AMSAT-NA has announced it’s revamping the design of its high-Earth orbit (HEO) Project Eagle satellite, currently in the development stages http://www.amsat.org/amsat-new/eagle/ The next generation satellite will take maximum advantage of software-defined transponder (SDX) technology to offer a broader range of easily accessible Amateur Radio payloads. The AMSAT Board of Directors okayed the Eagle upgrade plans during the 2006 AMSAT-NA Space Symposium and Annual Meeting held October 6-8 in San Francisco. Eagle Project Manager Jim Sanford, WB4GCS, outlined the changes at his Space Symposium forum October 7.
“The structure which we have been presenting for several years is not going to meet our mission needs,” Sanford explained. “We have moved on to a later structure.”
Under the new plan, Sanford says, Eagle’s communications payloads will include a mode U/V linear transponder for SSB, CW and other modes. A second SSB/CW transponder will uplink on L band (1.2 GHz) and downlink on S1 band (2.4 GHz). Both would be usable over 75 percent of the satellite’s orbit by an AO-13 or AO-40-capable ground station, AMSAT says.
Something new to Amateur Radio satellites is a planned low-rate text messaging system similar to cellular telephone SMS. Sanford said the text-messaging capability may prove valuable for providing emergency and disaster communication. It will operate in mode U/V and also will be available to modest ground stations over 75 percent of Eagle’s orbit.
Eagle will also carry an advanced communications payload (ACP). The ACP will accommodate voice communication using an S2 band (3.4 GHz) uplink and a C band (5.8 GHz) downlink via a single 60 cm dish on the ground. As an alternative — for stations in those parts of the world where 3.4 GHz is unavailable — Eagle will provide an additional L band uplink.
The ACP also will offer high data rate communication including the possibility of full-motion compressed video in S2/C mode. The same mode also could support an Internet link. Ground-station antennas for Eagle may even pass muster in neighborhoods governed by private deed covenants, conditions and restrictions (CC&Rs), Sanford suggested.
During a presentation on the ACP, Matt Ettus, N2MJI, said one of the goals of the package is to open up the satellite to a new base of users, not just restrict it to elite satellite operators and sophisticated ground stations. Embracing SDR technology simplifies signal handling, he explained, because going digital is just a matter of transmitting bits up and down.
“The satellite doesn’t really care what the bits mean,” he said. The satellite “just reflects bits,” and most policy-type issues will be handled by ground stations.
The satellite’s signal will present one wideband downlink containing multiplexed data. “There will be room for many, many carriers in the passband,” Ettus predicted. The mix of users would be apportioned among both low and high-rate modes, depending on overall traffic.
Plans call for electronically steering the satellite’s antennas to mitigate the effects of the spacecraft’s spin and maximize the spacecraft’s accessibility. In a subsequent forum, AMSAT board member and well-known satellite expert Tom Clark, K3IO (ex-W3IWI) discussed some of the mathematics and physics that would permit steering a 37-element S band antenna array on Eagle.
“We would intentionally steer that pattern, so the array is always pointing toward Earth,” Clark said, regardless of spin factor. He described a system of interferometers to do the pointing on the basis of “master beacon signals” uplinked from different points on Earth’s surface. “It [Eagle] will measure where they are and know where to point the beam,” he explained.
In a presentation on applying SDR techniques to satellite transponders, Howard Long, G6LVB, described and demonstrated a prototype SDX board. “This is the holy grail of what we’ve been trying to do,” he told his audience. Long showed how his hand-soldered SDX could be configured to accommodate various signal strengths and types within the same passband and even to easily notch interfering signals quickly and flawlessly.
Sanford concluded his presentation by saying it’s time to take the AMSAT board’s concrete decisions and plan, schedule and build Eagle. “We’re about to start spending some serous money,” he said. During a later question-and-answer session, Sanford stressed that reliability of the ultimate Eagle satellite is a key goal. “I want no single-failure mission kills on this satellite,” he said.
Project Eagle still needs to raise $33,500 by December. Eagle could launch by 2010. The whole project will cost some $600,000.
During the AMSAT-NA annual meeting October 8, President Rick Hambly, W2GPS, expressed his enthusiasm for Project Eagle. “I think it will be the greatest thing we’ve ever done!” he said. The 2007 AMSAT Symposium and Annual Meeting will take place in Pittsburgh.