K^2

Causality is only locally relevant in General Relativity. FTL is not a violation by any measure. Otherwise, Universe wouldn't be expanding at FTL speeds. The biggest inaccuracy of KSP's Alcubierre Drive is that it doesn't properly take into account curvature due to gravity. You drop out of warp traveling at the same speed that you went into the warp at, but the frame of reference is accelerated. To account for this properly, author should have carried out parallel transport of the velocity vector in a curved space-time. Naturally, since gravity in KSP is a patched-conics approximation, it would be entirely acceptable to use Schwarzschild Metric for parallel transport as well, patching at SOI boundaries as necessary. There are a few minor issues as well. Energy consumption, visual effect of the warp, etc. But these could be chalked up to sacrifices in the name of gameplay and limitations of the rendering engine.

Yeah, I'm aware of these things. I've wired my own charger. It's honestly not too complicated, so long as you are aware of this property. My only concern is how expensive and/or hard to obtain are diodes that we can safely use in space. I don't know about ordinary diodes, but Zeners sound to me like they'd be pretty rad-sensitive.

An unfortunate code name, perhaps, which I'm sure they've never meant to be made public.

Only if they lose. If they win, they get to decide who the bad guys are, and why they had to use the orbital asteroid defense platform to help fight these bad guys. I've always thought that "Death Star" was only called that because the Rebels won. Had it been the other way around, it'd probably be known as "Orbital Installation Infallible," or something else that's neutral but firm.

Streetwind, all of your arguments, without exception, apply to the 10 year journey of the Rosetta mission tenfold. They had to place it within a few km of target while tracking it from distances on the order of 10 light minutes. Time after time. Compared to that, a few meters from 20km is peanuts. Oh, and they do have GPS. That's basically what CONSERT data is. Just a shame that they have to come up with hacks on the fly, rather than have it as a feature from the start. And I'm well aware that they are doing all they can with what they have. But therein lies the irony. They've planned out this impossible 10 year mission, managed to pull it off with just a few close calls, and then they lose the probe. Because nobody, during the entire design of this voyage, has thought that they might want to search for the probe on the comet. The fact that it might bounce off and roll away relatively unharmed just flat out did not occur to anyone. Else, CONSERT would have been dual-purposed for it from the get go. I'm not saying I could have done better. I would like to think that were I involved, I'd pull my weight on the team. But that's precisely why I made that last comment. This whole thing is very human. We do this all the time. We come up with super intricate ways to solve absurdly complex problems, but what actually catches us off guard are little trivial things. Usually, right at the finish line. And then we come up with a new set of crazy things to do to try and fix it. When we can. And space exploration is like a showcase of that. Philae. Genesis. Mars Climate Orbiter. Hubble. Even Apollo 13 to some extent. It makes some logical sense that it's always a small detail. But I'm amazed at how trivial it usually is, and that it's almost always the last thing that could have gone wrong. Then again, maybe we just don't hear as much about cases where things go wrong from the start.

Wait, I somehow missed that part of the news about lander trouble. They've lost it? They actually lost the lander? As in, the thing that traveled through Solar System for a decade, performing a triple Earth flyby, came so close to Mars that it nearly scraped atmosphere, and managed to visit several other rocks before rendezvous with 67P? They managed to lose it on a 4km dusty snowball after all that? How embarrassing. You know, whether they find it or not, and regardless of what other data we gather from the whole deal, this says something about us as a species. We'll do the impossible just to get there, and then go home, because we lost the keys.

That's also the reason to go with nVidia over AMD for graphics. While there is software out there that will use GPU compression on AMD cards (e.g. Raptr), nVidia's ShadowPlay does it with zero hit to performance and works out of the box for absolutely any game. So if you are interested in recording and/or streaming, I'd definitely go with nVidia, even if it is going to be slightly more expensive. Better support on Linux is another reason. Windows support tends to vary from generation to generation, but currently both nVidia and AMD are doing pretty well, so there isn't a major difference there.

