Osaka Prefecture University Satellite-II (OPUSAT-II) is a 2U CubeSat. Its size is 10cm × 10cm × 20cm. The bus system is developed based on OPUSAT which is operated successfully in 2014. In the development of OPUSAT-II, we introduce a system modeling method which are suited for developing satellite systems. This satellite will be launched and released from the Japanese Experiment Module “Kibo” of the International Space Station (ISS) in 2020.
- High-speed communication performance evaluation
In OPUSAT-II, when we downlink data with modulation schemes GMSK (13.6kbps)，4FSK (19.2kbps), we employ AX.25 or T.B.D. protocols. In the downlink transmission test, it is evaluated whether it has superiority over the communication speed (1200 to 9600 bps) which is the main stream in the conventional amateur satellite link operating in the VHF or UHF bands.
- Message box service
Amateur radio operators all over the world uplink to OPUSAT-II. When they send a command containing arbitrary character strings, OPUSAT-II holds it. They can also set the downlink time with that command, and they can downlink that string from OPUSAT – II at the downlink time set by themselves. The uplink signals are transmitted with AFSK (1200bps) via AX.25 protocol. Depending on the command, we can select the transmission scheme from among the four modulation schemes, AFSK (1200bps), GMSK (9600bps), GMSK (13.6kbps), 4FSK (19.2kbps) and the protocol from among the two protocols, AX.25 and T.B.D. To allow amateur radio operators to construct the receiving system, we will distribute the information about the receiving system through the Internet. We will also inform the amateur radio operators around the world of the time when they can transmit uplink commands to the OPUSAT-II through the Internet. We will award the amateur radio operators who succeeded in receiving character string a prize.
- Increase the population of amateur radio operators
We will solicit messages from those who are not amateur radio operators. We uplink messages selected from the collected messages and amateur radio operators around the world downlink the message. We receive comments from the amateur radio operators who received the message and release the comments on the Internet. This will create connections between amateur radio operators and the people who are interested in amateur radio and increase the population of amateur radio operators.
satellite mission 1: High-speed data transmission in an amateur radio band
Many of the nanosatellites launched so far adopted the data transmission rates of 1200 or 9600 bps in the UHF or VHF amateur satellite bands. OPUSAT-II will downlink the data not only with 1200-bps AFSK and 9600-bps GMSK but also with 13.6 kbps GMSK and 19.2 kbps 4FSK. We are going to conduct communication experiments to evaluate the usefulness of these communication schemes. If the usefulness of these communication schemes is demonstrated, many other nanosatellites using amateur radio bands will be able to communicate more efficiently than before. Moreover, OPUSAT-II will demonstrate not only the AX.25 protocol but also various protocols. We conduct communication experiments on each protocol and evaluate its suitability for operations of nanosatellites. We will publish these experimental results as well as the system designs of the satellite and ground stations in order to allow amateur radio operators worldwide to use these high-speed data transmission schemes.
Communication speed on our mission
satellite mission 2: Demonstration of an on-orbit measurement system
- Mission definition
① To deploy two-dimensionally deployable plate.
② To measure the shape of this structure.
③ To measure the variation of the flatness of this structure.
- Mission objectives
High storage performance would be the important subject of large-scale space structures in the next generation due to the transportations restriction. We research on the realization of the high storage performance of a thin deployable plate and a method to measure the structural accuracy of the deployed plate on orbit. We apply Miura-folding pattern in ORIGAMI engineering to the deployable plate, and the surface shape is measured optically by using two-dimensional grating method. The purpose of the project is to demonstrate the deployable plate and the measurement method in space for the first time in the world.
- Two-dimensionally deployable plate
Two-dimensional deployment based on Miura-folding is applied to a thin plate with thickness. Miura-folding is one of two-dimensional packing and deployment methods, and has an advantage that the pattern can deploy synchronously deployment by a tension toward a diagonal direction, when the thickness can be neglected. On the other hand, in the case of an actual plate, the thickness effect should be considered. We propose a new folding pattern based on the Miura-folding pattern with considering the plate thickness. The research of ORIGAMI engineering with a finite thickness is getting much attention in the world. We have already formulated this folding pattern, and the performance of packing and deployment will be demonstrated in our space project.
Deployment process of two-dimensionally deployable plate
- Measurement method
We optically measure the surface shape precisely by a using two-dimensional grating method. This method can acquire three-dimensional shape of the object surface in a short time without making physical contact with it with a simple configuration and a high precision. First, two cameras take photographs of the two-dimensional grating pattern printed on the object surface. Then, the three-dimensional shape of the object surface is calculated by analyzing the distortion of the grating pattern.
Surface shape measurement summary
satellite mission 3: Acquisition of vibration data of flexible structures in space and identification of their dynamic characteristics
OPUSAT-II has a deployable antenna for communication.
Its thickness is 0.1 mm and the length is about 50 cm. Thus this antenna is a very flexible structure.
It is predicted that this flexible antenna structure will vibrate after deployment. The vibration will decay rapidly due to the air friction due to the thick atmosphere on the ground surface of the Earth.
On the other hand on orbit, it takes a long time to decay.
Since the vibration of the antenna on the satellite may affect the performance of the earth-space communication link,, it is very important to understand the behavior of the antenna on orbit.
Therefore, this mission aim to estimate the vibration of the antenna on orbit by a deformation sensor attached on the antenna elements.
Use of OPUSAT-KIT
The OPUSAT-II will be a satellite with a height of 20 cm. The bus system of OPUSAT-KIT occupies about 35 percent of the space. The structure storage and deployment system and the measurement system will be installed in the remaining space.