aerial engineering

Energy from the Sun

Company from São José dos Campos develops technique for manufacturing solar panels used in artificial satellites

MIGUEL BOYAYAN and SOHO (ESA & NASA) Solar cells: small parts that, grouped together, form the solar panelsMIGUEL BOYAYAN and SOHO (ESA & NASA)

The manufacture of solar panels that capture energy from the Sun to supply electricity to satellites that orbit around our planet is the technological novelty produced in the city of São José dos Campos in the state of São Paulo. The merit belongs to Orbital Engenharia, a small company that since last year has mastered the complete cycle for producing these artifacts. “Besides Brazil, only countries like the United States, France, Germany, Japan, Russia, and China have the capacity for making these panels”, says mechanical engineer Célio Costa Vaz, a director of Orbital. To acquire the knowledge and to join the select group of producers of solar space panels, the company was funded by FAPESP, through the Small Business Innovation Research Program (PIPE).

Also known as photovoltaic cells, these panels are the most efficient form of generating electricity for satellites and stratospheric balloons. They transform the solar radiation found in space into electricity, energy that is essential for these space vehicles to work. The explanation of why only a small number of nations has mastered the technology for producing these generators lies in the difficulty of assembling their basic unit, a part called a Solar Cell Assembly (SCA). “If we compare a panel with a box of batteries, each cell is a battery”, says Vaz. It is made up of three components: the solar cell, the interconnector, and a protective cover, known as a cover glass.

The solar cells can be made of various materials, including silicon and gallium arsenide. They are usually 0.2 millimeters (mm) thick and normally of a width that varies between 2 centimeters (cm) by 4 cm to 4 cm by 7 cm. The interconnectors are tiny silver parts, with 0.012 millimeters in thickness, used to make the electrical contact between the cells. The cover glass, in turn, is a very thin glass (between 0.1 mm and 0.2 mm in thickness), similar to the slide of a microscope, and is fitted with an antireflective coating. It is stuck onto the solar cell and protects it from the radiation that exists in space, like protons and electrons.

Essential tools
These three components – solar cell, interconnector, and cover glass – can be bought easily, but the problem is to the assemble the cell. “At first sight, it may seem to be a simple challenge, but it isn’t. There are various quality requirements that make this assembly very complex. In the past, we tried to develop it and to qualify it, but we failed to succeed”, explains Célio Vaz, who worked for 18 years at the National Institute for Space Research (Inpe), with its headquarters in São José dos Campos. The complicating factor is that the tools needed for SCA production are not found on the market, unlike the components. “We had to carry out the development of the equipment, devices, and tools to make the Solar Cell Assembly. This was only possible with the funds from PIPE.”

During the first stage of the project, the researcher designed the equipment for producing the cells and the solar panel, defined the processes and procedures for manufacture, and outlined the product’s warranty plan, the inspection programs, and the qualification tests. This work, which began in April 2001, took about six months. In the second stage, with a duration of two years, the equipment was actually produced, the processes developed, and the samples made and tested.

“The results achieved show that we have at our disposal the technological quality and the qualified means of manufacture to attend to the demand for equipment from the aerospace sector”, explains Célio Vaz. According to the engineer, mastering this technology will bring the country great benefits, such as the replacement of imports, the creation of local jobs – Orbital employs four people, two of which with a higher education, and the possibility of exporting products and services with a high added value.

Two orders
Orbital’s end customers are the Brazilian Space Agency (AEB) and Inpe, the research center with which the company signed its first contract, in December 2001. The company took part in an international tender and was chosen to manufacture four solar panels for the Scientific Satellite (Satec), each measuring 50 cm by 66 cm. 1,100 imported cells were used in this project, because up until that date Orbital was not yet producing these components. Made of monocrystalline silicon, each cell measured 20 mm by 40 mm. Satec was programmed to be launched into orbit by the Satellite-Launching Vehicle (SLV) that exploded at the rocket launching base at Alcântara, in Maranhão, in August last year.

In September 2002, the company was subcontracted to take part in a still more ambitious enterprise: designing and making the solar panels that will be installed in a service module common to a series of satellites, called a Multimission Platform (MMP), with the capacity for taking on each flight variable payloads, such as cameras to capture images of the Earth, radars, or scientific experiments, for example. It is being built for the AEB and for the National Institute for Space Research (Inpe) by a consortium of Brazilian companies: Atech, from São Paulo, and Cenic, Fibraforte, and Mectron, from São José dos Campos.

The platform is fitted with basic equipment (energy supply system, propulsion, telecommunications, etc.) that serves to keep in operation the satellite’s payload, such as land imaging cameras, radars, sensors, and scientific experiments. “The platform is now at the stage of detailing the project. We are going to design, develop, and assemble solar panels for the two wings of the platform, each one of them measuring about 80 cm by 130 cm, and with almost 1,500 cells”, Orbital’s director explains. The forecast is that the panels and the platform will be ready by the beginning of 2006.

International quality
As the domestic market for satellites is limited and seasonal, Orbital is setting its sights on customers abroad to grow. “We intend to go in for international tenders, and to do so, we are in the process of getting certification under the NBR 15100 Space Quality System standard, which corresponds, on the international level, to the AS9100A”, says Célio Vaz. According to the engineer, the United States manufactures a few dozens of these scientific satellites a year and is an excellent market. “I believe that we shall be able to be successful there, if we have a competitive price. In addition, countries like Mexico, Chile, and Argentina have space programs and have not mastered the technology for making these panels.” Another alternative for surviving in this market is to diversify production. “We thought of using the technology and the equipment developed by us to make other products, such as optic sensors and equipment for storing and conditioning the energy captured by these panels”, Célio Vaz says.

The space solar panels, though, cannot be used here on Earth, because they are very different from the similar devices for terrestrial use. The terrestrial solar panels are designed for the kind of light that reaches the surface of the Earth, with a different electromagnetic spectrum from the one to be found outside the atmosphere. Another difference lies in the encapsulation of the panel. The terrestrial one has to be protected against humidity and physical shocks, caused, for example, by hailstorms.

The Project
Photovoltaic Generators for Aerospace Applications (nº 01/03041-2); Modality Small Business Innovation Research Program (PIPE); Coordinator Célio Costa Vaz – Orbital; Investment R$ 236,700.00 and US$ 41,308.95