Micro-Scanning Laser Range Finders and Position-Attitude Determination for Formation Flight

There are several space missions which require a cluster of micro spacecraft with small area of several kilometer. We propose an asteroid mission by means of several micro spacecraft in formation flight. We are in progress to develop a micro-scanning laser range finder (MS-LRF) for navigation system of such cluster missions. The MS-LRF is a LRF which utilized a two-dimensional scanner fabricated by micromachine technology. Also we propose navigation algorithm to determine the relative position and attitude of member spacecraft in the cluster using MS-LRFs

Low Cost SAR Antenna with Wide Swath and High Ground Resolution

This paper describes our developments of SAR (Synthetic Aperture Radar) antennas for low-cost, wide swath and high ground resolution (0.5-0.25m). The antennas are 1D deployable, plane slot array antennas with a wide elevation beam pattern. RF is fed to each panel with a novel patented technology, non-contact waveguide system between panels. These types of SAR antennas make feasible a newly proposed DiskSat with SAR sensor system. The SAR antenna 600MHz bandwidth in X band for 0.5m SAR resolution is made from carbon fiber reinforced plastic (CFRP) for light weight and thermal stability. Furthermore, range resolution improves with wider frequency bandwidth. Our novel technology, corporate feed slot array antenna is applied to the SAR antenna in X band with 1200MHz bandwidth aiming at 0.25m range resolution. Also, for a higher azimuth resolution, a sliding-spotlight SAR observation mode is effective. Then a wide area (20kmx20km) SAR observation with high resolution (0.25m) is briefly discussed

SAR-DiskSat for Mega-Constellation

We have developed and demonstrated in 2021 small SAR satellites of 1-m ground resolution with novel deployable slot array antennas. This paper newly proposes a novel concept of quasi-two-dimensional SAR satellites, SAR-DiskSats with this deployable passive slot array antenna. The deployable slot array antennas can be compactly folded in the quasi-two-dimensional satellite body. Also, it is possible to install flexible solar cell sheets on the back side of the antenna because the antennas do not dissipate heat. This quasi-two-dimensional satellite configuration is suitable to for stacking in a rocket faring for mega-constellation launching. Another advantage of the SAR-DiskSat is the possibility of VELEO (very low Earth orbit) operation. A thin edge cross-section makes aero drag small and there is an advantage of short range in terms of signal-to-noise ratio. This advantage of RF power makes it easier to improve its ground resolution. We are developing a new corporate feed slot array antenna with very wide-band (1.2-GHz bandwidth in X band) for 0.25-m ground resolution. The final goal of this SAR-DiskSat would be a mega- constellation of 0.25-m ground resolution in VLEO

Test and Development of Prototype 1000W X-band Microwave Solid-State Power Amplifier for Small SAR Satellite

Our team has been developing an X-band SAR (Synthetic Aperture Radar) system on 75cm*75cm*75cm (paddles folding), 130kg class small satellite including folding flat antenna paddles under ImPACT program [1,2]. SAR observation has advantages under cloudy or bad weather conditions and directly obtaining three-dimensional data, however, requires a high power microwave transmitter. Therefore, we are developing a 1000W solid-state power amplifier (SSPA) that can be mounted on a small satellite by utilizing latest technologies such as GaN HEMT, power combiner, low impedance capacitor and the like. We tested and measured the performances of our manufactured amplifier EM (engineering model). The weight of our amplifier EM was approximately 12.8 kg (including structural panel 4.4kg). It was confirmed that its output capability exceeded 1000 W and continuous operation for more than 5 minutes, which is equivalent to 2000 km observation, was possible

The Development Status of the First Demonstration Satellite of Our Commercial Small Synthetic Aperture Radar Satellite Constellation

Expectations for SAR (Synthetic Aperture Radar) satellites that can observe a target area through clouds and during nighttime are emerging, especially in Asia where high cloud cover rate prevent from the satellite monitoring with optical sensors. We are now developing a small SAR satellite based on technologies of ImPACT (Impulsing PAradigm Change through disruptive Technologies) program. This program aims to develop a responsive earth observation system with the small SAR satellite, originally target for disaster monitoring. We will build a constellation of the small SAR satellites to realize short term revisits, shorter than one day to take advantage of SAR sensor that can acquire data regardless of weather and time in a day. We expect the constellation expands needs of the SAR data to business and private decision making, and develop a market for commercial use. We have almost completed the development of mission FM components of the first demo satellite. The bus system is under EM testing and FM procurements. We will launch the first demo satellite in Q1 of 2020. We are already preparing to build the second satellite and will make six satellite constellation until 2021. Our final goal is to build a constellation of 25 satellites

