The MYRIADE Platform
The platform is constituted of a set of functional items which can independently evolve. Such a platform was used for the first microsatellite of the series DEMETER, as well as for PARASOL.
As the atmospheric drag modifies the pointing performances especially below 600 km, and as the radiation limits the lifetime typically above 1000 km, the platform is designed for low orbit operation ranging from 600 km to 1000 km and for a typical 2-year mission. The orbit inclination covers the range 20 to 98°.
An extension to lower inclinations as well as the use on the GTO orbit, are under study.
The platform structure is cubic with dimension of 60 cm by 60 cm and an height of 50 cm. It is constituted of:
- A rigid base plate providing the interface with the launcher, and which can host the propulsion module,
- 4 NIDA lateral panels to accommodate the equipments: those panels can be opened out to make possible the integration operations,
- 4 aluminium corners to rigidify the structure,
- An upper panel, also in NIDA, to accommodate the payload.
The thermal control uses passive (insulating mattress MLI, SSM) and active (heaters, thermistors) means controlled either by thermostats or by on-board software.
The attitude control allows the satellite orientation on 3 axes. The pointing can be geocentric, inertial, solar or oriented according to the velocity vector with an precision of 5.10-3 arcdegree and a stability better than 2.10-2 arcdegree. The attitude control system in nominal mode uses a stellar sensor, four reaction wheels and three magnetic torquers. Three solar sensors and a magnetometer are used during the satellite positioning phase.
The orbit control is achieved by a propulsion module using four one-Newton hydrazine thrusters, and a tank with a capacity of 4.5 liters.
The onboard data handling is centralised: it uses serial data buses following a star architecture. The computer only uses commercial components which have been selected to verify their behaviour in space environment. It includes a T805 processor, with 256 Mbytes flash memory, and a 1 Gbits RAM.
The onboard computer hosts the flight software which achieves the mission operations as a function of time and its different modes, the communication with the ground and with the payload, the automatic attitude and orbit control, the housekeeping and the reconfiguration of the satellite, as well as its thermal control.
A 16 Gbits solid state mass memory is optionally available to store the payload data.
The telemetry and telecommand systems use a RF link in S band and is compatible with the international standard established by the Consultative Committee for Space Data Systems (CCSDS). The useful rates are of 20 kbits/s for the commands and of 625 kbits/s for the telemetry.
A high rate telemetry (16.8 Mbits/s), using X band transmission, is made available for the mission requiring to download important data volumes. A GPS receiver with an integrated navigation system is the last of the options.
The power supply uses a solar generator constituted of two hinged panels folded against the platform during launch. When deployed in orbit, this 0,8 m² surface generator, provides approximately 180 W of electrical power at the beginning of its life, thanks to the utilization of high efficient AsGA cells. It can rotate around an axis through a drive mechanism. The system also includes a Li-ion battery and an electronic box supplying a regulated power delivered to all the equipments of the spacecraft.