K^2

If we can't find someone here, I know some 3D artists that can help getting visuals for a video.

Hm... That can be used to double the interplanetary delta-V, at least. I'm having hard time coming up with a way to improve on it further. But that's a neat idea. I'll have to look at the mission they did and see how much can be scraped out of that. If that can be modified to push us to Venus/Mars fly-by, then we could try for some really crazy mission ideas. These would be high risk, but seeing how any of these missions would open with a Moon fly-by, I doubt it'd be a total loss in any outcome. Edit: Oh... Yeah... I think I'm starting to get that. Yes, with an Earth fly-by, it's possible to change both aphelion and perihelion, using energy from lowering the later to raise the former and get to a Mars fly-by. From there on, it's smooth sailing. It's an insanely challenging mission profile for something like this, but it can be done. I like that. For 3U + GTO launch, L1/L2 are definitely legitimate targets we can try for. GTO -> LTO -> fly-by, correction -> L1/L2 transfer -> circularize and park. About 800m/s total.

I want to get some more ideas, run some more numbers, and put up a page here first. We still need a basic mission. Something we can definitely get done. Preferably something interesting and Kerbalish. But as I've pointed out, our baseline mission would have minimal delta-V, an ok camera, and ability to send a picture via series of bursts every once in a while. The two most likely rides we'd be able to catch are either GTO or ISS mission. Based on that, is there anything more interesting we can do than just shoot a few pictures of Earth? If we do manage a 3U + GTO, I can come up with things to do. And I might be able to get us proper telemetry. There are some radio-astronomy education projects we could tap to get a radio telescope for tracking. But that's a huge stretch goal. Basic mission is still needed.

There is terrible lack of precision control. I mean, if we end up with no decent mission profile that requires precision, we can just go for broke and fire up a solid booster. Might as well be an Estes motor. (Especially if they contribute to the costs.) But if we need precise placement of delta-V, there is really no substitute for an electrostat. And they are expensive, but not that expensive. When I was looking for something to get me close to 1km/s on a 3U, just for an estimate, I've found some for under $10k. If all we need is some 1U maneuvering, we can probably find something or even have it custom built for a couple of $k. That's not even the largest expense. We'd have to spend more on space-hardened electronics for nav and control, as well as power. We can't budget for less than $5k - $10k range + launch. That's almost out of the question. I can find a way to put a cubesat into interplanetary space, but not with enough delta-V left over for an interplanetary transfer. There is just no way to get enough propellant in the volume/weight that can be brought along. On the other hand, if we could do Venus/Mars fly-by, then there is no reason to stop there. If you can get just one fly-by, you can go anywhere in the Solar System. I'll do the math, but I don't think it can be done.

You mean 6"x3"? Because 6'x3' is no cubesat. But yeah. These are the 1U, 2U, and 3U. The 1U is a standard cube. But you can have one with double or triple length. Based on electrostat thrusters available on the market, if you want a lot of dV, you have to go with 3U. On a 1U, the weight of a typical thruster + panels just doesn't leave much room for propellant. Still, sacrificing thrust and efficiency, we could maneuver 1U a bit. Problem with going 2U/3U is that the price scales with the size. You can get 1U into space for about $30k. A 3U is closer to $100k. And I don't know if NASA would launch a 2U/3U for free. So ideally, we should come up with a mission we can pull with a 1U. I'm all for leaving room to expand the mission, however. The minimal requirement should be getting a 1U into space, taking pictures, and beaming them to Earth. From there, we can scale up. Ultimate goal being an interplanetary space mission, for which a 2U/3U + GTO ride is a minimal requirement. Not to mention much better navs and coms. On the plus side, Lunar fly-by is pretty hard to miss. So even a failure would range from being lost to interplanetary on the wrong escape trajectory or lithobraking into the Moon. Which is pretty spectacular either way. Edit: Yeah, GregroxMun, fairly serious. If we can find the funds and a launch opportunity, it's something we can actually do. Maybe not the interplanetary space mission, but a LEO one for sure.

I don't think we can do a deorbit demo. We wouldn't be able to find anything small enough for a cubesat to deorbit quietly, and anything else would produce too much debris. But yeah, if you can come up with a good LEO mission, I'm all for it. Navs in LEO are very easy. We can get an unlocked GPS for primary navs. Couple that with some optical gyros and a camera to take pictures of the stars to reference against the charts, and you can have position tracking good enough to put you within a few hundred meters of any target. And since an LEO cube sat has short life time, we don't have to worry about expensive components, either. The whole thing can be done on a few $k budget, plus the launch. If you think we can qualify for a free launch with NASA, then that's all we have to worry about. Like I said before, there are definitely a few areas where I don't have enough knowledge to build something with sufficient reliability, but if you can get me mission parameters, I can probably do a cost estimate on the components, at least. Edit: For LEO mission, we definitely want to fit in U1, so I can't promise more than 200m/s delta-V. That means, no inclination changes. Any mission has to be very close to the plane of the launch. It is enough dV to raise/lower orbit to catch up with something that's already in the same plane.

