KSP Community CubeSat

[K^2]

I was picturing this with a camera that has integrated compression chip. 8051 would only have to grab compressed data and package it.

But a co-processor approach has merit. So long as it is only powered on for media operations, and no mode of failure, including a total short, can fry the whole sat. In that case, might as well have video as an option, as well as whole bunch of other features.

Is Pi the best option, then? I agree that it should be ARM based. But custom solution would allow for better resource cross-use. If you want two CPUs, for example, you definitely do not need two boards. But I do appreciate simplicity of simply grabbing a board and libs.

[Nicholander]

Is Pi the best option, then?

Well, I still think we should have a CPU designed for CubeSats.

[K^2]

This would be secondary. Not critical.

[MBobrik]

I was picturing this with a camera that has integrated compression chip. 8051 would only have to grab compressed data and package it.

AFAIK there is no rad hard camera module that can do that. Either bare chips w/o compression, or complete stand-alone cameras which cost an arm and leg. And the 8051 we are going to use got not enough processing power to interface directly with either of the two anyway.

So long as it is only powered on for media operations, and no mode of failure, including a total short, can fry the whole sat.

We can ( and should ) make it completely separated from the flight computer, communicating only through optocouplers and powered through converter-isolated transformer, which cuts the power instantaneously in case of overcurrent.

Is Pi the best option, then? I agree that it should be ARM based. But custom solution would allow for better resource cross-use. If you want two CPUs, for example, you definitely do not need two boards. But I do appreciate simplicity of simply grabbing a board and libs.

Well, I still think we should have a CPU designed for CubeSats.

I am inclined to say that the raspberry pi compute module is our best choice. it got ARM11@700 MHz plus additional 24 GFLOPS GPU, weights only 7 g, and costs ~$30.

"professional" cubesat computers got comparable or smaller computing power, weight 5-10 times more, and costs two orders of magnitude more.

Other boards of comparable size and price range got much less computing power (the r pi compute module is the newest of the newest, released only in April this year )

Even if we were to solder together our own custom hardware, I seriously doubt we could beat that. Most probably we would end up with something comparably small, only less powerful, and we would need man-years of development of both the hardware and software. If we had a few hardware pros on team, which we don't.

Having two processors on one board for redundancy would also not help much because supporting circuitry working with high-speed processors would not be hard rad either. We would end up duplicating the whole board anyway.

Edited November 27, 2014 by MBobrik

[K^2]

Is that GPU good for general computations, though? Is there something like CUDA that could be used with it? At any rate, I am not sure what we need all that power for. Well, other than video compression.

The basic ability to use ARM as FPU is nice. But since primaries must be capable of running independent of co-processor, all flight nav and control will probably be fixed point, anyhow. So applications of these caps are limited. But I am sure we can find some secondary function for these.

I second optocouplers. Power, there are options on. Transformer requires converter. I would rather just fuse it, and maybe drop in a low pass for interference.

Camera need not be rad-hard for the same reason that Pi does not. Not mission-critical, and redundancy is easier/cheaper. And off the shelf camera with JPEG support are cheap and plentiful.

Anyhow, I will now look more into Pi/ARM/other options for "media" co-processor.

[MBobrik]

I second optocouplers. Power, there are options on. Transformer requires converter. I would rather just fuse it, and maybe drop in a low pass for interference.

Since both boards use different voltages, we will have to use a DC-DC converter, or have the main power supply produce two voltages. In both cases, electrical separation of the two and overcurrent protection

comes at neglible, even zero additional cost. Anyway, a fuse alone is not fast enough to protect circuitry that can burn out in microseconds, so an overcurrent shutdown circuit is necessary anyway.

And off the shelf camera with JPEG support are cheap and plentiful.

And requires the same decoupling as co-processor, but got more than order of magnitude worse compresion, and the 8051 will have to shovel the data from it to the transmitter, which would be a significant load for it... And that all to save ~ $30 and ~ 1 watt of power.

Anyhow, I will now look more into Pi/ARM/other options for "media" co-processor.

I will keep searching for other potential processors/boards/camera candidates. Maybe we find something better, though rasp pi will be hard to beat.

[henryrasia]

I'm surprised everyone is talking about rad-hardening everything, I'd think the lack of an atmosphere would cause overheating instead, or other problems. Just to catch up, we decided the whole cubesat would be sealed against light. This was because we needed to keep the experiment in the dark, and an on-off-on-off rotating sun combined with 90 minute "days" would not be so nice on the plant, especially in the "keep uncontrolled variable count low" commandment of scientific experiments.

So how about this: We rad-hard the metal cube in which everything else goes into, letting only small gaps for cables (if we go with deployable solar panels) and an external camera peephole. Unless I'm missing something here, that should be enough for covering all bases. Or does radiation phase through anti-radiation surfaces? If it does, then how can anything be rad-hard? I understand why the external camera needs to be rad-hard, as it's going outside and image quality decreases significantly with radiation exposure.

