When the AMSAT-OSCAR 7 (AO-7) amateur radio satellite was launched in 1974, its expected lifespan was about five years. The plucky little satellite made it to 1981 when a battery failure caused it to be written off as dead. Then, in 2002 it came back to life. The prevailing theory being that one of the cells in the satellites NiCd battery pack, in an extremely rare event, failed open — thus allowing the satellite to run (intermittently) off its solar panels.
In a recent video by [Ben] on the AE4JC Amateur Radio YouTube channel goes over the construction of AO-7, its operation, death and subsequent revival are covered, as well as a recent QSO (direct contact).
The solar panels covering this satellite provided a grand total of 14 watts at maximum illumination, which later dropped to 10 watts, making for a pretty small power budget. The entire satellite was assembled in a ‘clean room’ consisting of a sectioned off part of a basement, with components produced by enthusiasts associated with AMSAT around the world. Onboard are two radio transponders: Mode A at 2 meters and Mode B at 10 meters, as well as four beacons, three of which are active due to an international treaty affecting the 13 cm beacon.
Positioned in a geocentric LEO (1,447 – 1,465 km) orbit, it’s quite amazing that after 50 years it’s still mostly operational. Most of this is due to how the satellite smartly uses the Earth’s magnetic field for alignment with magnets as well as the impact of photons to maintain its spin. This passive control combined with the relatively high altitude should allow AO-7 to function pretty much indefinitely while the PV panels keep producing enough power. All because a NiCd battery failed in a very unusual way.
“Shorted open”? Is that an accepted technical expression / electrician’s term (in English)?
I know fail-safe, failed-closed and -open but “shorted open” makes no sense at all to me.
LEO = low EARTH orbit
geocentric = centered on the Earth(?)
Redundant redundancies are redundant?
Aren’t all of Earth’s (artificial?) satellites geocentric?
Do objects in the the lagrange point count as satellites?
According to https://en.wikipedia.org/wiki/Satellite?useskin=vector
all artificial satellite are by definition objects in an orbit around a planet.
Okay, now that I’ve stumbled over “orbit” it makes a little sense.
There may be satellites in elliptical orbits, thus not geocentric but at least all LEO & GEO satellites are, aren’t they?
Thank you, Jeff Albertson!
lagrange points arent geocentric so there’s that.
Well, a closed circuit is a connected circuit, and an open circuit is a disconnected circuit. Normally a “short” closes a connection that shouldn’t be connected, so presumably “shorted open” means the battery circuit is no longer connected all the way through. I’m not sure whether that should be called a “short” anymore, but I don’t really have a better brief description than “shorted open”, so.
A “short” is understood to mean a closed circuit…typically other than the one intended.
You might have an electronic assembly with two contacts that can be momentarily bridged with a screwdriver tip (to trigger a reset or a test function, for example.) In this case the ” short” induced by the screwdriver is intentional, but it still denotes the closure of circuit path.
To say something ” shorted open” is nonsensical. Why not just say the nicads “failed open?”
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Just came here to say same “failed open” is what I generally call it. The wikipedia article on this satellite say s~ the battery failed from a short circuit …. that later became open… Something I have seen, usually quickly!
The is what I use as well, but I have seen reasonable people colloquially use “shorted open” for that process, then put down “Failed Open” in documentation.
You are all correct and we all know the probable sequence of events that led the AO7 is “back to life”. For lack of better terminology I think the term “shorted open” is acceptable as of the moment. The term can be discussed in an international convention then changed to something better to be part of a universally acceptable terminology. As of now I am happy to know that the satellite is working. 😃
The supply rails were dragged down by a shorted NiCd cell in a series connected battery pack. So the satellite went dark since some components required the designed supply voltage to work. Charging from PV doesn’t help since the shorted cell clamps the supply rails below the design voltage. Then the shorted cell burned through its short which in a NiCd is typically a pinhole in the dielectric separating the two battery poles. Back in the day rechargable cells that failed this way could be revitalized by blasting them with a much higher voltage, effectively cauterizing the short. For a 1.2 volt cell this was typically done by momentarily connecting it across a very low source resistance supply like a car battery. This might be what happened in the satellite – a transient blew the short loose. The cell failure as effectively an open instead of the more typical short (0 volts, 0 ohms), because the pack is connected in series, basically takes the cell array off line and leaves the PV charging system as the sole source of power. The PV charge system would typically run at a slightly higher voltage than the sum of the cells would deliver and would be current limited by circuitry or maybe just the maximum power available from the PV cells. Think of it like an automobile charging system where the 12.6 volt battery (determined by the cell chemistry) lives in a 13.5 volt environment when the automobile is running. If you disconnected the battery with the car running, most functions would continue. This is what failing as an open has done for the satellite.
