The authors have investigated the effects of uncertainties on the pointing performance of an extensible optical bench (EOB), used for a large, highly precise, space X-ray telescope. The uncertainties considered are in member length, position due to backlash, and friction at connecting nodes. This study mainly investigates the effect of friction on the pointing performance. First, the pointing performance analysis is briefly investigated. The extended EOB is modeled as a truss structure, and the distortion due to the member length imperfection is evaluated by a nonlinear, finite element analysis (FEA). Subsequently, the backlash at connecting nodes is modeled by introducing a virtual cable element with a natural length equal to the size of backlash. In addition, the deformation due to a friction force acting at the connecting node is calculated as a perturbation from the equilibrium condition without performing a contact analysis. This friction model is further extended to identify effects of friction uncertainty with reduced computational costs. Through numerical examples, the effects of friction uncertainty on the deployment repeatability for the EOB, and effects of the number of stages of EOB on the pointing performance are investigated.
Invar alloys with low thermal expansion are often used in the structural and optical components of space telescopes and sensors, which require high accuracy and thermal dimensional stability. The thermal expansion of Invar can be reduced through partial substitution of Ni by Co. This alloy is known as Super Invar. However, the decrease in Ni content increases the martensitic transformation temperature (Ms). Consequently, the conventional Super Invar cannot be used at temperatures below 243K. Further, some high performance detectors, such as infrared sensors and bolometers, require cryogenic environment to avoid thermal noise. We resolve this contradiction of low coefficient of thermal expansion (CTE) and low Ms by optimizing the contents of Ni and Co, purifying the alloys, and improving the thermal treatment. We have developed novel alloys, which exhibit near-zero CTE and low Ms simultaneously. The developed Super Invar, IC-LTX, exhibited CTE of 0±5×10-8/K (273-303K), and it can be used at 173K. Stainless Invar (IC-DX) was also developed for applications at cryogenic temperatures. It exhibited CTE of 0±1×10-7/K (60-100K) and martensitic transformation did not occur even at liquid He temperature (4K). These alloys are being tested as telescope components for Small JASMINE satellite, Thirty Meter Telescope (TMT), and other applications.
JAXA is constructing a new deep space station employing a 54 m diameter antenna for supporting missions beyond HAYABUSA2 both in X-band and Ka-band. In the design of this station, functional extensions were well considered from the beginning. We concluded that a concept based on the symmetric reserved resource allocation was suitable. In this concept, we basically keep reserved resources of every instrument for its redundancy in a symmetrical manner. We introduce this simple rule as a practical way to determine or limit our future investment. In the reserved spaces prepared in such a manner, we prove that we will be able to implement not only a redundant instrument, but also an upgraded power amplifier and a new feeding structure for lunar and liberation-point missions. It is also remarkable that those incorporation will be completed by minimizing disturbance to station operations. We also introduce how new technologies will become available within this concept. As examples, we discuss our future prospects on auto-tracking, multiple uplinks, and improvement in Ka-band operations.
GAPS is an international balloon-borne project that contributes to solving the dark-matter mystery through a highly sensitive survey of cosmic-ray antiparticles, especially undiscovered antideuterons. To achieve a sufficient sensitivity to rare antideuterons, a novel particle identification method based on exotic atom capture and decay has been developed. In parallel to utilizing this unique event signature in a conventional likelihood-based event identification scheme, we have begun investigating a complementary approach using a machine learning technique. In this new approach, a deep-learning package is trained on a large amount of input data from simulated antiparticle events through a multi-layered neural network. By applying this unbiased approach, we expect to mine unknown patterns and give feedback to the conventional method. In this paper, we report results from exploratory investigations that illustrate the promise of this new approach.
SLIM (Smart Lander for Investigating Moon) of ISAS/JAXA is a demonstration mission of lunar pinpoint landing technology with a small spacecraft. The navigation cameras of SLIM require the function of the so-called global shutter in order to take lunar surface images under high orbital velocity. Since the requirement of miniaturization is also critical, we decide to use the commercial CMOS image sensor for the SLIM cameras. The package of the selected CMOS image sensor is the 48-pin CLCC (Ceramic Leadless Chip Carrier). It is known that there are some matters of concerns about reliability of the CLCC solder joints when applied to space missions. So the detailed results of thermal cycle tests for the CLCC packages soldered on the substrates are described in this paper. Several counterplans to improve the robustness of the solder joints are investigated from the substrates and the solders to the pad pattern. From the results of the thermal cycles tests, it is confirmed that the most promising approach to solder the CLCC packages without the significant cracks is to select adequate substrate materials with coefficients of thermal expansion similar to the ceramic.
