PakledHostage

While we've got your attention, K^2, I've always been curious about neutrinos? They are known to precede super novas becoming visible in our sky by a day or so. Do they get emitted a day or so before the star explodes, or do they get here faster than photons because they are slightly faster than photons?

So may we call you Ensign Crusher?

My understanding is that the f(t) is hard coded in the system, and only certain parameters are broadcast. They are downlinked as part of the almanac data when the satellite is first acquired by your receiver. I do not know how the actual pattern matching / time delay is computed at the low level or how tolerant it is of loss of signal. Most receivers only update at a rate of between 0.5Hz and 5Hz, so maybe short signal drop outs during the update cycle can be tolerated? It is a good question though. I will do some digging...

I'm going to give my mod a shameless plug here... And expand on nhnifong's post while I am at it. The time signal is actually built in to the GPS signal. Each satellite sends a unique, time dependent pseudo-random signal. The receiver compares the expected signal for that satellite to the received signal. The time delay between when the signal was transmitted and received is evident from the difference in the pattern. The pseudo-random nature of the signal also makes it difficult to jamb and easier to pick out the very weak signal from the background noise. The clocks in the satellites and receiver are updated from atomic clocks in the network's control segment. The time delay allows determination of the distance between the transmitter and receiver. The satellites positions are known from the orbital elements that are downlinked along with the pseudo-random signal. Trilateration is then used to calculate navigation solutions using combinations of three satellites. A minimum of four satellites are needed to obtain a fix, because each combination of three satellites generally yields two solutions and there is no way of knowing which is the correct position without more information. If any of you are interested in learning more about how GPS works, consider setting up by your own network in the game then add the working Figaro receiver part to your air, space or ground vehicles.

Bunsen already makes some good suggestions, but can you post a picture? (Of the flywheel, rather than the mouse's nest...)

Or as I mentioned previously, an IMU. In the case of ICBMs, you need some internal reference for trajectory information. You can't rely on external references for targeting because those external references may well get destroyed. The technology is reliable in other applications because of that military background.

Another important method is inertial navigation. The gyros and accelerometers in the IMU (Inertial Measurement Unit) "add up" all of the accelerations and rotations that have happened since the IMU was initialized, and use that to determine the orbit and position in real time. IMUs accumulate error over time, so ground radar and star tracking is used to correct accumulated error. In the case of commercial aircraft like the 747, laser gyros are used to measure rotations. The gyros are so accurate that the aircraft can determine its latitude while sitting at the gate, just from the Earth's rotation.

There's also the added complexity that the planets may not have formed in their current positions. For example, for some initial conditions, the Nice model predicts that Uranus and Neptune may have actually switched places during the evolution of the solar system. More generally, the Nice model "proposes the migration of the giant planets from an initial compact configuration into their present positions, long after the dissipation of the initial protoplanetary gas disk."

On a related note, I found an interesting essay titled Apollo lunar landing launch window: The controlling factors and constraints on the NASA History Program Office's website. I recall reading in Michael Collin's book that conics were used in planning and executing the Apollo missions. Apparently it lead to some confusion in the media while Apollo 11 was enroute to the moon.

RTGs have been used on many missions, such as the Voyager probes, Cassini, New Horizons, etc. There was no "slipping by" involved in lobbing radioactive material into orbit along with those missions. The publicly available documentation for the Curiosity mission talked about the contingencies and range safety considerations that were the direct result of RTGs being aboard. For example, the mission was required to launch early in the morning so that there would be sufficient daylight remaining in Africa that they could be recovered before nightfall if the RTGs came down there. The launch trajectory was also restricted from passing over major population centres in Africa.

Agreed. What does this have to do with general science?

There’s a big difference between setting up an outpost similar to the Amundsen-Scott station and setting up a proper self-sustaining colony… And the motivation to avoid an impact by a 1km+ sized asteroid would be sufficient that we very likely would be able to do something about it with today’s technology if we had enough advanced warning. Remember that it may only require a delta-V of 1-2 mm per second to avoid an impact if we’ve got enough time. Not only that, but even a dinosaur killer impact wouldn’t kill off everyone. Very likely we’d do the same thing that our mammal ancestors did: hide underground. At least here you can go outside, breath the air and be protected from the cosmic radiation, without being dependent on life support. I think I recall seeing something like that in a movie once... It had some nice footage of Iceland in it.