A connection that is open when it isn’t supposed to be is an “open”.
Wait till you notice what a fuse does when it gets overloaded!
De-fused? De-functioned?
In case we weren’t con-fused enough.
Oh and have you folks gotten around to “British Standard Whitworth” sizes yet?
argh,, I forgot to mention the space jargon re: the battery shorted open.
An ” Astronomical Impedance ” ?
One of the definitions of the word “fuse” is “liquify by heating,” which is what happens to the thin part of a fuse’s conductor when its current rating is substantially exceeded. The liquified conductor either drops away or is vaporized, breaking the conduction path.
A fuse which has melted open is “fused”, which just means “melted”, although it’s usually just referred to as “blown”, because when it fails it’s usually a touch bit violent.
Yes, LEO and GEO are both geocentric by definition, so saying “LEO geocentric orbit” is redundant. But “geocentric” helps distinguish Earth orbits from heliocentric or areocentric ones. Elliptical orbits can still be geocentric if Earth is the center of mass. Objects at Lagrange points aren’t technically in geocentric orbit — they’re in gravitational balance points, not orbiting Earth directly.
Assume they mean “failed open”, e.g. high resistance.
“There may be satellites in elliptical orbit”.
There are and there were. AO7’s successor AO13 was on a highly elliptical orbit, made for some very interesting QSOs back in the 90s.
Geocentric is not about what the satellite is orbiting, but rather how you are measuring it. There are Geocentric orbiting asteroids that make horseshoe shaped patterns. From a Heliocentric perspective they just seem to have a 1AU or ‘one year’ orbit.
Earth-moon Lagrange orbits, aka rotating frame of reference restricted three body problems for the Earth Moon system, are often plotted in a frame of reference that have several points appear stationary. but hey are mostly perturbed Earth orbits. Consider EML3, a nice circular earth orbit where the Earth appears to have a slightly larger mass. on the Lagrange map, it’s a stationary point on the side of the Earth opposite of the moon.
Then you can look at the heliocentric Luna orbit. a 1AU orbit that is slightly shallower or steeper in it’s curve toward the sun 13 times a year.
So there are at least 3 simple ways to look at Luna’s orbit. heliocentric, geocentric, and on a Lagrange map.
Obligatory XKCD reference:
https://imgs.xkcd.com/comics/centrifugal_force.png
Basically, try not to be so pedantic, you kinda look like a fool, and I doubt that you really are.
-G.
I’ve always considered a ‘short’ circuit as two wires inadvertently contacting… but do some feel that if a wire is open, the circuit is ‘short’??? (ai: here I come…!)
The word “shorted” does not appear at all in the article. The author only said “failed open”, which is one of ways in which a rechargeable battery can fail. It’s internal resistance becomes infinite.
An orbit around Earth can be geocentric or eccentric, depending on whether the planet is at the center of the orbit or offset from it in the same plane as the orbit itself.
Or… a cold solder joint on a board failed due to heat and over current trying to charge a shorted battery pack.. or a diode overheated and went to open state thus removing battery charging load allowing the unit to start functioning.
The cell shorts, the resultant current overload then vaporizes some surrounding material which then opens the circuit. (My clothes dryer did this last week!)
This. It describes the sequence of events, not just the current state.
The cell has shorted
A great deal of current flows
The circuit opens
That makes sense if the satellite returned to service immediately after the battery failed. It took 21 years to return to service. My first guess would be that the electrolyte in one cell of the battery evaporated, causing an open circuit in that cell. My second guess would be a random open in the battery circuit
It took 21 days for an amateur to try to contact the satellite. We do not know exactly when the satellite came back to life, only when it was discovered to work.
Did it really take that long, or was nobody listening for it?
Roaming hack-a-day
Electronics haiku found
Existence noted
What are you saying?
Someone wrote some poetry?
That surprises me!
https://soldersmoke.blogspot.com/2024/11/oscar-7-and-oscar-11-aka-uosat-2-did.html
I was wondering where I’d read about this recently. Mystery solved.
A lucky short:) I like that.
