brdavis

I'm not sure… if you are using things like KER than you understand things like delta-V, thrust-to-mass ratios, etc., correct? I can recommend some good books on aerospace, but they're going to cover things a lot more in depth than KSP simulates… If you feel like you are "missing something fundamental", well… where and when do you start to feel like that? Getting to Duna means you've done a good bit. Getting back from Duna requires planning. And once you've done that thinking and planning, you can start thinking of scaling up to Jool or Dres or something (or in towards Eve and Moho… although catching MoHo is *still* something I've not personally managed…) If you want to "do it yourself", try it in a scientific fashion: trial and rror aren't bad *if* you analyze what worked and what didn't (and why) afterward. A little confused on how to help you, while letting you "do it all on your own"… :|

When you say "burn prograde"… how closely did you put your orientation relative to the NavBall marker? To better than a degree? Good, but not good enough… especially at the end of the maneuver. To better than 0.1 degrees? Good… but if you push it "to the end", not good enough. "It's always something"… be that finite burn time (which should result in a predictable drift), or error in sighting the marker (are you pointed right at it to 0.000001 degrees?), or numerical error… there's always a residual. When you say "tends to move upward"… relative to the ship marker on the NavBall? Or relative to the artificial horizon? On *all* burns, or prograde ones?

The marker on the NavBall shows the orientation to burn in to reduce the current difference between your velocity vector and the selected velocity vector… but there's no such thing as "zero". So when you get close, although the error (residual) is really small, it's still there, and the game adjusts the nav marker to show the current orientation to try to burn in. It happens all the time (try a simple Kerbin-Mun insertion, and you'll see the same thing… or at least I do). Note there is a "you're good enough" indicator - the dV tag on the maneuver (shown to the right of the NavBall) turns green when the game things you are "close enough", but it will still keep moving around the nav marker. Think about it this way: if you are trying to walk to a mark on the floor 10 meters away that's north of you, I can tell you "go north". But when you are within 10 cm of it, unless I was *perfect* on telling you the heading, and you were *perfect* at executing it, you might be a little to the east or west of the mark… so I would have to tell you to go "north but a little bit east as well". As you try to do that, and get within 1 cm of the mark, I realize you've overshot slightly, and tell you "oh, yeah, now the mark's just behind you, head sort of southwest." And when you do that and end up 2 mm to the side, and ask "am I there yet", I say "no but almost, now go due east just a little bit." This would be the point where you slap my silly and realize that the error isn't important, and wander off to get a corn beef sandwich instead.

Here's why, perhaps, the Devs have a really tough job. My experience with 0.90 is exactly the opposite: I loved the fact that early in the tech tree, I now have to fight for a good manual ascent, and the nerving of the reaction wheels as well. It made the game more challenging in a *less* grind-like way for me. The weak reaction wheels and tech-tree progression of control strategies… exactly what you are feeling put-out by… was one of the biggest things I *enjoyed* in 0.90. To each their own?

Yep, my bad; my first post was too quick, and your second post hadn't propagated out to me yet; I just left my mistake "visible" because I really hate retconning reality Then you move it out further. Seriously, the outer edge of the habitable zone would be populated (for habitable planets) with planets with dense atmospheres. Those aren't a problem - in the habitable zone doesn't mean "habitable", it means "possible" in this context. So you could have a habitable planet close in with a thin atmosphere, or a habitable planet further out with the thick atmosphere. Look at some of Kasting's work on the continuously habitable zones around main sequences stars (Kasting is another planetary atmospheres guy). Venus has too much only for its current insolation. Move it out further, and it will be cooler. Move it out far enough, and that 90 bar CO2 atmosphere will be cooler still. Not by much. Other papers I've read show that the habitable band in terms of insolation extends out to Mars and beyond… but with dense CO2 rich atmospheres of something like pCO2 of 8 bars. And while those calculations are generally done for roughly solar-type stars, the shift in frequency of the light really isn't very significant (our Sun is at 5000 K, while the coolest M stars are around 3000+ K… about the same temperature, and therefore color balance, as an incandescent lightbulb. It's still "short wave", both to your eye, and things like the CO2 IR window).

