Development of Gas Multiplier Counters (GMCs) Onboard the 6U CubeSat X-Ray Observatory NinjaSat

We report the development of Gas Multiplier Counters (GMCs) onboard the 6U CubeSat X-ray observatory NinjaSat, scheduled to be launched in October 2023. GMC is a 1U-size non-imaging gas X-ray detector sensitive to 2–50 keV X-rays, and two identical GMCs are mounted on NinjaSat. GMC consists of a gas cell filled with a xenon/argon/dimethyl ether (75%/24%/1%) gas mixture with a pressure of 1.2 atm at 0◦C, a high voltage supply and analog signal processing board, a digital signal processing board, an X-ray collimator of a 2.1◦ field of view, and an iron-55 calibration source. The most significant feature of the GMC is its large effective area of 32 cm2 at 6 keV, which is more than two orders of magnitude larger than the X-ray detectors onboard previously launched CubeSats. We have achieved this at a low cost and in a short development time by employing a gas detector that can easily increase its effective area and using a space-proven gas electron multiplier. GMC was characterized with X-rays from an X-ray generator in a laboratory and monochromatic X-rays on the BL-14A beamline at the KEK synchrotron radiation facility. In this paper, we present the design of GMC and the preliminary results of the detector calibration

NinjaSat: 6U CubeSat Observatory for Bright X-Ray Sources

NinjaSat is a 6U CubeSat observatory designed for long-term monitoring of bright X-ray sources, such as binary systems between normal stars and black holes or neutron stars. NinjaSat is the first Japanese CubeSat dedicated to astronomical observation, and it is also a mission to demonstrate that even a small satellite, which can be developed quickly and inexpensively, unlike large satellites, can perform excellent scientific observations. NinjaSat realizes the world’s highest X-ray sensitivity in CubeSat missions by using gas X-ray detectors filling the entire space allocated for science payloads. The fabrication of the flight model payloads began in 2021, and testing at the payload component level was completed in August 2022; as of April 2023, the payloads were integrated into the Nano Avionics 6U bus (M6P) in Lithuania. After four months of testing, the payload will be stored in the Exolaunch deployer in August and launched by the SpaceX Transporter-9 mission in October 2023. This paper will describe the scientific objectives, satellite structure, payloads, and operations of NinjaSat

Development of Radiation Belt Monitors for the 6U CubeSat X-Ray Observatory NinjaSat

NinjaSat is a 6U CubeSat-sized X-ray observatory to be launched into the low Earth orbit at an altitude of 550 km, and is scheduled for launch this October. NinjaSat is equipped with two 1U-sized gas X-ray detectors (GMC) and is expected to operate mainly for astronomical observations of bright X-ray objects in the sky, such as neutron stars and black holes. Since high voltages are applied to the gas cells of GMC, two radiation belt monitors (RBM) will also be installed to protect GMC from electrical discharges potentially caused by excessively high rate of charged particles. NinjaSat RBM will play a fail-safe function in the voltage suppression operation of GMC in the auroral zone and South Atlantic Anomaly, and also protect GMC from charged particles such as protons and electrons that arrive unexpectedly due to solar flares or other low-Earth orbit radiation events. RBM uses a 9 mm x 9 mm Si-PIN photodiode as a charged particle sensor. By taking advantage of the difference in sensor response to protons and electrons, the sensor is designed to simultaneously count charged particle rates at multiple energy thresholds so that GMC protection function will operate even if either the proton or electron rate increases. RBM can count up to about 10 kcps with almost no loss of counts, and proton beam tests have confirmed that the response performance is sufficient to protect GMC against excessively high charged particle rates above 10 Mcps without choking the circuitry. The flight models of the RBM have passed the thermal vacuum and vibration tests last year. The developed RBM occupies only about 6% of the 1U CubeSat size in volume and weighs only 70g. In addition, since the RBM uses inexpensive, commercially available sensors, it could be installed on small satellites other than NinjaSat with relatively small development resources

NinjaSat: Initial Operation Results of the First Japanese 6U CubeSat for Bright X-ray Sources

We report the initial operation results of the first Japanese 6U CubeSat X-ray observatory NinjaSat, which was launched into a sun-synchronous orbit at an altitude of 530 km on November 11, 2023, by the SpaceX Transporter-9 mission. NinjaSat is designed to observe bright X-ray sources in the sky, such as black holes and neutron stars, which are often difficult to observe with modern large X-ray satellites due to instrument limitations. After the payload verification, NinjaSat observed the Crab Nebula on February 9 and correctly detected the 33.8 ms pulsation from the neutron star. With this observation, NinjaSat met the minimum success criteria. NinjaSat observed 10 X-ray sources by June 20 and successfully demonstrated that many X- ray sources can be observed even with a CubeSat, which is limited in terms of resources available for science payloads. Specifically, NinjaSat conducted the follow-up observation of a newly discovered X-ray transient SRGA J144459.2−604207 two days after its discovery, detecting multiple type I X-ray bursts. NinjaSat also observed type II X-ray bursts from a rapid burster MXB 1730−335. To the best of our knowledge, these are the first observations of X-ray bursts with a CubeSat, enabled by the large effective area of NinjaSat. NinjaSat continues observations to achieve full success and extra success

Improved Culture-Based Isolation of Differentiating Endothelial Progenitor Cells from Mouse Bone Marrow Mononuclear Cells

Numerous endothelial progenitor cell (EPC)-related investigations have been performed in mouse experiments. However, defined characteristics of mouse cultured EPC have not been examined. We focused on fast versus slow adherent cell population in bone marrow mononuclear cells (BMMNCs) in culture and examined their characteristics. After 24 h-culture of BMMNCs, attached (AT) cells and floating (FL) cells were further cultured in endothelial differentiation medium separately. Immunological and molecular analyses exhibited more endothelial-like and less monocyte/macrophage-like characteristics in FL cells compared with AT cells. FL cells formed thick/stable tube and hypoxia or shear stress overload further enhanced these endothelial-like features with increased angiogenic cytokine/growth factor mRNA expressions. Finally, FL cells exhibited therapeutic potential in a mouse myocardial infarction model showing the specific local recruitment to ischemic border zone and tissue preservation. These findings suggest that slow adherent (FL) but not fast attached (AT) BMMNCs in culture are EPC-rich population in mouse