In the near future, it is a lot more technologically feasible to build a "Project SPACEGUARD" and the means to do something about it if we discover a threat, than it is to expect to disperse to colonies around the solar system or beyond.

While I agree it is a good idea to think about ways to "get over there", Diche Bach's mindset is exactly what more people need to appreciate. If you've ever been to sea in a small boat, you will have at some time stopped to reflect on the fact that you are totally dependent on your boat for survival. You are vulnerable and won't survive long in the alien environment of the open ocean, but if you take care of your boat, it will take care of you. The Earth is much like that boat, but having been born here, many of us are ignorant of the fact that this is all we've got and all we ever will have for many generations to come. Scientific progress has been incredibly rapid over the past century, but we need a lot more of it before we can build colonies in space that are anything more than prisons for the few willing inhabitants that live there. Short sighted ideas like Orion make great science fiction, but do nothing to ensure the long term well being of this "unique planet that we are fortunate to dwell on" for the hundreds or possibly even thousands or tens of thousands of years that it will take before we move out into the stars.

The Concorde is optimized for supersonic cruise, while launch vehicles are optimized for maximizing payload delivered into orbit. Given that launch vehicles climb through the thickest part of the atmosphere at sub-sonic speeds, their optimal aerodynamic shapes are different than that of supersonic aircraft. I would imagine that the mass and cost of the lasers, together with the energy requirements to run them would outweigh the benefit. The process of compressing the air and pushing it out of the way happens by default. The speed of sound is the speed at which an infinitesimal pressure wave propagates through the air. Stronger pressure waves (such as blast waves from explosions) propagate at higher speeds. A body moving through the air “notifies the air ahead of it that it is coming†by means of pressure. Supersonic objects develop pressure waves (shock waves) around themselves that are strong enough to propagate at the speed that the object is moving. Air passing through a supersonic shock will increase in pressure, density and temperature. The shock can be either normal or oblique. Oblique shocks are weaker than normal shocks and cause less drag. Again, the faster the object is moving, the stronger the shock must be. The Concorde’s pointy nose was chosen to ensure that the Concorde forms a (lower drag) oblique shock while flying at supersonic speeds. Missiles also have pointy nose fairings like the Concorde, but the aerodynamic fairings on launch vehicles would be optimized to minimize drag over the full range of speeds that they encounter during the flight phase where they are required.

Have a look at Closette's Mini-challenge: max altitude with this supplied spacecraft thread from about a year and a half ago. That thread documents the great deal of effort that several members of this forum undertook to study the one dimensional (i.e. vertical climb only) version of this very problem. Many of the key contributors in that thread went on to collaborate on MechJeb's initial development. As far as I know, that thread is the origin of the "climb at terminal velocity" and "design for TWR=2" rules of thumb that everyone on these forums cites as gospel. More recently, Tarmenius' Launch Efficiency Exercise thread attempted to find the optimal two-dimensional launch trajectory (i.e. vertical and horizontal acceleration into an orbital trajectory) by "crowd sourced" trial and error. Both threads were specific to two unique spacecraft designs, but the principles discussed are still relevant to more general designs.

As promised, here are the calculations. There aren't much in the way of comments in the calculations because they weren't meant to be presentable. The result of 19.6 million km is about 40% bigger than the actual value. The calculation depends on an accurate measurement of the transit time at the northern and southern observatory, as well as on an accurate measurement of the diameter of the angular size of Kerbol's disk as seen from Kerbin. One encouraging thing about the calculations is that they predict that Eve crosses Kerbol's disk at an angle of 5 degrees. That is consistent with measurements. It also predicts that Eve transits about 40% of the way between the centre of Kerbol's disk and the edge. That too is consistent with measurements. There may well be a mistake in the calculations, so feel free to point it out if you find one. Be aware that some of the values that I calculated on the spreadsheet weren't actually used for anything, however.

Part of the problem is the effect it will likely have on the existing arable land and availability of fresh water. Places like India, China, Russia, plus large areas in North America and Europe are as fertile as they are due to the current climate. Factors such as how much snow falls in the Himalaya, Alps and Rocky mountains and how and when it melts to irrigate crops during the summer growing season are important to our food production. Those fertile lands are home to the world's most powerful countries. What happens geopolitically as the "haves" become the "have nots"?

