The spacecraft mass is 94 kg, with 25 kg dedicated to scientific and Earth observation instruments, in addition to the technology demonstration payloads. The principal objective is the in-orbit evaluation of new spacecraft technologies. PROBA-1, however, has also been intended as a flight opportunity for Earth observation instruments that can benefit from the agile pointing capabilities and the autonomy features of the satellite.
PROBA-1 onboard automatic functions include all payload operations scheduling and execution, target fly-by prediction and control of camera pointing and scanning from raw user inputs (target latitude, longitude and altitude). The point and stare requirements of the High Resolution Camera (HRC), as well as the multiple image scan requirement to support Bi-directional Reflectance Distribution Function (BRDF) measurements with the Compact High Resolution Imaging Spectrometer (CHRIS) are satisfied with the specified accuracy, by this small and agile gyro-less platform, whose attitude determination is based on autonomous star tracker only.
The main Earth imaging payload, CHRIS, weighing only 14 kg, is used to measure directional spectral reflectance. The instrument is capable of imaging up to 200 spectral bands simultaneously at full resolution with a spatial resolution of 20m at nadir and swath width of 15 km. The HRC is a black and white camera with a miniaturised Cassegrain telescope providing 5m geometrical resolution images. Each image covers a ground area of approximately 4 km by 4 km. The pointing agility of the spacecraft allows both cameras to take multiple images of the same target area at different viewing angles on the same orbital pass.
PROBA-1 is compatible with Ariane ASAP5 and PSLV launcher requirements. Its structure is built using aluminium honeycomb panels. Body-mounted solar panels provide power to the spacecraft and a Li-Ion battery is used for energy storage. A centrally switched regulated bus distributes the power to the units and instruments.
An ERC32 (SPARC) based computer provides the computing power for all the platform functions and a TSC21020 (DSP) provides the processing power to the imaging payload. All software components, either in the central computer or embedded in the spacecraft units can be reprogrammed in flight. The S-band telecommunications subsystem is omnidirectional and CCSDS-compatible. The set of ACNS units support Earth and inertial 3-axis attitude pointing as well as on-board navigation and manoeuvring computations. The thermal control of the spacecraft is completely passive. The following figures show PROBA-1 ready for flight and an exploded view of the spacecraft. The table below summarizes the characteristics of the spacecraft.
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