[Ground-station] Please vote - Ambasat sensor
John Ackermann N8UR
jra at febo.com
Sat Sep 28 17:30:44 PDT 2019
Well... I'd *like* to do that experiment, but I don't have quite enough
Cesium standards to do it reliably. :-)
My friend Tom Van Baak, whom I call the spiritual leader of the
time-nuts, is the one who took three Cesium clocks along with his kids
to the top of a mountain near Seattle to prove the relativistic effect,
and then he repeated it at Mt. Lemmon near Tucson for the PBS citizen
science show a couple of years ago. Sadly, Tom isn't a ham, though I'm
working on it.
In the satellite biz, an "ultra stable oscillator" is a thing -- it's
what the oscillators flown on the deep space probes are called. That's
why the term sent me into la-la land.
Basically, the probe receives the uplink from the earth station and
translates it to be the carrier of the downlink frequency, so the earth
end can compare phase of the received vs. sent signal.
To do that requires hydrogen masers at the earth station, and the best
possible LO in the probe. Power and volume budgets, and reliability
concerns, have ruled out atomic clocks (but see below) for this purpose,
and the USO is a hand-made (by JPL, I think) oven-controlled crystal
oscillator with incredible stability and aging characteristics. I think
the "list price" (or whatever the accounting term is) of a space
qualified USO is well into the six figures.
I just Googled and found that NASA recently turned on the Deep Space
Atomic Clock test system which is aboard an earth-orbit satellite. It's
a mercury-ion clock that's way better than any crystal and it or
something like it will be on future probes. I can't imagine what it cost!
73,
John
----
On 9/28/19 6:56 PM, Bruce Perens wrote:
> N8UR is not just a time-nut, he is in some senses THE time-nut.
> Ultra-stable to you might mean it doesn't drift a kilohertz. To John, it
> means he can fly one oscillator around the world, and then measure the
> relativistic difference against one that stayed home. :-)
>
> On Sat, Sep 28, 2019 at 1:16 PM John Ackermann. N8UR via Ground-Station
> <ground-station at lists.openresearch.institute> wrote:
>
> Hi Douglas --
>
> OK, that makes sense as a neat experiment, but "ultra-stable"
> implies something a lot more complex and sent me off into the
> weeds. I think the biggest challenge, as someone else pointed out,
> is that getting a transmitter authorized, even at very low power,
> probably creates a bunch of bureaucratic hurdles.
> On Sep 28, 2019, at 2:52 PM, Douglas Quagliana <dquagliana at gmail.com
> <mailto:dquagliana at gmail.com>> wrote:
>
> Hi John,
>
> The idea was to have a very simple crystal oscillator (perhaps a very
> small milliwatt class amplifier) and an antenna
> such that the oscillator's signal (with Doppler) can be detected on
> the ground. No data, just a carrier that a
> ground station with a simple antenna and perhaps a FunCube or RTLSDR
> dongle can detect.
>
> The overriding principle is "keep it simple." Generate just enough RF
> output so that the oscillator's signal can be
> detected on the ground -- and detection can be done at MUCH lower
> signal levels than are needed to demodulate
> a data signal. Ground stations know the frequency to listen at. This
> experiment would be placed on a short lived
> LEO so that as the orbit decays and the spacecraft slowly spirals in
> (over several months/years) the changing
> orbit can be observed by watching the signal and it's Doppler
> characteristics change over time. It's not a very
> interesting experiment at GEO where the orbit really never changes.
>
> The whole experiment (except the antenna) should fit on postage stamp
> sized circuit board, weigh only a few
> grams, and pull just a couple of milliamps. The frequency could be
> any frequency in any amateur band
> authorized for satellite downlinks.
>
> I'm not sure what the specifications should be except that the
> oscillator should be as stable as reasonably
> possible within whatever the budget it, but if someone can help out
> then let me know and we can
> write the specification and propose it to be included as an experiment
> on some future satellite. The
> experiment also needs a cool name.
>
> Perhaps we should move this to another thread... if anyone is
> interested, please let me know.
>
> 73,
> Douglas KA2UPW/5
>
> On Fri, Sep 27, 2019 at 7:37 AM John Ackermann. N8UR <jra at febo.com <mailto:jra at febo.com>> wrote:
>
>
> In this context, what does "Ultra Stable" mean? There are a
> bunch of interesting challenges with crystals in space
> because of the launch shock, the huge temperature swings,
> and the thermal insulating properties of vacuum.
>
> I know people who know about these things and would be glad
> to help if we wanted to do this, but a spec is the first
> requirement. It would need to include (at a minimum) nominal
> frequency, short-term stability,
> phase noise, drift/aging, temperature response, and absolute
> frequency accuracy, along with mechanical things like shock
> rating, physical dimensions, and power budget. There would
> have to be consideration
> of thermal management as well, given the likely need for an
> oven.
>
> (Note: I've never done spacecraft design, but I've picked up
> on these issues from conversations with those who have
> worked on space-borne USOs.)
