LordQ

Alright, thanks to deljr15, we have a board! Go sign up here everyone: http://forums.mossat.org/index.php And make sure to introduce yourself.

We don't have any means for accepting donations yet, but thanks for your enthusiasm. I believe the targets for the moss experiments are to see how the moss grows in centrifuge 'gravity' of something similar to lunar and martian gravity. I'm not 100% versed i this though, so I can't really give more details. We do have another thread that discusses the moss actually, however, there's not much in that thread just yet.

@Nicholander, sadly, that's exactly the problem. vBulletin is a great forum software, but it costs money. @K^2, I haven't been considering software like Simple Machines so far because they only offer the forum software and not hosting space. Places like Zetaboards or Lefora offer forum software as well as free hosting space, and so are easier to set up. However, I do see that deljr15 has some server space, so I'll definitely look into Simple Machines as well. Also, the name KSP Community CubeSat is a bit too long for a forum name. The zetaboards forum I quickly started up last night to explore features rejects the name because it exceeds its 20 character limit for a forum name. Any other suggestions? Some quick and snappy would be best, ideally one word or two. And clearly we should reference Poland ball.

Sadly, I think we will have to go with zetaboards, as it's probably the best free option. Other free things like phpbb are nontrivial to set up. I'll go ahead and start up a zetaboards forum for us. Does anyone have any suggestions for forum name btw? Currently I have Kommunity Kubesat, which just sounds ridiculous.

Alright, it looks like it'll have to be vBulletin for now. A quick google suggested it would be superior to a zetaboards forum as well. I'll get one started once I get home later today.

Been a while since I last posted, but I have been keeping myself up to date on things thankfully. Good to see that some 3D models have come out. I hadn't thought of picking up Sketchup for this - I'll make sure to grab it ASAP. I do actually have some experience with forum administration and construction, so I'd be happy to set something up. I agree with henryrasia that it's probably a bad idea to start filling up this forum with our threads. Even one additional one, like we have now, is probably bad. I actually administered a zetaboards forum though, so my preference would be to make a zetaboards forum if everyone is alright with it. If not, I'm sure I'll be able to figure out how to make a vbulletin forum just as easily. Do let me know.

I have to say that an in orbit solution seems the most practical. But wouldn't ejecta from the impact damage the station?

Nicely done. The one quibble I have left is that coil turns and wire diameter should be inputs instead of outputs, but that's an easy fix. I've added some of my calculations where I did that at the bottom of your spreadsheet for reference. The numbers in there don't necessarily mean anything, so feel free to change them. In which case, I'll focus on figuring out how fast we can precess the cubesat with a given magnetorquer.

Alright, so my investigations of MBobrik's calcs have come to a sort of end. Unfortunately, I wasn't able to get the same numbers as you did MBobrik, but that's probably because I was putting in wrong numbers. Could I ask you to put all your calculations in a google spreadsheet? In the end, what I did was calculate the magnetic moment of MBobrik's system for an input power of 0.2W (200mW, the same input power as the magnetorquer coil I found earlier). Interestingly, I found that MBobrik's system only has a magnetic moment of 0.09Nm/T at this input power. In comparison, the magnetorquer coil I found gave a magnetic moment of 0.2Nm/T, and thus has a much higher level of performance for the given level of input power. Of course, that magnetorquer would probably catch fire or melt if you tried giving it 10W of power. Which highlights the fact that the theoretical coil that MBobrik has described doesn't have any actual physical parameters attached to it, particular wire cross sectional area or number of turns, so we don't actually know if it would be able to withstand 10W of power. So I took another approach, and am currently experimenting with the basic t = B * I * N * Sc formula with the R = ÃÆ’ * N * Cc / A and P = I^2 * R formulas, with inputs including the wire cross sectional area and number of turns that weren't present in MBobrik's analysis. I'll see what I can get.

My investigation of your results is ongoing MBobrik, but I've found something odd. I'm not sure how I missed this before, but I think you may have converted from rad/s^2 to RPM/min incorrectly. Your a = 0.012rad/s^2 converts to 6.88RPM/min using the conversion 3600*("input")/(2*pi), instead of the much higher value you calculated. I also found this website, which correctly verifies the conversion method I used.

