Bunsen

Wait, was that not the point of model rocketry? I... I may have been doing it wrong.

Forgive me if this was also discussed, but I don't see "tiny encapsulated atmosphere" being compatible with "growing in the dark." If it grows in the dark, it must get its energy from metabolizing something, and that usually requires either taking oxygen, getting rid of carbon dioxide or something, or both. If you want an organism to grow for long in a small, closed atmosphere, you have to provide some continued energy input. Otherwise, there's going to be a pretty tight limit on how much interesting stuff can happen before the chemistry hits a wall.

Thanks for the summary! I took a look at the cubesat thread many months ago, got frustrated with 75% of the comments being from people not reading the thread and posting the same crap that had been posted and answered a dozen times over, and gave up after about 20 pages. There's no way I'd survive slogging through nigh 200 pages of that. [edit: having glanced at the last couple pages of the enormothread, I notice that I kinda did that myself. Mea maxima culpa.] Sensors for humidity, pressure, and O2 are all small, cheap, common, and consume extremely little power. I don't know about CO2 off the top of my head, but I think those are similarly easy. I would be concerned about temperature variation -- a 1U doesn't have a lot of thermal mass for its surface area, and its temperature can swing pretty wildly between sunlight and eclipse. I'd want to check that 90-something minute temperature cycling doesn't mess up the moss. Otherwise, you're going to need to stabilize its temperature somehow -- I see two obvious options: (1) design the craft to give the sample chamber a natural average temperature below what you really want, insulate it well to slow down heat exchange, and provide heaters (you really don't want to deal with the power consumption of active cooling, which is why I suggest designing it to need heaters) or (2) use a phase-change thermal buffer (basically a capsule of wax chosen to have a melting point near your desired stable temperature) which would passively limit temperature swings, but would provide no direct control. Temperature cycling becomes a non-issue if you can swing a sun-synchronous orbit, but there are far more launch opportunities to lower inclinations, and sun-sync orbits require some real attention to thermal management to avoid overheating things.

A grape split nearly in half and laid split-sides-down, with a tiny bit of skin connecting the two halves, acts as a dipole antenna. Most grapes are of such a size as to get within the ballpark of being a half wavelength at 2.4 GHz, even. The connecting skin quickly heats up from the large currents, and then it either ignites or ceases to conduct and then arcs over. Either way you get a little bit of plasma to seed the process.

Um, how does the position of the launch site relative to the equator change with time of day? Think of it in an Earth-fixed reference frame -- the only things I can see changing are distant objects, like the sun and moon, and therefore their gravitational influences. Tidal forces certainly factor in to orbital calculations, and are more significant for larger-radius orbits than for lower ones, so maybe that's what sets the launch window? I wouldn't think that would be large enough to make a go/no go decision versus a small correction to burn times.

Cal Poly's original P-POD design is limited to 3U, but the concept has been extended by others. NanoRacks' ISS-based system uses 1x6U tubes, many of which are presently loaded with pairs of Planet Labs 3U satellites. Planetary Systems sells a 2x3U "Canisterized Satellite Dispenser" with a different mounting system from the P-POD family, and I've seen several in-progress projects being built to that spec (I'm working on one, in fact).

Thank you! That's a totally acceptable hit to the mass budget. We've got carbon fiber rods^W^W^W massless struts and epoxy and whatnot for secure mounting. Now to slip it into the, um, budget budget.

We are working on a repeat flight to perform the same measurements on a bunch of other frequencies, with a software-defined receiver, lighter weight, higher apogee, custom APRS tracker (the old one was hilariously overpowered and had an inconvenient requirement for 12V power, new one will be much smaller), and generally more engineering and less last-minute duct tape. Naturally, we'll be making sure the new Kerbonaught is more securely affixed. Anybody know how heavy the Shapeways version is?