Finns are only good for air cooling. In vacuum, all you need is a rough, black surface. If we have solar panels fold out, yes, we can use back side as additional radiators, but that seems like unnecessary complexity at this point. Sorry, missed your post there. Gravity gradients will be exactly the same. The actual amount of space we can dedicate to the payload, however, gets smaller. And same goes for usable space in general, simply because it's going to be awkward to fit everything in the cube at these angles without throwing the system out of balance. It's workable, but it's going to reduce amount of stuff we can do, and it still gives us only a little over 50% usage on our solar panels, which are going to be expensive.

That's because using rotors to push air straight down is a stupid way to fly an aircraft carrier. What you want to do is use the structure itself as a lifting body. So you want to be blowing air over the surface, rather than straight down. This also lets you distribute the load much, much better. The overall shape of the craft would probably be roughly oval. Though, it might make sense to just go with a disk at that point.

I'm assuming standard LiPo is fine. These are 3.7V standard. CPU needs 5V, and there aren't good opportunities to step it up. Solar panels will bring something like 4V-5V, depending on temperature. So that means two banks in series (each bank can have 1 or more cells in parallel) that charge at roughly 2.5A with full illumination of 5 panels. That gives us a total of a little over 900mAh of charge in 45 minutes. I would like to at least double capacity from that to 1,800mAh. That would allow for more than 3 minutes uninterrupted broadcast at full 200W, assuming we build transmitter to work with these 7.4V. It also means that 45 minutes would only half-charge the batteries. But even at half, it'd be safe to send some transmissions. The CPU drawing only 5V is a bit of an inconvenience, but I think I can split that 7.4V source into a 5V + 2.4V using a Zener diode, and use the 2.4V for something non-essential, rather than waste them as heat. Everything else that draws considerable power can be designed to use these 7.4V specifically. Sensors, etc. shouldn't draw enough to worry about such details. One last bit, I don't know if there is a good way to distribute power dynamically. It will be easier, and more reliable, if we simply have a charge cycle and work cycle. During charge cycle, each LiPo cell charges through its own constant current circuit using the 4V+ from the solar panels. Every other systems runs off the panels as well, effectively isolated from batteries. Once voltage on panels drops, it will switch to drawing power from batteries. That will isolate solar batteries. Part of the advantage here is that we'll have less heat loss in this mode. Since rear face will always be shade-facing, I propose using it as a radiator by painting it black and insulating it from the rest of the sat, except via a thermocouple. We can then use the later to control heat flow out of the craft. On the day side, we'll probably be wasting some power to actively push heat to the radiator panel, and on the night side, cut that flow down. This isn't something that most cubesats have to worry about, but it might be critical for a bio experiment. I'll do estimates on expected heat flows later.

I'd rather have a safety cutoff that cuts transmission if voltage drops bellow certain level. But in the worst case scenario, the system should be self-restarting. Hopefully, even if it runs out of power, it can last 45 minutes without total loss.

There is never going to be a real sleep mode. CPU will have to be awake to listen to comms. That's 125mW. Amps on receiver can be comparable. I don't even know how much power we'll need for attitude control. Plus various losses, and potentially cooling power requirements. It's going to be hard fitting into 1W average as it is. And then we still need to be storing power for transmitter. I don't know how much power we really need for this, but 200W seems to be limit for most amateur frequencies. That points to a very long recharge time. And I don't know about you, but I'd like to be able to at least have the juice to beam down a JPEG every time we talk to the sat.

We are getting better at using memory past 4GB. So this is going to change very soon. Because modern consoles are so PC-like, a lot of optimizations we do target XBox One or PS4, and are directly carried over to PC. Then, we add compatibility hacks for any system that doesn't measure up to these standards. That means that you need to have at least as much RAM as a console does, so that the game doesn't get thrown into some sort of internal compatibility mode. With modern consoles, that means 4 cores, SSE4 support, 8GB of RAM, and DirectX 11. Of course, you need to go out of your way to build a modern mid-ranger and not hit all of these.

