An amateur radio satellite is an artificial satellite built and used by amateur radio operators. It forms part of the Amateur-satellite service.ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.57, definition: amateur-satellite service / amateur-satellite radiocommunication service These satellites use amateur radio frequency allocations to facilitate communication between amateur radio stations.
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 free of charge by licensed amateur radio operators for voice (FM, SSB) and data (AX.25, packet radio, APRS) communications. Currently, over 18 fully operational amateur radio satellites are in orbit. They may be designed to act as repeaters, as linear transponders, and as store and forward digital relays.
Amateur radio satellites have helped advance the science of satellite communications. Contributions include the launch of the first satellite voice transponder (OSCAR 3) and the development of highly advanced digital "store-and-forward" messaging transponder techniques.
The Amateur Radio Satellite community is very active in building satellites and in finding launch opportunities. Lists of functioning satellites need updating regularly, as new satellites are launched and older ones fail. Current information is published by AMSAT. AMSAT has not been actively involved in the launch and operation of most amateur satellites in the last two decades beyond allocating an OSCAR number.
History OSCAR 1
The first amateur satellite, simply named OSCAR 1, was launched on December 12, 1961, barely four years after the launch of the world's first satellite, Sputnik I. The satellite had to be built in a very specific shape and weight, so it could be used in place of one of the launch vehicle ballast weights. OSCAR 1 was the first satellite to be ejected as a secondary payload (the primary payload was Discoverer 36) and to subsequently enter a separate orbit. It carried no on-board propulsion and its orbit decayed quickly. Despite orbiting for only 22 days, OSCAR 1 was an immediate success and led to follow-on missions. Over 570 amateur radio operators in 28 countries forwarded observations to Project OSCAR.
OSCAR 10 Most of the components for OSCAR 10 were "off the shelf". 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 a couple of times to evaluate its performance and reliability. Special QSL cards were issued to those who participated in the airplane-based tests. Once it was found to be operative and reliable, the satellite was shipped to Kennedy Space Center, where it was mounted in the launch vehicle's third stage. OSCAR 10's dimensions were: Height: 1.35 m (53 in) Width: 2.0 m (78.75 in) Weight: 140 kg at launch; 90 kg post engine firings.
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).
Es’hail 2 / QO-100 Launched November 15, 2018.In geostationary orbit covering Brazil to Thailand.
Narrowband Linear transponder
2400.050 - 2400.300 MHz Uplink
10489.550 - 10489.800 MHz Downlink
Wideband digital transponder
2401.500 - 2409.500 MHz Uplink
10491.000 - 10499.000 MHz Downlink
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.
Operations
Satellite communications Currently, amateur satellites support many different types of operation, including FM voice and 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:Standard Radar Frequency Letter-Band Nomenclature (IEEE Standard 521-1984, IEEE Std 521-2002(R2009))
{|class="wikitable" |- !Designator
!Band |15 m |10 m |2 m |70 cm |23 cm |13 cm |9 cm |5 cm |3 cm |1.2 cm |6 mm |- !Frequency(General) |21 MHz |29 MHz |145 MHz |435 MHz |1.2 GHz |2.4 GHz |3.4 GHz |5 GHz |10 GHz |24 GHz |47 GHz
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.
Mode A: 2 m uplink / 10 m downlink Mode B: 70 cm uplink / 2 m downlink Mode J: 2 m uplink / 70 cm downlink
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. Hence, the receiver frequency at the ground station must be adjusted higher 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 to be received by the satellite. After the satellite passes overhead and begins to move away, this process is reversed. 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: = doppler corrected downlink frequency = doppler corrected uplink frequency = original frequency = velocity of the satellite relative to ground station in m/s.Positive when moving towards, negative when moving away. = the speed of light in a vacuum ( m/s).
Change in frequencyDownlink CorrectionUplink Correction
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 satellites
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 commonly available amateur radio equipment. Communication can be achieved with handheld transceivers using manual doppler correction. Satellite passes are typically less than 15 minutes long.
Launches 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 (or never successfully left it). The country listing denotes the country that constructed the satellite and not the launching country.