Site: Alenia Spazio S.p.A.
Via Saccomuro, 24
Date Visited: June 25, 1992
Report Author: C. Bostian
Alenia Spazio (and its predecessor companies) was the prime contractor for SIRIO 1, SIRIO 2, and ITALSAT F1 and is the prime contractor for ITALSAT F2 and the Advanced Relay and Technology Mission Satellite (ARTEMIS). The company describes its areas of interest as (a) telecommunications, (b) manned and unmanned space infrastructure, (c) remote sensing, (d) scientific satellites, (e) transport, launch and retrieval systems, and (f) fixed and mobile ground stations. It employs 2,860 people in 14 plants.
Alenia has an excellent reputation as a leader in antenna design and construction, and the corporate commitment to these activities is impressive. About 50 people work on antennas in Alenia itself plus perhaps 20 others in companies that it owns or controls. Alenia also cooperates with antenna groups at Turin University and at CSELT. In our hosts' words, "Investing in antenna technology always pays. This is a very crucial technology."
Much of the discussion with Alenia involved the ARTEMIS spacecraft. This is still in a state of flux, apparently because of problems with the Semiconductor Intersatellite Link Experiment (SILEX) optical payload. As the cost of SILEX has risen significantly, the money available for the rest of the program has declined proportionally. Simultaneously there has been a serious decrease in SILEX's expected performance. The design for ARTEMIS is to be frozen by the end of 1992.
Alenia was exceptionally well prepared for the site visit. Mr. Perrotta had studied our questions in detail, and he had a large amount of written material ready. His knowledge of the company and its programs was encyclopedic. He also mailed a large quantity of information to us.
The EMS package on ITALSAT F2 will be a precursor to the ARTEMIS Mobile Package. It will replace the 40/50 GHz propagation package carried by ITALSAT F1. A 1994 launch is expected. (Most of the other packages on ITALSAT F2 will be duplicates of their counterparts on F1.) Much of the ARTEMIS EMS L-band package will differ only slightly from that carried by ITALSAT F2, and the ARTEMIS payload can emulate the F2 package, thus providing in-orbit backup for European mobile services.
Nevertheless there may be some significant differences between the F2 and ARTEMIS EMS antennas. F2 will provide a single, 46 dBW EIRP fixed beam that covers Europe, part of Russia, and North Africa. ARTEMIS may use an inflatable antenna offering three or four beams (the original plans called for five) and an EIRP in the 48-49 dBW range.
All of the hardware for the ARTEMIS mobile package is under construction except for the antenna reflector. Breadboards exist for most of the electronic subsystems, the antenna feed, and BFN. A design review is scheduled soon on these breadboard and engineering models.
But nothing is firm on the final reflector design. MBB originally proposed a fairly large mesh reflector but then withdrew it. Recently there has been discussion about flying an inflatable reflector. This came close to an engineering model, but it wasn't built. The final reflector design may very well be rigid, although some options (or requirements) could require a folding reflector. An important factor in the final decision will be the kind of shroud to be used and how much space is available for the reflector.
Alenia Spazio was asked if the Inmarsat III P2 system is as advanced as ARTEMIS. Their answer was "Probably more so." Apparently a more sophisticated ARTEMIS EMS payload using digital techniques was proposed some years ago, but ESA did not accept it.
As to what had been the biggest technological challenge of the EMS payload, our hosts felt that the payload itself hasn't been that much of a problem. The real challenge is in deciding what kind of services will be offered to the users.
ARTEMIS was originally intended to provide S-band crosslinks to multiple low earth orbit satellites (LEOSATs) using phased array technology. The hardware to do this was called the S-band Multiple Access Data Relay Payload. Currently, the ARTEMIS spacecraft has been scaled down to implement only one single S-band access in the two directions (i.e., it will be capable of talking with only one LEOSAT at a time), using a mechanically steered reflector. The latter will also be used to perform Ka-band crosslink experiments, time sharing with the S-band access.