Yeah, a LEO cubesat would also be kind of neat. But it's not terribly exciting in terms of the results. NASA would do all the work for you, basically. We wouldn't be able to get it far from LEO, and in LEO, all you can do is take pictures which anyone on ISS can do without effort. So it's hardly a rocketry mission. Look at the edit I added above on what can be done with a GTO launch. Budget is going to be higher, but this would be a proper KSP-style challenge. I know I can design the nav and control portion. If we can get some people who know their space-hardened electronics and a bit more about tele-com than I do, it'd be just a matter of buying the right parts and writing the right code. Totally doable.

If we launch something as a community, we should do a cubesat. Something with basic propulsion, at any rate. It'd still be in the $100k budget range, but it's not going to be just a piece of debris. We could definitely build something with an actual mission and an ability to send at least burst communications back to Earth. Edit: I did some preliminary calculations. If we can get a ride to GTO with the right timing, a Moon fly-by can be done for about 670m/s. That's within caps of a cubesat with an electrothruster. Though, it might be tough to spec that on a U1, and U3 would cost $100k just for typical launch, GTO being more expensive. But at any rate, fly-by from GTO entry can give you up to 320m/s in interplanetary. That, plus whatever's left in the tanks is enough to do a near-Earth asteroid mission. On a $100k - $200k budget! We should all totally try and do that. I doubt we'd be able to collect all of that from community, but something like 10% is definitely doable. Maybe we can get Squad to pitch in another 10-20%. The rest can come from various education grants (we can get some HS/Undergrad students helping out) and maybe some private companies would be willing to help out. (Heck, if we get enough interest, maybe we can get a free GTO ride out of some tele-com company.) Anyone has interesting targets in mind? On the 300-500m/s we'd get in interplanetary, we can't move far from Earth, so it'd have to be something that passes very close. And the slower it passes near Earth, the better. It would allow for closer approach and better opportunities for pictures. (Landing is probably out of the question, and I wouldn't want to crash into the rock, because we'll need time to burst data back to Earth.)

Sure. If you plan to bury the probe in the ground. If you are planning to slow it down, then you can't count on drag as you touch down. Not to mention that it's a big "if" to begin with. Sure, one could always build a lawn dart. But seeing how the system has to be capable of maintaining stability at zero velocity, it's just extra weight and complexity.

Hobby rockets achieve stability due to the fins. You will have aerodynamics working against you. The whole thing is going to be unstable, both statically and dynamically. You'll have to achieve active stability with control software. That's the only way.

The angular momentum, L, is conserved. And for arbitrary rotation axis, L = Ỉۡ. However, the moment of inertia tensor, I, rotates along with the body. If ̉ۡ happens to lie along one of the principal axes, then Ỉۡ product remains constant despite the object'r rotation. But if not, Ỉۡ would change with object's rotation. So in order to keep L constant, ̉ۡ must change as well. That's axis tumbling.

What is this, 17th century? If you can extrude an optical fiber, you can assemble a telescope. Certainly, if you are building it on Earth and want to send it in one piece, mirror is much simpler and will give you better quality for the weight. But if we are talking about a sort of thing that an orbital 3D printer can assemble, astronomical inteferometer will do just fine. Classically, these are built from smaller telescopes, but utilizing Faraday effect in the optical fiber, you can build an astronomical interferometer that will rival any telescope we have sent into space to date or plan to send in the near future.

You are still looking at less than a second of operation. In that time frame, you need to do a couple of dozen of corrections. You need both precision and fast response there. In terms of servo mechanics, they are PWM controlled. Older style servos, the cheap ones, consist essentially of a capacitor to turn PWM signal into average reference voltage, a potentiometer hooked up to servo arm to turn arm's position into another voltage, and a differential amplifier hooked up to these two voltages to drive the electric motor. There are all sorts of delays there. It will take a good fraction of a second just for the reference voltage on the cap to adjust to the new PWM control signal. There are much better servos out there. With stepper motors and digital controls. These can have absurdly short response time and more precision than you'd need. They tend not to find as much use in hobbies, though, because of higher cost. So you might have trouble finding some that would work for you. In principle, you might be better off just going with steppers and setting up your own controls. After all, it's the nozzle position that you are interested in. Not the servo position. P.S. All of that said, this might, indeed, be a better option in terms of delays. At least, it shifts mechanical problems of valve control to digital problem of nozzle control. Maybe I'm just better with the later, but I think I'd also go with that. Keep in mind, however, that you are going from a semi-stable problem to a totally unstable one. So you'll have to introduce stability in your control algorithm. You'll probably end up needing better response than PID, but understanding how PID works would be a fine first step.

