The JAESat mission will ultimately comprise two microsatellites called Master and Slave (see Figure 1) which will fly in a formation. JAESat Master and Slave will be separated in space, after the release of JAESat from the launcher. The mission is designed to conduct a variety of experiments based on the mode of interoperation between the payloads on-board the two satellites. A RF Inter-Satellite Link (ISL) for communication between the two satellites will be established. JAESat will be launched in 2007. The final orbit depends on the launch opportunity. It will have a circular, nearly polar orbit with an orbit height between 600 km and 800 km. The operational life time of JAESat is expected to be between 12 and 15 months. After the separation of the slave from the master satellite the two satellites will drift away from
each other with a low drift rate. JAESat is designed to have a high degree of on-board autonomy. The operations will be conducted via a ground station located at the Queensland University of Technology in Brisbane, Australia.

The JAESat micro-satellite project is an educational and GNSS technology demonstration mission, which will also generate data for scientific use. JAESat’s high level mission objectives are:
• design, develop, manufacture, test, launch and operate the educational/ research micro-satellite JAESat
• develop payloads with a technological and scientific relevance
• use JAESat as a sensor in space and GNSS technology demonstrator mission

The education and training aspects play an important role in the JAESat mission. The GNSS mission objectives are driven by the SPARx (SPace Applications GPS Receiver), a development from the Cooperative Research Centre for Satellite Systems at the Queensland University of Technology. Functions and performance of SPARx will be tested and validated in space within the JAESat mission. A key element of the GNSS activities will be the testing of a new sensor concept for attitude determination, based on Star Sensor and GPS based attitude information. In JAESat mission the master satellite will be a cube with a side length of 390mm. The slave satellite will have the following dimensions 390mm x 390mm x 195mm. The JAESat master satellite will be 3-axis stabilized, whereas the JAESat slave satellite will be gravity gradient stabilized. The mass of the slave satellite will be around 10kg, and the mass of the master will be around 30 kg, so that the total mass of JAESat will be around 40 kg. The orbit of JAESat will be a Low Earth Orbit (LEO) with an altitude between 600 km and 800 km and an orbit inclination of around 90 deg. The ground track and the orbit in 3D space are outlined in Figure 2.

The JAESat structure concept is based on a tray design. JAESat will have a total of eight trays. The separation between master and slave will be based on a spring release mechanism.

The JAESat power system will consist of batteries and solar cells. The master satellite will have fi ve sides covered with solar cells, whereas the slave will have only one side covered with solar cells. The slave will have a peak power of around 10 Watts. The available power at the master satellite will be around 25 Watts.

The JAESat on-board flight computer will be an Intrinsyc CerfBoard. The JAESat communication concept is outlined in Figure 3. The transmitter module for the master communications system has been selected to be the Hamtronics TA451, operating at 400.400MHz. The modem is the Kantronics KPC-9612+. The receiver is the Hamtronics R451. It is a crystal based receiver operating at approximately 430MHz. The JAESat Attitude Control System (ACS) concept cannot be seen as one concept. The master satellite will be 3-axis stabilized by using magnet torquers (air coils). The slave satellite will be gravity gradient stabilized without using a boom. Instead the moments of inertia will be designed so that a gravity gradient stabilization will be the result. After separation from the launcher, the JAESat master and slave will still be attached to each other. JAESat master ACS will then reduce the rotation rates around each axis and fi nally orient the satellite in such an orientation that the slave will be in its gravity gradient orientation and then JAESat will split into two satellites. The ACS of the master will be used for controlling the orientation and changing of rotation rates, necessary for testing of the new integrated Star Sensor GPS attitude sensor concept. Only one requirement for the attitude accuracy of the master has been derived, resulting from the need to have an Inter Satellite Link established. The master attitude accuracy requirement is in the order of 5 deg.

The JAESat payloads concept is driven by simplicity. The payloads itself will be distributed between the JAESat master and slave satellite. One of the positive aspects of this distributed concept is that in the event of problems on one of the two satellites, or in the worst case scenario, the loss of the slave satellite, significant research can still be conducted. The JAESat master satellite will have the following payloads on board:
• SPARx – GPS receiver capable of performing 3-axis Attitude Determination
• Star Sensor
• Specific antennas for atmospheric research The JAESat slave satellite will have the following payloads on board:
• SPARx - GPS receiver
• Mini Video Camera (Web camera type)
• Specific antennas for atmospheric research

The CRCSS/QUT GPS SPARx (see Figure 4) development is based on the MITEL GP2021, GP2015 and GP2010 Chip set and is a modification of the MITEL Orion GPS receiver demonstrator. The base for the development of the source code is the MITEL GPS Architect development kit. The source code modifications are specifically targeted towards robust and accurate operation onboard a satellite. Key elements of functionality are positioning and timing for satellites. Further R&D activities are the implementation of an on-board orbit determination capability (SPARx-OD) and GPS receiver modifi cations for satellite attitude determination (SPARx-AD) capabilities. The JAESat master satellite will have a GPS receiver with the capability of performing attitude determination. The on-board orbit - and attitude determination calculations will be performed within the Flight Computer. The main characteristics of a GPS SPARx are given in Table 1. In addition to orbit and attitude determination, it is also intended to perform relative navigation between the JAESat master and slave satellite. Finally, SPARx will be used for collecting data from specifi c GPS antennas attached to the sides (looking to the horizon) of JAESat in order to perform atmospheric research.

The Star Sensor KM-1303 is a contribution of the German Aerospace Company Kayser-Threde GmbH towards the JAESat project. This sensor is a low-cost single-package design for star tracking, star recognition, relative -and inertial attitude determination. The Star Sensor will be used for testing of a new integrated attitude determination sensor concept.

The JAESat main experiments can be summarized as follows:
• Testing and evaluation of CRCSS/QUT GPS SPARx, including Attitude apability
• Testing of a new integrated Star Sensor/GPS navigation sensor concept for 3-axis attitude determination
• Relative Navigation between JAESat Master and Slave satellite
• Orbit determination concepts
• On-Ground - Precise orbit determination based on GPS Code and Carrier phase measurements
• On-board orbit determination based on GPS receiver position solutions
• Relative Positioning between master and slave satellite
• Establishment of stable RF inter satellite links
• Atmospheric research