This question is deceptively simple: What is the oldest operational satellite still in use today?

Several questions should immediately come to mind. The first is, "What does 'oldest' mean?". The second is, "What does 'operational' mean?". The third is, "What does 'still in use today' mean?".

Since satellites are routinely launched, used for their intended purpose(s) and eventually discarded (either on purpose or through malfunction) the mantle of "oldest satellite" is constantly bestowed upon one orbiting object or another. If decayed (in the orbit sense) satellites also count, then the oldest man-made satellite of the Earth is obviously the Soviet "Sputnik 1" (and the rocket that placed it into orbit). However, if decayed satellites do not count, then that honour is bestowed upon the American "Vanguard 1", which is still orbiting Earth right now.

We can complicate matters by expanding the phrase to "oldest operational satellite". This modification obviously automatically disqualifies the decayed satellites. However, what does "operational" mean? For instance, if the satellite's sole mission was to be used as a light or laser reflector, then it is technically still operational until its orbit decays. Vanguard 1 has small solar panels on it that absorb and reflect light. They are still generating power right now (if Vanguard 1 is not being eclipsed by the Earth). If your definition of "operational" is sufficiently wide, then Vanguard 1 is the oldest operational satellite, since there is a piece of it that is still performing its duties as designed. However, few use such a wide definition since Vanguard 1 is not performing any duties that humans on Earth can receive or use.

Does "operational" mean that the satellite is still performing its intended duties? This would depend upon the critical requirements of the satellite. For instance, a laser ranging satellite will last hundreds of years (if placed at a sufficiently high altitude) and still be able to reflect laser light. Is this particularly impressive? Not really. You might as well say that it is the oldest mirror that is still reflecting light. A mirror will continue to reflect some light over thousands of years, though not at the same reflectivity as its initial manufacture.

So, the phrase "oldest operational satellite" should have some feel of "old beyond its intended lifetime" for it to be truly impressive and worthy of note. The final phrase, "still in use today" is added to make sure that you can't say that a satellite that lasted 50 years (but no longer functioning today) will hold the title of "oldest operational satellite" until a satellite lasts longer than 50 years. Indeed, there might be some satellites that were operational for 50 years, but none of them are "operational" (in the loose definition of the word) right now, as far as I know.

Having dealt with what "oldest operational satellite still in use today" means in the manner defined in this article, the only satellite that qualifies given the prerequisites described is the Amsat Oscar-7 (AO-07) amateur radio satellite. OSCAR is an acronym that stands for "Orbiting Satellite Carrying Amateur Radio". Oscar-7's current status can only be attributed to a series of miracles that kept it operational after nearly 40 years since its launch.
 

The Amsat Oscar-7 Amateur Radio Satellite. Image courtesy of the Radio Amateur Satellite Corporation (Amsat).

Assembling the Oscar-7 Satellite (1974) - Note the scale - Image courtesy of the Radio Amateur Satellite Corporation (Amsat).

Amsat Oscar-7 was launched on November 15, 1974 from Vandenberg AFB as the seventh in a series of amateur radio satellites that began with Oscar-1 at the end of 1961 (the same year cosmonaut Yuri Gagarin first orbited the Earth). Oscar-7's designed lifetime was three years. The spacecraft carried two repeaters, two experimental telemetry systems and a store-and-forward Morse (CW) and teletype (RTTY) message unit. The octahedral satellite had a height of 36cm (14.2 inches) (without antennas), a diameter of  42.4cm (16.7 inches) and a mass of 28.6kg (nearly 63 pounds). For its day, about 30 years before the cubesat (nanosat) era, it was considered to be a small satellite.

The Oscar-7 satellite was placed into a nearly circular retrograde orbit (101.7 degree inclination) with an average altitude of 1450km. The period of the orbit was approximately 115 minutes (nearly two hours). Because of its larger altitude (and consequently larger period), its footprint on Earth is larger than most present-day cubesats, allowing a longer accessibility time for a single ground-based communications site (the longest being nearly 20 minutes!).
 

The Retrograde Orbit of Oscar-7 - Generated using Analytical Graphics Inc. (AGI) Systems Tool Kit (STK) version 10.

The Full Footprint of Oscar-7 Covers most of North America - Generated using Analytical Graphics Inc. (AGI) Systems Tool Kit (STK) version 10.
 

