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Communications The Military Government United States Technology

Air Force Gives 10-Year-Old Orbiting Satellite To Ham Radio Operators (arrl.org) 74

Longtime Slashdot reader Bruce Perens writes: The U.S. Air Force has transferred control of a 10-year-old orbiting satellite to AMSAT, a ham radio organization, which has enabled it for any licensed ham to use on the air, as the satellite's Air Force missions have ended. Falconsat 3's first mission was science: measuring gravity gradient, spectrometry of the plasmasphere, electronic noise in the plasmasphere, and testing three-axis attitude control using microthrusters. Secondarily it was used to train Air Force Institute of Technology students in space operations, with close to 700 cadets obtaining ham licenses in order to operate a number of Air Force satellites using ham frequencies.

Now in its third mission, control of the satellite has been transferred to AMSAT, the Radio Amateur Satellite Corporation, and all government frequencies have been disabled with only ham ones remaining. The satellite will relay APRS (position and status reporting) signals, it will operate a BBS in the sky, and will broadcast telemetry.

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Air Force Gives 10-Year-Old Orbiting Satellite To Ham Radio Operators

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  • by gman003 ( 1693318 ) on Thursday September 28, 2017 @06:54PM (#55272959)

    The "FalconSAT" name certainly suggests a link to SpaceX's Falcon 9 rocket, but it is actually unrelated, predating SpaceX's founding. The satellite series has used a number of different lift vehicles - FalconSAT-3 used an Atlas V 401 rocket, as part of a multi-satellite launch.

    The closest the two Falcons came was the launch of FalconSAT-2, which got bumped from the Space Shuttle's manifest after Columbia. It got re-used as the payload on SpaceX's first-ever launch, the first Falcon 1 flight. Which failed catastrophically a half-minute in. The satellite apparently survived with "minor" damage, falling back onto the island, but it was never re-launched to my knowledge.

    The Air Force probably doesn't need FalconSAT-3 anymore because they have FalconSAT-5, which presumably can fill a similar purpose.

    • There is not currently any operating partnership between SpaceX and AMSAT. This might be more about AMSAT than SpaceX, though. I don't think they have satellites ready to go when an opportunity comes up. They generally get an opportunity years ahead and then build the satellite. I am peripherally involved with a geostationary satellite they are doing with FEMA.
    • by grumling ( 94709 )

      The Air Force Academy sports teams are the Falcons.

      http://www.goairforcefalcons.c... [goairforcefalcons.com]

    • "The "FalconSAT" name certainly suggests a link to SpaceX's Falcon 9 rocket,"

      No it doesn't. The US Air Force Academy's athletic mascot and team name is the 'Falcons'.

      Does your history begin in 2002?

      • My history does not begin in 2002, but sports are not something I have any real knowledge of, particularly not collegiate-level sports. Even for the military academies. It's just never been my thing.

        The name similarity, combined with my vague recollection of a FalconSAT on one of the Falcon rocket launches, was enough that I went to check whether there was an actual link between them. I found that there was not, and learned a couple other fun facts, and thought that it would be nice of me to share that info

  • by Anonymous Coward

    Falconsat 3 was built at the air force academy, not the AF institue of technology. '06 grad here. just google it -

    https://www.google.com/search?rlz=1C1GGRV_enUS750US750&{google:acceptedSuggestion}oq=falconsat+3&{google:instantFieldTrialGroupParameter}sourceid=chrome&ie=UTF-8&q=falconsat+3&pws=0

    • Did I say otherwise? It's been operated by AFIT people in recent time, but was built mainly by 3 hams and I accept that they were with Air Force Academy.
  • Can anyone explain why the uplink is in the 2m band while the downlink is in the 70 cm band? Having separate frequencies makes sense, but what purpose is there to having them this far apart?

