On 22 February 1986, a European Ariane 1 launcher orbited SPOT 1, the first satellite of the Earth observation programme decided by the governments of Belgium, Sweden and France. Initially designed to operate for three years, SPOT 1 has since supplied commercial operator Spot Image with more than 2.7 million high-quality satellite images. Now at the end of its service lifetime, SPOT 1 is set to be de-orbited by engineering teams at CNES’ Toulouse Space Centre starting on 17 November, to lower the satellite into an orbit below 600 kilometres.
Although still capable of acquiring high-quality imagery after 18 years in service, SPOT 1 has reached the end of its operating lifetime. Consequently, CNES has decided to use the satellite’s last reserves of fuel to place it in a lower orbit. If the satellite was left alone at its current altitude, it would continue to orbit the planet for another 200 years before re-entering the atmosphere, gradually breaking up over the years and leaving a trail of debris in its wake. Guidelines laid down in October 2002 by the Inter Agency Space Debris Coordination Committee (IADC) are designed to avert such situations by requiring all satellites in low-Earth orbit to be de-orbited within no more than 25 years. CNES is lending its full support to these guidelines at international level, since they are geared to mitigating the risks and costs of using space for future generations. Although the guidelines do not in fact apply to SPOT 1, which was built well before they came into effect, CNES has decided to set an example by voluntarily de-orbiting the satellite.
In readiness for de-orbiting operations, teams have been working with industrial prime contractor Astrium to make changes to the flight software. Basically, de-orbiting will involve configuring the satellite so that its attitude is controlled by its thrusters, then lowering the perigee to about 550 kilometres by performing daily braking manoeuvres for two weeks, then shutting down power to its systems. In this lower orbit, SPOT 1 will be subjected to higher drag that will cause it gradually to lose altitude and break up naturally in the atmosphere after about 15 years, thus posing no danger to populations on Earth.
CNES’ network of tracking stations—at Issus Aussaguel (France), Hartebeesthoek (South Africa), Kerguelen and Kourou (French Guiana)—and the ground station in Kiruna, Sweden, will track and control SPOT 1 through every phase of de-orbiting, assisted by Norway’s ground station in Svalbard.
"The de-orbiting of SPOT 1 illustrates the engineering expertise of CNES teams and, more besides, it shows that space activities remain closely governed by international guidelines, which guarantee that space will be used sustainably by and for future generations," said CNES President Yannick d'Escatha.
The other three SPOT satellites—SPOT 2, SPOT 4 and SPOT 5—will continue to deliver imagery, which is marketed by Spot Image. SPOT 5’s enhanced performance has confirmed the remarkable imaging capability of the SPOT Earth observation system in service since 1986. The recent contract awarded to EADS Astrium to build two Pleiades satellites carrying high-resolution instruments supplied by Alcatel Space assures continuity of service for the next decade.