Japan Aerospace Exploration Agency

About: Japan Aerospace Exploration Agency is a facility organization based out in Tokyo, Japan. It is known for research contribution in the topics: Galaxy & Telescope. The organization has 4327 authors who have published 12054 publications receiving 208330 citations.

Absolute photometric calibration of the infrared camera (IRC) aboard AKARI

Abstract: The absolute photometric calibration of imaging observations with the Infrared Camera (IRC) aboard the AKARI satellite was performed by monitoring the same stars regularly and by observing a set of standard stars. By our monitoring observations, we confirmed that all channels of the IRC were stable to within 4% and that their sensitivities were constant until the liquid helium was exhausted. Using the data of these repeated observations, we evaluated the intrinsic errors as a function of the brightnesses of objects and found that the errors increase rapidly toward fainter objects. We also checked the consistency between short and long exposure times, and confirmed that the data sampling had been executed as designed. Finally, by comparing the estimated in-band flux densities and the observed data values of standard stars, we obtained conversion factors to the absolute flux densities of all the band/exposure configurations. Their absolute uncertainties are estimated to be less than 6%.

Modeling and Hazard Analysis Using Stpa

Abstract: A joint research project between MIT and JAXA/JAMSS is investigating the application of a new hazard analysis to the system and software in the HTV. Traditional hazard analysis focuses on component failures but software does not fail in this way. Software most often contributes to accidents by commanding the spacecraft into an unsafe state (e.g., turning off the descent engines prematurely) or by not issuing required commands. That makes the standard hazard analysis techniques of limited usefulness on software-intensive systems, which describes most spacecraft built today. STPA is a new hazard analysis technique based on systems theory rather than reliability theory. It treats safety as a control problem rather than a failure problem. The goal of STPA, which is to create a set of scenarios that can lead to a hazard, is the same as FTA but STPA includes a broader set of potential scenarios including those in which no failures occur but the problems arise due to unsafe and unintended interactions among the system components. STPA also provides more guidance to the analysts that traditional fault tree analysis. Functional control diagrams are used to guide the analysis. In addition, JAXA uses a model-based system engineering development environment (created originally by Leveson and called SpecTRM) which also assists in the hazard analysis. One of the advantages of STPA is that it can be applied early in the system engineering and development process in a safety-driven design process where hazard analysis drives the design decisions rather than waiting until reviews identify problems that are then costly or difficult to fix. It can also be applied in an after-the-fact analysis and hazard assessment, which is what we did in this case study. This paper describes the experimental application of STPA to the JAXA HTV in order to determine the feasibility and usefulness of the new hazard analysis technique. Because the HTV was originally developed using fault tree analysis and following the NASA standards for safety-critical systems, the results of our experimental application of STPA can be compared with these more traditional safety engineering approaches in terms of the problems identified and the resources required to use it.

A surface plasmon resonance hydrogen sensor using Au/Ta2O5/Pd multi-layers on hetero-core optical fiber structures

Abstract: A novel fiber optic surface plasmon resonance (SPR) hydrogen sensor has been developed based on hetero-core structured fiber optics with multi-layer films of gold (Au), tantalum pentaoxide (Ta 2 O 5 ) and palladium (Pd) uniformly coated onto a cylindrical cladding surface. We experimentally observed that the SPR resonant wavelength is shifted 28 nm with 4%-hydrogen concentration in nitrogen. In a light intensity-based experiment with an LED operating at 850 nm, it has been presented that a transmitted loss change of 0.23 dB was induced with a response time of 15 s for 4% hydrogen in the case of 25-nm Au, 60-nm Ta 2 O 5 and 3-nm Pd multi-layer film. The proposed sensor has successfully detected hydrogen concentrations with a high sensitivity despite the usage of very thin Pd films.

A Parametric Experimental Study for Momentum Transfer by Plasma Actuator

Abstract: Momentum transfer performance of the plasma actuator was investigated experimentally for a variety of parameters including an ambient gas pressure, ambient gas species, alternating high voltage wave form, electrode configuration and dielectric plate material. It was found that an ambient gas pressure, under which a plasma actuator operates, has a significant effect on the momentum transfer performance. In fact, the performance does not decrease in a liner manner with decreasing an ambient gas pressure, but increases at first and then decreases. This suggests that the discharge manner, which governs the momentum transfer performance, significantly depends on the ambient gas pressure. Chemical species of an ambient gas has also a significant effect on the momentum transfer performance; The momentum transfer in air is larger than that in nitrogen gas over an entire pressure range less than 1 atm. This suggests a significant contribution of oxygen molecule in air. The momentum transfer performance in carbon dioxide gas is slightly larger than that in nitrogen gas over an entire pressure range less than 1 atm while they are comparable at a pressure of 1 atm. It was also found that the wave form of the high voltage has a significant effect; 1) the steeper the up-going part of the high voltage wave is, the larger the momentum transfer is, 2) both negative and positive part of the sinusoidal wave equivalently are foundamental for the net momentum trasfer and have a significant contribution to the momentum transfer. Furthermore the configuration of electrode were found to be an effective factor for the momentum transfer performance in a plasma actuator. Especially, a mesh type electrode can improve the performance significantly. Finally we clarified the effect of the material of the dielectric plate on the momentum transfer performance; The momentum transfer depends on the dielectric plate material in a manner depending on the ambient gas pressure.