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- Getting up close and personal with the researchers -

There are countless celestial bodies in the vast universe. Among them are high-energy celestial bodies that emit high-energy electromagnetic waves such as gamma rays and X-rays. When you hear the word "space," the first thing that comes to mind is probably the starry sky. Since it is very rare for anything to change suddenly in the starry sky, many people probably imagine the universe as a quiet world where nothing changes.

However, the universe also has a dynamic side, changing drastically in a short space of time. High-energy celestial objects show this side. When a massive star dies, a supernova explosion occurs and a beam of gamma rays is suddenly emitted. Gamma-ray bursts change brightness dramatically in a very short time, from a few seconds to a few tens of minutes, and emit large amounts of gamma rays and X-rays.

Among the many celestial bodies, black holes have the strongest gravity and are shrouded in mystery. Their gravity attracts the gas and celestial bodies around them. They emit strong X-rays, and many black hole candidates have been discovered using these X-rays. I am fascinated by the dynamic celestial phenomena unfolding in high-energy celestial bodies. Among these, I am working on research every day to understand gamma-ray bursts, which are still not very well understood.

It was installed at Aoyama Gakuin University Machida Grounds and began operation.

The Andromeda Galaxy observed with the 20cm wide-field visible light telescope TARGET.

When I was young, I joined the research group for the Swift gamma-ray burst observation satellite as a researcher at the Goddard Space Flight Center of NASA (National Aeronautics and Space Administration). Since then, I have been participating as one of the core members of the Swift satellite for more than 15 years. I am probably the first Japanese researcher to be named who is involved with the Swift satellite.

After returning to Japan, I became a member of the research group for the CALET (Collaboration Experimental Telescope for Electron and Gamma-ray Electrons), and have been continuing observations ever since, more than five years after its launch. CALET is installed on the International Space Station as an exposed facility, and by combining the results with those of the Monitor of All-sky X-ray Image (MAXI), another exposed facility, we were able to learn about the behavior of gamma-ray bursts from the two wavelengths of gamma rays and X-rays.

Observations of gamma rays and X-rays tend to be large-scale because they require the sending of instruments into space. In addition, combining them with observations of other wavelengths, such as radio waves and visible light, allows for a deeper understanding of the target phenomenon. For this reason, international cooperation is essential. The Swift satellite and CALET, which I am primarily involved in, are both international collaborative research projects in which researchers from multiple countries work together.

Recently, however, in parallel with these studies, my laboratory has been taking the lead in carrying out a small-scale research project called the ARICA Rapid Report Demonstration Satellite. ARICA is a microsatellite called a CubeSat, which is a cube with sides measuring 10cm. When you hear the word "artificial satellite," you might think of something large and expensive, but CubeSats can be built and operated on a budget that even university laboratories can afford, so they are being developed and operated at universities around the world.

ARICA is a 10cm square CubeSat.

ARICA's development takes place in a clean booth in a laboratory.

Gamma-ray bursts are a phenomenon that occurs suddenly and without warning. To observe this phenomenon, it is necessary to continue observing 24 hours a day, 365 days a year. In addition, if a gamma-ray burst signal is captured, it must be reported to researchers on the ground as soon as possible. Several satellites, including the Swift satellite, are able to report gamma-ray bursts, but Japan's own satellites have not yet achieved this.

One of the reasons for this is the communications environment. To report on gamma-ray bursts, constant communication is required between the satellite and ground equipment. In the case of the Swift satellite, a line is secured using a NASA communications relay satellite, but in Japan there are no dedicated lines available for researchers to use.

So I wondered if we could use the lines of a private satellite communications company to send out early reports of gamma-ray bursts. It is not uncommon for small artificial satellites to use private communications systems, but up until now, most communications have been short, such as when sending short commands from the ground to the satellite or when sending satellite data to the ground. In contrast, ARICA constantly communicates with the ground at one-minute intervals, reporting information about gamma rays picked up by its sensors to the ground. We plan to begin by demonstrating whether minute-by-minute communications are possible for a period of six months.

ARICA's basic structure and system use a commercially available CubeSat aircraft, but the so-called mission section, including the observation equipment and communication system, was designed from scratch by students. The opportunity to be involved in the development of equipment to be launched into space is a very valuable experience for students. Some students joined our laboratory because they wanted to develop ARICA, and each and every one of them is highly motivated.

It was selected as one of the projects for JAXA's (Japan Aerospace Exploration Agency) Innovative Satellite Technology Demonstration No. 2, and it has been decided that it will be launched by an Epsilon rocket by March 2022. Currently, the design of the mission circuitry to be incorporated into the satellite has been completed, and the performance testing and assembly stage has begun. The deadline for handing over the satellite itself to JAXA is August 2021, less than a year away. Some may think that a year is plenty of time. However, the most climax of the satellite's development is yet to come.

In the development of artificial satellites, it is common to create a structure called an engineering model before building the actual vehicle. Vibration tests are conducted on the engineering model, and once it is confirmed that the actual vehicle also meets the standards, production of the actual vehicle begins. However, in the case of ARICA, the time until launch is short and there is little budget to spare, so production of the actual vehicle begins immediately.

Once the actual vehicle is complete, we plan to conduct three tests - vibration tests, shock tests, and thermal vacuum tests - to confirm that ARICA can actually function in the harsh environment of outer space. If any problems occur during these tests, the development schedule will be significantly delayed, which is a concern. However, we hope to overcome a number of challenges in just under a year from now, complete the vehicle, and lead it through to launch.

The ARICA communication system is currently under development and is scheduled to be installed on Japan's own gamma-ray burst observation satellite HiZ-GUNDAM. This satellite is currently being considered as one of the candidates for JAXA's public small satellite mission. We will have to wait for the upcoming review to see if it can actually be launched. However, if the demonstration test with ARICA is successful, it will be a big boost to its adoption.

For me, who has mainly worked on large-scale international collaborative research up until now, the CubeSat project, which involves planning, designing, assembling, and operating, was a first for me, and I was at a loss as to what to do. However, now, through ARICA, I realize how easy it is to use CubeSats and what their potential is.

Up until now, space observation projects have required a long preparation period of 5 to 10 years. This means that each student cannot be involved in the project from start to finish. However, CubeSats can be developed in 3 to 4 years, so students involved in the launch of the project can be involved from the satellite's launch to observation and operation. In fact, the development of ARICA is being led by students belonging to our laboratory. I feel that this is also very effective in educating students.

The AROMA-N robotic telescope with a 35cm aperture on the roof of the Building L on Aoyama Gakuin University Sagamihara campus.

We are actively conducting observations of transient and time-varying celestial objects, including gamma-ray bursts.

Once ARICA is successfully launched next year, we would like to begin work on the second CubeSat. Since ARICA was primarily intended to demonstrate constant communication with the ground, next we would like to create a CubeSat that can properly observe gamma-ray bursts. By using the observation equipment planned to be installed on HiZ-GUNDAM, this satellite will also be able to play a role in demonstrating HiZ-GUNDAM's technology. By effectively combining CubeSats with large-scale projects, we will be able to send the necessary observation equipment into space at the right time and increase our knowledge of gamma-ray bursts. (Published in September 2020)