OSCAR Satellite Numbers: How Amateur Satellites Get Their Names

If you have started listening to amateur satellites, you have seen a long list of strange names: AO-7, FO-29, CO-57, IO-117, QO-100. They are not random. Each is an OSCAR satellite number, a sequential designation that has been given to amateur radio satellites since the very first one, in 1961. Understanding the system explains why a satellite you know as Fox-1B is also called AO-91, why the numbers are not always in launch order, and what the letters in front of the number say about who built the satellite. This guide explains what OSCAR stands for, who hands out the numbers, how AMSAT and its sister organizations are involved, what the Phase system means, and how to read the mode letters that appear next to the name of a satellite.

What OSCAR Means and Where It Began

OSCAR stands for Orbiting Satellite Carrying Amateur Radio. The designation is assigned by AMSAT, an organization that promotes the development and launch of amateur radio satellites, and because the label is so widely used, amateur satellites are often simply called OSCARs. According to the Wikipedia article on OSCAR, the first amateur satellite, OSCAR 1, was launched on 12 December 1961, barely four years after Sputnik 1. It was built in a special shape and weight so that it could replace a ballast weight on the launch vehicle, and it was the first satellite to be ejected as a secondary payload and then enter a separate orbit. It had no propulsion, and its orbit decayed after only 22 days, yet it was an immediate success: more than 570 radio amateurs in 28 countries sent observations to Project OSCAR.

The idea of a numbered series came naturally from that project. A later satellite, OSCAR 3, carried the first satellite voice transponder, and since 1965 most OSCARs have carried a linear transponder for real-time two-way communication. Others have carried a bulletin board for store-and-forward messages or a digipeater for packet radio. If you are new to these ideas, our guide to getting started with amateur radio satellites covers the equipment and the first steps.

Who Is AMSAT?

AMSAT is a name for several amateur satellite organizations around the world. It most often refers to the Radio Amateur Satellite Corporation, which was formed in the District of Columbia in 1969 as an educational organization to continue the work begun by Project OSCAR. According to the AMSAT website, its goal is to foster the participation of amateur radio in space research and communication, and most of the hardware and software on its satellites is still the product of volunteer effort and donated resources. The organization publishes the AMSAT Journal, a bi-monthly digital magazine for enthusiasts of amateur radio in space.

Its first project, in 1969 and 1970, was to coordinate the launch of OSCAR 5, which was built by students at the University of Melbourne and launched on 30 January 1970. The next, AMSAT-OSCAR 6, followed on 15 October 1972 and served for about four and a half years. AO-7 launched in 1974 with a transponder built by AMSAT Germany, and AO-8 carried a transponder contributed by JAMSAT, the Japanese organization. International cooperation has been a feature of the series from the start, and today many countries have their own AMSAT organization, including AMSAT-DL in Germany, AMSAT-UK in the United Kingdom, AMSAT-I in Italy, JAMSAT in Japan and AMSAT-NL in the Netherlands. The Wikipedia article on AMSAT lists many of them.

How a Satellite Gets Its Number

This is the part that surprises many newcomers. Most amateur satellites do not receive their sequential OSCAR designation until after they are successfully in orbit, and then only at the request of the launching organization. In other words, you cannot read a number from a satellite before it works. The builders give the satellite its own name first, for example Fox-1B, and when it has been launched and is operating, they request a number from AMSAT. That is why you often see two names for the same object: the project name, which is used before launch, and the OSCAR number, which is used afterward.

The numbers follow the order in which designations are issued, which is not always the exact order of the launches, so a satellite that was launched earlier but registered later may have a higher number than one launched afterward. The process also means that satellites that fail before they reach orbit never get a number at all. For the person tracking satellites, the practical lesson is to use the OSCAR designation when you look in a tracking program, and to be aware of the project name when you read news about the launch. Our article on Gpredict satellite tracking shows how the names appear in the software.

The Prefix Letters

A designation has two parts: letters that identify who built or sponsored the satellite, and the sequential number. The first part is usually the name of the organization or country followed by OSCAR, abbreviated to two letters. The following table lists examples that are mentioned in public sources.

In conversation the names are shortened. A satellite called CubeSat-OSCAR 57 becomes CO-57, and Fox-1A, designated AMSAT-OSCAR 85, becomes AO-85. The same satellite may be listed under both names in a tracking program, in a logging program and in a QSL. The odd one out in the history was SuitSat, an obsolete Russian space suit carrying a transmitter, launched in 2006 from the International Space Station. Its name was a joke on the book in which Oscar was the name of a space suit.

Fox, Phase 3 and Other Project Names

Before the sequential number, many satellites carry a project name that describes their design. The Fox series is a good example: AMSAT built a series of 1U CubeSats to carry university experiments and U/V FM repeaters. Fox-1A launched on 8 October 2015 and became AO-85, Fox-1B launched on 18 November 2017 and became AO-91, Fox-1D launched on 12 January 2018 and became AO-92, and Fox-1Cliff launched on 3 December 2018 and became AO-95. Four of them carry FM transponders with an uplink on the 70 centimeter band and a downlink on the 2 meter band, which is why they have been popular with newcomers who own only a dual-band handheld and a small antenna. Earlier big satellites used names such as Phase 3B, which became AO-10, and Phase 3D, which became AO-40.