Why do you need gimballing nozzle? And at any rate, it will not have the time to actually adjust.

Looking at the game's code, gravity and other inertial forces are applied at center of mass of the ship. In other words, no tidal effects are going to be present. On the other hand, drag and thrust are calculated per-part. ISS does a lot more attitude adjustment, however.

It's a bit more complicated than that. For starters, it doesn't have to be the long axis. It depends on mass distribution and the field. But in sufficiently uniform gradient, it will be a line along the moment of distribution. But it's even worse. An object can't rotate around an arbitrary axis. In fact, there are only three mutually perpendicular axes that an object can rotate about without external torque being applied. These are principal axes. If you try set rotation around any other axis, the axis will tumble. But these limitations are easy to design around if you specifically want a satellite that always points one end towards Earth. You need to design mass distribution so that tidal torque is minimized in that orientation and that one of principal axes, preferably the major one, is in the normal direction. You also want to balance light pressure and maybe add something to dampen oscillations. That way, if sat does end up getting knocked off the correct alignment, you can count on tidal torque to fix it, rather than just set the thing oscillating.

Even if you deliver oxygen directly to the blood stream, you'll be loosing it at too fast a rate through your lungs. Attempting to hold breath would only cause lung damage.

Active SETI: "We are here, we are not very technologically advanced, and we are very gullible!" Doesn't sound like a good idea, no.

Are we talking about real weapons, or something I can defend against with kitchen foil? Anything bellow hard X-Ray is just not serious for space combat.

One time, a vending machine ate my dollar. The war with machines has already begun. They just don't know it yet. But yeah, no predicting past singularity and/or collapse of society. We'll just have to wait for it. Won't be long now, either way.

A) As Scotius said, hard X-Ray or soft gamma is your best bet. There are a lot of reasons for that. Besides these Scotius mentions, it's very hard to reflect hard X-Ray or higher frequency. And it will punch through the armor, depositing energy, potentially, meters into the ship. These are all nice qualities for weapon. Of course, these are also the reasons why it's very difficult to build an X-Ray or gamma laser. For a good X-Ray beam, you need a particle accelerator. For gamma, at least a nuke and a very large superstructure for focusing the beam. Take diameter of your emitter squared, and divide it by the wavelength. That will give you maximum range at which you can deliver almost 100% of the power. Past that, the beam will suffer roughly the inverse square law. So, for example, if you take an emitter 10cm across and 100keV X-Ray beam, the effective range will be 1010 meters, or about 30 times distance from Earth to the Moon. Which is huge. Of course, that's a theoretical limit. If you don't manage to get the beam perfectly collimated, you'll suffer range penalties. But in either case, your main problem will be with aiming, not making the beam have sufficient range. C) Given time and sufficient power input, anything. The rate at which it will burn through armor will depend on material composition, what means of cooling are available to the target, and energy density of your beam. It's hard to estimate all of these without knowing specifics.

Yes. Planets too. In fact, Earth's gravitational time dilation is significant enough that it has to be accounted for by GPS satellites. In other words, if General Relativity was wrong, GPS would not work. There are a lot of other reasons that add up to us being more certain about General Relativity than tomorrow's sunrise. But these are mostly technical.

Seconded. If at all practical, run a wire. You'll be happier for it, and the motherboard you've selected already has a LAN port built in. Of course, running wires is not always possible. In that case, you will need to get a decent wireless adapter.

There is no objective splitting. Results of the measurement can be interpreted as world splitting simply because observer goes into a superposition of states. So each component of that superposition observes a different world. But the actual state of the system is the total of all possibilities, and it never splits or changes.

Yeah, the obvious up side is that you get more lift. The downside is that you hit diminishing returns, because as you have more blades, each blade is working against already moving air. You can end up with more problems with tip vortices as well. That can lead to settling with power, and other nasty business. Both of these problems are reduced if you place a cowling/duct around the propeller. Hence the ducted fans.