Technical Challenges for Small SAR Satellites with High Performance

We have developed a small SAR sensor, Micro X-SAR, compatible with 130 kg small satellite. It is capable of 3-meter resolution SAR image acquisition in strip-map mode and 1-meter resolution SAR image acquisition in sliding spotlight mode. This small SAR sensor was successfully demonstrated in orbit by a private company in 2021, Feb. This paper describes the next technical challenge of small SAR satellite with higher performance. We discuss on several types of SAR mission such as high resolution missions, wide swath missions, and constellation missions. Then we describe the present status of technical challenges to wideband, high power, and mass-productivity

Reimei Satellite Observations of Alfvénic Interaction Modulating Inverted‐V Electrons and Filamentary Auroral Forms at the Poleward Edge of a Discrete Arc

We present an event based on Reimei satellite observations in the low-altitude midnight auroral region, showing that intense and clear energy-dispersed electron precipitations, repetitively generated by field-aligned accelerations due to dispersive Alfvén waves, were modulating inverted-V electrons. These Alfvénic electrons had peak energies equal to or slightly larger than those of the inverted-Vs and were associated with the filamentary auroral forms rapidly streaming at the poleward edge of a broad discrete arc. This arc was caused by the inverted-V accompanied by ion depletions produced by quasi-electrostatic parallel potential drop. Assuming instantaneous electron accelerations over a wide energy range in a single location and a simple time-of-flight effect for the energy-time dispersions, the Alfvénic source distances were estimated 1, 500 ± 500 km above the satellite altitude of -- 676 km, a lower bound since the interaction locations are realistically distributed in altitudinally extended regions. The electron characteristics in detailed energy-pitch angle distributions obtained at high time resolution can be categorized into: (a) original inverted-V fluxes energized by quasi-electrostatic upward electric field, (b) accelerated and decelerated/reduced inverted-V fluxes, (c) field-aligned energy-dispersed precipitations accelerated by dispersive Alfvén waves, and (d) upwelling secondary components effectively produced by the field-aligned precipitations particularly at energies of a few tens of eV. This event is useful to reveal the interactions between the inverted-V and Alfvénic electrons and their related ionospheric effects in the magnetosphere-ionosphere coupling processes. The detailed energy-pitch angle distributions presented here provide constraints for models of these interactions and processes

Demonstration of 2.65 / 3.3 Gbit per sec X Band Radiowave Down Link Communications from LEO Small Satellite

This paper reports our new communication system and downlink demonstrations with a small satellite of 2.65 Gbps data rate with 64 APSK modulation and 3.3Gbps data rate with 256 APSK modulation by utilizing two circular polarization channels of X band. We have developed an on-board X-band transmitter, an on-board dual circularly polarized-wave antenna with 17dBi gain and \u3e37dB Cross Polarization Discrimination (XPD) and a 10m ground station with 39dB/K of G/T and \u3e37dB XPD for low-crosstalk polarization multiplexing. Since there are not real- time demodulator systems in such high communication speed, the downlinked signals are stored in a data recorder at an antenna site. Afterwards, we decode downlinked signals by using our non-real-time software demodulator. The system was demonstrated in orbit the RAPid Innovative payload demonstration Satellite (RAPIS-1) of JAXA in 2019. We have achieved 2.65 Gbps and 3.3Gbps communication speed in the X-band for LEO satellite at 300 M symbols per second (Msps) and polarization multiplexing of 64APSK (coding rate 4/5) and 256APSK (coding rate 3/4) following DVB-S2X protocol with roll-off factor α=0.05. The communication speeds correspond to of frequency efficiency 8.4 bit/s/Hz and 10.8 bit/s/Hz of frequency utilization efficiency. As far as authors know, these direct downlink communication speeds and frequency utilization efficiencies are the highest ones at present in LEO satellites, excluding bent-pipe communication systems

Micro Scanning Laser Range Sensor for Planetary Exploration

This paper proposes a new type of scanning laser range sensor for planetary exploration. The proposed sensor has advantages of small size, light weight, and low power consumption with the help of micro electrical mechanical systems technology. We are in the process of developing a miniature two dimensional optical sensor which is driven by a piezoelectric actuator. In this paper, we present the mechanisms and system concept of a micro scanning laser range sensor

Miniature Space GPS Receiver by means of Automobile-Navigation Technology

Miniature space GPS receivers have been developed by means of automobile-navigation technology. We expanded the frequency sweep range in order to cover large Doppler shift on orbit. The GPS receiver was modified to output pseudorange data with accurate time tag. We tested the performance in low earth orbits by means of a GPS simulator. The range error caused by the receiver is measured to be 0.9 meter in RMS. Receiver was on-boarded on INDEX (“REIMEI”) satellite, which was launched in 2005. Cold start positioning was confirmed repeatedly to finish within 30 minutes on orbit. The orbit determination was performed to evaluate the random position error of GPS receiver by means of the residual error. The random error of GPS position is as large as 2 meter for PDDP=2.5 on orbit. The RMS value of range error is evaluated to be 0.6m from the flight data. These results on orbit are consistent with the simulation results in use of a GPS simulator. This miniature space GPS receiver is at present in commercial market