Just goes to show you that amateurs as ever do the job far better than commercials I am at the end of my Radio Days but during my life the changes Have been astronomical
I saw a very first transistor or as it was known at that time as the transient resistor at the festival of Britain which was about 1951 I Managed to get one From bell labs and built my first hetrodyne receiver Which I demonstrated at the Royal Society London as part of Eric Laithwaite lecture on what he called the magnetic river
How things have changed I recently heard I have not tested or Proved that amateurs have managed to land a mobile phone on the moon and to all intense and purposes is operable but of course the three second ping is not conducive to sensible Voice transmissions, This of course has been rectified by the near Earth birds
Well done all you keen Amateurs Indeed all amateurs in proving that corporate and governments simply do not have a clue
Keep it up – the next Stage is just around the corner heaven’s knows What delights that will bring I wish you all the very best
Dr John L Dimmock – G1 UXG (UK)
In the beginning God created data
Then she created Man to corrupt it
Thank you for sharing your experiences. I hope to read more!
The Saudi sat 50 is another popular one
Mainly it’s one of the few working satellites that do 2m and 70cm fm voice
And can be keyed and contacted on a 5 w baofeng even with a stock antenna though I found diamond srh77ca with small adapter works better, more gain
Actually have a YouTube video of one of the random passes of so-50
Basically what to expect using a radio satellite
About 20 minutes at best, and you have a repeater with up to 1000miles of coverage
You can hear that they get a lot of traffic
https://youtu.be/IHgaRNojL5o?si=Ifh7LP0PmNkgCNoC
Haven’t used that old call sign in years
Got one of those callsigns to reflect the license
73 de W4TIA
Not much for having conversation
Just do it to get that qsl card and qso confirmation
Also gives good data on the atmospheric propagation as it moves over the horizon
I thought of putting a cube sat like this in the l1 point somewhere, geostationary or it
Apparently if you put a transmitter in the right spot in the magnetic field, the earth magnetic field will actually amplify the signal
By the sound of it Very efficienly atleast a by an order of magnitude
Easy to test with a cube sat, and 25w on 2meter and 70cm, and a 23cm link for digital
6 and 10meter link for hf qrp experiments under 10w
You can easily get over 100w of combined tx power in a cubsat nowadays, especially in a geostationary orbit with photovoltaics, and run a modern computer.
If you can get it to survive the g force of launch, and basically the nuclear radiation floating in space
And actually get it in orbit without it tumbling and at the right position, some gyroscopes, accelerometer, and cheat and use the solar panels as a way to detect the sun in space to maintain orientation. Super capacitors and rechargeable battery seem to have much better shelf life and a lot more capacity.
Nowadays they charge you by the kilo to launch a satellite in orbit
However I think l1 or l2 geo stationary, or at a very slow (higher) orbit around, probably costs more than iirc like 5-10 grand per pound or kilo for a lower orbit
Get coverage atleast of about 52 percent of the line of sight earth, so far above the horizon, what horizon?
Shit put one in orbit around the moon so that it’s always in line of sight of earth
That cost a lot more because nobody else is crowsourcing that launch window except foreign governments, and NASA, and esa.
They’ll pay millions…
At 10-20 grand for a cube sat launch nd you can fit 100 of em if there enough unused space
They made up to 2 mill extra from splitting the cost over 100 people
Make you wonder if you could use the van Allen belts to generate power….
a pvcell that’s designed to see ionizing radiation instead of infrared, because higher energy per square unit of surface, because higher energy photons, smaller panel to generate same power.
And I would assume the van Allen belts would produce enough ac fields that you can generate a voltage through a coil…..
Correction: 21 years
Amateur satellite work is what got me into ham radio to begin with. I’ve made QSOs with this “bird” and the couple of others in current use. Since then a few years ago I do HF and CW almost exclusively; probably time to get the little HT out and try the ISS repeater now that it seems to be back in operation.
For anyone thinking super awesome ham stuff is very expensive, as noted above, a janky Boafeng and a rubber duckie antenna is plenty enough to work the birds with minimal effort. The magic of getting that QSO through a pileup is intoxicating.
Pro tips- I call callsign “Handheld 5w..” and get better response rate.
If you’re young, like 12, EVERYONE will pile on for the QSL. Everyone loves young hams.
If you are a young female you can absolutely dominate the satellite- probably a dozen QSOs possible each pass
Get to it!!