Europe's Cheapo Satellite Takes Neato Pictures
June 17, 2004
When the European Space Agency launched its small "Proba" satellite in 2001, it was meant to crash after only a year. Well over a year later, the high-flying shutter bug continues to have one Kodak moment after another from an orbit of 600 kilometers above the Earth's surface. The pictures have been so good, in fact, that ESA doesn't want to retire the craft. Instead it will continue to operate Proba as an Earth Observation mission.
ESA hired the Belgian firm Verhaert to build the spacecraft, which is about the size of a washing machine, as a demonstration of its imaging technology. With a price tag of €10 million ($12 million), Proba, or Project for On Board Autonomy, was cheap to build for a satellite.
The onboard spectrometer Chris (Compact High Resolution Imaging Spectrometer) can grab photos with a resolution of up to 18 meters per image pixel. The images taken by Chris are used widely in Europe by scientists who need access to detailed environmental images.
Postcards from space
A second black and white high-resolution camera is capable of grabbing images with a resolution of five meters. It's been sending back pictures of major landmarks that are so crystal clear that you can make out the pyramids of Egypt or the Great Wall of China in perfect detail.
The images so far released by ESA take the concept of´"seen from above" into orbit, offering a space-eye perspective of landmarks like Australia's Ayers Rock, France's Mt. St. Michel cathedral, the pyramids along Egypt's Giza Plain, a massive Arizona meteor crater and the grid of crisscrossing streets and skyscrapers that is Manhattan.
Proba keeps track of its coordinates and steers itself using a global position system receiver. But because Proba travels at a much higher speed than GPS satellites, it is also equipped with a star-tracking database system that supplements GPS. Like the sailors of yesteryear, Proba uses the starry skies to aid its navigation.
Proba has a high degree of autonomy. ESA operators at the Redu Ground Station in Belgium beam up data on the target to be imaged -- giving its latitude, longitude and altitude -- and the satellite sends back the data that is then transformed into a crisp photo.
The satellite can take photos from virtually any direction since it turns on reaction wheels that allow it to change its position by up to 30 degrees. The reaction wheels are also used to compensate for natural movements of the Earth's orbit, allowing Proba to continue to keep an eye on its target.
ESA says it will launch a follow-up mission in 2005.