PakledHostage

How many of those technologies have been demonstrated in space? There's a big difference between concepts on paper and real life space hardware. Remember we're only talking about the next 100 years. Aside from electronics and biotech, how much technological progress has really happened since the Apollo program almost 50 years ago (I'm including the internet in "electronics")? And as kmMango asked, who's going to pay for it? It is far more likely that we'd build a successor to the James Webb telescope or possibly a large telescope on the lunar surface that will be able to resolve greater physical detail of exoplanets and/or perform spectroscopy on their atmospheres than that we'd send a probe to any neighborhood star.

Just putting this out there: At its current speed, Voyager would take 40000 years to reach the Proxima Centauri if it were actually headed there (it isn't). Where do you expect that are we going to get the technology to send a probe to any star and have it arrive there within the next 100 years?

All the optimism in the world won't change the limitations of physics, biology, economics, etc. We may come up with innovative ways of working within the restrictions of reality, but we can't change reality. As beautiful as it is, we're stuck on this rock for a long time. The most important thing we can do over the next 100 years is to learn to take better care of our home because there's nowhere else to go. Maybe we'll send increasingly capable robotic missions to visit places around the solar system, but I'd be surprised if we do much more than make brief manned visits to places like the Moon, an asteroid or maybe Mars. 100 years isn't that long a time. Remember that Apollo 11 was 45 years ago this month.

Perhaps "do you have any idea how much" isn't a solid argument against the possibility that a space elevator will ever be built, but "you don't need that many of them for the boostrap construction" is equally naive. Maybe you can explain how you envision that bootstrapping process to occur, or how you can be so certain of the strength of a material that hasn't been invented yet? You can't criticise Nibb31 for making a vague argument and then proceed to make one yourself.

This is why we can't have nice things...

When you see multiple stages of propellers configured like that, it is usually because the two stages rotate in opposite directions to each other. This is done in an attempt to increase overall efficiency of a propeller assembly that is constrained from operating at peak blade efficiency by other design considerations. You see propellers like this on some boats too. As has already been mentioned above, a propeller blade works like a wing to create lift perpendicular to the propeller disk. Like with wings, they also create downwash and tip vortices in the process of creating lift. Because propellers rotate, the downwash has a component that swirls about the axis of rotation and the tip vortices form a helical pattern behind the propeller. The more blades you have, the more disturbed the airflow is and the less efficient the disk is overall. Higher blade counts are required at the expense of individual blade efficiency for some of the reasons already mentioned, however. The counter-rotating second propellers shown in the image in cpast's link recover some of the energy in the swirling downwash (and upwash) of the propeller ahead/behind it. This same principle is used in axial compressors in jet engines. In jet engines, each stage of the axial compressor is followed by a stage of stationary stator blades that are oriented to harness maximum energy from the swirling flow within the engine. For low speed propellers, higher efficiency is obtained by using fewer blades because the blades are less affected by the disturbed airflow created by the blades around them. This can be seen in in AeroVelo's human powered helicopter design. Each of the four propellers on their human powered quad copter has only two blades. Presumably they chose the quad copter configuration because it simplifies flight control problems, but efficiency was critical to their success so they used a two blade propeller at each rotor.

I do realise that. And I even agree that the manned space program has value. To a point. But I was asking the question rhetorically in response to GeneCash's post. How manned space flight is funded vs. other scientific and "patriotic" endeavors is a complex issue. Especially so in the current financial climate that a lot of western countries find themselves in.

At the risk of throwing a cat among the pigeons, maybe the US is the first country in history to realise the pointlesness of manned space flight? Maybe NASA's thinking to themselves "Manned spaceflight? Been there, done that, got the t-shirt... Now, about those robotic missions!!!"

Not quite the same thing but close in that it is real time is NASA's Eyes on the Solar System application. It is basically KSP's map view of the real solar system, showing the location of spacecraft, planets and moons now or any other time you want to specify.

I'm guessing you're not an engineer? As materials science (basically chemistry and physics) has advanced over the past decades, we have learned a lot about what makes the strong ones strong, the fatigue resistant ones fatigue resistant, the creep resistant ones creep resistant, etc. We also have a better idea of the limits of material science. You are talking about building a structure two or more orders of magnitude taller and wider than anything ever built before. There is no doubt that would take major innovations in materials science to achieve. Yet the engineers who designed the current tallest structures in the world aren't dummies. They are already using the strongest materials that are currently available, and materials that are butting up against the limits of what is physically possible. Carbon nanotubes are promising and they may even be the breakthrough we need to make a space elevator or the type of structure you mentioned possible. I wouldn't hold my breath though.

