Retrotechtacular: The OSCAR 7 Satellite Died And Was Reborn 20 Years Later

If I were to ask you what is the oldest man-made orbiting satellite still in use, I’d expect to hear a variety of answers. Space geeks might mention the passive radar calibration spheres, or possibly one of the early weather satellites. But what about the oldest communication satellite still in use?

The answer is a complicated one. Oscar 7 is an amateur radio satellite launched on November 5th 1974, carrying two transponders and four beacons, all of which operate on bands available to amateur radio operators. Nearly 45 years later it still provides radio amateurs with contacts just as it did in the 1970s. But this bird’s history is anything but ordinary. It’s the satellite that came back from the dead after being thought lost forever. And just as it was fading from view it played an unexpected role in the resistance to the communist government in Poland.

Built to Last Just 3 Years

OSCAR 7 being prepared for a pre-launch vibration test. (AMSAT)
OSCAR 7 being prepared for a pre-launch vibration test. (AMSAT)

Upon its launch, OSCAR 7 had a designated lifespan of three years. That’s not unusual, these estimates tend towards the conservative and happily it continued operating beyond that timespan.

During its original life it achieved several firsts for an amateur radio satellite, including the first amateur inter-satellite relay between it and OSCAR 6. Eventually in June 1981 it suffered an intermittent failure and was abandoned by the amateur radio community, its beacons and two transponders considered silent forever just as those of previous OSCAR craft had been.

All was not however lost, because in July 2002 it was heard once more by [G4CUO] in the United Kingdom. It had achieved the impossible and returned from the dead, and before too long the amateur radio community was using it again for contacts.

A Very, Very Dead Battery

The resurrected OSCAR 7 could only operate when bathed in sunlight. The design included batteries to cover a full orbit, which almost 30 years after launch were obviously no longer operational. It is thought that the battery pack caused the original failure of the satellite, when it developed a short which drained the craft’s power supply. After two decades as little more than space junk, the battery further degraded to the point that it became an open circuit. With the fault effectively removed from the system, the transponders could receive power directly from the solar panels as long as the sun could reach them.

OSCAR 7 had sprung back to life, and I remember the surprise in the community at the time. By then there was no shortage of other satellites, but the return of a long-dead satellite was definitely something of a special event.

The Polish Communist leaderWojciech Jaruzelski announcing the introduction of martial law. Warsaw, on the 13th of December1981 [Public Domain]
The Polish Communist leader Wojciech Jaruzelski announcing the introduction of martial law. Warsaw, on the 13th of December1981 [Public Domain]
So the amateur radio community built a satellite, lost it, and through something of a miracle regained it. It’s a feel-good story, but it’s not the whole story of OSCAR 7.

When those batteries failed back in 1981 the satellite didn’t go out like a light, but continued to operate intermittently. While radio amateurs moved onto newer craft, people deprived of unrestricted communication options jumped at the opportunity to use an unattended satellite — even one that was faulty. The Solidarity movement in Poland was restricted by a Government clampdown on communications and used the satellite to relay messages internationally and between Polish cities (Polish language, Google Translate link.) to aid in coordinating their activities.

The highly directional nature of the antennas required to access an amateur radio satellite made them extremely difficult for the authorities to detect. OSCAR 7 presented the unthinkable: a relatively secure satellite communication system at no cost.

So if you ever ask yourself why amateur radio is relevant or if it’s still pushing the boundaries, think of OSCAR 7. One of the oldest spacecraft still in use, and one which played its own part in world history. Best of all, for the effort of getting an amateur radio licence, you can use it yourself.

35 thoughts on “Retrotechtacular: The OSCAR 7 Satellite Died And Was Reborn 20 Years Later

      1. Yes, for space missions especially, the phrase means “highly unlikely to fail during the core mission duration”. It’s very common for space hardware to last large multiples of the base mission duration.

        Although, the earlier missions weren’t “planned to last x years”. Instead, it was more like “We built this thing to fulfill the mission requirements, and after analyzing what we built, the statistical likelihood of any mission-critical component failing begins to exceed 5% at around M+3 years.”

        Opportunity had a 90-sol planned mission duration. It was expected to function for longer than that, but it survived to function for 57 times its minimum-design-lfiespan.