I'd be a bit cautious with diagrams for a moment. Consider everything as very-far-from-final. One of the big questions is how much power we need, and if we need to do something weird to get it. I see four options on power consumption ranging from most power to least. Keep in mind, "day" averages are given. Cut in half to get orbit averages. 4 side pannels open 90°. 5 panels total exposed to direct Sun light. 10W production. Rotation axis connects centers of front and rear faces. Advantages: Lots of power. Drawbacks: Mechanical complexity. 3 "front" faces covered. 3 panels at 58% exposure. 3.5W production. Rotation axis connects opposite corners. Advantages: Best usage with fixed geometry. Drawback: Trying to pack everything around a diagonal. 4 side panels covered. 1 to 2 panels at 0% to 100% exposure. 2.5W production. Rotation axis connects centers of opposite faces and is perpendicular to Sun light. Advantages: Standard axis. Drawbacks: Very poor cost efficiency and nightmare to control. Front panel only. 1 pannel exposed to direct Sun light. 2W production. Rotation axis connects centers of front and rear faces. Advantages: Simple. Cost-efficient. Drawbacks: 2W. That's 1W averaged over night/day, which barelly keeps us operational. In a nutshell, this is also my argument for folding side pannels. But there are at least 3 radically different configurations here, so we need to decide on which one we're going with before we start producing art.

It'd be a touch more expensive. But you'd also get a more future-proof motherboard with 1150, sure. So there isn't anyr eason not to go with Haswell. It's just that there is a lot of ambiguity in mid-range on where you should and shouldn't cut costs.

Unexpected. But thanks for making me work through some of these. I guess, I was expecting cosmic background and/or solar to be more significant. As it turned out, the entire band of solar radiation from 86MHz to 94MHz only adds up to 1.1x10-13W/m². The base sensitivity of instrumentation wasn't really a question in my mind. The GPS being able to pick up a fraction of pW/m² is really impressive. How is that not drowned out in all sorts of noise?

Russian engineers still don't believe that they don't need all that room for lamps.

sgt_flyer brings up a good point on HDDs. If you plan to record, at a minimum, you want a HDD from which you run the game, and a HDD to which you are going to record the video. The bottleneck here is seek time, so by having reads and writes go to different drives, you make sure that recording the video doesn't degrade performance of the game. SSD is totally optional, though. It's only really useful for the OS. Hybrid drive is probably a better choice for the game drive, but we are starting to get into not-so-mid-range sort of prices. If you are worried about HDD performance/reliability, Western Digital's VelociRaptor series is a pretty good compromise for reasonable price.

