Maki Akioka

Three Successive and Interacting Shock Waves Generated by a Solar Flare

We discovered three successive Moreton waves generated by a single solar flare on 2005 August 3. Although this flare was not special in magnitude or configuration, Moreton waves (shock waves) successively occurred three times. Multiple shock waves generated during a single flare have not been reported before. Furthermore, the faster second-generated Moreton wave caught up and merged with the slower first-generated one. This is the first report of shock-shock interaction associated with a solar flare. The shock-plasma interaction was also detected. When the third-generated Moreton wave passed through an erupting filament, the filament was accelerated by the Moreton wave. In this event, filaments also erupted three times. On the basis of this observation, we consider that filament eruption is indispensable to the generation of Moreton waves.

LEO-to-ground polarization measurements aiming for space QKD using Small Optical TrAnsponder (SOTA)

Quantum communication, and more specifically Quantum Key Distribution (QKD), enables the transmission of information in a theoretically secure way, guaranteed by the laws of quantum physics. Although fiber-based QKD has been readily available since several years ago, a global quantum communication network will require the development of space links, which remains to be demonstrated. NICT launched a LEO satellite in 2014 carrying a lasercom terminal (SOTA), designed for in-orbit technological demonstrations. In this paper, we present the results of the campaign to measure the polarization characteristics of the SOTA laser sources after propagating from LEO to ground. The most-widely used property for encoding information in free-space QKD is the polarization, and especially the linear polarization. Therefore, studying its behavior in a realistic link is a fundamental step for proving the feasibility of space quantum communications. The results of the polarization preservation of two highly-polarized lasers are presented here, including the first-time measurement of a linearly-polarized source at λ = 976 nm and a circularly-polarized source at λ = 1549 nm from space using a realistic QKD-like receiver, installed in the Optical Ground Station at the NICT Headquarters, in Tokyo, Japan.

First results of wavefront sensing on SOTA

For satellite to ground laser links, atmospheric turbulence is a major cause of impairments. The induced phase perturbations along the propagation path cause beam scintillation in the receiver plane and they can also severely compromise the coupling of the flux into a receiver of limited size. To address these impairments, dedicated mitigation strategies must be developed. This requires accurate understanding of the perturbation origin. Beam propagation models have demonstrated their ability to reproduce statistical characteristics of optical perturbations on a satellite to ground laser link for elevations as low as 20°. For smaller elevations, measurements performed on stars illustrated the limits of analytical approaches and the interest for end-to-end models. We report here the first propagation channel measurements performed on a LEO microsatellite with a Shack-Hartmann wavefront sensor (WFS). The laser beam at 976 nm provided by SOTA optical terminal have been analyzed with a Shack- Hartmann wavefront sensor located at Coudé focus of the French ground station (1,55 m MéO telescope) in July 2015. Wavefront characteristics and scintillation patterns recorded with the WFS are analyzed and compared to atmospheric turbulence perturbations model fed with in situ measurements of atmospheric parameters retrieved from GDIMM.

Experiment plan for a small optical transponder onboard a 50 kg-class small satellite

50kg-class satellites can reduce production cost and time compared to larger satellites. On the other hand, the communication capacity in radio frequency for 50 kg-class satellites is limited, however it can be improved by using optical communications. The National Institute of Information and Communications Technology (NICT) has begun to develop a Small Optical TrAnsponder (SOTA) onboard a 50kg-class satellite, which project is called the Space Optical Communications Research Advanced Technology Satellite (SOCRATES). We will introduce the experiment plan for SOTA onboard the 50 kg-class small satellite.

In-orbit verification of small optical transponder (SOTA): evaluation of satellite-to-ground laser communication links

Research and development of space optical communications is conducted in the National Institute of Information and Communications Technology (NICT). The NICT developed the Small Optical TrAnsponder (SOTA), which was embarked on a 50kg-class satellite and launched into a low earth orbit (LEO). The space-to-ground laser communication experiments have been conducted with the SOTA. Atmospheric turbulence causes signal fadings and becomes an issue to be solved in satellite-to-ground laser communication links. Therefore, as error-correcting functions, a Reed-Solomon (RS) code and a Low-Density Generator Matrix (LDGM) code are implemented in the communication system onboard the SOTA. In this paper, we present the in-orbit verification results of SOTA including the characteristic of the functions, the communication performance with the LDGM code via satellite-to-ground atmospheric paths, and the link budget analysis and the comparison between theoretical and experimental results.