        Commercial planned-lifetime/designed obsolescence factors are mainly a factor of trimming the costs.

        If you’re buying a new car that you will probably replace within 10 years, having up to 5% of them fail by the 7 year mark is acceptable (won’t dramatically impact consumer opinion). And most consumers would rather suffer a 5% failure rate at 7 years rather than paying the (usually significant) increased cost for building the car to last 20 years.

        Due to the extremely high cost of any space mission (cheapER isn’t *cheap*, after all), cost-to-build isn’t the major driver. Cost-to-replace is dominated by costs other than the device itself, and indeed, many space devices actually have multiple redundant copies built because it’s CHEAPER to build 5, destructively test 2, launch one, and keep one spare, than it is to scratch-build a replacement if something goes wrong.

        When launch and housekeeping costs are well over 95% of the total, cutting corners in engineering is a fool’s choice, and doesn’t lead to actual savings.

  1. In this article here, just the amateur radio askpects are covered. I just wonder if this was a project controlleed by the CDP1802 and the software IPS. Just recently I found out about it and there is an IPS book out now explaining how the IPS System worked – you find it at and as this is based ofn Forth, it is part of the Forth Bookshelf at

    1. Probably not. Someone from AMSAT gave a talk at our local ham club, buf I think it was kater. He did talk about the 1802,, chosen because it was radiation hardened, one of I think two at the time, and because the architecture made it easy to use the CPU without needing software in ROM. So if things went bad, they could reload the software from the ground. Any CPU could do that, but the 1802 made it simple, without a lot of external hardware.

      QST would have shown details of OSCAR 7 before launch, so what it used is fairly available, I just don’t have access right now.

      We all heard about microorocessors after the Altair came out, butthey saw use befire that. So maybe 7 used the 1802. Getting a launch took time, and I think testing became a bigger issue as time went on, nobody wanting a faulty satellite messing up a launch.

      Project OSCAR bootstrapped, startung simple and learning from it. So OSCAR 1 was buikt fast, but very primitive, and lasted something like a week. I forget the early ones after that, maybea faikure and one hit the wrong orbit so it wasn’t so useful. 3or 4 was an actual repeater, but had a short life too. They got more complicated, and longer lived, starting with OSCAR 6 in the fall of 1972, and most that followed lasted increasingly longer.

      Eventually so many went up, often smaller, that it’s hard to keep track.


  2. This was launched in 1974 which was before microprocessors became readily available, and given the leadtime in building/preparing the satellite, I doubt there was anything programmable onboard at all.

    1. Yeah but… The IPS dialect was developed, some say derived from Fourth for managing and causing birds like Oscar there to work. However…. The only ones available then didn’t have the capability of understanding something that complex. The later ones did.

  3. I want to send this article to my flat Earth relatives but it’s just not worth it…. I’m sure it would be some convenient story about how the radio amatuers at being tricked, we need to figure out a way to hack the minds of flat earthers and wake them up. These amatuer interactions with space stuff is a handy example point to serve then for any that have the energy. I don’t. These people are the problem of the world, heavy “thinkers” that engineer complex unrealities to support the belief set that props of their emotional needs.

    Non sequiter over. I don’t know why I write this, maybe a plee to smart people to know that even though the flat Earth thing seems to be a huge troll, there are very small needy people that believe it. And it’s growing. If you don’t poke you head out of your bubble to much, you may not know how bad it is out there

  4. If the satellite came back on, solar only, because the battery degraded to an open circuit why didn’t they just design it so when the battery failed it switched to an open circuit?

        1. Ah… supercaps. I have tried to learn about , there pro and cons, but to date I fell short. As best I can tell, their low operating voltage, make difficult to make them into compact lightweight assemblies that can store appreciable power.

  5. OSCAR 7 was launched the same year I received my Novice license and a few years later I had the thrill of listening to one of the transponders. A bigger thrill was actually hearing my own weak signal pass through that little bird.

    1. OSCAR 6 launched 3 months after I got my license in July of 1972, and I did hear it early on. I had a general coverage receiver, a boid one, but the downlink was a tiny slice on 10meters. The satellite went overhead, and suddenly that slice was alive, until it got out of range.

      I think I heard myself through the satellite, but was never certain if it was through the satellite, or just receiver overload.