And then there's the deal with beaming down images/video. From what we've has been saying, I strongly suggest we put a stretch goal on the kickstarter, because then more money => bigger solar panels => more powerful comms => More bandwidth / signal quality => More and prettier pictures/videos/data! I think this is a nice solution, though it still does not answer how we'd do it without the extra money. We should't rely on strech goals.

(PS Mazon Del, if you're reading this, I still think 1U will make a gravity gradient in the experiment big enough to mess with our data, what's your take on that?)

[Nicholander]

From what I understand, the radiation in LEO isn't that much anyway, so how about we just have the 2 cameras be rad-hard? Or is the radiation significant enough that we should do what you suggested, henryrasia.

[Treldon]

I believe the idea to rad harden the entire cube came up earlier, and the outcome was that the only viable method would be a lead layer, of which sufficient quantities would weight more than the entire unit can

[Bill Phil]

A cubesat?

Interesting...

It would certainly be a good publicity stunt, but that's about it.

Unless you did something nobody's done before....

Land on Callisto or any of the Galilean moons.

Or maybe a Titan landing but in the oceans.

I'm sure you already have plans for what you're doing, though.

Come to think of it, what exactly are you doing?

[bounding star]

~snip~

Land on Callisto or any of the Galilean moons.

~snip~

Come to think of it, what exactly are you doing?

is it that hard to read the first post?

[Treldon]

In this case the reading the OP does not suffice.

The goal is to send up a 1U cubesat to LEO with a small experiment on board.

The experiment:

step 1: spin up the sat using magnetorques to simulate gravity (~0.1g)

step 2: observe the reaction of the moss on board (how it grows - the moss has been/will have been selected by a biology professor for this experiment especially because of its sensitivity to gravity)

step 3: further spin the sat to achieve ~0.31g

repeat step 2

All the while sending back pictures and measurement data to ground station

[Bill Phil]

In this case the reading the OP does not suffice.

The goal is to send up a 1U cubesat to LEO with a small experiment on board.

The experiment:

step 1: spin up the sat using magnetorques to simulate gravity (~0.1g)

step 2: observe the reaction of the moss on board (how it grows - the moss has been/will have been selected by a biology professor for this experiment especially because of its sensitivity to gravity)

step 3: further spin the sat to achieve ~0.31g

repeat step 2

All the while sending back pictures and measurement data to ground station

Thanks.

Also, wouldn't the sat have to be spinning at quite a large rate? Or will it split and spin like a bola?

[Treldon]

Thanks.

Also, wouldn't the sat have to be spinning at quite a large rate? Or will it split and spin like a bola?

If I remember correctly for the second part it would be about 85 RPM - K^2 ha the numbers

[monstah]

I believe the idea to rad harden the entire cube came up earlier, and the outcome was that the only viable method would be a lead layer, of which sufficient quantities would weight more than the entire unit can

Isn't the gold foil many probes use for this purpose? It is probably not cheap, but is sure light.

[MBobrik]

Isn't the gold foil many probes use for this purpose? It is probably not cheap, but is sure light.

it is thermal insulation.

[MBobrik]

So how about this: We rad-hard the metal cube in which everything else goes into, letting only small gaps for cables (if we go with deployable solar panels) and an external camera peephole. Unless I'm missing something here, that should be enough for covering all bases. Or does radiation phase through anti-radiation surfaces? If it does, then how can anything be rad-hard? I understand why the external camera needs to be rad-hard, as it's going outside and image quality decreases significantly with radiation exposure.

Basically yes. the high energy cosmic rays punch through everything we, or anything less than battlecruiser sized, feasibly can have on board. There are the lower energy protons and electrons from the solar wind, but against those even the chip package, or the lens in front of the camera would be an adequate protection, because the magnetosphere already has taken care for the most of them.

The average radiation at LEO is so low that it would take years till the chips start to be affected by cumulative dose. The problem are occasional strikes (so called single events) of high energy particles, which, though rare, can cause the whole chip to short out destructively, thus any time interval a non-rad hard chip is powered, is like playing a round of the Russian roulette.

When the chip is not powered, it can not short out, and thus only a hit energetic enough to obliterate a whole transistor at once could harm it. ( but such a hit would most probably take the rad hard chip out too).

Rad hardened chips are different, they are built internally so that they are largely immune to this type of glitches.

The physical structure of a gate is altered so that even flooding it with carriers does not cause it to short out (co called "latch up"), but only transiently open. On top of that, all important logic is tripled, with additional voting logic, so that when only one gate gets hit, it does not affect the output at all.

And of course, the transistors are larger and made from more ionizing radiation resistant materials to soak up more of the cumulative dose before their junctions start to degrade. Technically, since we will stick to LEO and we won't perform any time critical maneuvers, only protection against destructive single events is relevant to us.

