February 27, 2017

Platform

The platform is composed of a set of functional items that can be upgrated independently. Such a platform was used for Demeter the first microsatellite of the series, as well as for Parasol.
As atmospheric drag alters pointing performance, especially below 600 km, and as radiation limits the lifetime typically above 1,000 km, the platform is designed for low-orbit operation ranging from 600 km to 1,000 km and for a typical 2-year mission. The orbit inclination covers the range 20 to 98°.
An extension to lower inclinations and to geostationary tranfer orbit (GTO), are under study.

The platform is a cubic structure with dimension of 60 cm by 60 cm and a height of 50 cm. It is composed of:

  • A rigid baseplate providing the interface with the launcher and able to accommodate the propulsion module
  • 4 honeycomb lateral panels to accommodate equipments, able to be opened out for integration operations
  • 4 aluminium corners to give the structure extra rigidity
  • An upper panel, also in honeycomb, to accommodate the payload

Thermal control is achieved using passive (MLI insulating blanket, SSM) and active (heaters, thermistors) systems controlled either by thermostats or by onboard software.

The platform allows three-axis attitude control of the satellite. Pointing can be geocentric, inertial, solar or along the velocity vector with a precision of 5.10-3 arcdegrees and a stability better than 2.10-2 arcdegrees. The attitude control system in nominal mode uses a star tracker, four reaction wheels and three magnetic torquers. Three star trackers and a magnetometer are used during the satellite positioning phase.
Orbit control is achieved by a propulsion module using four one-Newton hydrazine thrusters, and a fuel tank with a capacity of 4.5 litres.

Onboard data handling is centralized using serial data buses in a star architecture. The computer only uses space-rated commercial components. It has a T805 processor, with 256 Mbytes flash memory, and 1 Gbit of RAM.

The onboard computer hosts the flight software, communications with the ground and with the payload, automatic attitude and orbit control, housekeeping and reconfiguration of the satellite, and its thermal control.

A 16-Gbit solid-state mass memory is optionally available to store payload data.
The telemetry and telecommand systems use an S-band RF link and are compatible with the international standard established by the Consultative Committee for Space Data Systems (CCSDS). The useful data rates are 20 kbits/s for commands and 625 kbits/s for telemetry.
A high telemetry rate (16.8 Mbits/s) using X-band transmission is made available for the mission when large volume of data need to be downloaded. A GPS receiver with an integrated navigation system is also optional.

The power supply uses a solar array composed of two hinged panels folded against the platform during launch. When deployed in orbit, this 0.8-m² surface array, provides approximately 180 W of electrical power at the beginning of its life, thanks to the utilization of highly efficient GaAs cells. It can be rotated by a drive mechanism. The system also includes a Li-ion battery and an electronic unit supplying regulated power to all spacecraft equipment.

Performance offered to the payloads:
Mass: up to 80 kg
Power: 60 W permanent (orbit with eclipse)
Pointing: accuracy < 5.10-³ °, stability < 2.10-² °
Propulsion: 80 m/s
Mass memory: 16 Gbits
Telemetry rate: 400 kbits/s
High-rate telemetry: 16.8 Mbits/s