These names also reveal the generation. The Phase system, which AMSAT uses to describe the capabilities and orbits of its satellites, is the other half of the story.

The Phase System

The AMSAT Phase system describes a satellite by its capabilities, and it roughly follows the history of the hobby. The descriptions below come from public descriptions of the system.

• Phase 1. No solar cells, powered by battery only, short-lived, a technology test bed. It must be able to orbit to be classified as a satellite.
• Phase 2. Long life with solar cells and communications capabilities, in low Earth orbit.
• Phase 3. Long life with more powerful communications, telemetry and command systems, usually in a highly elliptical orbit. Because the satellite stays over one area for long periods, amateurs can make longer contacts.
• Phase 4. A satellite in geostationary orbit. The only amateur radio transponders in such an orbit are a secondary mission aboard Es’hail-2, which AMSAT designated QO-100 on 26 February 2019.
• Phase 5. A spacecraft capable of lunar or planetary missions.

QO-100 is a good example of how the system works in practice. It is a Phase 4 satellite and is covered in detail in our QO-100 geostationary satellite guide. Its narrowband linear transponder uses an uplink of 2400.050 to 2400.300 MHz and a downlink of 10489.550 to 10489.800 MHz, and the wideband digital transponder uses 2401.500 to 2409.500 MHz for the uplink and 10491.000 to 10499.000 MHz for the downlink. Because it stays over one part of the world, it behaves more like a fixed repeater than like a low-orbit satellite.

Reading the Mode Letters

Next to many satellite names you will see a mode, such as U/V or V/U. These are the uplink and downlink band letters. In the current system, a mode is written as X/Y, where X is the uplink band and Y is the downlink band. The letters mostly follow the IEEE radar band designations. The letter V stands for the 2 meter band, U for 70 centimeters, L for 23 centimeters, S for 13 centimeters, C for 5 centimeters, X for 3 centimeters, K for 1.2 centimeters and R for 6 millimeters. H and A stand for 15 meters and 10 meters.

The older system used single letters for both bands, and it is still heard in casual speech: Mode A means a 2 meter uplink and a 10 meter downlink, Mode B a 70 centimeter uplink and a 2 meter downlink, and Mode J a 2 meter uplink and a 70 centimeter downlink. The modern format came after the launch of OSCAR 40. A satellite that uses mode U/V, for example, takes your signal on 70 centimeters and retransmits it on 2 meters. You will also need to correct for Doppler shift: the high orbital speed means that both frequencies change during a pass. For the observing and tracking side, see our article on contacting the International Space Station, which shows the use of a similar uplink and downlink scheme.

Using the Numbers in Practice

Knowing the designations is useful in several ways. First, they make searching easier. A tracking program, a satellite status page or a club newsletter will all list satellites by their OSCAR numbers, and a name like AO-91 is shorter and less ambiguous than Fox-1B or RadFxSat. Second, they help you to keep a log: when you confirm a contact, you can record the satellite by its designation and, for awards, you can count the number of different OSCARs worked. Third, they help you to judge the age and design of a satellite. A number in the single digits is an old satellite, from the 1970s, while a number in the 80s or 90s is a CubeSat from the last decade. Finally, the numbers allow you to follow the work of an organization, since AMSAT-DL, JAMSAT, AMSAT-UK and others use the same system.

Remember that the operating status of satellites changes. Some in the lists are semi-operational, some are non-operational, and some have re-entered the atmosphere. A list on a website is only a snapshot, and for current information you should visit the AMSAT status pages or listen for a few minutes during a pass. Do not rely on a printed table or an old article for operational use. The same caution applies to the frequencies, which can change when a satellite is reconfigured.

The Bottom Line

An OSCAR satellite number is a simple but useful label: a pair of letters that says who built the satellite, followed by a sequential number that AMSAT assigns after the satellite has reached orbit and its builders have asked for it. The system began in 1961 with OSCAR 1, was carried on by AMSAT from 1969, and now covers CubeSats, geostationary transponders and satellites from many countries. Learn the prefixes, the Phase system and the mode letters, and a list of satellite names will turn into a readable map of the history and the technology of amateur space radio.

Frequently Asked Questions

What does OSCAR stand for?

Orbiting Satellite Carrying Amateur Radio. The first satellite of the series, OSCAR 1, was launched on 12 December 1961.

Who assigns OSCAR numbers?

AMSAT assigns the designation, usually after a satellite has reached orbit and its builders have asked for a number.

Why does one satellite have two names?

The builders give it a project name before launch, such as Fox-1B, and receive an OSCAR number afterward, such as AO-91. Both names are used.

What do AO, FO and CO mean?

AO means AMSAT-OSCAR, FO means Fuji-OSCAR from Japan, and CO means CubeSat-OSCAR. Other prefixes show the country or organization, such as IO for Italy and PO for the Philippines.

What is the Phase system?

A classification of AMSAT satellites by capability and orbit, from Phase 1 test beds to Phase 5 lunar or planetary missions. Phase 4 is geostationary, as with QO-100.

What does mode U/V mean?

The uplink is on 70 centimeters (U) and the downlink is on 2 meters (V). The first letter is the uplink band and the second is the downlink band.