KSP Community CubeSat

[LvL]

Once the plant dies, it's going to start decomposing and the absence of gravity isn't going to help the situation. we'll have to have it pretty well sealed

[Nicholander]

Well, if the moss dies before we've lost contact or it burns up in the atmosphere, then the missions over, there's nothing to be done. We've done our experimemt, and it's now just orbiting the Earth, just with a camera to take pictures of the plant and in space. So it doesn't matter if it depresurizes now, and it might be cool to see how it looks through the plant camera.

[Mazon Del]

Honestly I am still lightly in favor of the idea of having a mechanism where we can actually vent the atmosphere of the chamber after some point (plant dies, whatever) so that we can observe what happens to plant matter in a vacuum over time. Able to be simulated on Earth honestly, but still interesting.

Status update on Luis (biologist professor that is willing to chat with us), I'm going to be sending him an email with our questions today for status and such. Here is a summary of the current questions, last chance to chime in before I send them,

In no particular order:

1) If we choose to use moss, what species are the most common model species in the field?

2) Which introductory text or texts would you recommend we familiarize ourselves with?

3) Which journals are well-respected in the field? (As sources for information similar to what we are working to provide.)

4) What (if any) are the well-known effects of gravity on the mosses (such as size or reproduction rate) that we can try to observe with a webcam instead of a microscope?

5) Do you know of any small scale equipment that can be obtained that will help take care of the plant? (keeping the atmosphere moist enough, balancing CO2 and O2 properly, etc)

6) What information should we be gathering on the plant and its environment? (Mainly, what type of data collection instrumentation should we provide?)

7) How much research has been done on bacteria in low-G?

[Nicholander]

Honestly I am still lightly in favor of the idea of having a mechanism where we can actually vent the atmosphere of the chamber after some point (plant dies, whatever) so that we can observe what happens to plant matter in a vacuum over time. Able to be simulated on Earth honestly, but still interesting.

Hmmm... that's actually be a good idea, as from what I understand, that type of mechanism would be simple, cheap, and compact. So there's no reason to not do it. (Well, unless you REALLY want to see how it looks after there's be a decompression in the pressurized area)

[dharak1]

It would complicate the structure slightly, no big problems if it fails. The way I see it as long as it doesn't cost a million dollars I don't see why not.

[Mazon Del]

Really the big reason why you might not want to do it is a fear that something could trigger it early, which would suck.

Anyway, the email has been sent! I'll let you guys know what response I get.

Also, celebrating my 200th post! Woo!

[Nicholander]

Really the big reason why you might not want to do it is a fear that something could trigger it early, which would suck.

Oh... So maybe we shouldn't do that...

[K^2]

Short of software error, I do not see why it would open early. It is pretty likely to get stuck shut, bu that's not a big deal. As for software, there are more serious risks there, bugs that can result in total loss. Fortunately, software can be well tested on the ground. Plus, we might actually need to vent atmo in case of pressure buildup. So I am all in favor of a vent valve. So long as it is light and simple.

[kenbobo]

Not sure if mentioned, why don't we use Hydrazine for RCS control, and 1-2 small hydrazine thrusters for sat course correction thrusters?

[dharak1]

I never thought of pressure buildup. Depending on what system we use what would be the cause and could we intentionally cause it? It would be kind of cool to have the thing go pop at the end of the experiment or before re-entry. I'm sure the results of carefully dropping the pressure would be much better though.

[Nicholander]

Not sure if mentioned, why don't we use Hydrazine for RCS control, and 1-2 small hydrazine thrusters for sat course correction thrusters?

Uh... Hydrazine, you see, is toxic stuff...

[Kryten]

Not sure if mentioned, why don't we use Hydrazine for RCS control, and 1-2 small hydrazine thrusters for sat course correction thrusters?

Not many providers would let you put a bargain-basement chemical thruster system next to their primary payload. Nobody sane would allow you to bring one onto the ISS, which is what the cheapest launch option entails.

[kenbobo]

Uh... Hydrazine, you see, is toxic stuff...

Yes i realise that. But most RCS systems (mercury, gemini, space shuttle) use Hydrazine.

[Nicholander]

Well, as Kryten said, we wouldn't be able to put it on anyway, so how do we point our CubeSat with stuff that LV providers and the ISS guys will let us send up there?

