Andrzej Jeziorski/KOUROU

Arianespace successfully launched the Spot 4 Earth observation satellite for the French Space Agency (CNES) on 23 March after three days of delays. The hold-up was caused by a single bent connector pin on communications equipment.

The 2,755kg satellite, built by prime contractor Matra Marconi Space, was finally launched from Kourou in French Guiana at 22.46 local time (01.46 GMT). The launch vehicle was an Ariane 4 in its AR40 configuration, without strap-on boosters.

The delay was caused by a faulty connector pin in a cable used to release the clamps on the Passager Telecom (PASTEL) optical communication terminal, which forms part of the semiconductor laser intersatellite link experiment (SILEX). This is designed to establish a high-speed, optical datalink between satellites, allowing images to be relayed to Earth immediately rather than being stored in the observation satellite's memory until it comes within range of a ground station. The bent pin caused a short circuit, and it was decided to delay the launch despite the existence of a back-up cable which appeared fully functional.

The SILEX experiment will begin with the launch of the geostationary Artemis telecommunications satellite in 1999, which will carry a corresponding Optical Payload for Intersatellite Link Experiment (OPALE).

Alongside the PASTEL terminal, the Spot 4 also carries two new high resolution in the visible and infrared range (HRVIR)cameras, with 10m resolution in the mono-spectral and 20m resolution in multi-spectral modes, and a 60km swath.

The system is derived from the HRV cameras of the first three Spot satellites, with a new band in the mid-infrared range for applications such as vegetation monitoring and crop forecasting.

The satellite also carries a vegetation monitoring instrument, which has similar spectral bands to the HRVIR cameras and a wider, 2,200km, swathe, allowing daily monitoring of vegetation and soil dynamics with a 1km resolution.

The satellite was injected into a Sun-synchronous low Earth orbit, with a 790km perigee and 811.7km apogee. It is designed for a five-year service life, although the earlier Spot 1 and 2 satellites are still functional, beyond their intended three-year lifespans.

According to Michel Arnaud, deputy director of the Spot/Helios programme for CNES, the Spot 4 cost Fr3.4 billion ($560 million) to develop and launch. The satellite's operating costs should be covered by selling the images it generates via the Spot image joint venture between CNESand Matra Marconi.

The next Ariane 4 launch, Flight 108, is scheduled for 28 April, carrying two direct broadcast satellites: the Matra Marconi Space-built Nilesat 101 and the Hughes-produced BSAT-1b.

Source: Flight International