I wish I had seen this thread back when it started, because I've learned some pretty direct lessons about this: 1. The electronics can be assembled very cheaply by anyone with Arduino-level knowledge. Raspberry Pi works too, and Linux can make managing data flow a hell of a lot easier. Simple sensors like those being discussed here probably won't generate enough data to be an issue, though. 2. Getting the balloon is trivial and not terribly expensive. Getting helium may be tough due to supply shortages, but once you've found somebody that will sell you a tank of non-oxygenated helium you're pretty much set. 3. Real-time tracking in flight is important. If anybody involved in the flight has an amateur radio license, there are off-the-shelf APRS trackers that work quite well. Not all GPS receivers cooperate at high altitude, but there are plenty that do. Ublox units seem happy with high altitude after being commanded to enter "flight mode." 4. If you don't mind putting in some design and assembly work, you can make a functional payload amazingly small and light. There's a community of balloonists in the UK that goes utterly crazy at this, and they make their designs pretty public. 5. Make sure Jeb is well affixed to the payload, to avoid what happened to ours at 1:37:14 in the video: The actual, plastic Jeb was a bit of an afterthought on our mission, the University at Buffalo Nanosat/SEDS Joint Experimental Balloon (which was launched to measure radio noise levels for a proposed 2.4 GHz link for our cubesat). He was a totally unauthorized model cranked out from our 3D printer in clear and green PLA, then decorated with white-out and Sharpie. The visor on his helmet was from a $1 pair of sunglasses, and was intended to serve as a mirror for watching the envelope during flight. It ended up misaligned enough that you could only see the edge of the envelope once in a while. Shortly after the balloon burst, it becomes evident that Jeb and his carefully engineered mounting structure (i.e. some foam, tape, hot glue, and a scrap of 1/8" all-thread that we slapped together in about 2 minutes) were aerodynamically unstable, and the resulting vibration fatigued the mount to the point of failure after about 25 seconds. Starting around 26km altitude, Jeb then conducted an unplanned, independent descent toward an unknown (and likely subterranean) resting place in rural New York. While this may be a completely appropriate fate for a Kerbal, we want to make sure it does not happen again. It was pure luck that we didn't end up reading about somebody getting impaled by a plastic space alien on a metal rod.

There are two parts to it: which way the inlet points, and which way the exhaust goes. I think maccollo is right about using thrust to augment the wings' lift. Most aircraft don't do that, because when you design something to spend its entire operational life in the atmosphere, it makes sense to give it efficient wings. And other planes' engines may not be close to the center of mass anyway, so pointing them away from horizontal would create large pitching torques. So Skylon's nozzles are pointed more downward than other jets. The other half is the inlet. Again, conventional aircraft have more efficient wings, so they fly with a relatively small angle of attack (i.e. the degree to which the nose or wing is pointed above the direction of flight). Small wings and thin air necessitate a large angle of attack. Also, flying at high Mach numbers requires inlets that use shock waves as part of their mechanism of action, and those are much pickier about angle of attack than those designed for subsonic flight. So the inlet has to be aligned with the airflow during high-speed, high-altitude flight, where the angle of attack is quite large. You can see a similar, though less pronounced, bend in the SR-71's inlets. They're pointed inward and slightly downward, since the Blackbird also maintained a fairly high angle of attack in the stratosphere and the fuselage would be pushing the air significantly outward by the time it reached the nacelles.

The latest model predictions show it hitting around 08:00 GMT on Thursday. For us eastern 'Mericans, that's 3:00 tomorrow morning. There's probably a few hours of uncertainty in that, though. I'll be keeping an eye on solarham.net tonight for signs of impending activity in case it shows up before I fall asleep.

Oxygen is very reactive stuff, and it doesn't tend to hang around on its own. Its natural state, at low enough temperatures to not be a plasma, is to be stuck to something like hydrogen, or silicon, or aluminum, or carbon, or iron. Having an oxygen atmosphere on a planet that's mostly metals is far from normal, and in our case it's only possible since some photosynthetic bacteria started stripping oxygen out of other compounds and dumping it into the air. Before Earth got itself covered in green stuff, it had lots of oxides, silicates, and carbonates, and no gaseous O2.

That can even be done with decay heat, if the power requirements are low enough. There's been a design or two for radiothermal-powered jets capable of flying around Titan.

I'm not sure you caught K^2's actual point. Knowing how the Higgs field works doesn't open up the ability to change particle masses any more than knowing how electrodynamics works allows you to change the charge of an electron, or knowing about W/Z boson couplings lets you turn beta decay on and off. We've learned to exploit the electromagnetic properties of nature in very important ways, and maybe someday the other fundamental forces will also have technological application (beyond clumsy, tangential uses like nuclear reactions), but physics as we know it contains no indication that you can change how any of those fundamental interactions work.

Good luck to all of those, and may Murphy look the other way for your entire mission. I'm more than a little jealous that you got to have a hand in spaceflight in friggin' high school. I got to see a good part of it all the way from Buffalo -- last 20 or 30 seconds of stage 2 through maybe the first 40 seconds of stage 3, then it went behind the clouds. That's the first launch I've seen with my own eyes that wasn't powered by Estes.