    • by Bruce Perens ( 3872 ) <bruce@perens.com> on Thursday September 28, 2017 @07:00PM (#55273013) Homepage Journal
      Receivers are de-sensitized by close-by transmitters on the same band. Having the uplink and downlink be in a separate band avoids this. Terrestrial repeaters use a big piece of RF plumbing to avoid this, which would increase the weight of the satellite.
      • by Mal-2 ( 675116 )

        Thanks for making it simple without being condescending. I don't stand a snowball's chance in hell of hitting this repeater, but I may at least attempt to listen for it.

        • by Bruce Perens ( 3872 ) <bruce@perens.com> on Thursday September 28, 2017 @07:24PM (#55273163) Homepage Journal

          You might be surprised. It only requires the Technician class license, which is no big deal to pass. A hand-held crossed 440/146 beam antenna will make it and costs less than $100, you don't really need an azimuth-elevation rotator. You learn how to point this by hand and wave it around until you hear the satellite. The required radio power would work with a walkie-talkie but a mobile/base radio is more likely to have the input and output that works with 9600 Baud modems. I am not clear whether a 9600 TNC [wikipedia.org] works or whether you just use sound cards and a software modem.

          The voice birds require that handheld antenna and a dual-band walkie-talkie, and that's all.

          • I'm guessing this is 9600 baud packet, which would require a PK-232 or similar TNC.

            • by ipb ( 569735 )

              "I'm guessing this is 9600 baud packet, which would require a PK-232 or similar TNC."

              Hardware TNCs are old technology and are now far out performed by modern sound card based modems. I have a stack of them that will probably never see power again.

              Take a Raspberry Pi, a cheap USB sound card and run direwolf software and you have the basis of support for multiple low speed data modes.

          • by DeQueue ( 112880 )

            HI Bruce

            Hardware TNCs, or software modems taking the signal from a soundcard from the radio's discriminator (NOT from the speaker) or software modems getting a signal from software defined radio (a $15 RTLSDR USB dongle for example) -- any will work for the satellite's 9600 baud signal.

            The satellite transmits what amateurs consider a "standard" 9600 baud packet radio signal -- G3RUH modulation, 9600 bits per second, bit scrambled, NRZI, HDLC with zero bit stuffing, AX.25 packets.

            Dequeue

            • How hard would this be for a SDR/RaspPi combo? Seems doable, but I would need a month to study up for Tech license. At least no code, I couldn't copy 2 wpm today without a recorder... Naw, I would rather go QRP with all the cool new tech and old school technique. Or not.

              • by DeQueue ( 112880 )

                The original RaspPi probably has just enough CPU horsepower to demodulate the signal and compose the appropriate replies in order to use the onboard BBS in real time. The RaspPi3 has a better chance of working. I haven't tried it yet, but it's on the bottom of the "to do" list.

                The original RaspPi certainly has enough horsepower to record the signal during the pass (say, to an attached USB thumb drive), and then after the pass it can demodulate the 9600 baud data stream out of the recording. This is fine if

        • Satellites aren't that far up.

          • by Mal-2 ( 675116 )

            Well they're either That Far Up (geostationary), or they're moving. I'd actually prefer That Far Up, at least I'd always know where to aim.

            • I have seen people do this by hand, it really doesn't look so bad. The satellite is always going to start at the horizon at a predicted time, and then cross over you. So, you can always start at the lowest elevation that is clear, and just do azimuth with a compass (remember declination).

      • by Strider- ( 39683 )

        As I recall, the other primary reason why AMSAT typically uses this configuration is due to doppler. The frequency shift at VHF is only something like +/- 15kHz, which is usually within the capture window of a VHF receiver, whereas at UHF it's +/- 45 kHz, which is beyond your typical receiver. Since we can retune our earth based receivers on the fly, the whole thing works.

    • by Anonymous Coward

      The equipment that is required to allow receive and transmit to happen in the same band is extremely heavy. For example see this install for a repeater [wa7x.com]. I would imagine the satellite designers didn't want to include a hundred extra pounds of cans when they could just use two different bands and not worry about it.

    • by Obfuscant ( 592200 ) on Thursday September 28, 2017 @07:13PM (#55273091)

      Having separate frequencies makes sense, but what purpose is there to having them this far apart?

