PROBA (Project for On-Board Autonomy), renamed PROBA-1, is a Belgian satellite technology demonstration mission launched atop an Indian Polar Satellite Launch Vehicle by ISRO on 22 October 2001. The satellite was funded through the ESA's MicroSat and General Study Program with the objective of addressing issues regarding on-board operational autonomy of a generic satellite platform. This small (60×60×80 cm; 95 kg) boxlike system, with solar panel collectors on its surface, hosts two Earth Observation instruments dubbed CHRIS and HRC. CHRIS is a hyperspectral system (200 narrow bands) that images at 17 m resolution, while HRC is a monochromatic camera that images visible light at 5 m resolution. With an initial lifetime of one to two years, the satellite celebrated its 20th year of operations in 2021. On 9 March 2018, it surpassed ERS-2 as ESA's longest operated Earth observation mission of all time. ESA aims to deorbit the satellite through the ClearSpace-1 mission in 2026.

Series of satellites

PROBA is also the name of the series of satellites starting with PROBA-1. The name is also used to refer to the bus of the satellites. The second satellite in the PROBA series, PROBA-2, was launched on 2 November 2009 together with the SMOS satellite. The third satellite to be launched was PROBA-V (PROBA-Vegetation), on 7 May 2013. Further planned satellites in the PROBA series include the formation flying demonstration mission PROBA-3 and limb sounder ALTIUS.