The first repeater would be active in "Mode-A". In this case (and ignoring Doppler effects), the Earth-bound amateur radio operator would transmit at a frequency between 145.850 and 145.950 MHz (in the VHF range) and listen for a response at a frequency of between 29.400 and 29.500 MHz (in the high HF range). The second repeater would be active in "Mode-B". In this case (and again ignoring Doppler effects), the Earth-bound amateur radio operator would transmit at a frequency between 432.120 and 432.180 MHz (in the UHF range) and listen for a response at a frequency of between 145.920 and 145.980 MHz (in the VHF range). Only one of the repeaters would be available at a time, with each repeater being operational for approximately 24 hours on an alternating basis. The designed output power of the Oscar-7 repeaters was approximately 2 Watts, which is rather large when compared to the outputs of the modern-day cubesats which are normally in the few hundred mW range. However, the present-day power output might be lower since the solar panels have no doubt degraded due to the harsh solar radiation constantly bombarding them for nearly 40 years.

Inspecting the Oscar-7 UHF/VHF (Mode-B) Transponder (1974). This very transponder is now 40 years old and is still operating.
Image courtesy of the Radio Amateur Satellite Corporation (Amsat).
 

Oscar-7 was reliably used by the amateur radio community all over the world from just after launch until June 1981 when its batteries likely shorted. This in turn short-circuited the entire power system, just like shorting your car battery would short out your alternator and deprive your car of any power. This prevented any power (including that from the solar panels) from reaching its repeater circuitry. The satellite remained dormant for just over two decades until what seemed to be a miracle occurred on or before July 2002.

In late July 2002, an amateur radio enthusiast in the United Kingdom (callsign: G4CUO) heard familiar signals from what he believed to be the "silent" Oscar-7 satellite. A quick check confirmed that Oscar-7 had indeed been somehow revived from the dead and was transmitting once again. Soon after this sudden and amazing revelation, amateur radio enthusiasts were once again using Oscar-7 for communications after a 21-year hiatus. It was believed that the electrical short in the batteries had somehow opened up (due to thermal extremes?), once again permitting the solar panels to provide power to the onboard repeaters. At that time, the satellite was nearly 30 years old, which is very long in the tooth relative to most satellite missions and nearly 10 times longer than the designed lifetime of the satellite.

Since the satellite's batteries are long dead, nobody can use the satellite when it is being eclipsed by the Earth. However, when its solar panels are being lit by the Sun, there is still sufficient power, despite four decades of constant solar panel degradation, to operate the satellite's two repeaters. The satellite still automatically switches between the Mode-A and Mode-B repeaters, albeit more sporadically than it once did.

I first heard this miraculous satellite's Mode-B beacon on February 1, 2012 using the VE3RMC amateur radio satellite communications station at the Royal Military College during my MSc studies. Click here to listen to my first Oscar-7 recording. I didn't know what information it was transmitting (if it wasn't gibberish) but it sounded to me like "musical popcorn" (my phrase). After slowing down a recording of it, I had determined that it was not a fast Morse code. Over time, the speed of the tone variations slowed down. Today, I can't hear it at all. This beacon might have been designed to inform the user that the Mode-B repeater is operational. Mode-A might have a similar beacon.

After a few weeks and some tuning around, I learned that people were talking to each other using Oscar-7. My first recording of voice transmissions via the Oscar-7 Mode-B repeater can be heard here. At that time, I could not attempt to transmit to the satellite since I did not yet have my amateur radio license. That would have to wait until April or May 2013. I could not hear the satellite when it was in Mode-A because the VE3RMC transceiver (an iCom IC-910) is VHF/UHF only.

After I received my amateur radio license (my callsign is VE3HEO) on April 12, 2013, I decided to first try out the FM transponders (such as the SO-50 cubesat). I contacted my first cubesat (SO-50) on May 9, 2013. Unfortunately, I did not record my very first satellite contacts. Click here to hear some of my subsequent contacts using this repeater, recorded on May 9, 2013.

Several weeks later, I decided to try and contact the historic Oscar-7 satellite. Opposite to the SO-50 repeater, the Oscar-7 Mode-B repeater has a UHF uplink and a VHF downlink, so I had to transmit to the satellite using UHF. The problem with UHF is that it has a smaller range than VHF and the Oscar-7 satellite was over twice as far away as SO-50. From June 2013 to early 2014, no matter how much I tried, I could not contact Oscar-7. At the time I had no idea why but I would eventually find out.

