Optimization of body configuration and joint-driven attitude stabilization for transformable spacecrafts under solar radiation pressure

A solar sail is one of the most promising space exploration system because of its theoretically infinite specific impulse using solar radiation pressure (SRP). Recently, some researchers proposed "transformable spacecrafts" that can actively reconfigure their body configurations with actuatable joints. The transformable spacecrafts are expected to greatly enhance orbit and attitude control capability due to its high redundancy in control degree of freedom if they are used as solar sails. However, its large number of input poses difficulties in control, and therefore, previous researchers imposed strong constraints to limit its potential control capabilities. This paper addresses novel attitude control techniques for the transformable spacecrafts under SRP. The authors have constructed two proposed methods; one of those is a joint angle optimization to acquire arbitrary SRP force and torque, and the other is a momentum damping control driven by joint angle actuation. Our proposed methods are formulated in general forms and applicable to any transformable solar sail that consists of flat and thin body components. Validity of the proposed methods are confirmed by numerical simulations. This paper contributes to making most of the high control redundancy of transformable solar sails without consuming any expendable propellants, which is expected to greatly enhance orbit and attitude control capability.Comment: 16 pages, 11 figures, submitted to Astrodynamics published by Tsinghua University Press and Springe

Initial In-Orbit Operation Result of Microsatellite HIBARI: Attitude Control by Driving Solar Array Paddles

We have developed a 50kg class microsatellite HIBARI . The mission of this satellite is to demonstrate a novel attitude control method for microsatellites which is called “Variable Shape Attitude Control (VSAC).” VSAC is a method using anti-torque by driving variable shape structures. HIBARI has four drivable solar array paddles, and will demonstrate VSAC. The development of HIBARI began in 2019, and it was injected into orbit in November 2021 under the Innovative Satellite Technology Demonstration Program led by JAXA. Currently, HIBARI has completed its critical phase and paddle deployment phase, and is conducting paddle drive experiments in orbit. In paddle drive experiments, the paddles are driven according to the command values, and the accompanying attitude change is confirmed. These results indicate that the satellite can generate angular velocities of 4 deg/s or more and achieve the target agile maneuver of 30deg in 10seconds, which is comparable to that of CMG for microsatellite

Engineering Model Development of HIBARI: MicroSatellite for Technology Demonstration of Variable-Shape Attitude Control

We are developing a 40kg class microsatellite “HIBARI”. The main technical mission is demonstration a novel attitude control method called “Variable Shape Attitude Control (VSAC)” proposed by Matunaga, Tokyo Institute of Technology. This VSAC is based on an idea to utilize a reaction torque generated by changing the shape of satellites, for example driving solar array paddles by actuators. HIBARI is planned to be launched in fiscal year 2021 under “Innovative Satellite Technology Demonstration Program” led by JAXA. We are developing EM of HIBARI and describes those in this paper. Specifically, the results of missions, systems, and various tests are shown and the validity is derived

Lessons Learned in the Operation of the HIBARI: Variable Shape Satellite

We have developed the 50 kg microsatellite “HIBARI”. The satellite demonstrated a novel attitude control method called “Variable Shape Attitude Control (VSAC)”. VSAC is a method that can quickly control attitude and has low energy consumption using reaction torque by driving variable shape structures. HIBARI was launched in 2021 under the Innovative Satellite Technology Demonstration Program led by JAXA. We have been operating the satellite for two years and have demonstrated the VSAC mission. We achieved all minimum and full success criteria, including 30 deg/10sec agile attitude change. On the other hand, we experienced problems like the degradation of satellite components and other problems that could not be confirmed by ground tests. There was degradation of the paddle drive unit and influence of the paddles on bus components, which are unique to variable shape satellites. In addition, there was a case in which a paddle collided with the satellite structure due to an operational error. After the collision, the satellite’s integrity was evaluated by taking images of the paddle with the onboard camera and checking the telemetry data before and after the collision. During more than two years of operation, we have obtained knowledge about possible failures and countermeasures for satellites with variable shape structures

Radiation-Induced Degradation of Si-CMOS Detector Aboard HIBARI Satellite in Low Earth Orbit

Degradation of Si-CMOS detectors of STTs in low earth orbit is presented. The 50kg microsatellite HIBARI was launched on November 2021, and designed for demonstrating a new attitude control method, named Variable Shape Attitude Control (VSAC) . The attitude determination is therefore the key issue to evaluate the performance of VSAC. For this requirement, HIBARI possesses two star-trackers (STTs) equipped with Si-CMOS detectors. The space radiation environment in low Earth orbit poses significant challenges to Si-devices, which are susceptible to critical damage from exposure to high-energy protons. We have monitored the degradation of Si-CMOS of STTs aboard HIBARI for 2.5 years since its launch. Due to the limited bandwidth of RF-communication, we have only recorded the number of hot-pixels on the Si-CMOS detector, but with detector temperatures and the aim-point directions of STTs. First, we found that the number of hot-pixels strongly depends on the detector temperature, however it is inconvenient to evaluate the degradation because the temperature of STTs are not actively managed and varies by about ±7K every orbit. To evaluate the degradation tendency, we took into account the physical mechanism of activation of hot-pixels by radiations. For hot-pixel activation, defection formation due to non-ionizing interactions can be dominant effect. We proposed an empirical model describing the temperature-dependence of hot-pixel numbers based on the simple physical models. By making use of this model function, we calculated the number of hot-pixels at isothermal conditions of T=25˚C. This clearly shows that the two STTs change its characteristics with exactly the same behavior in spite of different pointing directions, temperatures and parameter settings. Furthermore, we discuss the correlation between these damages and solar activity, as well as the correlation with imaging parameters. These results provide useful insight into the various Si-devices on board spacecraft

PETREL: Platform for Extra and Terrestrial Remote Examination with LCTF

A small satellite ”PETREL” for UV astronomy and remote sensing with ”tunable” multi-spectral cameras conducted by an academia-industrial collaboration is presented. This project was originally proposed by an astronomer who desired a satellite for exploration of explosive objects in ultraviolet. To avoid the earthshine the astronomical observations are scheduled only in the nighttime. To utilize the daytime more electively we conceived a plan of ”satellite sharing” with the industrial collaborators, that can also reduce the developing cost drastically. The daytime mission is spectroscopy that is one of the potential fields in terms of data business, because that can provide chemical and biological information on the surface of the earth. We employ multi-spectral cameras making use of liquid crystal tunable filters (LCTFs) that enable adaptive observations at the optimized wave-bands for each targets. In 2020, this remote-sensing project and ultraviolet astronomy mission were accepted as a small satellite project of JAXA’s Innovative Satellite Technology Demonstration program and as an ISAS/JAXA’s small-scale program, respectively. This satellit

Feasibility Study of Technology Demonstration Mission for Integrated Attitude-Orbit Control of Solar Sail

We are developing a micro solar sail called PIERIS . The purpose of this project is to demonstrate the following two world-first technologies in Low Earth Orbit. The first technology is to control the external torque with a single gimbal motor. It will be possible to achieve a completely propellant-free Integrated Attitude-Orbit Control. The second technology is a sail structure that guarantees the accuracy of the Pyramid-Shaped sail membrane shape and reduces disturbance torque caused by membrane surface deformation. This project has been selected for the Feasibility-Study phase of the JAXA Small Satellite Rush Program and is scheduled for launch in FY2026 if approved to proceed to the next phase. We are currently conducting mission and system feasibility studies and developing a Bread Board Model