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...