 |
 |
|
|
|
|
|
|
||||||||||||||||||
|
|
|||||||||||||||||||
|
|
|||||||||||||||||||
|
|||||
|
|
 Previous: In Brief |  Next: Radio Camp: Making Contacts, Making Friends |
By Anthony R. Curtis, K3RXK
Contributing Editor
March 13, 2003
As NASA recovers from the debilitating shuttle Columbia disaster, let's remember how our own Amateur Radio space organization--AMSAT--recovered from its own spacecraft losses.
It was the end of the 1970s and more and more Amateur Radio operators were sharing the fun of talking via satellite when AMSAT began work on a new generation of larger satellites to be known as Phase 3. Until then, hamsats had been categorized as Phase 1 and Phase 2. That meant they flew in north-south polar orbits or low east-west equatorial orbits from 200-1000 miles altitude. By comparison, that's about where a space shuttle usually flies or a bit higher.
These kinds of low-flying hamsats circle the globe, coming within range of a station on the ground every hour or so. The satellite stays overhead only 15 to 30 minutes. Polar-orbit satellites come within range of a ground station about the same time every day. These are Low Earth Orbit (LEO) satellites.
The original Phase 1 satellites had severely limited electrical power and could last only a few weeks. Phase 2 hamsats could work longer and communicate over distances up to 4000 miles.
Heading into the 1980s, AMSAT's vision was of a few larger amateur satellites in long elliptical orbits that would keep them in view of ground stations for hours at a time. They would be more complex and use higher radio frequencies. They would be the so-called Phase 3 hamsats.
Phase 3 satellites could provide communication over longer distances because of their higher altitudes. These high fliers would range out 20,000 to 30,000 miles from Earth, then loop back around the planet, dropping to within 1500 to 2500 miles of Earth's surface every 10 to 12 hours. Such long elliptical tracks were known as Molniya orbits after a class of Russian communications satellites that followed similar paths through space.
Phase 3A
The first of these third-generation satellites--nine years in planning and four years in construction--was built, integrated and tested by hams at Goddard Space Flight Center in Maryland. Radio amateurs in Canada, Hungary, Japan, West Germany and the United States built parts for the spacecraft. It became known as AMSAT Phase 3A.
Phase 3A was to be launched on the second flight of Europe's new Ariane rocket (L-02 23) from a site outside Kourou, French Guiana, on the northeast coast of South America. In a promising preliminary development, the European Space Agency's first Ariane rocket had made a successful flight from Kourou in December 1979.
Unfortunately, when the Phase 3A launch window opened on May 23, 1980, equipment breakdowns and rain in French Guiana forced three hours of launch holds. Finally, a go order was signaled, and the Ariane rocket was fired.
Just three minutes into the flight, as the Ariane was lumbering upward from the South American coastline, the rocket's first stage failed. The Phase 3A hamsat fell into the Atlantic Ocean and was lost (see "Phase III Suffers Watery Fate," QST, Jul 1980).
 Paul Willmott's drawing of AO-10 from the "Unofficial" AMSAT-OSCAR 10 Web page of Stacey Mills, W4SM. Mills is a primary US ground controller for AO-40. |
Phase 3B Becomes AO-10
Undaunted, AMSAT within weeks began work on Phase 3B, which would go to space on June 16, 1983, to become the successful AMSAT-OSCAR 10 (AO-10). Phase 3B was a 200-pound clone of 3A. The new hamsat was built mostly by German amateurs and launched on an Ariane rocket from Kourou.
In another unfortunate turn of events just seconds after dropping AO-10 into orbit, the Ariane bumped it, damaging an antenna on the hamsat and spinning the satellite wildly away. AMSAT had to wait for the satellite to stabilize in space before firing an internal thruster July 11 to change the orbit. In yet another turn of bad luck, that thruster didn't shut off as ordered and blasted 50 percent longer than planned. The thruster malfunction threw the satellite into an exaggerated orbit that took it nearly twice as far away from Earth as planned.
Then, during another kick-motor firing attempt July 26, ground controllers discovered that helium had leaked from the satellite after the Ariane bump, and the fuel valves didn't operate. AO-10 ended up in an uncontrollable orbit ranging from 2390 miles at perigee to 22,126 miles at apogee.
What else could disappoint the eager hams on the ground? The damaged antenna wouldn't work properly. The orbit--farther from Earth than planned--exposed the satellite to more radiation damage. The incorrect attitude kept solar panels from orienting toward the sun, so batteries couldn't charge properly.
There was some good news. AO-10's transponders worked, although the broken antenna and low inclination made the satellite less useful than it might have been. Its signals were weak. Access time was limited. Even so, hundreds of radio amateurs used AO-10 to communicate.
Three years later in 1986, intense subatomic particles trapped in Earth's magnetic field bombarded AO-10's computer memory chips, leaving behind false information. The memory began to turn up mysterious data bits, and the satellite became harder to control.
AO-10's transponders switched off from time to time as voltage dropped when sunlight was low. The satellite required solar illumination 90 percent of the time, but sometimes received it only 50 percent of the time. Then AO-10 would turn itself off and a command station would be required to transmit a reset order.
Phase 3C Becomes AO-13
After the AO-10 launch, the intrepid crew at AMSAT started building a third Phase 3 satellite. Phase 3C was built by an international team of amateurs led by Karl Meinzer, DJ4ZC, of AMSAT-DL (Germany). On June 15, 1988, the new hamsat was blasted into Earth orbit from Kourou on an Ariane vehicle. It became the successful AMSAT-OSCAR 13 (AO-13).
Of course, Amateur Radio satellites are experimental. For instance, ground controllers had trouble commanding AO-13 while the satellite was looking down on North America. Uplink signals were being corrupted by a powerful government radar. Commands had to be forwarded to Australia for transmission to the satellite.