If you read the paper, you'll find Birch thought even bigger than that. Near the end he figures out how long it would take to bring the Sun and Alpha Centari to relative rest using this method. Targeting the mass streams is evidently… just an engineering problem. Conclusion: it would only take about 1 kyr to bring the two systems to relative rest. - - - Updated - - - While the Hill sphere is an excellent approximation for satellite stability, I think it might not be valid when the "satellite" is fully 1/3rd the mass of the "primary" - - - Updated - - - I suspect he was talking about making Mars and Venus a co-orbital planet pair (the two orbiting a common barycenter and the barycenter in a reasonable orbit around the Sun), not putting Mars at Venus's Lagrange point. For the pair in question L4/L5 wouldn't be stable anyway (Mars is much too big; L4/L5 are only stable when the mass ratio is around 26:1 or better, which isn't even close to the case for Venus:Mars).

(Edit: never mind, while I was out it seems you read the paper; let me catch up here for a moment "Hmm… I think the best way to address this might be to read the paper I linked to. It addresses a lot of your points in ways I seem to be doing poorly. Try reading it; it's not too difficult, and might address some of the points you and I seem to be sticking on.") Good question; I'm not sure we know. Can you have a carbonate-silicate cycle without plate tectonics and a nearly global ocean? Perhaps not. You actually won't have one if you have too much ocean as well (no climate-controled influx of things like Ca++). So here the question might be just how much of an ocean do you need, and do you enter a runaway greenhouse anyway (note that Mars, for example, hasn't, despite lacking a carbonate-silicate cycle for a very long time). Why not? what's wrong with a significant CO2 atmosphere and potential habitability? Again, this is a problem… how? Are we assuming that for habitability you need an Earth-normal atmosphere? For a planetary scientists, habitability is perhaps much broader - can.potentially, support liquid water. It's not ideal for terrestrial-style photosynthesis… which is not surprising to me as it didn't evolve to cope with that. True, very true. I'm not sure if that's true or not. Yes, the area available may be small… but the diversity of environments is plenty large. And by far most of the biodiversity of life on Earth is microscopic. We may be arguing different things here. I'm pointing out that among all the possible planets in the galaxy, it seems likely that the majority of potentially habitable ones (that could support life, not terrestrially-evolved life) may be tide-locked. It's not that they are 'better' than Earth, or even 'as habitable'… it's that they are not less likely, and that by virtue of their much greater potential number they are therefore a higher probability. The CO2 limit is interesting. It was my understanding that C3 plants limit at around a pCO2 of 0.1 mb, while C4 can still support growth down to pCO2s as low as 0.01 mb (if memory serves here). What sort of … ignorant fool … would argue we're near any sort of reasonable lower limit for plants with regard to pCO2?!? Then again when you are already denying well-understood science… sigh… Thank you for reading the paper. Did you have a chance to look at the bioenergetics one, dealing with an origin at alkaline hydrothermal vents? I'm curious what your take on that is as well (to me it was really really interesting… but I admit outside my field. Significantly outside my field

Yeah, believe it or not… the thought has occurred. And been seriously worked on, in peer-reviewed literature: How To Move A Planet, by Paul Birch (Yes, Paul Birch thought big. Very, very big. Another of his papers considers how to roof-over Jupiter (yes, the entire planet) and develop the "surface" at the 1 G level)

