What happens right after the launch ?
How long does the in-orbit commissioning phase last ?
General organization
Description of main operations completed during in-orbit commissioning:

top of page, article

What happens right after the launch ?

Once the launch has been successfully completed, i.e. once the satellite has separated from the Ariane launch vehicle, the Operations Control Centre begins to monitor and control the satellite. However, before declaring the system " OK " for use by Spot Image customers, it needs to be positioned on operational orbit. Operation and system performance also have to be validated in a real environment through full-scale tests that cannot be performed on the ground: this is the in-orbit commissioning phase.

This phase includes a certain number of operations to qualify all functions that the system will subsequently manage.

top of page, article

How long does in-orbit commissioning take ?

As for its three predecessors (SPOT 1 to SPOT 3), SPOT 4's in-orbit commissioning phase is planned to last two months, following which Spot Image, the company which programs and distributes imagery, will be able to use the main payload to the full for commercial purposes. Once in-orbit commissioning has been completed, the passenger instruments are also ready for operationnal use.

Two periods may be distinguished during in-orbit commissioning:

General organization

All the capabilities of each system entity must be validated as quickly as possible by a set of predefined operations. In-orbit commissioning is organized to handle any conflicting situations by establishing priority levels.

The daily schedule of operations is described in a General Operations Plan common to all entities. This Plan is validated during Operational Qualification prior to initial use.

Throughout in-orbit commissioning, the General Operations Plan is adjusted in the light of results and according to which sites are accessible. Adjustments are decided upon during the daily meetings of the Operational Coordination Group.

These meetings are organized according to topic: (Satellite bus, Payload, Payload Programming, Image Quality etc.). They bring together all those involved in in-orbit commissioning: future operational teams, onboard equipment specialists, image processing specialists, in short those who are most capable of validating a given system function quickly and efficiently.

top of page, article

image2.jpg (6379 octets)

Description of the main operations carried out during in-orbit commissioning

Monitoring the satellite bus

10 hours before the planned launch time, telemetry signals are sent and relayed via the network of TT&C stations to the Operations Control Centre. There, each expert analyses the variations in the measured parameters on dedicated mimic displays. They may thus check that the equipment for which they are responsible is working correctly. Other tests are carried out automatically by the Control Centre based on nominal monitoring ranges for certain parameters. If the parameters lie outside the permitted range, a decision is taken to solve the problem and the appropriate actions are carried out as a priority.

top of page, article, section

Validating Payload programming and operation

The onboard recorders must be validated as quickly as possible. This is done through "dumping"operations. These recorders, comprising electronics and particularly critical mechanical parts, are vital to the mission as they are used to record the imagery when outside station range: great care is therefore taken at the beginning of their lifetime so as to avoid any degradation. Two types of operation are carried out on each recorder:

Everyone is waiting to see the actual images produced in order to appreciate the new capabilities offered by SPOT 4's payload: performance of the new HRVIR instruments and the additional SWIR (shortwave infrared) spectral band.
SPOT 4 has an additional constraint compared with its predecessors: it has been found necessary to schedule a three-day desorption period (during which moisture dissipates into space) before using the new SWIR detector for the first time. It is therefore only three days after the launch that a few imaging strips will be programmed when in range of the Aussaguel Image Receiving Station near Toulouse (France). Each Payload equipment specialist will then be able to monitor and analyse equipment performance "live".

In order to obtain the final image as quickly as possible, all CNES and Spot Image facilities involved have been organized for maximum efficiency: a scene acquired during a pass over Aussaguel around midday will be available for production (or "image development") at Spot Image by late afternoon.

top of page, article, section

Image Quality

The aim of the QIS (System Image Quality) centre is to analyse the characteristics of preprocessed imagery not only to validate it with respect to specifications, but also to assess system performance: location compared to a cartographic reference system, uniformity of response of detectors in each CCD linear array, stability of response over time, evaluation of optimal programming gains in each spectral mode etc. Depending on the results, the QIS centre may request an adjustment of the focal length of one or both of the viewing instruments; this operation would then be fitted into the General Operations Plan as soon as possible and controlled from the Operations Centre in Toulouse.

To achieve its objective, the QIS programs various operations to calibrate the imaging instruments using geographic sites scattered throughout the world, whose properties are already well-known. These include:

The validation workload for in-orbit commissioning is estimated at 40 to 50 images per day.

QIS programming of these sites means that once the in-orbit commissioning has been completed, all SPOT 4 imagery, whatever its spectral mode, viewing angle or photographed surface, is worthy of the "System quality"label.

top of page, article, section

The satellite's in-orbit behaviour

Experts from CNES and Matra Marconi Space use the information provided by housekeeping telemetry to check that all equipment is working optimally.

top of page, article, section

Closing the in-orbit commissioning phase

Once the Operations Plan has been completed and validated, the SPOT 4 system, integrated with SPOT 1 and 2 operation, will be declared "ready for service", during a review for in-orbit commissioning (RRV). During this project review, each expert specializing in a particular item of onboard equipment or ground software will present a synopsis of the main events that occurred during in-orbit commissioning, suggest solutions to any technical problems encountered and, where applicable, recommend a particular use of the item of equipment in question so as to optimize its lifetime. The routine operations phase may then begin...

top of page, article, section

image2.jpg (6379 octets)

  page updated le 00-06-06