The China-Brazil Earth Resources Satellite (CBERS) programme is a joint Chinese/Brazilian initiative to develop a satellite to monitor natural resources and the environment. Although the majority of the work is to be undertaken by the Brazilians and the Chinese themselves for their own technology development, some key elements of the programme have been procured through competition, on the international market. One of these items is the Overall Checkout Equipment (OCOE) to be used in the assembly, integration and test programme of the satellite. The ESA/ETOL system has been selected as the main component of the OCOE. Two flight models are currently planned, one of which will be integrated at the Integration and Test Laboratory (LIT) at the INPE premises in São José dos Campos, Brazil - the largest and most advanced integration and test facilities in the southern hemisphere. The use of ETOL in this programme represents another commercial exploitation of this highly successful European development.
ESA originally developed its Test Operations Language (ETOL) software to meet the requirements for pre-launch checkout of the Agency's own satellites. The ETOL normally forms the main component of the Overall Checkout Equipment (OCOE) used for system-level electrical testing. Many ESA and non-ESA projects have used it, including ECS, Marecs, Olympus, Hubble-FOC, Ulysses, Giotto, Hipparcos, ISO, IRAS, ROSAT, ItalSat and SAX. It has proven to be a competitive, viable and robust product for European companies interested in supporting emerging nations and industries entering the satellite development arena.
One recent example of such a successful use of the system is in the China-Brazil Earth Resources Satellite (CBERS) programme. When the Chinese Academy of Space Technology (CAST) and the Brazilian National Institute for Space Research (INPE) decided to develop jointly a satellite to monitor natural resources and the environment, they chose the ESA/ETOL standard for their OCOE. By bringing a ready-made solution to their testing activity, INPE and CAST will bring significant benefits to the development of the programme.
ESA and industry have continued to work together to bring new technology into the electrical testing domain. Extensive use of off-the-shelf software, increased commonality between test and flight operations through standardisation, together with new informatics technology, are methods being used to meet the challenges of reducing the cost of ESA's programmes and retaining European industry's competitive position in the global marketplace.
Co-operation between ESTEC and INPE dates back to the mid-1980s, when INPE staff were seconded to ESTEC's Data Handling Division for a period of training. With the background of this experience of the methods and tools used in Europe, it was decided to adopt the ESA/ETOL standard, which is implemented in a wide range of products from European suppliers, for the CBERS OCOE.
In January 1994, INPE issued an international call-for-tender for the supply of two satellite-level OCOE systems. The publication of the call-for-tender raised considerable interest from a range of suppliers not only in Europe but around the world. A contract was awarded to a US company with the European company, Computer Resources International A/S (CRI), to supply and customise the ETOL software.
The other elements of the OCOE have been supplied by:
The award of the prime contract to a company from a non-member state of ESA raised, for ESA, the question of access to European technology by non-ESA member states. It was necessary to obtain the approval of ESA's delegate committee for transfer of technology. In order to protect the rights of European industry, it was a condition of the software licence issued by ESA that only executable code would be delivered, thus protecting the position of European suppliers in sub-sequent tendering actions on the world market.
The international context of the contract brought added complications. It was necessary to configure the software for the CBERS characteristics on a computer platform in Europe, to deliver and perform acceptance in the United States on the target hardware, and to train users who would eventually exploit the system in Brazil and China.
This could only be achieved with confidence by starting from a stable product with a proven history of success, and by paying attention to a thorough rehearsal of tests and procedures before facing the customer.
In addition, the user documentation had to be of a high standard to ensure that extensive support was not required in the utilisation phase.
The total development time was five months, with a further one month of OCOE acceptance and training activities in the USA prior to delivery of the systems to the customers. This is being followed up with further training and support activities by CRI, both in China and Brazil. The software was also installed in the EGSE reference facility at ESTEC.
The ETOL system supports the following main functions (Fig. 1):
Figure 1. Structure of the ETOL system
The software was originally developed by CRI for ESA/ESTEC in the late 1970s. Since that time, it has been used on numerous ESA and non-ESA missions. During its lifetime it has undergone numerous enhancements, both functionally and technologically, being currently available on VAX computers under the VMS operating system.