In June 2014 another miracle (not related to Oscar-7) occurred for me this time. The physics department (where I am currently doing my PhD) was about to begin renovations. Actually, the entire building where the physics department was housed would be renovated for about one year or more. I learned that the VE3RMC amateur station's Yagi antennas would be taken down from its tower atop the building because of the renovations. I had also learned that the radio equipment would be put into storage for the entire time. I had thought that it would be a shame for the VE3RMC amateur station to be totally silent for that time, so I asked if I could borrow the equipment for a year or more during the time the renovations were taking place. After some thought, the department granted my request and I began to reassemble the VE3RMC communications station off site from RMC. I began the task of inspecting and making minor repairs to the equipment (mainly the antennas and the Az-El rotator cabling).

After I had made my repairs to the antennas and the rotator, I began testing the VE3RMC station within its new surroundings. I immediately found that the received signal strength of the cubesats was much higher after I had finished my repairs. I began to think that the failure to communicate with Oscar-7 might have been due to the degraded performance of the UHF Yagi antenna due to the many years of sitting on the RMC rooftop and being battered by sunlight, wind, snow and rain (sort of what Oscar-7 went through, but with space weather).

I was able to easily contact the SO-50 (FM) and FO-29 (SSB) repeaters with the newly repaired system. One satellite remained: Oscar-7. On the afternoon (EDT) of July 28, 2014, Oscar-7 was predicted to have a high elevation from VE3RMC's new location and so I decided to go for it. The question I had was, will it be in Mode-A (not accessible with VE3RMC) or in Mode-B at that time?

When the time came to go for Oscar-7, I used Ham Radio Deluxe (HRD) to automatically track the Oscar-7 satellite with the Yagi antennas. The VE3RMC station does not yet have an interface cable that would allow HRD to automatically adjust for Doppler shift, so I would have to tune the radio (both transmit and receive frequencies) by hand. Fortunately, I already had a lot of experience from using both SO-50 and FO-29 repeaters. I was relieved when I began hearing voices (on the radio, not in my head) when the satellite was about 5 degrees above the horizon. I turned the RF output power to full (100W theoretically) and began transmitting to the satellite. First result: no response. Maybe the satellite was still too far away. I waited for the satellite to get higher in elevation before I tried again. I once again transmitted to the satellite using full RF power.

On the second try to reach Oscar-7, I heard a very faint voice saying "VE3RMC this is K8YSE"! I had finally contacted the nearly 40-year old satellite! It was an amazing experience to know that I had just contacted a satellite that was designed, built and launched all before my first day at Kindergarten. I also found it amazing that I might have just reached the oldest satellite that was still operating. I made a second contact soon after and I might have caught the satellite randomly switching from Mode-B to Mode-A as I was hearing the second QSO make his final salutations to me. Right after the second QSO, I could no longer hear anyone on the normal Mode-B frequencies and I could not reach anyone else. This was confirmation that the satellite had indeed switched from Mode-B to Mode-A. I knew that the satellite would switch back to Mode-B within 24 hours, so I was eager to try again the next day. On the afternoon of July 29, 2014, I made one contact with Oscar-7, thus confirming that I could regularly use Oscar-7 to contact fellow amateurs in North America. I had felt a satisfying sense of accomplishment as I turned off the VE3RMC transceiver after a job very well done.

The full recording of my first contact with Oscar-7 can be heard here. I hope you will share the wonder and excitement that I had when contacting this miraculous satellite, constructed by highly experienced people when I was just a toddler first experiencing my world.

Several months shy of its 40th anniversary, Oscar-7 is still operational which is another miracle in itself. Oscar-7 has braved many solar storms and cosmic radiation and yet still fulfils some of its original designed mission requirements day after day. In other words, it is still "operational" and is still being used by Earth-bound "customers" after nearly four decades; half of that time being asleep and waiting for its next opportunity to serve.

So, the question still to be pondered here is, "Is Oscar-7 the oldest operational satellite still in use today?". it would certainly be interesting to find out!

73s to everyone.

Michael A. Earl (VE3HEO)
PhD Candidate and Temporary Caretaker of the VE3RMC Amateur Satellite Communications Station
Department of Physics
Royal Military College of Canada (RMC)