Research and development of free-space laser communications and quantum key distribution technologies at NICT

Since 2006, ground-to-satellite laser communication experiments have been successfully performed using intensity modulation/direct detection (IMDD) between the National Institute of Information and Communications Technology (NICT) optical ground station located in Tokyo and a low earth orbit (LEO) satellite. With the advent of coherent binary phase-shift keying (BPSK) receivers in orbit by a German satellite, it is now absolutely imperative to establish interoperability between the different optical communications systems. At NICT, an optical receiver that can demodulate both IMDD and coherent optical signals for free-space laser communications has been developed that can recover the carrier phase after homodyne detection by means of digital signal processing (DSP). A transportable optical ground station has also been developed for site-diversity purposes in order to increase accessibility between terrestrial and space systems. A new NICT mid-term research plan has started since April 2011 and this paper presents research and development in free-space laser communications technologies at NICT.

Adaptive optics results with SOTA

Next generation satellite-to-ground laser link systems, either for telemetry or satcom will request very high data rate. This goal could be achieved with a manageable cost if the benefits from the fibered technologies are reaped. For downlink the wave therefore needs to be coupled into a single mode fiber. Due to atmospheric turbulence its spatial coherence is compromised. This causes strong coupling losses that result into deep fadings. To cope with this, adaptive optics (AO) is envisaged. Thanks to a real time compensation of atmospheric induced optical path differences, it might enable to reach average coupling efficiencies as high as 0,5 (3 dB average losses). AO is now a mature technology, mostly brought to market by astronomy or biomedical applications. Usual correction bandwidth and available flux to perform the wavefront measurement are rather small (typically 50 Hz bandwidth and tenth of photons per subaperture and per frame). The specificity of AO for LEO satellite to ground optical links resides into higher requested bandwidth, optimal operation for a wide variety of atmospheric conditions (daytime and nighttime) with potentially low elevations that might severely affect wavefront sensing due to scintillation. In addition to this the performance criterion of the correction is different from usual imaging applications, with appropriate constraints on coupling statistics and temporal characteristics. To address these specificities, AO dimensioning approach needs to be adapted and consolidated by in situ measurements. We report here the first AO results on a LEO microsatellite as far as we know. The AO bench located at Coudé focus of the MéO telescope, designed for imaging applications, is used to correct for optical aberrations on a 976 nm laser beam provided by SOTA terminal. AO performances are investigated and confronted to state of the art performance evaluations for satellite to ground laser links.

Current development status of Small Optical TrAnsponder (SOTA) for satellite-ground laser communications

Current development status of the small optical transponder (SOTA) to be installed into a small satellite is described, where the breadboard model, the engineering model and the protoflight model are respectively introduced. The tracking performance is estimated to show that the angular error is low enough in comparison to the divergence angle of the transmitted beam.

100-300KG CLASS SATELLITE STANDARD BUS SYSTEM DESIGN AND APPLICATIONS

This paper describes the design and applications of the standard bus system for 100-300 kg class satellites that is studied in MHI. It aims to meet the recent demand for fast space demonstration opportunities at low cost. One of the design concepts of the present bus system is to separate the satellite bus module and mission payload module thermally and mechanically as much as possible. Another is to apply standard electric interface. The architecture of the bus system is kept as simple as possible, and off-the-shelf and flight-proven bus components are selected. These design approaches will make it possible to minimize the design change of the bus system across missions. As a result, user’s procurement cost and lead-time would be reduced without losing the adaptability. Demonstrations of On -Orbit Servicing, Corona Observation from CRL, and Optical inter-satellite communication from NeLS are given as the examples of the applications of the bus system. The bus system can be applied to practical missions by plural satellites or formation flying system in the future as well.

Introduction of a terrestrial free-space optical communications network facility: IN-orbit and Networked Optical ground stations experimental Verification Advanced testbed (INNOVA)

A terrestrial free-space optical communications network facility, named IN-orbit and Networked Optical ground stations experimental Verification Advanced testbed (INNOVA) is introduced. Many demonstrations have been conducted to verify the usability of sophisticated optical communications equipment in orbit. However, the influence of terrestrial weather conditions remains as an issue to be solved. One potential solution is site diversity, where several ground stations are used. In such systems, implementing direct high-speed optical communications links for transmission of data from satellites to terrestrial sites requires that links can be established even in the presence of clouds and rain. NICT is developing a terrestrial free-space optical communications network called INNOVA for future airborne and satellitebased optical communications projects. Several ground stations and environmental monitoring stations around Japan are being used to explore the site diversity concept. This paper describes the terrestrial free-space optical communications network facility, the monitoring stations around Japan for free-space laser communications, and potential research at NICT.