One of the main features of the CBERS OCOE is that it eliminates the need for specialised hardware, both for the data acquisition interface and the Colour Display Subsystems. The telemetry acquisition and telecommand sending to the TM/TC station is achieved by means of an Ethernet-TCP/IP interface. This is also the case for the interface to the Special Checkout Equipments (SCOEs). The Colour Display Subsystem is implemented as a software package running under MS-DOS on an IBM-compatible PC. The OCOE is therefore made up of a standard VAX computer and IBM-compatible PCs, both with Ethernet-TCP/ IP interfaces.
The ETOL software has also been updated to meet the CBERS data-handling requirements. The housekeeping telemetry data is sent to the ground at two different bit rates, 625 and 2500 bits/s. The science data is sent to the ground via higher speed telemetry links. The telecommand link uses a mixture of simple telecommands and block telecommands. Both the telemetry and telecommand conform to ESA PCM Standards.
In the past decade, remote-sensing technology has been applied to studies of natural resources and is proving to be the most efficient way to collect data for monitoring and planning national development. Given the importance of remote-sensing data, a co-operative programme was signed in July 1988, between the People's Republic of China and Brazil, to develop two Earth resources satellites. The organisations involved are the Chinese CAST and the Brazilian INPE. The CBERS programme thus pools the financial resources and skilled manpower of two developing countries to establish a complete remote-sensing system.
The satellite will provide an effective and rapid tool to survey Earth resources and monitor disasters, contamination and the ecological environment. Both countries will use the results obtained by the mission in a wide variety of areas, including agriculture, forestry, mining, geology, meteorology, environment, water conservation, and mapping.
The use of satellite-based Earth resources monitoring can be highly effective. For example, to survey the whole of China's territory, only about 500 photos are needed and the task can be accomplished in several days. An equivalent aircraft survey would require over a million photos and take ten years to complete. A satellite-based system permits monitoring of areas not yet thoroughly investigated because of their vast expanse and inaccessibility such as oceans, deserts or forests. The use of a satellite also allows repeated and regular observations to be made, periodic surveys being necessary to provide information on plant growth, deforestation, river course changes, the forming and melting of ice and snow, to give but a few examples.
This cooperative programme is based on the principles of mutual aid and mutual benefit. It has also promoted and stimulated the development of space technology and satellite applications in both countries. This cooperation between the two countries sets a precedent for international cooperation in space and other high technology spheres, setting a valuable example to other developing countries as to what can be achieved by pooling of resources.
The project is funded 70% by China and 30% by Brazil. The first satellite will be integrated in China at the CAST facility in Beijing. The second will be integrated in Brazil at the Integration and Test Laboratory (LIT) in São José dos Campos. The first CBERS satellite is scheduled to be launched in 1997, by a Chinese Long March launcher from the Taiyuan Launching Site, in the People's Republic of China. The second is to follow two years later. Each satellite will have an expected lifetime of two years.
Satellite description
The CBERS satellite (Figure 2) consists of a
payload module and a platform. The main body is a box measuring
2.0 m 1.8 m 3.2 m, with the width increasing to 8.4 m with
the solar array deployed. CBERS weighs 1450 kg in initial orbit.
It has a single solar array on one side of the satellite.
Figure 2. An artist's impression of the CBERS satellite
The satellite is designed to operate in a sun-synchronous orbit of 778 km altitude with a 98.5 ° inclination. The local time at the descending node is 10:30 a.m. The repeat cycle is 26 days and the satellite can provide global imaging coverage.
Payload
The characteristic of CBERS that
differentiates it from existing Earth resources satellites, is
its multisensor payload with different spatial resolutions and
data-collection frequencies. The three imaging sensors on board
are:
Their characteristics are shown in Figure 3. The WFI has a large swath of 900 km which gives a synoptic view with a ground resolution of 250 m and covers the Earth surface during a period of less than five days. In addition, the CCD and the IR-MSS sensors provide detailed information of a sampled area of 120 km (20 m and 80 m respectively). The CCD has a pointable capability of +/- 32°, providing an increased observation frequency or stereoscopic capability for a given region. Thus, any phenomenon detected by the WFI may be zoomed in on by the oblique view of the CCD with a minimum time lag of three days. These multisensor data are especially interesting for ecosystem monitoring where a high frequency of information is required.