Exactly. And because Musk isn't building rockets by himself (or even with just his dog), in his lair under his mansion. He's hired people with the knowledge and experience to make it work.

Something to think about: When was the last time that millions of people stayed awake until late in the night to watch a space event unfold in real time? When even non-space enthusiasts like my wife sat and watched in amazement? No, it wasn't the Apollo landings. It was the night of August 5th, 2012 when Curiosity, a robotic probe, landed on Mars. Clearly it is still possible for space missions to capture the imaginations of people around the world and, to borrow a phrase from Niel deGrasse Tyson, to inspire a new generation of scientists and engineers. It doesn't have to be manned spaceflight to be exciting. It just has to do something new, interesting and allow the public to share in the experience. Given the choice between spending billions to send a handful of astronauts into LEO, or spending the same money to send robotic probes to Europa, Titan, the outer gas giants, etc, I am sure many would choose the latter.

UPDATE Thanks to AviatorDSB's help, I have been able to narrow down the cause of the bug that people have been reporting. The bug causes the game to bog down when you go to launch your spacecraft. It does not occur when you use the old method of naming all of your satellites with a certain acronym. It only occurs when using the new Figaro Transmitter part. I was finally able to duplicate those symptoms on my computer by having one spacecraft that contains the Figaro Receiver part in a game save, and then trying to launch a second one. That's an oversight on my part and I have to fix it. I will work on it this coming weekend and will hopefully post v1.0.21.03 of the plugin by early next week. Until then, you can avoid the bug by only having one craft at a time carry the receiver, or reverting to the old method of using a unique acronym in the names of all of your satellites (change the "GNSSAcronym" parameter in the Figaro Receiver's Part.cfg file to match the acronym you are using if you choose this work around).

I watched both the ISS and HTV-4 fly over twice this evening. I was lucky to have two opportunities that were both 6 minutes long. During the first pass, HTV-4 was about 1.5 thumb widths behind the ISS. During the second pass, it was about 1/2 the width of my little finger behind (as viewed with my arm outstretched). On both passes, HTV-4's brightness flared up for a second or two while it was in the western part of the sky. I tried to take photos, but they mostly didn't work out. It would have been cool if I'd managed to catch the flare. The one below is the best I was able to achieve. It isn't much to write home about... The faint bit at the beginning of the bright light streak is HTV-4. The bright streak is, of course, the ISS. The two blend together because they are on the same trajectory, as viewed from the surface.

It is all too easy to judge from the comfort of your armchair. Have you ever been out there? There's a funny little thing called the Gulf Stream that flows between the North American mainland and Bermuda. Water temperatures change incredibly fast at the north wall of the stream. I've personally witnessed it go from 6°C to 30°C in a distance of only 20 NM. What do you think that does to the weather? Add the effect of wind over current on the waves and you can get some properly nasty conditions. The same wind speed and MSWH that might only be uncomfortable in some parts of the ocean could well be deadly in the Gulf Stream.

UPDATE Regarding the reports that I'm getting of people's systems bogging down when spacecraft with the Figaro Receiver part installed first load: I have done some more testing and still haven't been able to duplicate the bug on my own system (a slow little netbook). Even so, I polished up the code a bit and tested a few things that I hadn't previously tested. The improvements will be included in the next update, but I won't release it until I have a real reason to. I'd like to find the "smoking gun" that's behind the bug people are reporting. If anyone who's encountered the bug can provide a detailed description of how to duplicate it, or better yet a copy of their persistence file, it would be greatly appreciated. Please include in your description a list of all mods that you've got installed, in case the problem is due to an interaction between Figaro and some other mod.

You could explain it away by saying that they obtain oxygen by melting/electrolyzing water ice to create hydrogen and oxygen. I read in the book "Titan Unveiled: Saturn's Mysterious Moon Explored", by Ralph Lorenz and Jacqueline Mitton that Titan's density is consistent with it being composed of about 50% water ice. It isn't massive enough for it to be composed entirely of rock. There may even be liquid water deep within its core.