A lot of discussion since I went to bed last night, great to see! @K^2: Yep, understanding precession isn't the problem, the problem is that the coning manoeuvre analysis that I attempted last night just isn't suitable for analysing how fast we can precess our cubesat. This is because the coning manoeuvre analysis assumes instantaneous impulses, like you might see with monopropellant thrusters, and a magnetorquer, at least the one I analysed, is not powerful enough to be able to provide "instantaneous" impulses. Similar to how it's a terrible idea to analyse an ion probe using standard Hohmann transfer analysis. @MBobrik: Nice work again! I don't have much time right now, but your numbers certainly look better now. When I get home, I'll be sure to go through it. It might also be worth investigating whether the magnetic fields induced by our magnetorquers get close to or exceed magnetic field limits for cubesat hardware. Probably a bad example, but you wouldn't hold a magnet up to your phone. Edit: So on the train now, so I've had some time to look through your calcs at least a little MBobrik. I noticed that you're putting in an input power of 10 watts, which is a lot of power. In comparison, the coil I found onlineonly uses 200mW, 50 times less power. With an input power of 200mW, your coil would produce less than 1 RPM/min of acceleration. I'm not 100% sure if just changing the power like that us valid however, and I will have to check properly once I get home.

Alright, my report from what I've investigated. Your calculations seem to be alright MBobrik, but some of the underlying assumptions don't quite work. I think it would be unreasonable to have a magnetorquer the coils of which are larger than our spacecraft itself, especially since it wouldn't then have a mass ratio of 5%, as K^2 pointed out. Pretty high amounts of power would then be needed to push enough current through all that coil as well, which would lead to heating issues. Instead, I think it would be best if we bought or made a magnetorquer like this one. So going off the specs for that magnetorquer, I did a quick calc going off its magnetic moment (mu) spec of 0.2Am^2. I then used T = mu*B, where T is torque and B is Earth's magnetic field strength. I used MBobrik's value of B for my calcs, which was 4e-05 T. Thus I got T = 8e-06 Nm. I then calculated moment of inertia in the same way as MBobrik, though I upped the mass to 1.3kg, as I think that's more accurated. This allowed me to calculate angular acceleration, which is just 0.0037rad/s^2, or about 2.1RPM/min. Going off the 60 or so RPM we need to achieve 0.16g (given a radius of 4cm), this means it'll take approximately 28 minutes to achieve this spin rate. Certainly a long fraction of our orbital period, but not unreasonable. So next I went to analyse how long it would take to change the orientation of the spin axis. However, the analysis technique I know makes the assumption of instantaneous impulses, like you might see with monopropellant thrusters, and the magnetorquer simply isn't powerful enough to be considered capable of providing "instantaneous" impulses. So I need to figure out how to analyse the precession that results caused if the magnetorquer is kept on for a given period of time. I'll get back to you guys when I figure it out.

Are you kidding me? A rocket that sets fire to itself at launch? That's AWESOME.

Sadly not. We don't want to change the spin axis, we want to change the direction the spin axis points. Which we need to do with precession. Which isn't a difficult analysis given all the inputs at all, but it's not very intuitive. I just did a course that dealt with this sort of thing, so I think I understand it well enough to attempt an analysis. Later today once I get home.

Very nicely done. I'll be more than happy to check your numbers once I have some time. I'm not too sure about having the magnetorquer fold out like you said, as it would be exposed to radiation and potentially complicate thermal management. It's definitely a cool idea though. Again, when I get some time, I'll look into how fast we can precess the satellite once it is already rotating. Having had a look at passive spin stabilisation, I managed to remind myself that spin around the major axis of rotation ( the axis of rotation with the highest angular momentum) on a semi-rigid body (like any spacecraft, including our cubesat) is asymptotically stable. If there is any spin around one of the other axes of rotation that results through a disturbance of some sort, this spin will eventually dissipate, again leaving us with just major axis spin. Considering we'll already be spinning up our sat to high speeds, this sort of passive spin stabilisation will be best. The questions then are time and power requirements for: 1) Initial spin up 2) Latter spin up/down if necessary 3) Pointing at the Sun or ground station, once the satellite is already spinning. MBobrik has already given a pretty good answer to 1 & 2, and I'll have a look at 3 later today.