Looks good! A couple comments/observations: 1. I'd skip the SD card. We have lost so many of them on orbit, we have given up using them. Never used MRAM on orbit, but I've heard good things. We usually go with FRAM. 2. I'm not sure how accurate of a sun sensor you need, but you may be able to get away with using the power output from each solar panel (if they aren't tied together). We did this on one cubesat we launched when I was in grad school and had ok results. 3. Don't worry too much about the crazy temperature ratings. At the end of the day, your batteries are by far the most temperature sensitive component you will have on your spacecraft. So don't fret too much about it. Additionally, from the variety of spacecraft I've been involved with, you really only start to have temperature issues when you get into bigger cubesats. Even 3U's are pretty easy going with respect to temperature. 4. The off chip watchdog is invaluable. I'd recommend that circuit be able to power cycle as much of the spacecraft as possible. SEUs are gonna happen, it's important to plan for a strategy to deal with them.
Hey Nick! Thanks for the feedback. 1) The SD card is starting to sound like more trouble than it is worth. It's just a convenient & cheap interface to bulk storage. Have you had any experience with eMMC storage? Not that I have any storage requirements at the moment, I just like having the ability. 2) Right. And it's not like I _need_ super accurate sun sensing right now, Im more interested in finding a cheap way of accomplishing it. 3) Makes sense! 4) I'll try to incorporate that! On the topic, I get stuck thinking about "who watchdogs the watchdog". Since nothing on this board is rad hard, everything could experience SEUs or SELs. What if the watchdog fails and permanently holds the MCU in reset? What if my current-monitoring circuit latches up? Are these things I should worry about?
@@RGSAT I've had less on orbit experience with soldered on eMMC, but the single data point I have had similar behavior to an SD card. As for RAD hard components, the majority of the spacecraft I have launched have not had any RAD hard components. There is indeed some risk to having a single point of failure, and usually you just have to hope your watchdog circuit is going to be robust enough. If it is simple enough, you'd be more likely to see the watchdog occasionally trip when it shouldn't instead of it hanging partway through a reset (and keeping your MCU in reset). As for your power monitoring circuitry, if possible, I'd put that under your watchdog's control as well. Normally, you would use a sort of hierarchical watchdog system and have software on your flight computer that can power cycle things automatically if they aren't responding or giving bad data. This sort of thing is usually called FDIR, if you want to read more about it.
Your TCXO could be GPS-locked since your including a gps chip which BTW a usb gps chip on board is available from amazon for $6. Your temp sensors could double as sun sensors espically if you use the solar cells for redundancy.
That actually gives huge relief on the whole, well explained tho some btw can u pls send this Schematic diagram of CubeSAT avionics board for Electrical Reference buddy!
because of bitflipping planes use blockchain style tech so redundencies and positioning are something you might need in a cube sat maybe design a board, if you make this a manufacturing idea design 2 boards that interlock with a cut in their middle so they become a cross and the middle part can be a connector Water based microsatelite propultion is currently being tested using energy from ambient radiation to create steam out of ice as for the solar panels you could stick the antena in one of the edges, on one of the edges so that it covers more 2 dimentional surface area relative to the sun
1. Blockchain works by spreading the data across nodes and then run a majority vote on the data. So writing some data into 3 locations in memory and ignoring a bit flipped version may be a good idea. It requires 3 times more memory. Simplest Hamming code (4 bits of data on 7 bits of memory) is more efficient. 2. Cool idea for solar-thermal propulsion
I was thinking of using the MLX75306, but I'm not sure. It isn't very cheap, and I think it is obsolete. I'm currently re-thinking what sort of sun sensor I could design.