Cubesat-sized objects have pretty short lifetimes at 500km. These will deorbit within a few years. The problem gets worse for things at higher altitudes where small debris can last for decades.

Got a source on those launch costs? I've taken a look around, and the only prices I can find explicitly stated are well over $100k for a 3U launch (these guys, for example, charge $325k for a 3U P-POD, integration, and launch, and that seems in line with other vague figures I've seen).

Pulsing an electric thruster isn't hard. The size is a bigger problem -- the efficient electric thrusters I've seen aren't so much designed to be a supporting component of a cubesat with a payload as they are technology demonstrations just barely squeezed into a 3U with no room for much of anything else. The ones I've seen that are small enough to coexist with a respectable payload have terrible propellant fractions and correspondingly terrible system Isp.

Radiation shielding is way, way too heavy to be practical. Keep in mind that the comsats the size of small school buses still use rad-hardened electronics, because significant amounts of radiation make it clear through something that size. For a short mission, it's possible to get away with non-rad-hard components through careful design. Radiation problems fall into two general categories: total ionizing dose effects (things that slowly and predictably get worse with more radiation exposure), and single event effects (things caused by individual particle impacts, you can only predict how often they're likely to happen). TID effects take a while to show up (months or years, usually) if you don't pick uncommonly vulnerable parts, and are a big part of what rad-hardening focuses on. SEEs are always a problem, and cause things like memory corruption, incorrect instructions, random resets, and occasional internal short-circuits that let the magic smoke out of the chips if you aren't careful. But SEEs can be mitigated with defensive circuit design and paranoid programming. This is the approach cubesats usually take, because they're built for short-term operation and don't have the budget for rad-hardened electronics (which are obscenely expensive). Raspberry Pis don't have those circuit-level protective measures, and are kinda power hungry for what they do, but embedded computers in that ballpark are a decent choice for some small satellites. Sufficiently simple missions can run on something closer to Arduino-scale hardware.

That depends on what you're doing with the satellite. If it's not in support of somebody's job (and the FCC is now starting to count university research projects as somebody's job), you may be able to operate under an amateur license. As for the universities, the FCC now wants them to apply for experimental licenses -- more paperwork than ham, but still not the expensive commercial licenses. If you aren't under the FCC's jurisdiction, though, I have no idea.

The big questions are (1) how much information do you have to move and (2) how much electric power can the satellite spend on its radio. If you're talking about a cubesat-scale thing, which usually goes along with the cheap, off-the-shelf components, transmitting from beyond GEO down to Earth is going to be very hard.

Reentry heating depends quite a lot on how much surface area you have per unit mass. Large, dense objects require a lot of dynamic pressure to decelerate from orbital speed, and that means lots of compression and high surface temperatures. Small, lightweight objects can do it with lower pressures and temperatures. There have been a couple research projects on developing large inflatable heat shields, which don't need to survive quite such severe heating as their compact counterparts. Some tiny objects (I think the little circuit boards on KickSat are close) can survive reentry without any special shielding.

Arcjet thrusters have been used on satellites for quite a while. Like the electrolysis system, it's because not all rocket engines are used as boosters, and there's more to whole-system performance than just thrust. When you're looking at a spacecraft that generates and uses tons of electricity anyway, you can get a lot more mileage (well, lifetime of attitude control and station keeping) out of a tank of propellant and simple, lightweight plumbing by adding electrical energy rather than depending on stored chemical energy. Yes, there are other ways of electrically expelling propellants, and they can have better-looking theoretical performance numbers, but messy practicalities can create niches where simple approaches like arcjets are a better fit.

The slow electrolysis/fast burn version is already in commercial development. http://www.tethers.com/HYDROS.html It's made for cubesats where several factors make regular rockets impractical: the propellants need to be storable (no H2), the materials need to be safe (hazmat handling can be brutally expensive, so no hydrazine), and there isn't enough power (or the service life is too short) to make an ion engine practical.

You can do even better than that. Low gravity, low temperature, and a dense atmosphere all make flying easier. So easy that an airplane can fly for years on a radiothermal power source that doesn't even make up much of its mass. There have been a few proposed missions along these lines, most recently AVIATR, based on NASA's newfangled Stirling generator. I'm a big fan of the concept -- imagine a probe doing radar and optical mapping of the entire surface of Titan from a few kilometers of altitude, with the freedom to dip lower over interesting sites for a better view. And all the atmospheric science you could possibly want, too.