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Aerospace engineering

Space for conquests

Brazil now has thrusters and catalysts, two essential components for satellites

Without making a lot of noise about it, Brazil is ready to take a great step towards mastering for once and for all the technique for making artificial satellites. Researchers from the National Institute for Space Research (INPE), which is linked to the Ministry of Science and Technology, and from Fibraforte Engenharia, a company from São José dos Campos, have successfully concluded a sequence of tests to validate a thruster for satellites and a catalyst, a chemical substance that participates in the burning of the fuel. The fact is important because few countries have mastered the technology for manufacturing these components. The thrusters, are responsible for handling the position and the corrections to orbit during the useful lives of the satellites, estimated at four years. The equipment designed and built by Fibraforte is of the monopropellant kind, that is, it works with only one liquid fuel, in this case, anhydrous hydrazine, and does not need an oxidant element to carry out the combustions. The national catalyst, essential in monopropellant satellites, was developed by the researchers from Inpe’s Associated Combustion and Propulsion Laboratory (LCP).

“The Brazilian Space Program is the great beneficiary of the development of these components. From now onwards, we are one of the few countries in the world with the capacity to produce complete propulsion systems with a catalyst”, explains mechanical engineer Humberto Pontes Cardoso, the coordinator of the team from Fibraforte responsible for the thruster project. The equipment will be part of the propulsion subsystem of the Multimission Platform (PMM in the Portuguese acronym), a modern concept of satellite architecture that brings together in a single structure all the equipment necessary for the survival and the operation of these artifacts in space. Forecast to be ready at the end of 2007, the PMM is currently in a process of qualifying its equipment and subsystems (for more information on the PMM.

Funded by FAPESP’s the Small Business Innovation Research Program (PIPE), the thruster developed by Fibraforte will have the function of providing the necessary thrust for the Multimission Platform to carry out orbital maneuvers, after its separation from the launch vehicle.  These maneuvers are necessary because the Earth observation satellites, positioned at between 600 and 1,200 kilometers in altitude, suffer from perturbations in their orbit due to the magnetic anomalies and the gravitational field of our plant. The thruster corrects the positioning of the satellite, and the precision of its maneuvers depends in great measure on the marriage between the thruster and the catalyst. This is because the thrust to move the satellite is a result of the expulsion at a high velocity of gases derived from the decomposition of the hydrazine by the catalyst, according to Cardoso. “When coming into contact with the catalyst in the catalytic chamber, the hydrazine is decomposed, generating hydrogen, nitrogen and ammonia. When they go through the nozzle of the thruster, the gases are accelerated, generating the thrust needed for the maneuvers of the satellite.”

Perfect union
The PMM’s propulsion module will weigh 10 kilos and will be made up of six engines, each with 5 Newtons (N) of thrust. This force corresponds to the effort necessary to balance 500 grams in the pan of a scale. The equipment will also have a spherical fuel tank of 50 centimeters in diameter and capacity for 45 liters of liquid hydrazine (N2H4), two valves for filling and draining the tank, a tube that connects the thruster for the fuel tank, also manufactured by Fibraforte, besides a pressure sensor and a set of valves to isolate the tank from the engines during the launch.

“The great secret of a monopropellant thruster is a perfect union between the catalyst used and the fuel injection system in the catalytic chamber”, Cardoso explains. The ideal, says the researcher, a former engineer from Inpe, is for the injector to vaporize the hydrazine before it comes into contact with the catalyst. “This eliminates two serious problems. The first is the mechanical impact of the fluid with the catalyst, which is going to reduce its useful life. And the second is to prevent it from becoming soaked, because the accumulation of fuel in a liquid state in the catalytic chamber may made the particles go so far as to explode”, Cardoso explains.

In the last few years, Fibraforte has acquired wide experience in the development of technology for manufacturing satellite engines. At the end of the 1990s, the company was jointly responsible for the development of monopropellant thrusters with 2N of thrust and a cylindrical fuel tank for a suborbital platform of Inpe. “This was the first thruster designed by the company. It was a good apprenticeship, but it was a far simpler project, because the requirements were not so rigorous”, explains aeronautical engineer Jadir Nogueira Gonçalves, a partner and director of Fibraforte. Next, the company worked on the project for a 200N bipropellant thruster, which did not fly. “We made three prototypes for Inpe, which were engineering models for testing”, says Gonçalves.

Just as Fibraforte’s thruster, the catalyst developed by Inpe also represents an important conquest for Brazil’s technological independence in the space area. “It is very difficult to import this material. The last two times we tried to purchase it from an American company, we didn’t even get a reply. As far as we are aware, only the United States and France, and, probably, Russia and China, have mastered the technology for making this kind of catalyst”, says researcher Demétrio Bastos Netto, the head of Inpe’s LCP.

Amongst the catalysts most used in monopropellant satellites is Shell-405 – a reference to the Anglo-Dutch oil company which made up the consortium, together with the Reynolds Metal Company, charged with developing it for the American space agency, NASA, in the 1950s. Since 2003, S-405 has been marketed by the American company Aerojet General Corporation, which can only sell it with the approval of the government of the United States. The last time that Inpe managed to buy the product was in 1984. In that year, half a kilo of the material cost the equivalent of US$ 7 thousand, and it served only for ground testing. So far, the satellites that Brazil has developed, like the Data Collection Satellites (SCD1 and SCD2) and the Scientific Applications Satellite (Saci), do not have propulsion systems. Correcting their position in space is done using a system that used the magnetic field of the Earth. In the two China-Brazil Earth Resources Satellites (Cbers), larger in size and weight, Chinese thrusters and catalysts were used. “The production of a national catalyst opens up the prospect for Brazil to compete in this restricted market with Aerojet and other producers, supplying the material for other countries, like Argentina, Chile and Peru”, explains Bastos Netto.