EDIT: Also, have any of you seen this crowdfunded thing on IndieGoGo of these people who want to send a lander to Mars with giant lawn darts to look for life? It's called ExoLance.

Edited August 19, 2014 by Nicholander

[Rakaydos]

question concernting the "advnced" flights beyond LEO... a magtorquer works with the earths magnetic field, but how do we intend to aim our craft once we go beyond earth's magetosphere? Can a magtorquer interact with the solar wind at all?

[K^2]

Yes i realise that. But most RCS systems (mercury, gemini, space shuttle) use Hydrazine.

Which were built by professionals and extensively tested. We can't afford construction, testing, and insurance costs this would require.

We might be able to attach an electrospray thruster, but at this point, I don't see any reason for one. We don't need reaction control, since magneto-torque is quite sufficient. And from ISS orbit, decay time is sufficiently long.

I'm still open to suggestions on a propulsion mission instead of the bio one. It just seems to me that the only options available are either already in common use (like the electrospray), are guaranteed not to work (gyros, etc.), or require a much larger satellite to test properly (like tether).

This still, potentially, leaves options for something like a high I_SP beer can ion drive. The I_SP of electrospray is pretty low, and conventional ion drives tend to be heavy and bulky. There ought to be something in between, suitable for a cube sat.

[Aethon]

Back to origami for cubesats.

[dharak1]

That looks pretty cool and might be able to be used on an outer planets mission because of the mount of area it provides, but we only need about 2 panels 10x10. Something like that requires a telescoping pole and we would be screwed if one didn't deploy because we wouldn't be able to spin the cubesat because it would throw off the center of mass.

[Mazon Del]

Short of software error, I do not see why it would open early. It is pretty likely to get stuck shut, bu that's not a big deal. As for software, there are more serious risks there, bugs that can result in total loss. Fortunately, software can be well tested on the ground. Plus, we might actually need to vent atmo in case of pressure buildup. So I am all in favor of a vent valve. So long as it is light and simple.

I am less worried about the software improperly triggering it because of software faults. It is more the thought that a randomly flipped bit (cosmic ray, etc) could make the software THINK that the "should I vent?" system has declared "Go!". There is some data to suggest that this has been observed in computers on cars (deep inside atmo) causing things like uncontrolled accel/braking.

Possibly what we could do though which would likely fix this problem and might help with another. We could have a sort of atmosphere "airlock". This could be useful if we go with stored CO2 or something, because we could vent a little bit of pressure in controlled bursts(open outter valve, close outter valve, open inner, close inner, repeat) then 'refill' from the CO2. It would cause a higher percentage of CO2 to exist without permanently (to a degree anyway) changing the pressure of the bio-container.

For what its worth, if we did this and planned for it, we could possibly set these releases to happen in an attempt to help boost our orbit a little.

Vacuum rated seals are probably a little pricey for seals, but I wouldn't expect them to break the bank honestly.

[Nicholander]

Okay, so I think we COULD do the vent system, if we make super-sure that the software won't screw us over by killing the moss with the deadly powers of the vacuum of space, and since it is easy to test the software, I say change that to a "Probably". And Mazon Del, and airlock, really? remember, we're just working with 0.5U of CubeSat, which most of it will contain the pressurized area, and the rest of it filled with the systems to sustain the pressurized area.

[Mazon Del]

For the device I described it wouldn't take too much space, such valves can come quite small. By airlock I wasn't meaning the crazy system that things could go through, just two valves with a pipe between them, one valve leading 'into' the bio-container, the other leading to the outside of the craft. By airlock I was describing how with the two valves, if we had a spurious "OPEN!" command, we wouldn't vent the bio-container. Worst case, just whatever was in the tube.

[K^2]

I am less worried about the software improperly triggering it because of software faults. It is more the thought that a randomly flipped bit (cosmic ray, etc) could make the software THINK that the "should I vent?" system has declared "Go!". There is some data to suggest that this has been observed in computers on cars (deep inside atmo) causing things like uncontrolled accel/braking.

