Ar beam is added by the dual-pulsed supersonic valve-equipped laser-detonation system developed at Kobe University. The experimental results indicate that the erosion of polyimide in the laser-detonation system is promoted by the presence of O 2 and Ar in the beam, corresponding to N 2 in the sub-LEO. On-ground experimental results are compared with in-orbit AO measurements. Previous space shuttle, international space station-based exposure experiments, as well as the world’s first real-time sub-LEO material erosion data aboard a super low altitude test satellite (SLATS) orbiting at an altitude of 216.8 km are presented. The SLATS data suggests the presence of an acceleration effect by N 2 collision on AO-induced polyimide erosion, as predicted by ground-based experiments.

Satellites in low Earth orbit (LEO) are subject to several environmental factors, atomic oxygen (AO) having the greatest effect on space materials, especially polymers. Recently, the possibility of utilizing orbits at an altitude lower than 300 km (super LEO or S-LEO) has been explored, but one complication in using these orbits is that AO fluence is expected to far exceed that in an ordinary LEO. The effect of S-LEO AO on materials used in space is not well understood. To investigate the influence of S-LEO AO on space materials, we developed the Material Degradation Monitor (MDM), which is installed on a JAXA spacecraft, the Super Low Altitude Test Satellite (SLATS, also known as TSUBAME). The SLATS is the first S-LEO satellite to operate at an altitude under 200 km and the MDM is the first near real-time experiment to examine the effects of AO on materials in this orbit. The aim of the MDM is to clarify degradation behaviors of the space materials according to AO fluence. We developed the instruments needed to detect AO fluence and the changes it causes to samples of various materials in S-LEO. The MDM performed as expected until the end of the SLATS operation. Some changes in materials were found from the images taken from front and back LEDs. Although there was no breakage by AO, optical properties changed that are assumed to be due to material erosion by AO.

In this paper, we propose a new Quartz Crystal Microbalance (QCM) sensor with temperature control, which can assess outgassing properties during spacecraft development. It will be referred to as the “Twin-QCM sensor.” There are two types. The Twin-Cryogenic QCM (Twin-CQCM) sensor is warmed by a built-in heater with an operating temperature of −190 to $+ 125^{\circ }\text{C}$ , and the Twin-Thermoelectric QCM (Twin-TQCM) sensor is warmed and cooled by a built-in Peltier module that can control the temperature within −80 to $+ 125^{\circ }\text{C}$ . Using a temperature compensation technique, the temperature-dependent drift of the frequency was found to be less than ±10 ppm over all operating temperatures. An RTD temperature sensor was mounted on the quartz crystal to improve the accuracy of temperature measurement. To confirm the accuracy, an additional temperature sensor installed at the center of the crystal. The sensor output temperature value was compared to that of the additional sensor, with the difference between both temperature sensors being +0.4 to $+ 2.6^{\circ }\text{C}$ in the temperature range from −130 to $+ 100^{\circ }\text{C}$ . Through the measurement of the sensor’s dynamic range, it was found that the deposited contaminant film in a vacuum increasingly changed such physical properties as viscoelasticity as the temperature increases.

Molecular contamination phenomena depend on temperature. For example, the morphology of a contaminant can change from a uniform film to droplets. The authors believe that the surface morphology of thin-film contamination affects optical transmittance and reflectance of camera lenses and other sensors, so it is important to gain a better understanding of the morphology of contamination. The authors investigated a simple measurement technique to determine molecular contamination morphology in a vacuum and at low temperatures using a CMOS camera sensor chip. The CMOS camera operates down to −60°C, which covers our range of interest (i.e., from −60°C to room temperature). Furthermore, using a combination of the camera sensor and the optical measurement setup in a vacuum chamber, the morphology and optical transmittance were measured simultaneously. The advantages of the technique are that the equipment is inexpensive and can be installed in many chambers now in use.

Space instruments such as solar arrays, radiators, or optics can be strongly impacted by molecular contaminants outgassed from spacecraft materials. For optics, transmittance and reflectance performances could indeed be modified by the deposit of contaminants. We report the transmittance measurements and predictions in the ultraviolet-visible-near-infrared range of contaminated optics from the outgassing of a mixture of two common materials used in space industry: EC2216 material (epoxy compound) and RTVS691 material (silicone compound). The Swanepoel model, commonly used in many fields, was employed for the first time in such conditions to easily and quickly predict transmittance. Transmittance was fully recovered at 20 degrees C; a decontamination plan could be based on heating at this temperature at least during a duration depending on the silicone/epoxy contaminants layer thickness. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)