With the appearance of spheroid grains, black in color, the catalyst is made up of a substance that works as a support, in this case a highly porous special aluminum oxide (Al2O3), and a metal, iridium (Ir), which is the active element in the reaction that decomposes hydrazine, a fuel obtained from the dehydration of hydrazine hydrate, a colorless and highly toxic liquid substance that is produced in the laboratory. “Aluminum oxide is extremely difficult to be obtained with suitable properties for giving support to the catalyst and to the iridium, because they can optimize or even prevent the process of catalyzing the hydrazine”, explains chemical engineer José Augusto Jorge Rodrigues, a researcher at Inpe. An important property of aluminum oxide is its high thermal and mechanical resistance and the high crystallinity that guarantee the macroporosity of the material. Resistance to heat is indispensable, because the temperature of the catalytic chamber, during the decomposition of the hydrazine, is very high, around 900°C, and mechanical resistance is necessary because the catalyst works under a high pressure, of as much as 22 atmospheres, equivalent to the pressure on the bottom of the sea at a depth of 220 meters.

The choice of iridium as an active metal occurs because it is the only chemical element capable of decomposing hydrazine spontaneously at a low temperature – a condition encountered in space. “Iridium is an expensive metal, a byproduct of the extraction of gold. One gram costs around US$ 200”, says chemist David dos Santos Cunha, a researcher from Inpe. The content of iridium in the catalyst is from 30% to 36%, far higher than the majority of industrial catalysts, in which the metal content does not exceed 5%. “The greatest difficulty is to make the correct impregnation of the iridium in the aluminum oxide, improving its distribution, so as to get iridium particles of 2 nanometers”, Cunha explains. The researchers from Inpe also had contributions to the project from the Military Engineering Institute, the Petrobras Research Center and from Université Pierre et Marie Curie, of Paris, France. Besides the catalyst for use in space, the LCP is also researching into catalysts to be used in the chemical industry and in refining petroleum.

Inpe’s space catalyst has now been qualified and is ready to be put on board the PMM or other satellites. During the qualification process, the material was submitted to a campaign of 39 sequences of being activated, accumulating a total of 11 thousand seconds or some three hours, twice the time that it will work in space over the four years of the satellite’s life. The qualification of the thruster-catalyst set was done at Inpe’s Altitude Simulation Test Bench (BTSA), in the city of Cachoeira Paulista, in the state of São Paulo. “The first step of the campaign was to use the commercial S-405 catalyst to qualify Fibraforte’s thruster and to choose the best injector, the component responsible for injecting the hydrazine into the catalytic chamber. Having defined the injector, we went on to test our catalyst. We did a comparison of the performance of the two systems, in identical operating conditions, and we concluded that the catalyst fulfills the requirements called for by the Multimission Platform”, claims physicist Carlos Eduardo Rolfsen Salles, a researcher from the LCP who is responsible for the Test Bench, the only one of this size in Latin America. “A campaign of tests like this one costs around US$ 80 thousand in Brazil. Without our Test Bench, any development project would be unviable, because it would have to be carried out abroad, at a higher price”, Salles says.

So far, four prototype thrusters have now been built, and another six are being manufactured by Fibraforte. They will undergo new batteries of tests until, in June next year, the qualification model of the PMM’s propulsion module should be ready. “The final module, also called the flight model, will be a true copy of the qualification model, at which stage all the equipment will be integrated”, says Humberto Cardoso. According to the researcher, for the thrusters and the catalyst to acquire international credibility, there will have to be a successful track record of flights. “That means flying successfully, at least twice. The first is to take place in 2007, and the second is forecast for before 2012, always with the PMM”, the researcher says. From then on, Brazil will be accredited to supply this sophisticated technology to customers in other countries.

A versatile platform

Regarded as one of the main projects currently being run by Inpe, the Multimission Platform (PMM) is expected to be ready in December 2007. The Remote Sensing Satellite 1 (SSR-1) should be the first to be assembled on this structure. According to aeronautical engineer Mário Marcos Quintino, the manager responsible for the development of the PMM, in this kind of architecture, there is a physical separation between the various modules of the platform like energy supply, propulsion, communications, on board supervision, thermal and attitude control and the payload (imaging radar, for example), which can be developed, constructed and tested separately, before the integration of the modules and the final tests. Furthermore, there is also the advantage of the project being reused, with the consequent reduction in the costs of the new satellite, since the PMM will be able to take several kinds of mission into space.

“The first model of the PMM will have a cost in the order of US$ 25 million, but this amount may fall to something around US$ 10 million to US$ 15 million, depending on the configuration, in the following models”, Quintino says. Totally conceived at Inpe, the PMM has national content of about 80%. Almost all its subsystems are designed and developed by Brazilian companies. “We believe that the platform is an interesting product to be offered in the space market, thanks to its great commercial potential. Several kinds of payloads fit the PMM, in particular medium sized satellites weighing up to 600 kilos, used to observe the Earth.” The adoption of multimission platforms is a worldwide tendency, because they ally technical and commercial advantages.

The Project
Development and qualification of the 5N monopropellant thruster for a satellite (nº 03/07755-5); Modality The Small Business Innovation Research Program (PIPE); Coordinator Humberto Pontes Cardoso – Fibraforte; Investment R$ 400,000.00 (FAPESP)