Everything that goes up must come down, of course. All satellites orbiting Earth are pulled slowly by gravity down into the atmosphere where they burn. Some fall more slowly than others. AO-13 remained in orbit and working for eight years. The Phase 3C hamsat burned up when it reentered Earth's atmosphere on December 5, 1996.
AO-10 Lives On
On the brighter side, the older AO-10 remains in a highly stable orbit. That Phase 3B hamsat should stay in Earth orbit for hundreds of years before it reenters the atmosphere. When AO-13 was in orbit and working, AO-10 continued to transmit, but later satellites siphoned away most of its users.
AO-10's orbit ranges from an apogee of 22,079 miles (35,533 km) down to a perigee of 2412 miles (3881 km). Similarly, AO-13's Molniya-style elliptical orbit had brought it down as close as 1500 miles and then pushed it out to 22,000 miles from Earth. Today, AO-10 remains on the air intermittently, using its high-gain antennas to transmit in Mode B at 145.825-145.977 MHz (downlink) and receive at 435.027-435.179 MHz (uplink).
AO-10's batteries are long dead, so AO-10 derives power only from its solar panels. Whenever the hamsat is out of view of the sun, the transponder goes off the air.
 An artist's conception of the Phase 3D (AO-40) spacecraft. To date, the solar panels have not been fully deployed. More AO-40 photos are available on the AMSAT-NA Web site. |
The Phase 3D Saga
Meanwhile, the stout-hearted members of AMSAT kept moving forward. They began developing a fourth model of the third-generation satellites--Phase 3D. It would be the largest and most complex amateur satellite ever flown. The construction and launch project involved hams in Belgium, Finland, Germany, Great Britain, Hungary, South Africa and the US.
After years of planning, development, construction and integration--some of which was spent just waiting for an affordable ride into space--Phase 3D was launched from Kourou on an Ariane 5 rocket on November 16, 2000, to become AMSAT-OSCAR 40 (AO-40). Its high-altitude, elliptical, Molniya orbit ranges from 2485 miles (4000 km) to 29,204 miles (47,000 km).
 Karl Meinzer, DJ4ZC, the Phase 3D Project Leader. |
Immediately after launch, AO-40 seemed to be working properly, although something was wrong with its 70-cm transmitter. The satellite's elliptical orbit needed to be optimized for best communications. On December 13, 2000, as ground controllers tried to maneuver AO-40 in orbit, the satellite unexpectedly went silent.
After a couple of weeks of consternation and efforts to communicate with AO-40 and restart the onboard equipment, there were great sighs of relief in the AMSAT world when the 2401 MHz S-band beacon turned on at ground command on December 25, 2000. The resurrection of AO-40 was viewed as a marvelous Christmas present.
Unfortunately, other systems in the satellite now were either not working at all or not working correctly. Most noticeably, the 2-meter beacon transmitter, which had been heard loud and clear transmitting telemetry in the days right after launch, now appeared to be dead.
AMSAT-NA President Robin Haighton, VE3FRH, said that while the Phase 3D team may never know exactly what happened, the likely scenario includes what Haighton--in an interview with ARRL--called "a minor explosion" aboard AO-40 that apparently damaged or destroyed some systems. Haighton said that the 400 N propulsion motor could have "burped" or "popped' as out-of-place fuel mixed and then ignited as a result of a blocked exhaust port on a helium valve. The problem was attributed to a pre-launch human error.
On May 5, 2001, controllers turned on a transponder for testing, allowing two-way communication for a trial period until May 30. Reports of successful reception and two-way contacts came in from around the world. AO-40 was declared a success.
 The Phase 3D launch from Kourou, French Guiana. AMSAT-DL's Peter Gülzow, DB2OS, headed the Phase 3D launch campaign, since Meinzer was unable to be on site. |
More orbital maneuvering was initiated on June 21, 2001, using the satellite's built-in arcjet. The motor fired for about two hours at each orbit's perigee. Taking stock after firings were finished on June 30, AMSAT noted that AO-40 was in a slightly better orbit, but all of its fuel had been consumed in the process.
AO-40 remains in regular amateur use, with uplinks on U band (70 cm) and L band (1.2 GHz) and downlink and beacon on S band (2.4 GHz). More information is available on the AMSAT-NA Web site.
Life Goes On: Project Eagle
Even as radio amateurs are using AO-40 to experiment with new modes and higher frequencies, AMSAT is looking toward yet another Phase 3 satellite, this one to be called Eagle. The design for Eagle is expected to be revealed by the end of 2003, with construction and integration taking place through 2005. Eagle could be launched into orbit as early as 2006.
What can we learn from two dozen years of such endurance tests? It's important to keep in mind that, despite a variety of glitches and gremlins, all hamsats have been successful experiments in the end because amateurs have learned from each and applied their findings to later models.
Editor's note:
ARRL Life Member Anthony R. Curtis, K3RXK, wrote about OSCAR 6 in the October
2002 issue of QST and VUCC in the
February 2003 issue. Licensed since 1954, he originally was W8TIZ. Now living
in Laurinburg, North Carolina, he is an Extra class licensee and holds a PhD in
mass communication. Curtis has written 72 books about space, astronomy,
computers and electronics and is editor of Space Today Online. Curtis has
served as a Section Emergency Coordinator, emergency net manager and club
president. An ARRL Educational Advisor, Roanoke Division Assistant Director,
NASA Solar System Ambassador and Apple Distinguished Educator, Curtis chairs
the Mass Communication Department at the University of North Carolina-Pembroke.
Readers can contact Curtis via e-mail.
| Previous: In Brief | Next: Radio Camp: Making Contacts, Making Friends |
