SPOT Series Background
SPOT (Satellite Pour l’Observation de la Terre) is a commercial high-resolution optical imaging Earth observation satellite system operating from space. It is run by Spot Image, based in Toulouse, France. It was initiated by CNES, the French space agency, in the 1970s and was developed in association with Belgium and Sweden. It has been designed to improve the knowledge and management of Earth by exploring the planet's resources, detecting and forecasting phenomena involving climatology and oceanography, and monitoring human activities and natural phenomena.
The United States developed Landsat at least five years ahead of SPOT. However, Landsat data prices climbed by 1984, making SPOT data a much more affordable option for satellite imaging data. This was a direct result of the attempted commercialisation of Landsat by the United States government, a decision overturned much later.
The spacecraft was three-axis stabilised to 0.1° using momentum wheels. A single solar array generated 1,000 W of power. Downlink at 8 GHz and 2 x 25 Mbps. A hydrazine propulsion system provided orbit maintenance.
A CNES innovation compared with Landsat was the equipping of the SPOT satellites with steerable mirrors to enable viewing on either side of the ground track, over a 950 km swath, and to acquire imagery from different angles for relief mapping, notably to generate digital terrain models.
|Dimensions||3.5 m x 15.6 m|
|Design Lifetime||3 years|
The SPOT orbit is polar, circular, Sun-synchronous and phased. The inclination of the orbital plane combined with the rotation of Earth around the polar axis allows the satellite to fly over any point on Earth within 26 days. The orbit has an altitude of 832 kilometres, an inclination of 98.7°, and completing over 14 revolutions per day.