The S-band Multiple Access Data Relay Payload will be implemented, instead, on the Data Relay Satellite (DRS). This payload has also been scaled down from the original concept, calling for four simultaneous accesses on receive and two on transmit. The current design, in fact, will implement only two simultaneous accesses on receive (LEOSATs to DRS) and only one on transmit (DRS to LEOSAT). The payload implements separate transmit and receive active phased arrays: the current receive array design incorporates 64 microstrip patch elements. Alenia already has the MMICs for it and the BFN, whose modular design can be easily adapted to control more than two beams. With the S-band multiple access payload, the DRS will be able to talk to any LEO carrying a standard ESA TT&C package.
Our hosts were asked why the original design included separate arrays for transmitting and receiving. There were problems with interference, intermodulation, and the general complexity of trying to build a single array for receiving and transmitting. These problems are exacerbated by the relatively close spacing of the transmit and receive frequencies. The IMD requirements for the array MMICs are severe. Levels of 150 to 160 dB below the carrier are required to keep passive intermodulation (PIM) products at or below the thermal noise level.
Examples of the receive array hardware were passed around in the meeting. They consisted of modules that include power splitters and combiners and phase shifters. There are apparently four phase shifters in each module, each built up by high pass/low pass complementary filters -- basically lumped constant delay lines. The control chips are CMOS. The electrical design was done jointly by Alenia and Plessey. The computer-aided design (CAD) tool was "Touchstone" running on a Sun workstation.
Alenia has developed a Ku-band MMIC for TV receive only (TVRO) applications and apparently is using it in some other VSATs. All of their MMICs use MOSFETs. They are using some discrete HEMTs mainly for LNAs, not MMICs. Their goal is to develop MMICs that will develop outputs in the one to five watt range; present results are in the 0.1 to 1 W range.
Alenia is studying small satellites intensely. Most of this work is done for them by a small company (10-12 engineers) called Italspazio which they own. Alenia's interest in small satellites is related to the total mass of the procurement; they would go after jobs that involved making a large number of very small satellites or a small number of larger satellites. The spacecraft size itself doesn't necessarily determine their degree of interest, and they probably would bid any jobs involving satellites with masses of 200 kg and above.
According to our hosts, ESA's minisat program has a low priority in ESA's mind and could even be deleted from the budget. Part of the reason is that the first response from industry showed little interest; now most companies have people looking closely at small satellites. ESA will probably wait for a large company to propose a minisat project and become the driver for it.
Alenia proposed an adaptive uplink power control (UPC) system with about a 3 dB dynamic range for the ITALSAT 20/30 GHz links. This was not accepted by the Italian Space Agency and thus not implemented. The company is continuing to look at UPC for earth stations, but the problem has gotten much simpler since the last WARC authorized beacons at the uplink frequency.
The 20/30 GHz transponders on ITALSAT F1 are experimental; those on F2 will be operational. But the commercial value of 20/30 GHz is questionable. Alenia hopes that operation in the 20/30 GHz bands will attract the attention of its customers, but it may be too late since optical fiber terrestrial links are now available. The carriers don't see why they should invest in big new untried satellite systems when they are already spending heavily for fiber. In our host's opinion, 20/30 GHz may see some very limited use in satellite news gathering applications (SNGA). Otherwise the commercial potential is probably nil. Even if the price of 20/30 GHz earth stations goes down a little, they still won't be cost competitive with Ku-band.
When asked if ITALSAT F3 will carry the last 20/30 payload, our host thought probably not (see also material about proposed ITALSAT F3 in Telespazio site report); there might be some residual activity.
Alenia has developed Ka-band ground terminals; six have been delivered to the ITALSAT traffic stations. It is also providing 40/50 GHz propagation data collection terminals for about eight sites.
DRS will be the next ESA satellite for Alenia after ARTEMIS, but its scope is not yet fully defined. For example, if the SILEX experiment on ARTEMIS performs well, DRS will carry an optical communications payload.
