Small but agile Proba-1 reaches 10 years in orbit
A good photographer needs agility. So it is with ESA microsatellite Proba-1, which turns in space to capture terrestrial targets. Celebrating its tenth birthday this week, Proba-1鈥檚 unique images are used by hundreds of scientific teams worldwide.
A technology demonstrator turned into an Earth observation mission, the microsatellite 鈥� just a cubic metre in volume 鈥� has acquired nearly 20 000 environmental science images with its main Compact High Resolution Imaging Spectrometer (CHRIS), used by a total of 446 research groups in 60 countries.
ESA has a family of experimental 鈥楶roject for Onboard Autonomy鈥� microsatellites: the Sun-watching Proba-2 went into orbit in 2009 and the vegetation-imaging Proba-V will be launched next year.
But it was Proba-1, launched from India on 22 October 2001, that started it all.
鈥淧roba-1 remains the most agile and stable satellite platform in its range,鈥� explains Frank Preud鈥檋omme of QinetiQ Space Belgium, the company that built Proba-1 for ESA.
鈥淭hese attributes are a prerequisite for high performance remote sensing.鈥�
For most Earth-observing satellites, image acquisition is only a matter of opening a viewing aperture but Proba-1 is different.
This helps Proba-1 compensate for its 7.5 km/s speed, like a photographer panning to snap a moving target.
In addition, Proba-1 can record up to five differently angled views of the same target, important for researchers investigating how vegetation changes appearance with shifts in view.
鈥淟ook at a sunflower on the ground 鈥� you鈥檒l see a different mix of colours depending on where you stand, as well as the growing season and time of day,鈥� explains Mike Cutter of Surrey Satellite Technology Ltd, which designed CHRIS. 鈥淭he same is true in orbit.鈥�
Understanding this has proved beneficial for mapping and classifying land cover, from forest monitoring in Canada to crop yield predictions in Europe, Australia and China.
Other researchers favor the fact that CHRIS鈥檚 spectral response can be programmed as desired, to home in on diverse factors such as inland or coastal water quality 鈥搃dentifying oil spills, for example 鈥� atmospheric pollution or even desert lichens 鈥� significant for conserving topsoil in marginal environments.
CHRIS鈥檚 17 m resolution is useful in its own right, adds Mr Cutter: 鈥淚t can give extra detail of a local section of a larger satellite image acquired at lower resolution.鈥�
For instance, more than 500 CHRIS images have been delivered for the International Charter 鈥楽pace and Major Disasters鈥�, a space agency agreement to prioritise damage mapping of disaster-struck regions.
鈥淭his mission came down to an experiment 鈥� Proba鈥檚 name derived is from the Latin word Probare: 鈥榣et鈥檚 try鈥�,鈥� comments Frederic Teston, head of ESA鈥檚 In-Orbit Demonstration Programme, giving Europe鈥檚 space industry the opportunity to flight-test new technologies.
鈥淲e were demonstrating as many new technologies as possible on a single platform, the resulting satellite being able to operate itself with minimum ground control.鈥�
CHRIS users simply submit the latitude, longitude and altitude of their chosen target and Proba-1鈥檚 computer navigates to the correct location, tilts, shoots and delivers the scene.
Other innovations included then-novel gallium arsenide solar cells and one of the first laptop-style lithium ion batteries 鈥� now the longest operating example in Earth orbit.
CHRIS is only the largest of Proba-1鈥檚 payloads. A smaller imager, the High Resolution Camera developed by Belgian company OIP Sensor Systems, provides black-and-white 5鈥�10 m-resolution images.
The microsatellite is overseen from ESA鈥檚 Redu ground station in Belgium and the use of Proba-1's instruments is managed from ESA's ESRIN Earth observation center in Italy.
Provided by European Space Agency