      The uplink was 2m, and tbe down!ink 10m presumable because that made it more accessible. As satellites got longer life, most moved higher in frequency, so lock out lower frequencies for regular use.


  6. After the failure radio amateurs continued to listen for many months to the satellite frequencies in the hope it might recover.
    Given neither the beacons or transponders were operational from July 1981 until June 2002 it raises significant questions over the claim in the Polish language story that AO-7 was used by Solidarity in 1982. The Polish story provides no sources and runs counter to the observations of radio amateurs at the time

    1. This entry did say “after the satellite stopped being used” which suggests it was put out to pasture after a certain time, a later satellite in orbit.

      But yes, the time frame seems off. I’m sure I got a Solidarity button in 1981, soon after a local article said someone was selling them locally.. Maybe the union began earlier, before outsiders knew about it, but that wouldn’t leave much time to use the satellite before it went bad.


      1. The satellite was not “put out to pasture after a certain time” it ceased functioning, no communications could be made using it. The loss was a devastating blow to the amateur radio community as there was no equivalent to replace it. If it had been even partially usable amateurs would have continued using it. The Polish story has no substance. An archive of the Amateur Satellite Report for 1981 is available, pages 37-40 cover the battery failure

    1. That is interesting. I assumed all those early satellites would have long ago reentered the atmosphere. Likely some did, leaving Vanguard to hold the record.

      I actually had a model kit of Vanguard. I can’t remember why I chose that one, complete with antennas sticking out.

      In those early days, the hobby magazines paid attention to satellites. One plus was that they often were transmitting on low frequencies, so people could receive them with existing receivers, or a bit of addition. Popular Electronics for a while had a listing of new satellites, their name and frequency. CQ Magazine, for hams , had a regular column about space in the early sixties, also covering recent satellites. Though with long lead times, and short satellite life, I wonder how useful such lists were when they got to the readers.

      Sputnik obviously got a lot of attention, made stronger because it’s beacon was at 18 MHz, so shirtwave receivers couod tune it in. Vanguard was at 108 MHz, but Popular Electronics ran a construction article about a converter to receive that frequency on a shortwave receiver.

      In the Apollo era, CQ ran some construction articles about receiving Apollo transmissions, but they had to guess at the frequency, and the distance made it harder.

  7. This documentation here might be of interest. As in German, I did a quick translation for the non-German world.
    FORTH (IPS) at its best :

    IPS – High Level Programming of Small Systems for the AMSAT Space Projects

    IPS – Interpreter for Process Structures developed by Prof. Dr. Karl Meinzer, DJ4ZC


    IPS was developed more than 40 years ago by Prof. Dr. Karl Meinzer DJ4ZC for the AMSAT space projects
    (communication satellites for radio amateurs).
    It has proven to be a very useful tool for programming small systems for many years,
    but has recently been forgotten.
    IPS takes an extremely modular and structured approach to interactively develop programs.
    Because IPS is a high-level language, it enables sharing programs regardless of which processor they are designed for.


    IPS is mainly a high-level language that enables extremely modular structured programming.
    Unlike other languages, IPS is essentially free of syntax rules.
    It uses Reverse Polish Notation (RPN) to make parameter passing between modules extremely easy
    and is as unrestricted as a low-level assembler design.

    The high-level emulation technology is extremely economical in terms of memory usage
    – the entire system is in 6 Kbytes of memory.
    But programs execute only two to three times slower than optimized assembler code.
    In most cases, this is not a problem,
    but extremely time-critical applications or specialized hardware may require some assembly language interfaces.
    IPS therefore uses a built-in assembler to facilitate these extensions.

    The Operating System of the P3 satellites

    An important application of IPS was and is its use as the operating system for AMSAT’s Phase 3 amateur radio satellites.
    The OSCAR-13 (P3-C) satellites’ 1802 / IPS computer operated uninterrupted for eight years before returning to the atmosphere in 1996.
    Impressive for the operating system of any computer, let alone one that has to work in space.

