Intersatellite-link demonstration mission between CubeSOTA (LEO CubeSat) and ETS9-HICALI (GEO satellite)

LEO-to-GEO intersatellite links using laser communications bring important benefits to greatly enhance applications such as downloading big amounts of data from LEO satellites by using the GEO satellite as a relay. By using this strategy, the total availability of the LEO satellite increases from less than 1% if the data is downloaded directly to the ground up to about 60% if the data is relayed through GEO. The main drawback of using a GEO relay is that link budget is much more difficult to close due to the much larger distance. However, this can be partially compensated by transmitting at a lower data rate, and still benefiting from the much-higher link availability when compared to LEO-to-ground downlinks, which additionally are more limited by the clouds than the relay option. After carrying out a feasibility study, NICT and the University of Tokyo started preparing a mission to demonstrate the technologies needed to perform these challenging lasercom links. Furthermore, to demonstrate the feasibility of this technique, an extremely-small satellite, i.e. a 6U CubeSat, will be used to achieve data rates as high as 10 Gbit/s between LEO and GEO. Some of the biggest challenges of this mission are the extremely low size, weight and power available in the CubeSat, the accurate pointing precision required for the lasercom link, and the difficulties of closing the link at such a high speed as 10 Gbit/s.Comment: 5 pages, 10 figures, 3 table

A Precise Attitude Determination and Control Strategy for Small Astrometry Satellite “Nano-JASMINE”

Intelligent Space Systems Laboratory (ISSL) Universityof Tokyo has developed a 35 kgastrometry satellite,“Nano-JASMINE”(Nano JAPAN Astrometry Satellite Mission for INfraredExploration)in cooperation with National Astronomical Observatoryof Japan (NAOJ). In the Nano-JASMINE mission, the satellite attitude spin rate should be controlled to an accuracy of 4 × 10−7 rad/s duringthe observation. To accomplish such severe attitude stabilization, we have developed two novelmethods. The first method is amagnetic disturbance estimation and compensation method. In conventional large satellites, a Magnetic torqueisnot the dominant attitude disturbance. However, in small satellites, the magnetic torqueis the dominant attitude disturbance.This is becausethe moments of inertia of small satellites are muchsmaller than those of the large satellites.Therefore, it is necessaryto developanovel magnetic disturbance estimation and compensation method. The second method is ahigh-accuracy spinrate estimation method. In small satellites, high-accuracyrate sensors which are widely used in large satellites are not available,since the power consumptions andthe sizes of thesesensors are too large for small satellites. Thus, we develop a new spinrate estimation method for Nano-JASMINE. This paper proposesthese two methods, the magnetic compensation and estimation method and the high-accuracyspinrate estimation method for the precise attitude estimationand controlin the Nano-JAMINE mission.The verificationresults with the simulations and the experiment show the effectiveness of these methods. The methods enable future small satellites to control its attitude more accurately

Modeling of piezoelectric actuator's hysteresis and its effect on the control accuracy of a LEO-to-GEO laser-communication for a small satellite

Compared to conventional large satellites in the past, small satellite classes (less than 150 kg) show their advantages for mass production, such as short time and low cost for development and launch, to cope with the demand for emerging missions that require a sufficient number of satellites in orbit. However, the traditional communication method, in which a low earth orbit (LEO) small satellite sends data to a ground station using radio frequency, has several disadvantages. Firstly, the limitation of radio-frequency bandwidth leads to a low data rate and difficulty in getting a frequency license. Secondly, there is a significant delay during which data cannot be sent to the ground due to lacking a line of sight between the LEO satellite and the ground station. Additionally, the duration time for the small satellite to communicate with the ground station is just less than 10 minutes approximately. To resolve the above issues, we investigate the case that a less-than-150-kg satellite carries out a laser communication link from LEO to a satellite in geostationary orbit (GEO). Due to the constraints of size, weight, and power (SWaP), traditional bulky LEO-GEO relay systems cannot be applied for the small satellite. However, using the combination of the satellite body pointing and a piezo Fast-Steering Mirror (FSM), which reduces the SWaP considerably, makes it feasible that the LEO-to-GEO communication can be implemented in a small satellite for the first time. While utilizing laser communication can increase the data rate, the relay communication via the GEO satellite helps the small satellite to extend the communication duration significantly. Moreover, since there is a line of sight between the two terminals in any of about 15 orbits per day of the LEO satellite, data taken by the small satellite can be downloaded to the ground via the GEO one in almost real time. This research aims at investigating and proving the feasibility of a small satellite to transmit a laser communication link to its GEO counterpart. In this paper, we describe the LEO-to-GEO laser communication of the small satellite with a study of pointing-budget and link-budget analysis. Furthermore, a hardware-based simulation of the fine control mechanism is conducted. The hysteresis that affects severely to the piezo mechanism, and hence, the final control accuracy, is modeled accurately and its effect is shown