Aim: We reviewed intraoperative video recordings (IVRs) of laparoscopic percutaneous extraperitoneal closure (LPEC) for inguinal hernia in children blindly to assess performance. Methods: IVRs of 183 LPEC performed between April 2013 and March 2016, graded by the operating surgeon as difficult (D; n = 8), straightforward (S; n = 96), or easy (E; n = 79), were scored by a panel of reviewers with advanced (group A; >400 LPEC cases; n = 5), intermediate (group I; 50-150 cases; n = 5), and basic (group B; <10 cases; n = 5) experience, according to suturing, dissection plane, vas/vessel dissection, bleeding, and peritoneal injury. They also allocated a recurrence risk rank (RRR; highest = 6; lowest = 1) for each IVR. Mean score variance for each IVR was also compared between reviewers. Results: There was one recurrence (R; 4-year-old male; level E). RRR were: 1, 2, and 2 for reviewers A, I, and B, respectively. Reviewer A scores for "suturing" and "bleeding," and reviewer I scores for "dissection plane" and "peritoneal injury" correlated significantly with RRR. No reviewer B scores correlated with RRR. Score variance between A and I and A and B for cases D1 and D2 were statistically significant. Conclusion: Advanced reviewers showed greatest variance, questioning the validity of whether experience alone improves surgical technique.

The Quartz Crystal Microbalance (QCM) sensor is a key device used in evaluating outgas characteristics such as deposition, desorption, and temperature-dependent properties. We propose a new cryogenic QCM (CQCM) sensor with good usability and temperature measurement accuracy using the twin-electrode technique. The sensor was named "Twin-CQCM". Its operating temperature ranges from -190 to +125°C. The temperature-dependent drift of the frequency was less than ±10 ppm over the whole temperature range by using the temperature compensation technique. A temperature sensor placed directly on the quartz crystal improves temperature measurement accuracy. To confirm the accuracy, an additional platinum temperature sensor was installed at the center of the crystal. The original sensor temperature output was compared to that of the additional sensor, with the difference between both temperature sensors being +0.4 to +2.6°C in the temperature range from -130 to +100°C. Furthermore, the user can easily replace the sensor's crystal because of the simple structure. This good usability enables not only simplified sensor replacement but also new applications, such as atomic oxygen (AO) measurement. This paper describes the proposed twin-electrode technique and discusses the evaluation results.

In orbit, contamination outgassed from spacecraft materials has been reported to degrade optical systems such as CCD cameras, lenses, mirrors, and optical filters mounted on a spacecraft. We focus on TiO2 photocatalyst to solve this contamination problem. TiO2 has the potential to decompose contaminants and suppress the deterioration of optical systems in orbit. However, the resistance of TiO2 itself to electrically charged particles, i. e., electrons in space, has not been clarified. The TiO2 films were irradiated with an electron beam (EB) with an energy of <480 eV in a vacuum. The irradiation dose was about 2.4 MGy. Chemical properties, surface morphology, and photocatalytic activity were compared before and after EB irradiation. Almost basic properties except surface roughness were unchanged, and the change of surface roughness was very small. These results indicate that TiO2 has sufficient resistance to an EB.

Laparoscopic percutaneous extraperitoneal closure (LPEC) has become a common procedure for repairing inguinal hernia. As a laparoscopic approach, pediatric surgical trainees require more training to learn LPEC than a traditional open approach. This study aimed to clarify the experience needed to acquire the skill to perform LPEC adequately. This descriptive single-center study used clinical data from patients who underwent LPEC between May 2009 and May 2016. The mean operative time for ten consecutive unilateral repairs was used as an index of proficiency with the procedure. The number of repairs performed before the mean operative time became less than 20 min was evaluated for each trainee. During the study period, six pediatric surgical trainees participated in the training independently. The number of the patients was 987. The total number of repairs was 1436, including 538 unilateral repairs and 449 concurrent bilateral repairs. Overall, the mean operative time was 21.8 ± 8.1 min for unilateral repair and 31.4 ± 9.7 min for concurrent bilateral repairs. The mean number of repairs performed before the acquisition of skill for dexterous LPEC was 125.1 ± 29.5. Although there were individual differences, all trainees acquired the skill to perform LPEC adequately within one year. With appropriate guidance, LPEC can become a standard technique for pediatric surgical trainees, along with traditional open surgery. These results provide valuable information for planning LPEC training.

Molecular contaminants outgassed from organic materials used for the spacecraft degrade the performance of optical surfaces of spacecraft. The influence of contaminants outgassed from epoxy resin on the spectral transmittance of the quartz substrate was investigated with an in-situ measurement system. The system can deposit the contaminants on temperature-controlled quartz substrates and the transmittance spectra were measured immediately after deposition in vacuum ambient. We obtained the optical constants of the contaminant using transmittance spectrum and simple optical models for optical calculations. The optical constants were described with a harmonic oscillator model and an effective medium approximation model. This paper reports the in-situ measurement results of transmittance spectra of the epoxy-resin-induced contaminants in deposition and desorption process. The thin contamination layer decreased the transmittance in the ultraviolet region. However, the contamination was entirely desorbed at -20 degrees C and transmittance recovered to the initial value. In addition, the results of optical calculations using the obtained optical constants were compared to the measurement results.