The authors investigate the discharge chamber of the microwave ion thruster μ10 by using kinetic particle simulation. First, to investigate the plasma phenomena qualitatively, we conduct a particle-in-cell (PIC) simulation model. The simulation results indicate that the distribution of ion density is ring-shaped. To verify the simulation result with the experimental result, the simulation result is compared with the optical emission distribution. In low propellant flow rates, the distribution of ion density agrees with the optical emission distribution. However, in high propellant flow rates, the optical emission distribution is different from simulation results in the waveguide due to the excited neutral particles. In the thruster, the performance strongly depends on the location of injecting the propellant. Hence, to develop the plasma simulation for quantitative comparison with the experiment, the distribution of the neutral density is evaluated by using direct Monte Carlo simulation (DSMC). The results show the neutral density in the waveguide increases corresponding to the ratio of waveguide injection, which indicates that the density is one of the most important parameters for quantitative evaluation with the experiment.
We propose a new concept of a Mars airplane mission in order to extend a mission-period using a Mars balloon as a supporting system. In this study, the Mars airplane, the Mars balloon, and atmospheric entry capsule which stores the aerial vehicles were designed. Moreover, a feasibility of the proposed mission was discussed in terms of aerodynamic performance and energy consumption, operation of the balloon and the Mars airplane, atmospheric entry and descent of the aerial vehicles, and transportation from Earth to Mars.
In space exploration missions whose resources are severely restricted, miniaturization of onboard avionics by functional integration is crucial. While it seems reasonable to employ the board-level integration in the current technology level of the space community, the ultimate goal is considered to be the chip-level integration. In this paper, an innovative method for vertical assembly of various bare chips is proposed. Silicon substrates, on which bare chips are implemented, are piled up by room-temperature bonding. The room-temperature bonding is based on MEMS (Micro Electro Mechanical Systems) technology. Compared to the vertical assembly preparing the wafer-level TSV (Through Silicon Via), the method is appropriate for space-use of low-volume production because it is not necessary to develop the dedicated chips. Existing bare chips can be vertically integrated into the chip-level integrated avionics. Results of validation tests for the vertically assembled modules such as functional, vibration, and thermal tests, are also shown.
Satellites are exposed to various shock environments during launch. Large shock responses can be generated on rocket separation or deployment of solar arrays and antennas when the strain energy of retained parts is released. Therefore, a test to verify the shock resistance of spacecraft components is necessary. Specially designed separation mechanisms or explosive devices are used to facilitate separation but such methods are expensive to test. To reduce this cost, alternative methods (such as the falling weight shock method) are used but the shock excitation source and structural propagation paths of the test apparatus are different from the operational configurations. This poses problems in making adjustments to match the specified Shock Response Spectrum (SRS) and often causes over- and under-testing, decreasing confidence in the test. This paper reports the results of our study to improve the accuracy of the SRSs of satellite components in shock testing. In the mechanical impact method implemented by the drop weight shock test, the SRS is usually adjusted by changing the material at the impact point, but this method is often inadequate. Rather than changing the hardness of the impact point we modified the SRS adjustment by altering the structure in the path of shock propagation.
The Space Robotics Laboratory (SRL) of Tohoku University and ALE Co., Ltd. have developed a 60-kg-class microsatellite ALE-1, which generates artificial meteors by releasing meteor source pellets towards the Earth. The purpose of this research is to establish a system for ground evaluation and operation training of ALE-1. This satellite requires an accurate orbit and attitude determination technique for operation safety and mission success. A triple redundant system with multiple independent sensors is adopted for ensuring safe operation. A generic ground evaluation system “MEVIμS” is applied to evaluate such a complicated satellite bus system. MEVIμS has a high reliability and flexibility based on the results of its application to past micro-satellite projects. This system contains a satellite simulator with a space dynamics calculator with a high accuracy as well as mathematical models of the space environment and satellite components. A hardware-in-the-loop simulation can be carried out to evaluate the satellite hardware with on-board software by connecting to the simulator virtually. The performance evaluation of the attitude control system and comprehensive mission operational tests were carried out by MEVIμS. The simulation result demonstrated that ALE-1 reached a sufficient level of attitude control accuracy to realize the mission. The result also confirmed that the mission sequence was performed successfully as the mission feasibility and the operation safety were validated. ALE-1 was launched by the fourth Epsilon rocket on January 18, 2019 and initial operation is in progress. Further improvement of the ALE-1 system can be executed by repeated operation training under various conditions to enhance the chance of mission success.
