Satélite de Coleta de Dados - SCD

On February 9, 1993, the first satellite developed entirely in Brazil, the Data-Collecting Satellite (Satélite de Coleta de Dados - SCD-1), was launched from a United States B-52 plane carrying a Pegasus rocket made by the American Orbital Science Corporation. The useful load of the satellite consists basically of transponder of collection of data (Transponder PCD), which receives the signals emitted for the automatic platforms in land through antennas in UHF (monopolos in the inferior panel and quadripolo in the superior panel) and relays them in real time (without storage on board) in band S (quadripolos in the panels inferior and superior) for the terrenas stations.

The SCD-1, sometimes referred to as the "green" satellite, is used by INPE agencies, such as the Weather Forecasting and Climate Studies Center (Centro de Previsão do Tempo e Estudos Climáticos - CPTEC), for collecting meteorological and environmental data on the Amazon region, including the levels of carbon monoxide and carbon dioxide in the atmosphere. The data are transmitted to the INPE (National Institute of Space Research) and are used for monitoring forest fires. More than thirty companies were involved in the construction of the SCD-1, with the INPE providing most of the electronic hardware equipment. The SCD-2, which was scheduled to be launched by a Brazilian-made rocket, will also be used to collect environmental data.

Satellite SCD-1 is a satellite of Collection of Data and possesss the following characteristics:

• Form: prism of octogonal base
• Dimensions: 1m of diameter, 1,45m height
• Total Mass: 115 kg
• Electric power: 110W
• Structure: Paíneis aluminum beehives
• Stabilization of attitude: rotation
• Passive Thermal Control
• Transponder of collection of data in band UHF/S
• TT&C in band S
• Experiment of solar cells
• Circular orbit of 750Km of altitude, 25 degrees of inclination

The attitude control is made by rotation, imposed for the launch vehicle (approximately 120 rpm in the beginning, without speed control). A nutation shock absorber corrects eventual shunting lines in the separation. The correction of the direction of the rotation axle can be made with the use of a magnetic bobbin, telecomandada of land. The attitude determination is made from solar sensors and of a magnetometer.

The power generation is made from eight rectangular lateral panels and a composed superior octogonal for silicon cells. A PCU (Unit of Conditioning of Power) all conditions and directs the energy generated for the satellite. A nickel-cadmium battery (with capacity of 8 AH) accumulates energy for operation of the SCD-1 during eclipse. The generation excess is wasted in two spendthrifts (Shunts) located in the inferior panel. A converter DC/DC and a unit of power distribution (PDU) finish the composition it subsystem.

SCD2 is very similar to SCD1 and has the following characteristics of shape (octagonal base prism), dimension (1m diameter and 1 m height), mMass (117 kg), power (110W), structure (aluminum honeycomb solar panels), stabilization (spin constant of 34 rpm), tThermal Control (passive), data collection transponder on UHF/S bands, TT&C on S-band, reaction wheel experiment and orbit circular (750km height, 25 degrees of inclination). For radiation damage study purposes, other solar cell experiment flies with this satellite. This experiment was also totally produced in Brazil. Launched again with one Pegasus rocket on 22 October 1998, SCD2 is since the beginning of the orbital life performing the data collection mission, giving continuity and improving SCD1 services. Even though the nominal life specified for the mission is two years, it is expected that this period will be widely exceeded, in consonance with what is happening with SCD1.

The Brazilian Environmental Data Collection System which is based on satellites and on a data collecting platform (DCPs) network distributed over the country. This system aims to provide to Brazil environmental data collected daily in its different regions. The DCPs are small automatic stations usually installed in remote locations. The data received from DCP´s are transmitted to the satellites which retransmit in turn to a INPE ground station, Cuiabá and Alcântara. From these stations, the data are sent to the Mission Center, located in Cachoeira Paulista, where the data processing and its immediate distribution to the users are done. The registered users receive the processed files using Internet at most 30 min after satellite pass. See Users Services.

The data-collection satellite SCD-2, launched in 1998 by a Pegasus launcher, is the second in a series of satellites conceived to receive meteorological and environmental data, as well as rainfall and river water level data collected at and transmitted from hundreds of fixed automatic surface platforms settled on land and in oceanic buoys and to retransmit the data to ground receiving stations. The SCD-2 is a 115-kilogram, low-complexity satellite flying in an orbit at an altitude of 750 kilometres. Designed for a minimum lifetime of two years, it was still operating perfectly after five years.