      This is standard for satellite operations.

      There is one overriding technical goal in creating a working repeater. The receiver must not be swamped by the transmitter, which has a much stronger signal than anything it will hear from Earth. Earth-based repeaters (which this basically is) have physical isolation that is based on the wavelengths of the signals. A VHF duplexer [jet.com], as it is called, is about 3 feet tall and 6 to 8 inches in diameter, and there are usually four or six used. The physical cavity allows for very sharp notches and passbands that are applied to both transmit and receive. The receive duplexers selectively pass the receive signal and notch the transmit. The transmit duplexers selectively pass the transmit signal and notch the receive. The antenna end of the duplexer chain (e.g. three in series from the transmitter, three in series to the receiver) is simply tee'd together. This setup works when the signals are 600kHz apart.

      You can build smaller duplexers [radiotwoway.com], such as those used for ancient mobile telephone systems, or for some current repeater systems, but these require a minimum of 5MHz separation between transmit and receive, and support lower power transmitters. There is only 4 MHz in the entire amateur 2M band (2MHz in some countries), so this separation is not possible within that band.

      It is VERY easy to build an LC (coil/capacitor) duplexer [gigaparts.com] for considerable amounts of power when the frequencies are 300 MHz apart. Like VHF (146MHz) and UHF (440MHZ). This can fit in a package smaller than a pack of cigarettes. And it is much lighter (pun intended).

      That's why amateur satellite operations use widely-split duplex. If it is UHF uplink and VHF down it is referred to as U/V mode, opposite is V/U mode (or vice versa. I don't do satellite ops.)

  • by Bruce Perens ( 3872 ) <bruce@perens.com> on Thursday September 28, 2017 @08:11PM (#55273389) Homepage Journal

    I broke the ARRL web site :-). Try the AMSAT [amsat.org] site instead.

    - K6BP

  • by Anonymous Coward

    Not sure whether to be more concerned at the fact that there is a 10-year-old locked in orbit around a satellite, or that control of said youngster is being transferred to a ham radio organization.

    Strange...

  • I wonder if this was accelerated because of the need for HAM operators in Puerto Rico following Maria.

    • I don't think so. Red Cross asked for people who had experience with digital modems over HF radio, and VHF digital for shorter range. The satellite is usable, and we are indeed building a satellite that is geosynchronous (not geostationary) and designed for emergency communications, but satellite is probably not a major part of that operation.

  • Great, they get a beat up trainer. Seriously though, I'll bet a lot of those cadets go on to train for volunteer emergency communications later on.
    • " lot of those cadets go on to train for volunteer emergency communications later on."

      A lot of those cadets, when deployed, will be engaging in emergency communications daily as part of their mission. They are almost over trained for volunteer emergency communications. Almost.

  • Is that something William Shatner is involved in?

  • Which satellite are they orbiting?

    • Without knowing about the specific design, a good guess would be one of two things (perhaps both). This satt is obviously a low power device with a 1 watt transmitter. So its battery requirements are not large. So they could have packed extra batteries that they could switch out every so often as one went bad. Another thing that they might could do is operate just when the sun is available, like what trustworthy Oscar 7 is doing now. [amsat.org]

      • Nickel-hydrogen batteries in satellites can last 40,000 cycles.

        How has my Prius lasted for 10 years on the same battery pack? Because the software never discharges the battery below 20% or charges it above 80%.

        Good charge management software is one thing. Also, the satellite can be designed to work in sunlight with an open or shorted battery, which is how AO-7 is still working after 43 years. AMSAT's experience in space has taught them a lot about battery failure.

  • Will it run TradeWars???

    In order to qualify as a legit BBS, it has to have TW2002...

  • Thanks for posting this up Bruce, it's a wonderful story.

    • by HBI ( 604924 )

      I agree. This is a nice story, more interesting than 99% of what is seen here nowadays.

An age is called Dark not because the light fails to shine, but because people refuse to see it. -- James Michener, "Space"

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