Alenia is developing an antenna positioning module (APM) for DRS. DRS's Ka-band antennas must be able to scan across the earth (approximately 17 degrees from GEO) in 120 seconds. On most satellites this is done by moving the feeds, but that approach is not satisfactory for DRS because it would degrade antenna patterns unacceptably. Instead DRS must scan both antennas mechanically; moving two large antennas at such high rates will create unacceptable changes in spacecraft momentum if it not done cleverly.
The Alenia APM uses mounts (for each antenna) with two degrees of freedom for rotating the antenna about the feed, which is kept fixed to the spacecraft body. This configuration avoids rotary joints, present in former configuration studies, but which posed reliability and life problems. As regards alternative solutions, our hosts stated that they have looked at several possible beam waveguide approaches to eliminate or simplify the rotary joints, but selected the fixed feed/mechanically scanned reflector approach based on performance. Nevertheless, moving both reflectors about the feed focus will create large momenta which must be compensated for, or absorbed, by the Attitude Control System reaction wheels. At present, studies are underway to reduce requirements (e.g., for antenna repointing slew rates).
Alenia has developed a C-band reconfigurable feed system for INTELSAT applications that employs variable power dividers. It allows the spacecraft to adjust its footprint to compensate for changes in orbital position but is not a system for rapid feed reconfiguration.
Alenia has also worked on reconfigurable Ku-band antennas under INTELSAT sponsorship (INTELSAT contract IS-717). The system developed achieves continuous reconfigurability through variable power dividers (VPDs) and variable phase shifters (VPSs). It achieves 100 MHz of bandwidth and can cover the entire Ku-band. Pictures of the hardware were displayed and a sample provided for inspection.
Alenia has developed a multibeam Ku-band antenna for space whose main reflector is 3.7 m in diameter and has hinged tips. The feed uses a 1 m diameter dichroic subreflector. The subreflector is Kevlar and the main reflector is made of carbon fibers. The 20 GHz BFN was inspected; it was very complex and manufactured by electro-erosion. The antenna system is fully space-qualified and gives "very good performance."
For Italian military satellite communications applications, Alenia has developed a 20/44 GHz space antenna using a flat dichroic reflector. It is one of the first dichroic antennas made for 44 GHz. The antenna uses a cluster of rectangular feed horns and provides a "fully controlled" shaped beam with Italian domestic coverage.
For remote sensing, Alenia is designing a multifrequency radiometer antenna for operation at 6.8, 10.5, 18.7, 23.8, 36.5, and 90 GHz using a multiple feed cluster and a 1.5 m reflector. Although it was intended to have the same pattern at all the frequencies, this was not achieved. The antenna was developed under ESA sponsorship, but it may fly on a U.S. platform in the 1995-1996 time frame.
Alenia's antenna R&D program spans the frequency range from about 400 MHz to 90 GHz. At X-band, the company is developing an active phased array for synthetic aperture radar (SAR) applications that should fly in 1994-95 as part of the SIR-C program. The company plans to extend this work toward large arrays (10 m) for other X-band EOS applications, and it is currently seeking financing for this project. Alenia is also active at Ku- and C-bands, although that work concentrates on feeds and reflectors rather than phased arrays.
The DRS antennas described above are for a 27.5 GHz ISL. Alenia is also looking at optical links for this mission. The 27.5 GHz system will provide four 150 Mbits/sec channels. The French originally proposed a 700 Mbits/sec optical link, but this has since been reduced to 50 Mbits/sec. Problems with the optical system include beam wandering and acoustic noise. Thus a microwave system could have superior performance than the optical ISL. DRS must have an ISL which works; whether or not it is optical will depend on the performance of SILEX on ARTEMIS.
ITALSAT F1 has satellite-switched time division multiple access (SS-TDMA) with on-board regeneration. Reconfiguration is by ground command; the satellite is not autonomous. This and the INTELSAT VI SS-TDMA system are the only such systems flying, and thus it clearly is at the state of the art.
Alenia Spazio excels in antenna technology. All of the company's payload components are quite good, and it has had considerable success as a prime contractor for spacecraft. Its R&D efforts are most impressive.