C&DH

Power System

Communication System

Sensor System

Structure

 This is a part where data handling, Command reception from ground station and Data transmission to ground station is done.

 The solar battery is installed in SEEDS, and the battery is charged while supplying the electric power to the system. Moreover, CPU that manages the power supply is installed. And, the CPU observes the electric power situation, and controls the power supply actively.

 The communication system receives up-link from the ground station, transmits the command to each subsystem, transmits the housekeeping data by CW and transmits the FM doenlink data.

 The giro sensor, the magnetic field sensor, the thermal sensor, and the current sensor are installed in SEEDS. The atitude of SEEDS and etc. are analyzed from the data obtained from these sensors.

 In CubeSat, there is a limitation of designing the satellite within 1kg in weight. Moreover, to endure the vibration of the rocket which is 50Hz - 2000Hz and acceleration 10G, strength analysis is done.

Uplink command reception from ground station

  First of all, the satellite judges what command which is sent from the earth station. And, the satellite begins operating by forwarding the command to each MPU. The satellite can specify time to forward the command. Therefore, the satellite can be operated at arbitrary time by specifying time for operation to begin. This function enables data handling and the data down-link to be done excluding visible time (for instance, other side of the earth).

Data Handling

  The installing sensor acquires the status data of satellites such as temperature, argument velocity, magnetic field and etc.. As a result, we learn what state the satellite is. The acquired data is saved in the memory of the satellite at once, and read if it is necessary. In addition, it is also possible to adjust the sampling interval of data.

Make up the data for sending to ground station

  When the satellite is received the command of executing down link, C&DH System can load the data that has been saved in memory, and transmit the data of present state of the satellite.

  Moreover, it is possible to do the down link specifying the time series and the kind of data. (For instance, the data of the temperature sensor of Satellite Time 10sec to 100sec is transmitted.) This system can efficiently acquire data.

Digi Talker

  Digi Talker is a voice data transmission function that is one of the feature of SEEDS. It hears of voice messages recorded on the ground from the space. Operation information on Digi Talker will inform on the page of operation information on Nihon University CubeSat. The phrase concerning special QSL card given only to the reception of Digi Talker is included in the voice transmitted by Digi Talker. Please enjoy receiving the voice data.

Power Management

  The CPU of Power Sub System manage the state of power of SEEDS. And this CPU can decide to charge the battery, and stop the battery charging. Moreover, three selector switches concerning the power supply can be turned on/off by the command. The state of electric power is observed from the CW data, and it is also possible to start the battery charging and finish the battery charging.

Solar Panel

  SEEDS doesn't control its atitude. Therefore, Even the sun is incidence from which angle against the satellite, the solar cell should supply an electric power enough for the satellite. Result of considering this things, we installed the eight solar cells per each skin of the satellite.

  Therfore, it is possible to generate electricity with about 1600mW.

Li-ion Battery

  The four Li-ion batteries of the nominal voltage 3.7V is installed in SEEDS. When the satellite is in eclipse, and get the data for atitude analysis by using Gyro and Magnetic Field sensor which consume the electric power very much,these supply the electric power with the solar cell.

The Electric Power Simulation Software

  When SEEDS executes the command, the most important thing is the state of the electric power of SEEDS. It is necessary to operate it when the electric power of SEEDS is enough because power consumption is very large when the giro sensor, the Magnetic Field sensor, Digi Talker, and FM packet are transmitted doing. Then, to understand the state of the electric power of the satellite, the electric power simulation software was developed.

FM & CW all-in-one design transmitter

  The transmitter of SEEDS uses made of Musashino electric machine Ltd.. The down link frequency uses 437.485MHz according to the frequency adjustment result by IARU. The spec of the FM & CW transmitter is shown in the following. The state of the temperature of the satellite and the housekeeping data of the electric power system are transmitted by the CW transmitter. The data of the gyro and the magnetic field sensor is transmitted by FM transmitter.

FM  Reciever

  FM receiver of SEEDS uses made of the Nishimusen laboratory Ltd.. The up-link frequency uses the frequency according to the frequency adjustment result by IARU.

Transmission modem circuit

  It is a circuit that sends down-link FM packet data to FM transmitter as analog sound data after D/A converting. Data is transmitted by using the AX.25 protocol that is the standard of the amateur packet transmission.

Installing sensor

  The gyro sensor, the magnetic field sensor, the thermal sensor, and the current measurement sensor are installed in SEEDS.

  The thermal state and atitude are analyzed from information obtained from these sensors.

Gyro Sensor

  The giro sensor is a sensor that detects the angular speed of the body axis. These three giro sensors are installed in SEEDS, and the angular speed around each body axis is measured.

  The atitude of SEEDS is analyzed from these data.

Magnetic Field Sensor

  The magnetic field sensor is a sensor that measures the state of tmagnetic field. These also measure the value of the magnetic field of each body axis.

  The direction and the value of magnetic field in various places on the earth are decided though magnetic field depends at time, but there are a few changes. Therefore, the atitude of SEEDS can be analyzed from magnetic field sensor.

Thermal Sensor

  In SEEDS, the platinum resistance element is used as a temperature sensor. This resistive element is installed in 14 points (6 skins and internal equipment), and measures each temperature.

  The heat state of SEEDS is analyzed from the temperature data obtained from these sensor.

Current measurement sensor

  The current measurement sensor measures the current that flows by generating electricity with the solar cell of SEEDS. These current measurement sensor is installed in each six skins. The value of the current generated according to the amount of power generation of the solar cells moves up and down. Posture can be analyzed by using the current measurement sensor as the sun sensor by using this phenomenon.

Circuit of measurement of voltage of Li-ion battery

  The voltage measurement circuit judges which range in 3.0V or less, 3-4V or 4.0V or more in the voltage of the battery, and outputs the signal as a result. When the signal is judged to be a receipt 3.0V or less, EPS-PIC (microcomputer chip that manages the power supply) transmits the command to output the charge command to FMR-PIC (microcomputer that manages the command of SEEDS). When the amount of the battery remainder recovers in the charge mode and the voltage of the battery becomes 4.0V or more, EPS-PIC transmits the command to FMR-PIC so that FMR-PIC output Charge release command. FMR-PIC receives it, and issues the charge release command.

Design  Concept  -Simple and Strong.-

  The design concept of the structure of SEEDS is not design the hexahedron like the box but to compose of two boards and trusses.

  As a result, strength that can endure the vibration of the rocket at the launch can be given. All of the six faces are not covered with the skin but composing it of two boards and trusses facilitates the maintenance of an internal system. These things are the design concepts.

Material

Installing mechanism

• System start mechanism
  
    The system start mechanism is a mechanism installed to boot up a system after SEEDS is emitted by the rocket.



• Separation mechanism
  
    SEEDS adjoins other satellites in the rocket and is stored. Therefore, to separate SEEDS from the adjoined satellite when it is emitted by the rocket, the separation mechanism is installed.



• Antenna development mechanism
  
    When the satellite is stored in the rocket, it is necessary to put a cylinder shape antenna in the cube of 10-10-10cm. Therefore, the antenna development mechanism was installed because it was from shape that the antenna was stored to prescribed shape after the satellite had been emitted from the rocket.