Not bloody much of it. On the day side, there will be next to no water vapor in the atmosphere because while it is hot, there's also no source. On the dark side, the equilibrium vapor pressure will be very low due to the temperature. So, yes, water vapor in the atmosphere, but *not* remotely uniformly distributed, and not high levels (for some atmospheres). Nope, you're right - early on the planet would likely not be a synchronous rotator. So you are likely to end up with a warm wet atmosphere. Perhaps not unlike the Earth. Note that Earth isn't remotely in a runaway (or even moist) greenhouse state; due to the tropospheric cold trap, Earth holds onto water just fine at Earth-normal insolation. That's exactly the type of system the paper in question was studying; Earth-like sized worlds with Earth-like scale insolations. Those do not have problems with runaway greenhouse effects. Almost certainly. Take a look at the Earth. We have massive ice sheets at the poles (and have had still more massive ones in the past) which are location that are *not* in shadow at all times. Yep, if the Earth became tidally locked, it would build up a big ice sheet on the night side as well… remarkably rapidly actually (do the thermal analysis for the Earth and you find you could have effective cooling over the course of *months*, not years or decades under those conditions). Combinations of positive and negative feedbacks can… they can also lead to stabilizing systems (the carbonate-silicate feedback system on Earth, for a canonical example). It might take a larger than normal perturbance. That's why the GCM was run with the presence of starspots. To make sure that such a perturbance did *not* drive the climate state into an atmospheric collapse state. A reasonable question. So look at it this way: A Earth-sized world forms close enough to a red dwarf that it experiences Earth-normal heating. The result is, not surprisingly, and Earth-normal environment… possibly including plate tectonics, oceans, and all the rest. Over time the rotation rate slows, so "nights" get longer and longer… finally getting long enough that significant portions of the water cycle become trapped in "temporary" (month to year long 'nighttimes') on night side. The planet is still rotating, but now increasing amounts of water vapor are being trapped in ice sheets. Even while the day side becomes locally warm enough to loose its tropospheric cold trap, the amount of water vapor in the atmosphere is dropping… sharply dropping, since more and more of the water is being locked up, gradually, on the night side. Worse yet, those large sheets of ice (if we are talking "normal" oceans depths, piling the Earth's water on one hemisphere could produce a 4+ km thick hemispheric ice sheet) make tidal locking easier, and the process continues. Eventually a tidal lock occurs, with the climate having shifted fairly smoothly from Earth-normal to a locked state with a N2-dominated atmosphere and almost all the water locked up on the night side. Not very long, actually… *especially* for an Earth-sized world. Remember the models didn't require thick CO2 atmospheres, but fairly thin ones to prevent atmospheric collapse. Earth's natural variation in CO2 is more than enough to pop levels up to 30 mb in a few million to tens of million of years, much much shorter than the tidal locking timescales in this situation. As near as we can tell (based, again, on things like the responsiveness of the carbonate-silicate cycle here on Earth), the characteristic time for CO2 in the Earth's atmosphere is on the order of 10's of thousands of years; unless the tidal locking timescale is shorter than this (which it could be around *very* dim stars), that seems unlikely to be a problem. See the above evolution; if the Earth, with Earth-normal insolation, avoids this problem, there's no reason to think a tidally-locked Earth, with Earth-normal insolation would have a different one. Sorry, take a look here: http://crack.seismo.unr.edu/ftp/pub/gillett/joshi.pdf As a physicist who's done a lot of research about planetary science… yes, I'd like to have a bunch of controls too . Planetary science might not have the same standards as molecular biology does in this regard. But read the paper; they *do* consider a number of different atmospheres, including N2 dominated ones. (regarding life starting around deep-sea hydrothermal vents…) No, I understand the RNA world hypothesis. I was referring to the bioenergetic origin of a some of the basic energetic cycles. I mean I am NOT a molecular biologist, but I found this review-ish article in the Royal Transactions rather good: http://rstb.royalsocietypublishing.org/content/368/1622/20130088 In that case, the presence of a large ice sheet that would flow towards the dayside while sublimating and perhaps melting should be rather handy for kickstarting life… not to mention the number of sub-ice-sheet lake and rivers that would form (throw 4 km of ice over a whole hemisphere and think about what a little bit of geothermal heating will do.. or go to Antarctica and look for yourself). I agree a high thermal gradient can be useful for a lot of bioenergetic processes. I'm not sure why you think such things are less likely to exist on a tide-locked world than on a non-tidally locked one however. (Snipped a lot of other VERY good biochemistry… not because it wasn't interesting, it WAS, and it was great! Thank you!) True. So how long did it take for life to arrive on Earth? Rather quickly as I understand it? Around a billion years? So, perhaps you can form life if tidal locking takes more than a billion years? So that would specify a "near limit" based on tidal locking time, and constrain the likely stellar size based on that and its luminosity, assuming that diurnal cycles are needed. No, they dropped; precipitously. And if that happened on a hypothetical tide-locked world, the CO2 level would drop, driving down temperatures (and also potentially starving the carbon-fixation pathways in those early plants), which would stop plant growth… whereupon CO2 levels would build back up due to things like volcanoes. Very similar to how the carbonate-silicate cycle worked on Earth as a stabilizing climate feedback and pulled us out of the the nearly "icehouse Earth" scenario. Pretty much the same as Earth: again, start with Earth and evolve it into a tide-locked state. I'm not sure I see any significant problem. Not even for life (although it would certainly become rather oligotrophic in the process). You can have N2 dominated atmospheres; N2 isn't in *any* danger of atmospheric collapse under these circumstances. And while terrestrial life may do well with N2 as a (relatively) inert gas, it's not like it has a significant biological role (Nitrogen? Absolutely… but there's nothing that points to requiring an atmospheric source vs something else. Phosphorus is pretty critical to terrestrial biochemistry too, sometimes being the limiting factor, but it certainly doesn't stop life much that it doesn't exist in an incredibly difficult to fix form that forms 3/4's of the atmosphere). You've got every right to be. It's a hard problem. My point was it's a problem that has been known about, and worked on, in planetary science for decades… literally. Not just because planetary scientists like to think up weird things (that's SF writers), but because the statistics keep pointing in that direction. PS- Yeah, I'm long-winded. Apologies to all the TL;DR crowd, but this stuff is really interesting to some of us. If we spirits, have offended…

