Argentina has decided to enter the Communications Satellite area withe the contruction of a series of three medium-sized geostationary Communicatios satellites, for telephone, data and television transmission. These satellites will operate in different frequency bands, and with different geographic coverage. The first of these satellites is called ARSAT-1.
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The adopted Time Schedule predicts the three members of the series will be operative 2012, 2013 and 2014.
INVAP is the prime contractor for this Project launched by the recently created company, AR-SAT SA. INVAP is responsible for the managing aspects of the project, the engineering development in all its phases, the fabrication and integration of the components (with the exception of the transponders, which will be commercial), and quality assurance. Basic engineering aspects were recently approved by a PDR with the participation of international experts (cf. NEWS). Work on the detailed engineering is already under way. The engineering details of the present program begun in December, 2007, after the signature of the running contract with INVAP will be property of AR-SAT.
AR-SAR SA is a state-owned company – which will later incorporate private capital – which initiated operations in July, 2006, created by a national Law which makes it exclusively responsible for the operation of geostationary communications satellites, which will be placed in the positions assigned to Argentina, 81° (in Ku band, covering North and South America; and in C band, covering the whole hemisphere) and 72° W. |
Government has transferred to AR-SAT the assets of Nahuelsat SA, a private company which operated orbital position 72° W, with the foreign-made satellite NAHUEL-1.
We must keep in mind that a satellite is, in the first place, a vehicle apt to carry different kinas of payload. For the time being, ARSAT is a generic platform, since the payload has not yet been definitely defined, save its mass, which well weigh 400 kg. and its power level, 4700 W. About one third of this power is required to manoeuver and operating the service plant of the vehicle. The power will be generated by solar panels, which therefore are of considerable size (see artist´s conception of the relative sizes). The initial weight of ARSAT will be 3 tons, but about half of this weight is that of the fuel necessary to carry the satellite from its transfer orbit to the final geostationary orbit – a task being controlled from the control center, and will also be a task performed by INVAP.
Other institutions of the Argentine S&T system also participate in this Project. As mentioned before, the transponders shall be imported. At this time, these transponders are definitely defines only for the first of the series, ARSAT-1. The lifespan of these satellites is about 15 years.
Diverse launching alternatives are presently being considered by AR-SAT.
What is a Geostationary Satellite?
All the satellites we have constructed or have Ander construction for CONAE have the purpose of Herat-observation and orbit al altitudes of the order of 700 km. These are the so-called “LOS” or “low-orbit satellites". They continuously encircle the Earth.
Communication satellites, however, are geo-stationary: this means that the are stationed at some position of Earths Equator and encircle the Earth at precisely the same angular velocity as Earth itself. Therefore they seem to be stationed above a precise position regarding the ground. Receiving and emitting antennae thus always point in precisely the same position on the ground. For this to be possible, geostationary satellites must be placed in very high orbits – nearly 36,000 km above ground: six times the diameter of our planet and almost on tenth of the distance to the moon.
Position 83°W has been occupied by Nahuel-1, property of the private company Nahuelsat. Nahuel-1 has fulfilled its usefulness and has been pushed out of the position it held for the 13 years of its operation. Argentine-made satellites ARSAT-1, ARSAT-2 and ARSAT-3 will be placed at 83°W and 71°W.
The placing of a satellite into a geostationary orbit is very different from the launching of a LOS. The launching vehicle first places the satellite in a very eccentric low orbit, from which the satellite propels itself to its final position. Therefore ARSAT will have an initial mass of three tones, more than half of which is the mass of the fuel necessary to reach its final destination. Once there, small corrections have to be made every so often to keep the satellite in its position and the orientation of the antennae – an operation which also demands some fuel. This is one of the main limiting factors of the lifespan of these satellites. Also, during its lifespan, the satellite is subject to very intense radiations – another factor to be considered at the time of the design. |