I can not find the part, though K^2 said it was discussed, and I believe I saw something like it being discussed a few months ago. But the result was, that the chance of the CPU being fried by such an event, if it has to run continuously during the entire mission was too high, and we would thus risk losing the sat before obtaining enough data. Not sure how this conclusion squares with the results of previous cubesats flown with non-hardened CPUs. How many of them seized up prematurely. I feel that we might have been a little too pessimistic here.

But the rad hard low performance + on demand switched high performance non-hardened CPU combo* we seems to be coming to, got advantages of its own. The simple but rugged 8051 can babysit the more fragile CPU, allowing us to restart, power cycle, even debug it remotely, and even if the more powerful CPU is destroyed, we still get some data. And the high performance CPU, because it will not have to be powered the whole time, the overall probability of being fried will be correspondingly low.And because it will perform no function that can endanger the satellite, we can and let it run more complex ( and thus less throughoutly tested ) software, and generally experiment with it even in flight.

And then there's the deal with beaming down images/video. From what we've has been saying, I strongly suggest we put a stretch goal on the kickstarter, because then more money => bigger solar panels => more powerful comms => More bandwidth / signal quality => More and prettier pictures/videos/data! I think this is a nice solution, though it still does not answer how we'd do it without the extra money. We should't rely on strech goals.

Agreed. As I mentioned, someone should look into the possibility of going through amateur radio sats. I myself have zero experience with ham radio, and will be most probably busy searching and comparing suitable CPU boards.

*As K^2 named it, we should call them media computer and flight computer.

Edited November 28, 2014 by MBobrik

[henryrasia]

snip

This is well beyond my area of understanding. If you and/or anyone else could look into that, that'd be one problem solved! (Unless you're willing to tutorialize electronics to us laymen, do you know any good one in the internet? )

Agreed. As I mentioned, someone should look into the possibility of going through amateur radio sats.

Elfnet apparently has experience with real radio and has suggested using a 40W transmitter. If he can figure that out all that'd be left would be figuring out how to harness that much power.

[Nicholander]

Amateur Radio Sats? Brilliant idea! Just a question, but are there enough of them to have non-stop communications with our CubeSat?

[Treldon]

Amateur Radio Sats? Brilliant idea! Just a question, but are there enough of them to have non-stop communications with our CubeSat?

Based on this website there are 77. Whether they could be used for our goals and if that's enough is a different question

Note: this site has a list of sats that can be used specifically for this (I guess)

Edited November 29, 2014 by Treldon

[bounding star]

Just a question, but are there enough of them to have non-stop communications with our CubeSat?

just to be clear, we don't need continuous coverage by any means, just long enough to get data from the last several orbits

[Nicholander]

I know that, but it'd be convenient if we had continuous coverage.

[MBobrik]

If you and/or anyone else could look into that, that'd be one problem solved! (Unless you're willing to tutorialize electronics to us laymen, do you know any good one in the internet? )

Well, I did almost nothing last several years and have to catch up myself ( right now I am just sorting out the suitable CPU boards ), but ultimately, given the number of people involved, most of us will have to get involved in things electrical, and/or programming.

Based on this website there are 77. Whether they could be used for our goals and if that's enough is a different question

Note: this site has a list of sats that can be used specifically for this (I guess)

I looked briefly at it, and OMG it looks like an aftermath of a nuclear war, or repelling an alien invasion. reentered,reentered,reentered, dead,reentered, dead, partially dead, a few remaining operational... and all of them on ~1000 km polar orbits and with ~9.6 kbps bandwidths, which is practically useless for our purposes. So either we will go through C-band and professional geostationary satellites ( no clue how it could be made ), or we have to find other solutions.

just to be clear, we don't need continuous coverage by any means, just long enough to get data from the last several orbits

That would be very risky, leaving all the data just to sit there, waiting for the last moment to catch it. The sat might glitch out, or it may reenter a little sooner, or just radiation might erase the data ( It would have to be stored in non-volatile memory of sufficient capacity, which means purposes, non-hardened flash memory )

Edited November 29, 2014 by MBobrik

[K^2]

I would like to support C/S band, but that requires an expensive transceiver and a proper tracking station. If we get budget for it, it would be nice. A good stretch goal? But we need to plan to make do with UHF. That will work as fallback in either case. Cannot hurt to plan support for broadband ops on media CPU, though.

[MBobrik]

I've finished reviewing the media CPU boards, and, there is really no competition to the Raspberry Pi compute module. There used to be one, the almost unknown ODROID-W board, which was planned as a direct competitor, but it has been canceled. There is Arduino Nano. But it got no CSI interface. And the slightly larger and heavier Arduino Uno. But it got almost two orders of magnitude less performance and no real advantage. There are of course other, more powerful single board computers, but I don't think trading 50 % or so more CPU power for more than 7 times weight is a good idea. If someone else knows a CPU with CSI , ~10 g weight, > 500 MHz clock, and a very good software camera support, that has a clear advantage over rasp pi, any suggestion is welcome.

Edited November 30, 2014 by MBobrik