Or at a deeper level… why bother? What questions or problems does this address that don't already have more viable, better tested explanations? In particular, I find the idea of a close encounter between two planetary-scale objects creating Hellas to be… well, completely contrary to what would be expected? And the Roche limit certainly applies… you just have to account for the densities of the two objects.

Well, the paper in question used a global climate model, 3-D. For an Earth-sized planet with Earth-normal insolation, it turns out the atmosphere (a CO2 based atmosphere) is stable against collapse down to 30 mb… so about 3x the Martian surface pressure. An Earth-sized planet with 1 Atm of CO2 can prevent atmospheric collapse with an insolation level of just 30% Earth's. and a nitrogen-dominated atmosphere doesn't start to freeze out unit the dark-side temperature reaches about 80 K… which is very easy to maintain. Not really. Sure, you can come up with a "planet too close" scenario… but a dense CO2-rich atmosphere is in fact what you want if you are near the outer edge of the habitable zone. Agreed, it seems more than a bit outrageous… which is one of the reasons people have done peer-reviewed research on the subject. It turns out, our intuition (perhaps coming from evolving on a non-tidelocked planet) appears to be wrong. Agreed; there's a lot involved. for example, type M dwarfs tend to have both huge "sunspots", as well as often are flare stars. The first could drop temperatures to where atmospheric collapse does happen, while the 2nd could drive temperatures too high over too much of the surface. That was actually another thing the paper worked out - would such a planet be stable (maintain an atmosphere) under these conditions? It turns out… the models show it would. Surprise again . Current thinking is that life on Earth was likely started around oceanic thermal vents. I could certainly see that happening in a tide-locked world setting. There are plenty of other habitability issues (could you have a carbonate-silicate cycle without global oceans? Or would you stall plate tectonics? Would flares from the star start stripping the atmosphere?). But that's true for almost any planet. There are even some possible advantages: around a flare star, a one-faced world always has a protected side… not true for a rapid rotator like Earth. - - - Updated - - - Hmm. Not sure I follow - the super rotation of the upper atmosphere is a product of the heating, but also the slow rotation of the planet (like Venus). Being far from the star isn't going to help much (unless you are so far it's too cold or not tide-locked). True, but I don't have a good reference for the oceanic circulation of a global sea on a one-faced world . Yes, it would help. It would if nothing else have some interesting airflow patterns (fun story settings). Yeah that documentary is pretty inaccurate.

I was a junior in high school; I had asked our school to show the launch, but they wouldn't take the time. They didn't even announce it when it occurred… but somehow, word started passing around. I was in a government class when I heard the news… near the front on the left side of the classroom. I was standing when I heard. I couldn't believe it… thought it was a poor joke from the student who told us. Eventually we confirmed it with others. I was in shock the rest of the day. After that I coped the only way a teenage science and math nerd knew how; I learned, I analyzed, I figured out, and I understood (better) exactly what had happened that day. In terms of the physics. And the engineering. And the politics. But never fully grasped the humanity of what had happened. Then, years later, less than a week after the Challenger anniversary… …it all started again with Columbia. God Speed