Figure 3. Ground coverage provided by the satellite's main
instruments: CCD, IR-MSS, and WFI
Wilde Field Imager (WFI)
The WFI is used to get
low-resolution, wide-field image information in two visible
spectral bands: 0.63 to 0.69 µm and 0.77 to 0.89 µm. The ground
resolution is 250 m and the swath width is about 900 km. The
repeat cycle is reduced to five days owing to the wide swath
width.
CCD camera
The CCD camera is used to acquire high-
resolution remote-sensing image information about the Earth in
visible and near-infrared spectral bands. It has five spectral
bands: 0.45 to 0.52 µm, 0.52 to 0.59 µm, 0.63 to 0.69 µm, 0.77
to 0.89 µm, and 0.51 to 0.73 µm.
The ground resolution is 20 m and the swath width is 120 km. Earth images in the five spectral bands can be obtained simultaneously. The CCD camera, using scanning pushbroom techniques, mainly takes images of the areas around nadir, but also has side-looking capabilities to cover any specified area within a three-day period.
Infrared Multi Spectral Scanner
The IR-MSS obtains
medium resolution phanochromatic image information in four
spectral bands: 0.5 to 1.1 µm, 1.55 to 1.75 µm, 2.08 to 2.35 µm
and 10.4 to 12.5 µm. The ground resolutions are 80 m for the
first three bands and 160 m for the last band. The temperature
sensitivity for the last and far-infrared band is 1.2 K. The
instrument only takes the images of the areas around nadir. Its
imaging mode can be performed by ground command in real time or
deferred by time tagging.
Other payloads
In addition to the imaging payload,
the satellite carries a Data Collection System (DCS) for
environmental monitoring; a Space Environment Monitor (SEM) for
detecting high-energy radiation in space; and an experimental
High Density Tape Recorder (HDTR) to record imagery on board.
The platform consists of the structure subsystem, the thermal-control subsystem, the electrical power supply subsystem, the attitude-and-orbit-control subsystem, the on-board-data-handling subsystem, and the tracking, telemetry and command sub-system.
Thermal control is implemented mainly by passive methods such as using thermal coatings, multilayer insulation blankets, and heat pipes. Only in special circumstances is the active method of using an electric heater employed. The temperatures inside the satellite are generally maintained within a range of 0 °C to 45 °C, except for the Nickel-Cadmium (NiCd) battery which is kept at a range from 5 °C to +15 °C.
The function of the electrical power supply subsystem is to provide all the instruments and equipment on board the satellite with the required electrical power. The subsystem includes the solar array, the NiCd battery, regulators and converters. The output of the solar array will be 1100 W at the end of its lifetime, which is designed to be two years.
The attitude-and-orbit-control subsystem (AOCS) realises the Earth pointing of on-board remote sensors and three-axis attitude stabilisation, to keep the solar panel continuously tracking and pointing to the Sun, and to maintain the Sun-synchronous orbit. The main features of the AOCS are to achieve the three-axis pointing accuracy of 0.2 to 0.3 °, the three-axis measuring accuracy of 0.15 ° and the solar panel accuracy of 5 °.
The Integration and Test Laboratory (LIT) at INPE was designed and built to meet the needs of the Brazilian space programme (Fig. 4). It represents one of the most sophisticated and powerful facilities in the qualification of industrial products that demand a high reliability.
Figure 4. INPE's Integration and Test Laboratory (LIT)
The facility has two main areas in which integration and test activities are carried out. The larger is a class 100 000 clean area of 1600 m , with a useful crane height of 10 m. The types of tests performed there include thermal vacuum, climatic, vibration/shock, Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC). The second area is smaller, 450 square meters , with a crane hook height of 6 m and operates under class 10 000 conditions. Tests performed there include alignment measurements, centre of gravity and moment of inertia. There are also checkout equipment rooms, test control rooms, and additional laboratories.
The total area of the facility is 10 000 m with all the necessary utility infrastructure. This includes a filtered compressed air system, closed circuit water system, grounding system with less than 1 ohm resistance and an uninterruptable power supply.
ESA Bulletin Nr. 85.