Apart from the principle missions assigned to the HRVIRs (1) and Vegetation (7) other technological or scientific instruments will be carried by SPOT 4.

(6) - DORIS (Détermination d'Orbite et Radio Positionnement Intégrés par Satellite - Doppler Orbitography and Radiopositioning Integrated by Satellite) identical to the instruments carried by previous SPOT satellites. This system, tested since SPOT 2, uses ground processing to determine the satellite's position to within 10 cm. It can also be used to locate ground beacons with the same accuracy. On SPOT 4, complementary onboard software will be tested (the DIODE experiment) for real-time calculation of the satellite's position, to within about 20 metres, using data provided by DORIS. This position will be sent in the auxiliary data which accompany the image telemetry.

(10) - ESBT (Experimental S--Band Terminal) is the counterpart of PASTEL, but concerns SPOT 4 command and control functions. Exchanges will take place via Artemis, a relay satellite, with a slower transmission rate than that of PASTEL. However, it will enable much longer satellite visibility windows than those offered by the 2 Ghz TT&C stations. Safety and ease of operation will therefore be greatly increased with this type of instrument.

(9) - PASTEL (PAssager SPOT de TElécommunication Laser - SPOT Passenger for Laser Telecommunications) which is part of the SILEX (Semiconductor Intersatellite Link EXperiment) European Space Agency experiment. PASTEL will enable high speed transmission of imagery to the ground segment. This will be done on an optical channel, via the geostationary relay satellite, Artemis which is to be launched at the beginning of 2001.

(8) - PASTEC (PASsager TEChnologique ), designed to study the orbital environment. This is a set of technological experiments to confirm knowledge in areas such as ageing of materials, launch vibrations, etc.

(4) - POAM III (Polar Ozone and Aerosol Measurement), an experiment to be conducted by the United States Naval Research Laboratory (NRL) to measure the vertical distribution of atmospheric components by solar occultation.

(11) VEGA, a radar transponder, used on all SPOT family satellites to calibrate ground radars.

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