Actually, the most common worlds in the habitable zone would be expected to be tidally locked to their stars… far from uncommon. Rather the opposite. By far the most common stellar type are M Dwarfs… and their habitable zones are going to be very close. There have actually been a number of SF stories in such settings. If there was a strong pressure difference, you get winds. So what you'd expect is warming near the sub solar point with that hot air rising and flowing towards the terminator, cooling and sinking over the anti-solar point and then flowing back towards the sub-solar hemisphere. Ground winds would be blowing from the dark to the light side all across the terminator. It turns out that simulations (yes, there's peer-reviewed literature on this) shows that the slow rotation (tidally-locked does -not- mean non-rotating… very much to the contrary) changes this: general airflow is from the hot to the cold side other the terminator at the "east" and "west" (leading and trailing) poles, cooling and flowing back to the day side over the north & south poles (where the winds would be strongest). It turns out that for a reasonable atmosphere you would not suffer 'atmospheric collapse' (the dark side doesn't get cold enough to 'freeze out' the atmosphere), but you would certainly have an interesting problem with the water cycle. The dark side would accumulate massive ice sheets, which would flow (as glaciers… wind-carved glaciers) back across the terminator onto the day side, melting as they went, with the resulting melt water evaporating and moving back to the dark side to fall out as snow. Yeah, it would be a heck of a place Biologically, besides the "frozen hell" on the dark side, and the "scorching baked dry hell" of the day side, there would be a temperate band between fire and ice, with an active water cycle. Trees (or other plants) there would have an interesting advantage: the star would never move in the sky. Forget optimizing for for an energy source that never moves. Fixed leaves almost perpendicular to the ground (the star would be low on the horizon), nothing much growing in the shadows because anything shadowed is *always* shadowed, etc. Anything living on the night side would either be based on trace nutrients blowing in from the day side (atmospheric filter-feeders?), or hydrothermal vents (which may or may not exist… plate tectonics here would be questionable without a nice uniformly hydrated crust. Yeah, I teach university level planetary science… I love this stuff -- Brian Davis

The orbit of what? Of the asteroid around the Sun? Yes, and they take that into account in making future predictions. The orbit of the satellite around the asteroid? No, because only the tidal effects of the Earth on the asteroid-satellite system would matter there, and the distance between the asteroid and its satellite is much much much smaller than the distance between the two of them and the Earth. I wonder if we have the asteroidal mass from this observation (or at least some rough bounds). Satellite stability is roughly based on the Hill Sphere (if you aren't playing KSP anyway), so with the mass of the asteroid you could figure out just how close it would have to get to Earth to disrupt the satellite orbit… or, conversely, you could note that it's never gotten closer to Earth than XXX kilometers based on the observation that the satellite is still there.

Actually, it can be stable for at least millions to tens of millions of years. Gravity… works. Yes, there are perturbing forces photon pressure is way too small, and even the Yarkovsky Effect isn't going to be significant here… let alone dust blasting). There are a significant number of asteroids that are already known to have moons - this one joins a growing list.

Short answer: No. Longer answer: well, we know a lot of other people opinions… but beyond that, no.

I'm not disagree or agreeing with this (or a lot of other positions) here. But there are a lot of quotes like this. Stating this is/isn't a good decision, and they should move forward / immediately reverse their decision. And an awful lot of these statements are being made with apparently a lot of confidence and conviction. So I thought it might be good to ask: How many commentators here have personal experience with either the alpha-beta-early release process from the inside (not outside), -or- have direct inner knowledge of the inner decision-making mechanisms within Squad? Is it just possible… the Devs know and understand some things we don't? This being, very literally, their job?

Thank you Squad team… you've done a wonderful job, getting us a big brand new release just in time for Christmas… my wish for you is that *YOU* get a holiday off with your friends and families. Enjoy this Christmas season… you've just made it amazingly enjoyable for the rest of us

If all you are interested in is the quickest least-bothersome way of doing something… …go watch other people play on Youtube Seriously, for some of us the "fun" of something like KSP is very much a DIY attitude: I have to build the ship. I have to do the staging, and throttle control, and plan maneuver nodes, etc., etc. ALL those things take effort… and ALL those things can be automated. But if all you want is automation… this is probably not the sandbox you're looking for. My son (high school senior), like me, designs all his rockets using paper and pencil and a simple calculator. He's bugging me to teach him how to calculate ejection angles (he already knows simple transfers, how to calculate when a launch window is, different ways of changing inclinations). The joy for some of us is in working out the details. And, as a consequence, when it comes time to plan a multi-component mission to Duna and back with the spacecraft being reconfigured and refueled, with strap-on cross-fed boosters and complex stain schemes… it's not only doable, but doesn't involved a bunch of experimentation and trails and error. I'm not limited to what a tool like KER can provide me with… I can do anything I want, and it's not even a huge step in complexity. People don't run marathons because they need to get to someplace 26.2 miles away. The way you get there is (in many cases) even more important than the destination.

