[amsat-bb] AO92 L/V mode?? A suggestion

[Jerry Buxton]

On 2/21/2020 22:54, Mark Jessop via AMSAT-BB wrote:
> I heard rumours that the camera on AO-92 was only allowed to be activated
> over the US, for fixed time periods? Something to do with imagery licensing
> conditions...
>
> Perhaps someone from the team could provide further information?
I can speak to this Mark, and you are partially correct.  I will also
answer Scott's question about the duration of camera operation.

The original license permitted only "images of earth" because as amateur
radio we can not encrypt the downlink as is typically done with imaging
in order to protect images of sensitive 'things' for lack of a better
term, such as other satellites as I mentioned in a previous email.

Since the imaging is fairly automated in that we activate it and it
takes an image about every 50 seconds (the time it takes to download an
image) we had to come up with some ways to ensure we only image Earth,
given the passive magnetic stabilization of the Fox-1 satellites. 

You may have seen in some of the images we have captured, the camera may
be pointing more or less directly down or it may be pointing toward the
horizon, in somewhat random fashion.  BTW the images are successful only
with the help of a lot of hams copying the telemetry, thank you all who
do help make a complete image.
Passive stabilization generally keeps the +Z or camera end of the
satellite pointed toward the North magnetic pole, it tends to point down
toward Earth over the northern hemisphere where the magnetic field dips
to the pole.  That is by design.  The satellite always oscillates as it
moves through the uneven magnetic field and is influenced by a number of
things such as the "flip" that occurs around the magnetic equator
crossing when the magnet changes from south -Z end down toward the south
magnetic pole to the +Z down toward the north magnetic pole.  The magnet
is also slightly off the center of the Z axis of spin, and other
conditions make for it not being "rock solid" as far as pointing toward
the magnetic pole.

To "automate" the detection of Earth, the Virginia Tech student team
that built the camera experiment included in their software a method of
looking for brightness and "earth color" detection.  The software allows
for many levels of sensitivity and is pretty good at being able to tell
if Earth is in the picture.  While it takes images first, then
determines if Earth is in the image, it will not send any non-Earth
(determined) images to the IHU for downlink.  When testing the satellite
in Fox Labs, I set up several instances of various light and colors in
order to determine the best level for the software setting to select for
launch, so we didn't turn on the camera and get our first images of the
UFO over the North Pole and wind up putting myself in NOAA jail.  If you
look at the lower left corner of the images on the Fox Telemetry
Leaderboard web page, you will see the characters VT-2.  VT of course
indicates who gets the kudos for the image, and the number 2 indicates
that we are at sensitivity level 2.  We have been at that number since
launch.
In addition, you notice that all images are during daylight which of
course gives the best results as far as colors.  The camera has the
capability of imaging at night as the satellite is in eclipse but the
addition of the earth-only software negated any opportunities to
downlink images in low light.  We would have liked to see images of
daylight coming over the U.S. and then into night as it crossed the
pole, but that did not come to pass because of the license requirements.

The reason the camera is activated over the U.S. only is also a license
requirement, in that the command station operating the imager must be in
the U.S.  And the fact that the images are all taken in descending node
is a function of the orbit that Fox-1D/AO-92 wound up in, where the
daylight passes are descending nodes over the U.S. where it is
commanded.  It is possible to activate the camera on an ascending node
pass over the U.S. at night, and that should produce images of "the
other side" of Earth after the satellite crosses the pole, but...

The primary thing about that, which also affects the mention of having
the imager on for 24 hours a la L Band mode, is the fact that we had to
implement a 45 minute timer on the Data Mode (camera) for Fox-1Cliff and
Fox-1D because of the same license restriction of earth-images only. 
Why was that done?  The number was reached based on the latitudes of our
command stations in an ascending node pass, and the time it would take
from activation during a pass over the command station(s) until the
satellite reached the equator on the other side of Earth.  It is a hedge
against the earth-image detection software routine should that not work
as intended, so the satellite would switch out of Data Mode before it
flipped and took images of the UFO parked over the South Pole.  Too,
with the earth-image detection software working, it made no sense to
stay in Data Mode at 100% duty cycle while no images could be sent
because there was no Earth in the image.  Rather than wait until another
pass over a command station, we shut off Data Mode to save power.

What about these descending node passes during the day, where we got the
images that you have seen?  Since the orbit did turn out to be
descending during daylight, when we were commissioning the satellite we
tested the earth-image detection and verified that it worked (Data Mode
could be commanded off if it had failed during the tests).  Once we knew
that, we could confidently activate Data Mode on a descending U.S. pass
and while the camera would continue to operate past the equatorial flip,
we knew it would not be sending images and that the 45 minute timer
would shut it off soon enough that we do not waste a lot of power.

There is work underway to be able to switch the AO-92 camera from its
"native" 320x240 resolution to the camera's full 640x480 resolution,
which is what the AO-95 camera was set for its "native" launch
resolution.  This will require a license amendment by NOAA, and I am
working that process now.  I won't speculate on when that might be
completed because it involves Virginia Tech and satisfying whatever
requirements set forth by NOAA, two variables that are not under my
control.  I believe the current thinking is that once we have that
amended license, we will also experiment with the sensitivity of the
earth-image detection software to see if we can fine tune things to
capture even more and better images for all to see.  That is actually up
to operations, of course I am working with them on the resolution and
sensitivity since the NOAA license is in my charge.

I believe that covered the questions in the two emails I saw, if three
more didn't come in while I typed this (hihi) and gives everyone the
story of how and why AO-92 imaging is what it is.  We should all thank
Virginia Tech for engaging in their camera experiment and flying it on
the Fox-1 satellites, and for their cooperation and work when we had to
pursue the software earth-image detection.  I think they did a great job
of that, my testing showed it to be a good spread of sensitivities and
the on orbit performance of AO-92 has shown that at least for now, what
I saw as the best pick after testing their work turned out to be of the
same performance in orbit as it was in Fox Labs.  That shows good,
consistent work by their team.
We can thank the AMSAT Engineering software team for the 45 minute
timer, even though we went back and forth on it so many times with all
of the variables that kept coming of the NOAA license and power budget
and such - I think I'll take a little credit too for remembering the
final number we settled on, some two years later when Fox-1D finally
launched!

And as I said, we thank all of our satellite ham friends who copy the
telemetry with FoxTelem so that, while no one station may get the full
image, the sum of all of the stations that capturing the telemetry for
an image can be added together on the Fox server for a complete image
that all can see.  If you enjoy seeing the images, please consider
having your telemetry station ready for days that Operations might
operate the camera in the future especially with the new resolution and
sensitivities, so that we can all enjoy new images that we may not have
seen before!

Jerry Buxton, NØJY

I hope there ain't no typos, because I'm too tired to go back through and check...