Hélios 1A and Hélios 1B were French military photo-

reconnaissance satellite A reconnaissance satellite or intelligence satellite (commonly, although unofficially, referred to as a spy satellite) is an Earth observation satellite or communications satellite deployed for military or intelligence applications. The ...

s in which Italy and Spain also participated. Hélios 1A was launched from the

Guiana Space Centre The Guiana Space Centre (; CSG), also called Europe's Spaceport, is a spaceport to the northwest of Kourou in French Guiana, an Overseas departments and regions of France, overseas region of France in South America. Kourou is located approxim ...

French Guiana French Guiana, or Guyane in French, is an Overseas departments and regions of France, overseas department and region of France located on the northern coast of South America in the Guianas and the West Indies. Bordered by Suriname to the west ...

on 7 July 1995 by an

Ariane 4 The Ariane 4 was a European expendable rocket, expendable launch vehicle in the Ariane (rocket family), Ariane family, developed by the (CNES), the Government of France, French space agency, for the European Space Agency (ESA). The manufacturi ...

, riding alongside Cerise, another French military satellite. Hélios 1B was launched on 3 December 1999 by another Ariane 4, also co-manifested with another military satellite:

Clementine A clementine (''Citrus × clementina'') is a tangor, a citrus fruit hybrid between a willowleaf mandarin orange ( ''C.'' × ''deliciosa'') and a sweet orange (''C. × sinensis''), named in honor of Clément Rodier, a French missionary who f ...

Mission

The two Helios 1 satellites constitute the first generation of the program, the development of which was launched in 1985. They operated in a

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

at an altitude of 678 km. Their instruments offered a resolution of the order of one or two meters on the ground. Derived from SPOT 4, they retained the platform but were equipped with an attitude and orbit control system (SCAO). This system realized the kinematics of the orientation of the satellite via flywheels. This system allowed fine pointing of the shooting lens for several seconds, thus increasing the quality of the images. The SPOT 4 mirror was also replaced, making it possible to target targets outside the satellite's trajectory. The control of the orientation kinematics is ensured by the SCAO via the stellar sensors. Three in number, these are the three cones that we see protruding from the platform. Only two are active at the same time. The flywheels are then controlled by the SCAO which tries to follow a selection of the brightest stars in order to ensure the desired kinematics. This selection of stars is programmed by the ground mission software. Helios 1A and 1B are distinguished from SPOT 4 by the absence of polychromy of the images (they are in black and white) optimizing the image storage capacity. Helios 1A was launched on July 7, 1995 by an Ariane 4 launcher. Due to power supply failures, it had to be left to disintegrate in 2005. Helios 1B was launched on December 3, 1999. Helios 1B was voluntarily de-orbited in October 2004 before definitively losing control. The satellite has been the victim of a loss of charge of an accumulator since May of the same year which in turn leads to the premature wear of the others. Helios 1A ceased to be operational in February 2012 and was also purposely de-orbited. It has been replaced by Hélios 2A, launched in December 2004 on an

Ariane 5 Ariane 5 is a retired European heavy-lift space launch vehicle operated by Arianespace for the European Space Agency (ESA). It was launched from the Guiana Space Centre (CSG) in French Guiana. It was used to deliver payloads into geostationar ...

rocket.

Bibliography

* Guy Lebègue, (trad. Robert J. Amral), « Helios: The Orbiting Spyglass », in '' Revue aerospatiale'', n°118, May 1995.

References

External links

NASA - Helios 1B
Reconnaissance satellites of France Spacecraft launched in 1999 Satellites of Spain Satellites of Italy Spacecraft launched by Ariane rockets Derelict satellites orbiting Earth Military equipment introduced in the 1990s {{France-spacecraft-stub