Agreed. It feels like mining, because it rapidly becomes "do the same thing over and over". Personally I added KAS, and within a couple days was using it not for its intended purpose (because… well, who uses something for it's intended purpose in KSP?), but as 'role playing' for setting up ALSEP's for Munar missions. This gave the mission something to do, and the Kerbal something to do (build it piece by piece from the KAS-carried parts), and provided something to "see" when going back to a previous landing site. As much as I love KAS, it may not be part of stock… but allowing the design and deployment of *something* seems like a good idea. Long-term stations providing special science by *virtue* of being long-term? Or if 0.90.0 will add some form of resource scanning, science for complete mapping of a planet ("hey, I actually have to think about the orbit of this, not *just* spam back science when a contract requests it").

We're going to need a much bigger KSC...

Only real problem here is that it shouldn't be in LKO. Clearly you need to launch it on a hyperbolic trajectory...

Wish I had an image, but I don't… It was a simple launch in career mode - core stage surrounded by three liquid strap-ons, with those being fed asparagus-style from liquid tanks perched on top of BACC SRB's. Worked great before. But somewhere an error crept into the craft file I guess… during this launch, the SRB's staged off just fine. But unnoticed by the ground crew (me), one of the three liquid strap-ons was burning fuel very slightly slower than the others. Upon "burn-out" of the strap-ons, two burned out while the third kept firing for a couple seconds. This resulted in the entire stack tumbling end-over-end, 20+ km up and rising, with three dead liquid-fueld boosters hanging on to one end. As ground control (me) tried to figure out the right roll position to get in so the wildly cartwheeling central core would pass between (and not into) the cast-off strap-on booster, evidently Jeb (channeled by my teenage son) looks over my shoulder, shrugs, and says "well you can't get that under control until you stage those things off" <hits space bar>. Explosions resulted. Yelling ensued in ground control. What was left after the unplanned disassembly was enough to bring it under control, reducing the spin to zero, and drop Jeb into the nearest lake for a thorough cooling off (not sure there if I mean the little verbal guy, my son, or me… but somebody got pretty wet after this sequence of events). Probably the best accident I've ever recovered from during a launch anyway. And no, I have no idea what was going on. Yes, all the fuel ducts were present, yes fuel was flowing, yes, it was all built with symmetry, and no the engine thrusts hadn't been tweaked (any of them). No idea. I rebuilt, and it worked fine. I then modified that, and re-invented the same problem (by modifying the fuel tanks on top of the BACC's). Weird.

That moment when… the three liquid-fueled strap-ons that were all built with symmetry on do not burn out a the same time, resulting in just one burning long and the entire stack pinwheeling around much faster than the reaction wheels can do anything, and you have to try to regain control via manual control, after also striking the cast-off strap-ons that staged while you were spinning at about 0.5 revolutions per second… Yeah, it was an interesting day.

OK, not that this needs another opinion, but… as a PhD in physics, i've got to agree with others here. They, strangely, don't seem to know what they are doing in terms of theory. but that in and of itself doesn't bother me - there are plenty of strange (& useful* effects that have been found by experimentalists and only later did theorist try to figure them out. So that's not a fatal problem. The fatal problems? 1) This seems to contradict a whole lot of known, well-understood science. Basic, basic science. Like conservation of momentum. 2) A "crippled" test device and a "functioning" test device produced the exact same outcome. If so, it would seem they have no idea what's actually required to make this work (if it does). 3) (and this is the point I didn't find in the previous threads), this NASA test (if that's a fair name for it) was conducted in a vacuum chamber… under ambient conditions. In short, in air. It's hardly surprising that when you pump a bunch of EM energy into a gas that the gas might heat up, expanding, pushing on the device… and generating thrust. It's a poorly designed experiment, with no good theoretical basis, that would seem to contradict long-standing observations. The only thing they seem to have done right is design the test with a "null case", which seems to prove conclusively that the test is flawed. Testing this on a CubeSat is even tougher. There's actually a lot of ways to produce small accelerations: heating a thin gas in the chamber would work (put a hot plate on the retrograde side of the CubeSat, and you have a thruster in LEO, due to hot gas molecules bouncing off, same as a classic Crookes radiometer). Gas drag as the upper atmosphere inflates/deflates is very tough to estimate (in fact "watching" a CubeSat de-orbit over time is a good way to get a handle on those forces as they change, so to 'test this by CubeSat' you now need two, one with the Magic Drive and one without, but having the same mass, mass distribution, and external shape; the cost of your test just doubled). Propellent-less drive? let out a long wire from your CubeSat with a hot anode to boil off electrons at the far end, and solar cells on the CubeSat to provide power. Run it along the wire. Simple, easy, low-thrust acceleration (pro or retrograde) with no propellent. And it still won't work for you between planets.