 | ||
An amateur radio satellite is an artificial satellite built and used by amateur radio operators for use in the Amateur-satellite service. These satellites use amateur radio frequency allocations to facilitate communication between amateur radio stations.
Contents
- OSCAR 1
- OSCAR 10
- Other satellites
- Hardware
- Orbits
- Satellite communications
- Mode designators
- Doppler shift
- FM LEOs
- Past launches
- In development
- Multinational effort
- Related names
- References
Many amateur-satellites receive an OSCAR designation, which is an acronym for Orbiting Satellite Carrying Amateur Radio. The designation is assigned by AMSAT, an organization which promotes the development and launch of amateur radio satellites. Because of the prevalence of this designation, amateur radio satellites are often referred to as OSCARs.
These satellites can be used for free by licensed amateur radio operators for voice (FM, SSB) and data communications (AX.25, packet radio, APRS). Currently, over 5 fully operational amateur-satellites in orbit act as repeaters, linear transponders or store and forward digital relays.
Throughout the years, amateur-satellites have helped make breakthroughs in the science of satellite communications. A few advancements include the launch of the first satellite voice transponder (OSCAR 3) and the development of highly advanced digital "store-and-forward" messaging transponder techniques.
OSCAR 1
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 I. The beginning of this project was very humble. The satellite had to be built in a very specific shape and weight, so it could be used in place of one of the weights necessary for balancing the payload in the rocket stage. OSCAR 1 was the first satellite to be ejected as a secondary payload (with Discoverer 36 as the primary) and subsequently enter a separate orbit. The satellite carried no on-board propulsion and the orbit decayed quickly. Despite being in orbit for only 22 days, OSCAR 1 was an immediate success with over 570 amateur radio operators in 28 countries forwarding observations to Project OSCAR.
OSCAR 10
Most of the components for OSCAR 10 were "off the shelf" and tested by group members. Jan King led the project. Solar cells were bought in batches of 10 or 20 from Radio Shack and tested for efficiency by group members. The most efficient cells were kept for the project, the rest were returned to RadioShack. Once ready, OSCAR 10 was mounted aboard a private plane and flown on a couple of occasions to evaluate its performance and reliability. Special QSL cards were issued to those who participated in the airplane based flights. Once it was found to be operative and reliable, the satellite was shipped to Kennedy Space Center where it was mounted in the third stage of the launch vehicle.
Other satellites
Other programs besides OSCAR have included Iskra (Soviet Union) circa 1982, JAS-1 (Fuji-OSCAR 12) (Japan) in 1986, RS (Soviet Union and Russia), and CubeSats. (There is a list of major amateur satellites in Japanese Wikipedia).
Hardware
The first amateur satellites contained telemetry beacons. Since 1965, most OSCARs carry a linear transponder for two-way communications in real time. Some satellites have a bulletin board for store-and-forward digital communications, or a digipeater for direct packet radio connections.
Orbits
Amateur satellites have been launched into low Earth orbits and into highly elliptical orbits.
Satellite communications
Currently amateur-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
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. Occasionally, the downlink letter is rendered in lower case (i.e., X/y). With a few exceptions, the letters correspond to IEEE's standard for radar frequency letter bands
Prior to the launch of OSCAR 40, operating modes were designated using single letters to indicate both uplink and downlink bands. While deprecated, these older mode designations are still widely used in casual conversation.
Doppler shift
Due to the high orbital speed of the amateur-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.
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 effect correction. Manual frequency-shift correction is possible, but it is difficult to remain precisely near the frequency. Frequency modulation is more tolerant of doppler shifts than single-sideband, and therefore FM is much easier to tune manually.
FM LEOs
A number of low earth orbit (LEO) OSCAR satellites use frequency modulation (FM). These are also commonly referred to as "FM LEOs" or the "FM Birds". Such satellites act as FM amateur radio repeaters that can be communicated through using omni-directional antennas and commonly available amateur radio equipment. Due to the relative ease of tuning FM as compared to SSB and the decreased distance of LEO satellites from earth stations communication can be achieved even with handheld transceivers and using manual doppler correction. The orbit of these satellites however causes the available time in which to communicate to be limited to only a few minutes per pass.
Past launches
The names of the satellites below are sorted in chronological order by launch date, ascending. 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.
In development
Multinational effort
Currently, 23 countries have launched an OSCAR satellite. These countries, in chronological order by date of launch, include: The
Related names
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).