Depends on your budget. But I would strongly recommend going with at least four physical cores, and at least 600 series GeForce GPU. Modern games are getting better and better at utilizing multiple cores, and 4 cores is the typical target. (In part, because XBox One runs 4 cores.) Having multiple cores also improves your multi-tasking performance, so if you are recording or streaming, a CPU with 4+ cores will keep things running smoothly. nVidia introduced ShadowPlay with their 600 GeForce series. It was developed primarily for their Shield tech, but one of the advantages is that it lets you stream or record gameplay without tying up your CPU for encoding. In other words, you can be recording your gameplay without any performance degradation. For a solid mid-range PC, I'd build it around an Intel Core i5-3750K Ivy Bridge CPU and probably GeForce GTX 760 graphics card. The rest of the components don't make a huge difference. You just want everything to be compatible, and you want it to be reliable. For the later, check reviews. Personally, I try to stick with ASUS motherboards, but that might be personal bias. Basically, if you go with 3750K CPU above, just start looking for an LGA 1155 board that has all the features you want and has the size that matches your tower. It also needs to have a slot for your graphics card (PCI Express 3.0 for basically anything modern), but hardly any motherboard these days doesn't come with at least one. (And you only need multiple if you plan to SLI, which is not really a mid-range sort of thing to do.) An LGA 1155 board will also almost certainly come with DDR3 RAM slots, so you'll need to pick DDR3 memory. At least 8GB for a mid-range. I like Corsair, but again, read reviews. And the board will also come with some number of SATA ports for HDDs. You probably don't need RAID, so essentially anything will do. With HDDs, just read reviews, and look for capacity that works for you. Western Digital and Seagate tend to be pretty reliable, but absolutely all brands of HDDs vary from model to model. Seriously, read reviews. That basically leaves optical drives (hardly even matters what you chose at this point) and PSU. PSU is important. Don't go cheap. Last time I was replacing PSU, I've found one that looked like a bargain, only to discover that while it doesn't fail often, its principal mode of failure was catching on fire. You want your PC flaming hot, but not literally. It might feel like you are wasting money, paying twice as much for a PSU with good reviews, but you just don't want to be part of statistic on this one. Best case scenario, it burns out and you have to buy a new one. Worst cases are just, ugh. Common PSU-related problems cause anything from frying your other components to a literal fire. All that's left is finding a case to stick all of that into. Basically just get anything you like. The case usually supports certain sizes of motherboards which are called form factors. Make sure these match. And if you are putting a lot of crap into it, make sure it's a big enough box. But that's about it. There are a whole lot more considerations, from specialized cooling systems, to solid state and hybrid memory. But these don't really fall into mid-range sort of pricing. So the only real choices you are going to get is which CPU and which GPU to build your PC around. Everything else will fall into places once you decide. P.S. There are several pieces of hardware typically integrated into modern motherboard. Ethernet, USB ports, and audio. For most people, all three are quite sufficient. But if you happen to be an audiophile, you will definitely enjoy benefits of a specialized board. For all of such things, however, the question is basically how much money you are willing to part with.

It basically is, and laser would make it way worse. Not only wouldn't it improve your ability to direct a beam from that distance, but you'd be losing a whole bunch of power in conversion.

Depends on power of transmitter and skin depth of material. Ice at 94MHz is on the order of 1m (very rough estimate, depends a lot on composition). In other words, you'd be losing a factor of e for every meter. Transmitter on Rosetta is 2W. So at 20m, you'll be expecting ~4nW of power, which seems like too weak of a signal to detect. But if I'm underestimating resistivity (~50 ohm-meters) or simply making mistakes on composition (likely), this could be way off. Cometary nuclei tend to be on the order of .4g/cm³, which would point to large gaps or pores in ice. That could easily more than double the skin depth alone. All in all, I wouldn't be surprised if we're actually looking at something approaching mW ranges, which is easily detectable. But yeah, composition is going to make a huge difference. Certainly will. Antenna had to be a specific distance from surface for experiment to work correctly. How much of it they'll be able to salvage depends on how precisely they can determine orientation of the lander. Last I've heard, they aren't sure which end is up. maybe that changed. They probably have a pretty good guess to start with. If it's way wrong, then their choice of pulse lengths and frequency might not be optimal. But that's pretty unlikely. Anything too unusual would have shown up in spectra.

To be precise, the scanner looks for coincidence events, because an electron-positron annihilation event usually produces a pair of photons with almost exactly the opposite momenta. Detecting both of them gives you a line on which event took place, which is very useful for 3D reconstruction. And while nobody's using antimatter beams in medicine yet, there are people working on doing precisely that. Antiproton beams have been demonstrated to be very efficient at cancer treatment. So far, only tested on mice, however.

I don't know, capt'n. I'm giving 'er all she's got!

Actually, since they are planning to put a centrifuge in the saucer (blasphemy!), the off-center thrust would result in precession about a longitudinal axis. So it will corkscrew its way through space, rather than loop-de-loop as you guys suggest. Which, in principle, does get you going in direction you want to be going. Doesn't make it less stupid of a design, or anything.

Nope. The thing is made by design students. It's total fiction throughout.