In this study, we propose a frequency assignment method for high-throughput satellites (HTSs) with frequency flexibility. To meet the increase in communication traffic, next-generation HTSs will be equipped with digital channelizers and a frequency flexibility function, which can flexibly change the frequency assignment. Using this function, the bandwidth resources can be efficiently utilized. We propose a flexible channel assignment method to achieve higher throughput with fewer control actions, compared to conventional methods. This method divides the bandwidth into two types: one involves fixed assignment, whereas the other is utilized flexibly. The effectiveness of the proposed method is verified through numerical experiments, and the performance is compared with those of conventional methods. In these experiments, two different types of time-varying traffic, aircraft and disaster traffic, are assumed. It is established that the number of control actions in the proposed method is lesser than that in the conventional dynamic assignment method, with almost the same throughput as the conventional one.
Recently, a spatial resolution of several meters from LEO has been realized in small satellite remote sensing. However, it is difficult to increase a temporal resolution in LEO remote sensing. Therefore, GEO remote sensing which enables observation of high temporal resolution from GEO or its nearby orbit is getting important. In order to obtain enough spatial resolution in GEO remote sensing, an optical system having a diameter of several meters is required because of the diffraction limit. It takes huge cost to realize the optical system with such a large diameter due to manufacturability and required accuracy. To solve these problems, we propose a synthetic aperture telescope by small satellites formation flying. The synthetic aperture telescope is composed of mirror satellites constituting a primary mirror of the telescope and an imaging satellite having a focal plane assembly. By optically synthesizing the light collected by mirror satellites with the imaging satellite, a virtual large aperture telescope is constructed in orbit. In this paper, observations at near infrared to short wavelength infrared are assumed and required specifications are shown. Moreover, we describe optical performance of the synthetic aperture telescope and an adjustment method of the optical system by applying the adaptive optics technique.
High precision landing capability increases accessibility to scientifically interesting areas and makes a safe landing. Vision-based navigation is one of the GN&C functions to achieve that. The navigation technique requires onboard and real-time image processing algorithms performing image recognition, feature extraction, matching, tracking, etc. However, despite the demand for fast image processing task, space-grade computers have been slower than commercial ones, lagging behind them by 1-2 orders of magnitude in performance. To address the issue, we study the applicability of a vision-based navigation algorithm for crater classification in architecture of neuromorphic processor chips which are expected to operate with ultra-low power consumption. The neuromorphic processor chip operates asynchronously and in parallel mimicking neuro-biological architecture like our brain. Therefore, the processor operates as a spiking neural network (SNN). The difference in mechanisms between timing-based spiking neurons and rate-based artificial neurons has a problem of how to make the SNNs with equivalent functions as artificial neural networks (ANNs). This study proposes a method to train the SNN by transferring weights of the ANN trained specially as synaptic efficacy of the SNN, and also evaluates the accuracy and power consumption of the SNN.
Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu. The Hayabusa2 spacecraft was launched on 3 December 2014, arrived at Ryugu on 27 June 2018. It will stay in proximity of Ryugu until December 2019 for in situ observation and soil sample collection aiming to return to the Earth in December 2020 with the collected sample. During the 1.5-year asteroid proximity operation, the spacecraft performs several numbers of descent operation to deploy and land rovers, and to touchdown collecting soil sample. To obtain large amount of various data during asteroid proximity operation, data downlink from Hayabusa2 is realized using two high gain antennas (HGAs) which are designated to X-band (8GHz) downlink and Ka-band (32GHz) downlink respectively. This paper summarizes Ka-band capability of Hayabusa2 and its contribution to asteroid proximity operation including the Landing Site Selection (LSS) activity. Also, feedbacks for Ka-band equipped future deep space mission are extracted based on the comparison between X/Ka-band operation results.