ITALSAT

"ITALSAT was not intended to be a communications satellite similar to those already existing on the international market: it was a program which foresaw a wide range of technological innovations, as well as a breakthrough in the field of space telecommunication systems integrated in a ground network."
- L. Guerriero

Description

ITALSAT F1 is an experimental communications satellite built by Alenia Spazio for the Italian Space Agency and launched on January 16, 1991. It provides 30 GHz (uplink) and 20 GHz (downlink) Italian domestic coverage using six spot beams and a "global" national beam. The spacecraft also carries a telemetry beacon at 20 GHz and sophisticated propagation beacons at 40 and 50 GHz. Figure 5.17 shows the general appearance of the satellite and summarizes its major characteristics.

The spot beams carry domestic telephone traffic with a total capacity of about 12,000 voice channels. Each beam operates in the SS-TDMA mode with QPSK modulation at 147 Mbits/sec in a 100 MHz RF bandwidth. On-board regeneration (demodulation and remodulation) is provided, and the beams are fully interconnected by a space-division switching matrix. Satellite resources can be allocated on a call-by-call basis or left as assigned until changed by ground control. Reconfiguration is by ground command; the satellite is not autonomous.


Figure 5.17. ITALSAT F1 (Courtesy of Alenia Spazio)

The global beam provides three transparent transponders each of which has a 36 MHz RF bandwidth. These are intended to carry 24.576 Mbits/sec QPSK or analog frequency modulation (FM) television.

The propagation package includes a telemetry-modulated 20 GHz beacon (also used for tracking), a 40 GHz beacon phase modulated by a 505 MHz coherent subcarrier, and a polarization-switched (but otherwise unmodulated) 50 GHz beacon. It supports attenuation and depolarization measurements at 20, 40, and 50 GHz, as well as new measurements of phase and amplitude dispersion. The availability of a polarization-switched signal will enable earth stations to characterize fully the matrix depolarization characteristics of the 50 GHz channel.

Commercial Potential

The 20/30 GHz transponders on ITALSAT F1 are experimental; those on F2 will be operational. But the commercial value of 20/30 GHz service is in doubt. Even if the cost of 20/30 earth stations is reduced somewhat, they still won't be cost- competitive with Ku-band. Carriers who are already investing heavily in optical fiber see little reason to invest in what they view as new and untried satellite systems.

In the opinion of the panel's hosts at Alenia Spazio, 20/30 GHz may see very limited use in satellite news gathering applications. But otherwise, the commercial potential is thought to be probably negligible.

Significance

ITALSAT F1 is among the more sophisticated communications satellites now in orbit. It has influenced the design of ARTEMIS, the DRS, the Italian DBS SARIT series, and KOREASAT.


Published: July 1993; WTEC Hyper-Librarian