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Early OSCAR satellites
The first amateur satellite simply named OSCAR-1 , was launched on December 12, 1961, barely four years after the launch of world's first satellite, Sputnik. OSCAR-1 was the very first satellite to be ejected as a secondary payload and subsequently enter a separate orbit. Despite being in orbit only 22 days OSCAR-1 was an immediate success with over 570 amateur radio operators in 28 countries forwarding observations to Project OSCAR. Throughout the years OSCAR satellites have helped make significant breakthroughs in the science of satellite communications. A few advancements include the launch of the very first satellite voice transponders and the development of highly advanced digital "store-and-forward" messaging transponder techniques. To-date over 70 OSCAR's have been launched with more to be launched in the near future.
OSCAR satellite communications
Currently OSCAR satellites support many different types of operation including FM voice, SSB voice, as well as digital communications of AX.25 FSK (Packet radio) and PSK-31.
Mode designators
- Historically OSCAR uplink (transmit to) and downlink (receive from) frequencies were designated using single letter codes.
- New uplink and downlink designations use sets of paired letters following the structure X/Y where X is the uplink band and Y is the downlink band.
Doppler shift
Due to the high orbital speed of OSCAR satellites, the uplink and downlink frequencies will vary during the course of a satellite pass. This phenomenon is known as the Doppler effect. While the satellite is moving towards the ground station, the downlink frequency will appear to be higher than normal and therefore, the receiver frequency at the ground station must be adjusted higher in order to continue receiving the satellite. The satellite in turn, will be receiving the uplink signal at a higher frequency than normal so the ground station's transmitted uplink frequency must be lower in order to be received by the satellite. After the satellite passes overhead and begins to move away, this process reverses itself. The downlink frequency will appear lower and the uplink frequency will need to be adjusted higher. The following mathematical formulas relate the doppler shift to the velocity of the satellite.
| Where: | ||
|---|---|---|
| fd | = | doppler corrected downlink frequency |
| fu | = | doppler corrected uplink frequency |
| f | = | original frequency |
| v | = | velocity of the satellite relative to ground station in m/s. Positive when moving towards, negative when moving away. |
| C | = | the speed of light in a vacuum (3x108 m/s). |
| Change in frequency | Downlink Correction | Uplink Correction |
|---|---|---|
 |
 |
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Due to the complexity of finding the relative velocity of the satellite and the speed with which these corrections must be made, these calculations are normally accomplished using satellite tracking software. Many modern transceivers include a computer interface that allows for automatic doppler correction. Manual doppler correction is possible, however it is difficult to remain exactly on frequency. FM is more tolerant of doppler shift than SSB and therefore much easier to tune manually.
Satellites previously launched
The names of the satellites below are sorted in chronological order by launch date, acsending. The status column denotes the current operational status of the satellite. Green signifies that the satellite is currently operational, orange indicates that the satellite is partially operational or failing. Red indicates that the satellite is non operational and black indicates that the satellite has re-entered the earth's atmosphere. The country listing denotes the country that constructed the satellite and not the launching country.
Multinational effort
Currently 22 countries have launched an OSCAR satellite. These countries, in chronological order by date of launch, include: The United States of America, Australia, Spain, the United Kingdom, Japan, Brazil, Argentina, Russia, France, Portugal, Korea, Italy, Mexico, Israel, Thailand, South Africa, Malaysia, Saudi Arabia, Germany, India, Colombia, and the Netherlands.
Satellites in development
- BLUEsat - A microsatellite built by the students of The University of New South Wales. Unknown launch date.
- Prism - A nanosatellite built by the University of Tokyo. Unknown launch date.
- ZSAT - A microsatellite initiated and funded by the U.S. Department of Science and Technology. Unknown launch date.
- ALMASat - A microsatellite built by the University of Bologna in Forlì. Unknown launch date.
- AMSAT-Phase 3E - A satellite built by AMSAT. Scheduled to launch on March 12 2007
- KiwiSAT - A microsatellite built by AMSAT-ZL. Scheduled to launch on June 15 2008
- ESEO - A microsatellite built by SSETI. Scheduled to launch October 30 2008.
- AMSAT-Eagle - A satellite built by AMSAT. Scheduled to launch March 1 2009.
- Delfi-n3Xt - The second nano-satellite from Delft University of Technology. Scheduled to launch in the second half of 2010.
Trivia
SuitSat, an obsolete Russian space suit with a transmitter aboard, is officially known as OSCAR 54. In a twist of fate, "Oscar" was the name given to an obsolete space suit by its young owner in the book "Have Space Suit, Will Travel," by Robert A Heinlein. This book was originally published a year after the launch of the first artificial satellite (Sputnik).
References
- "Space Satellites from the World's Garage -- The Story of AMSAT". The Radio Amateur Satellite Corporation. Retrieved on 2006-09-05.
- "The Extraordinary History of Amateur Radio Satellites". Space Today Online. Retrieved on 2006-09-05.
- "A Brief History of Amateur Satellites". N7HPR. Retrieved on 2006-09-05.
- "Satellite Development Programs". The Radio Amateur Satellite Corporation. Retrieved on 2006-09-05.
- "Amateur (ham) Radio Satellites". Colorado State University. Retrieved on 2006-09-07.
External links
- AMSAT Corporation a nonprofit corporation that coordinates construction and launch of the satellites
- Project OSCAR organization that built "OSCAR-1"
- NASA J-Track Amateur Track amateur satellites in real-time
- SSTL Builders and operators of the UoSat series satellites