    The following AMSAT satellites used IPS on the on-board computer (Integrated Housekeeping Unit):

    1980 – AMSAT P3-A: (startup error) in May 1980
    1983 – AMSAT-OSCAR 10 (P3-B): successful launch on June 16, 1983
    1988 – AMSAT-OSCAR 13 (P3-C): successful introduction on June 15, 1988
    1991 – AMSAT OSCAR-21 (Radio Sputnik-14): RUDAK-II successfully launched on January 29, 1991
    2000 – AMSAT-OSCAR 40 (P3-D): successful launch on November 16, 2000
    AMSAT P3-E (in progress)

    Rescuing OSCAR-10 (P3-B)

    Unfortunately, when OSCAR-10 was successfully launched in 1988, the last rocket stage unexpectedly collided with the satellite.
    This example will show how IPS helped to save the mission.

    When OSCAR-10’s 400-bps PSK beacon auto-registered for the first time after launch, the telemetry data was terrifying:

    The solar cells were practically dead and delivered no energy
    The battery was becoming increasingly discharged
    The sun and earth sensors provided conflicting data

    Something had gone terribly wrong and the condition of the satellite was more than worrying.
    At this time it was not clear what the cause was.
    It took many weeks before the real reason became known. Until then, everybody was literally in the dark.

    In order not to lose the battery and the on-board computer, Karl DJ4ZC with its command station in Marburg,
    immediately switched off all unnecessary consumers on the satellite.
    But that was not enough, even the beacon was switched off to save electricity and get some charge into the battery.

    After a few hours it became apparent, that this emergency measure had already had some effect
    and the satellite was not lost.
    But time was still pressing, the mission was still on the verge to a total loss.

    In the meantime, Karl analysed the telemetry data and tried to solve the puzzle.
    It helped him that he could execute simple commands on the satellite directly in the interpreter.
    Individual functions could be changed without recompiling any programs, and by then uploading them,
    because of the angle in space the radio connection was rather unfavourable.

    So, Karl could find out very quickly that the satellite was turning the wrong way
    and the attitude was completely off the mark.
    The solar panels were practically no longer illuminated by the sun,
    instead, the sun was shining vertically on the top of the satellite.

    The P3 satellites are equipped with a sophisticated magnet system for position control,
    consisting of electromagnets in the side arms, which are pulsed by the on-board computer
    using the solar and earth sensors to apply together with the earth’s magnetic field a force on the axis of rotation
    and as result tilt the satellite.

    For the position control and sensors to work again,
    the software for the arithmetic and the coordinate system for the position sensors and attitude control had to be rewritten.

    The night was short and there was not much time left for extensive tests.
    But IPS is a very secure operating system.

    Actually, it seemed to work !!
    The sensors provided meaningful data again and already on the next flight through the perigee,
    the solar cells began to produce noticeably more electricity.

    OSCAR.10 was saved and was available to the radio amateur world for many years to come!

    It’s safe to say that without the flexibility of IPS,
    such a rescue would have been virtually impossible,
    and IPS has also shown its greatest strength.

    IPS at GitHub

    We have created a central IPS repository on GitHub for the entire documentation,
    the original flight software for the 1802 IHU, the source code, various ports on Linux and Windows.

    Until now, the files were distributed on different servers.
    In addition, with each change of server, something always got lost,
    as well as the generation and volume changes of ATARI800, via ATARI-ST, ACORN RISC PC, MSDOS, Windows 1-10.

    We have already recovered a lot of old and private hard drives, but there are still some things to work on and sort.
    This will happen gradually, unfortunately, very time consuming.
    Special thanks to Paul Willmott VP9MU, Stacey Mills W4SM, James Miller G3RUH, Peter Gülzow DB2OS and Karl Meinzer DJ4ZC.

    Of course, this almost forensic work is also associated with the hope that the community might still find an interest in IPS
    and the development will be driven by a larger group.

    IPS – the book!

    Already in 1978, Karl Meinzer, DJ4ZC has released the first version of IPS – High Level Programming of Small Systems.
    In 1997, the second edition was distributed by James Miller G3RUH,
    as well as a third edition in 2016, which is also available electronically as PDF.

    In 2019, a 4th edition of Prof. Dr. med. Karl Meinzer (author) and Juergen Pintaske (editor) was published.

    Mr. Pintaske wrote:
    “During preparation it became clear how much work was put into this IPS project – and hardly known.”

    The printed version of the book IPS – a Forth-like Language for Space:
    is now available on Amazon.

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