>
> 73,
> John
> On Sep 27, 2019, at 1:32 AM, Michelle Thompson via
> Ground-Station <ground-station at lists.openresearch.institute>
> wrote:
>
>
> We can design our own sensor. There's a blurb about it
> on the site and specs for the footprint and interface.
>
> If someone commits to build and test, I can work with
> Ambasat to see if we can get it on there.
>
> On Thu, Sep 26, 2019, 22:27 Douglas Quagliana <
> dquagliana at gmail.com <mailto:dquagliana at gmail.com>> wrote:
>
>
> Rather than a sensor, could we get an ulta stable
> oscillator (USO) for some frequency in an amateur
> satellite band? We would just need the USO, a small
> amplifier and an antenna. Even an inefficient
> antenna. Even if we’re only radiating a few
> milliwatts. There’s still a lot of good science we
> can do from an unmodulated carrier with Doppler.
>
> Regards,
> Douglas
>
> On Sep 26, 2019, at 6:24 PM, Michelle Thompson via
> Ground-Station <
> ground-station at lists.openresearch.institute> wrote:
>
> There are solar panels.
>
> From https://ambasat.com/ambasat-2/ambasat-1/
>
> "AmbaSats are just a little bigger than the size of
> a couple of postage stamps but have solar cells, a
> LoRaWAN radio transceiver..."
>
> For the dashboard, there's a big hint here:
> "Your AmbaSat-1 is fully TTN compliant so as well as
> viewing data in your Dashboard, you can sign-up for
> a TTN account and access your satellite’s sensor
> data directly using a range of different TTN
> extensions."
>
> I think the dashboard is essentially The Things
> Network. I'll see what I can find out about the
> dashboard availability.
>
> Interesting question about HABs! I think several
> people on this list are much more active than I am
> in designing and building payloads, and might be
> able to give an evaluation based on what's on the
> ambasat.com <http://ambasat.com> website.
>
> -Michelle W5NYV
>
>
>
>
> On Thu, Sep 26, 2019 at 11:56 AM KC9SGV <
> kc9sgv at gmail.com <mailto:kc9sgv at gmail.com>> wrote:
>
>
> The "three months in space" bit, makes me wonder.
> Maybe out of power by then ?
> (Don't see any solar panels on the board.)
> What would the possibility be to use the board
> as payload on a HAB (high altitude balloon).
> Maybe a Mylar balloon cluster achieving float,
> like the current Miami effort ?
> Then the environmental modules would make sense.
> Could you get the dashboard and web based
> tracking without buying the launch ?
>
> Bernard,
> KC9SGV
> Sent from my iPad
>
> On Sep 26, 2019, at 1:11 PM, Howie DeFelice via
> Ground-Station <
> ground-station at lists.openresearch.institute> wrote:
>
> It has a LoRA radio on board which is really
> cool. I always thought that LoRA on a LEO would
> make a great Store and Forward messaging sat.
> The chirp spread spectrum modulation handles
> doppler quite well and LoRA chips on carrier
> boards are easy to find to make ground stations.
> Unfortunately there is little chance we could
> license it since the FCC decided that anything
> smaller than a 1U cubesat is too small to track.
>
> Howie
> AB2S
> ------------------------------------------------------------------------
>
> From: Ground-Station
> <ground-station-bounces at lists.openresearch.institute>
> on behalf of Michelle Thompson via
> Ground-Station
> <ground-station at lists.openresearch.institute>
> Sent: Thursday, September 26, 2019 11:26 AM
> To: Michelle Thompson via Ground-Station
> <ground-station at lists.openresearch.institute>
> Subject: [Ground-station] Please vote - Ambasat
> sensor
>
> I bought into the Kickstarter for Ambasat.
> https://ambasat.com/
>
> I’d like you all to help choose the sensor!
>
> Choices here:
> https://ambasat.com/ambasat-2/sensor-options/
>
> Disclaimer:
> This has nothing to do with our project. I
> acknowledge that Ambasat is controversial. No
> project funds are involved.
>
> Why post this here?
>
> Details:
> I asked Ambasat about a custom amateur radio
> payload, so we could test something for us. The
> kickstarter had that option. The lead of Ambasat
> said yes, amateur payload ok, several people I
> asked at Virginia Tech said go for it, and a
> small group looked at the specs and tried to
> design something useful for us. But, the very
> compact size and power budget was quite
> daunting. And the time frame was very short. We
> don’t have enough miniaturization or time.
> Instead of a custom board, we have a standard
> flight and a ground version.
>
> Instead of quietly sending this up, I wanted to
> share it with the team as something fun. I just
> received the survey for the sensors, so we
> easily have a week at least to vote. It includes
> some sensors already. The free choice is an
> additional sensor slot.
>
> -Michelle W5NYV
>
>
> --
> -Michelle W5NYV
>
> "Potestatem obscuri lateris nescis."
>
>
>
>
> --
> Bruce Perens - Partner, OSS.Capital <http://OSS.Capital>.
More information about the Ground-Station
mailing list