Possibly what we could do though which would likely fix this problem and might help with another. We could have a sort of atmosphere "airlock". This could be useful if we go with stored CO2 or something, because we could vent a little bit of pressure in controlled bursts(open outter valve, close outter valve, open inner, close inner, repeat) then 'refill' from the CO2. It would cause a higher percentage of CO2 to exist without permanently (to a degree anyway) changing the pressure of the bio-container.

For what its worth, if we did this and planned for it, we could possibly set these releases to happen in an attempt to help boost our orbit a little.

Vacuum rated seals are probably a little pricey for seals, but I wouldn't expect them to break the bank honestly.

Good idea. And we can have software checks to make sure that neither valve is open when it shouldn't be. If just one opens up briefly due to a random bit flip, it's not a total loss.

As far as I know, vacuum-rated valves are more about the type of lubricant used, than the valve itself. So it should be reasonably priced. The sort of valves they use in projects where they need perfect vacuum, these are pricey. But we don't care if we end up "contaminating" the vacuum slightly. So long as lubricant lasts through the mission.

[Nicholander]

Ah, now I understand Mazon Del.

[K^2]

Ok, I think I have all of the formulae derived, but I can use some help checking the math. This probably mostly goes to Mazon Del, but if anyone else wants to take a crack at it, feel free.

Just to briefly cover the basics, I start out with Hamiltonian formulation. For central potential: H₀(q_i, p_i) = (1/2m) (p_r² + p_θ²/r²) - mμ/r. Given generating function S(q_i,α_i), such that p_i = ∂S/∂q_i, we solve Hamilton-Jacobi equation: H₀(q_i, ∂S/∂q_i) + ∂S/∂t = 0. That gives us new coordinates, α_i, β_i = ∂S/∂α_i which are constant in time.

Solving for S(q_i,α_i), we find that α₁ = mμ/(2a) = -E, α₂² = μm² a(1 - e²) = L², β₁ = T, and β₂ = Æ. Here, T is time of periapsis passage. In other words, anomaly is zero when t = T. Similarly, Æ is angle of the periapsis. So given these four parameters, we know the exact trajectory the satellite takes in central potential.

Up to this point, I've compared to standard texts, and everything seems to match. So I don't need any verification on constants of motion. From here on, however, things get a bit more fuzzy.

We wish to consider a perturbed potential H(q_i, p_i) = H₀(q_i, p_i) + U(r, θ). As a consequence, we have following equations of motion for the constants.

β'_i = ∂U/∂α_i

α'_i = - ∂U/∂β_i

I'm using the primed notation to denote derivatives with respect to time. Naturally, in a physics simulation, what I actually have available are forces, which are related to ∂U/∂r, and ∂U/∂θ. And I don't need to worry about alphas, because rate of change of energy and momentum can be trivially expressed in terms of state variables. What I need are the β'_i terms.

The following is known.

r = a(1-e²)/(1 - e Cos(ν))

r = a(1+e²)/(1 + e Cos(ν))

θ = ν + Æ

Here, ν is true anomaly, and that's the only term that depends on T. Specifically, it is a function of t - T. So ∂ν/∂T = - ∂θ/∂t = -θ'.

After expanding U in terms of alphas, taking derivatives, and plugging everything back in, I got the following expressions.

T' = β'₁ = ∂U/∂α₁ = r(∂U/∂r)/E

Æ' = β'₁ = ∂U/∂α₁ = θ'( er Sin(θ)/(1 - e Cos(θ)) (∂U/∂r) - (∂U/∂θ) )

These are the values I need verified, to make sure I didn't mess something up. I'll also check this with a simulation. But since dependence of true anomaly on time is not exactly trivial, I'm going to have to work out a good way to do this.

Edit: MAJOR derp. I took ∂U/∂T, which is ∂U/∂β₁, instead of ∂U/∂α₂. As a result the expression for Æ' is actually correct expression for -E'. And it is. If you work it out, that is exactly work done per unit time by external force on the orbiting body. So at least, that helps me verify some of the steps.

Minor derp. Got signs wrong in the radius equation, so I ended up with true anomaly counted from apoapsis instead of periapsis. Fixed that now.

So I still need to derive the correct equation for Æ', but T' should be right, and I'd still appreciate any checks on that.

Edited August 20, 2014 by K^2

[LvL]

*Math stuff*

uh, I'd rather stay out of that sort of stuff. I'm the helpful criticiser