Pffftt... Because we all know that space starts 60 miles up and that you float when you get there. Heck, some kids showed NASA a thing or two by sending a lego guy into space with a balloon. NASA. What a bunch of rocket scientists! lol

Fixed that for you

I realise you were quoting XKCD's "What if", but for what it is worth, aircraft routinely fly in Category-5 hurricane force winds. Even today here on Earth, the jet stream wind speeds are that high south of the Aleutians. (Ref: Environment Canada 250 hPa Geopotential height wind velocity chart.) Eastbound airliners will intentionally fly in jet streams that strong or stronger to save fuel. And sometimes they'll fly in winds that strong out of necessity. Currently, winds at ~35 000 feet above the east coast of Hokkaido are blowing at 105 knots (195 km/h). The NOPAC fixed track system of air traffic "lanes" goes through that area and aircraft are required by ATC to stay at their assigned altitude and on their assigned track. What matters more than wind speed is turbulence. From what I understand, winds at the 55 km level in Venus' atmosphere are very fast but the flow is uniform (i.e. no turbulence).

Well if all you're after are some equations to use in KSP, then why not start with something like Basics of Space Flight: Orbital Mechanics and leave the derivations of the equations used on that website until after you've done enough math and physics for it to mean something?

I would agree with him. I worked as a TA and a tutor for first and second year calculus students while I was studying engineering at university and I encountered far too many students who didn't have a good enough foundation in the basics of mathematics to succeed at calculus. Calculus isn't "plug and chug". You need solid algebra skills and a good understanding of concepts like limits and differentiation before you start with integration. It sounds like you're pretty smart and you'll progress quicker than most students, but do yourself a favor and start at the bottom and work your way up. Wax on, wax off, to use a cliche...

An interesting side note is that NASA policy required MSL "Curiosity" to be launched in daylight because it carried RTGs. Ref: Mars Science Laboratory Mission Design Overview. They were also restricted from using a launch trajectory that overflew major population centres in Africa. If I remember correctly, they were even required to have contingency plans in place to retrieve the RTGs within a fixed period of time should they come down on land after a failed launch.

Well if you are so well versed in the difference between testing and maintenance, then you would also know that maintenance involves testing. Complex systems like rockets or aircraft only work reliably if you perform routine maintenance. Routine maintenance requires testing because faults are often latent (meaning you don't know about them until you test for them). Commercial airliners are required to undergo "checks" at regular intervals, where the aircraft comes in to the hangar and mechanics perform routine tests on the aircraft's systems and structure. These checks range from overnight hangar visits every couple of weeks to more extended hangar visits every year or so, to complete overhauls requiring a month or more every 6-8 years. And don't, for a second, believe that problems aren't discovered during those tests. Dispatch reliability and safety of modern airliners is very good because the aircraft are designed with built in redundancy, but I guarantee you that every aircraft you have ever flown on had at least one deferred maintenance item and many more latent maintenance problems. The significant additional cost of designing, building and maintaining those redundant systems is necessary to maintain dispatch reliability and safety of commercial airliners. Reusable rockets will only be more critical and expensive to maintain and test because they are operated in harsher environments and with thinner performance margins.

Post them up if you manage to get some!

You need to save some payload for fuel. Fuel load is very significant portion of the gross takeoff weight. A 747-400 (gross takeoff weight of ~875 000 pounds) departing on a long haul flight like LA to Sydney or Hong Kong - Frankfurt will be carrying on the order of 350 000 pounds of fuel. Thats about three times as much as the passengers, baggage and cargo. And most transport category aircraft have a maximum zero fuel weight (MZFW). That is the maximum aircraft gross weight prior to loading fuel. It defines the maximum non-fuel payload. For a 747-400, the maximum zero fuel weight is about 540 000 pounds, meaning a 747-400 taking off at maximum gross weight must have over 100 000 pounds of fuel on board. Note: The maximum zero fuel weight is a structural limitation. Fuel is carried in the wings while other payload is carried in the fuselage. Bending loads on the wing are different for the two cases.

It is an interesting question... One that I'd never really thought about until you mentioned it. I guess I always regarded the "light year" as a somewhat inexact number. But standards are standards and there should be a standard conversion for light years into metres. I pulled out my trusty HP48 to see what unit conversions are stored in it. It gives 1 light year = 9.46052840488x10^15 metres. Comfortingly, the HP48's value for c is 299742458 m/s. I also had a look at the Wikipedia entry for Light year. It says that the IAU has defined a light year as exactly 9460730472580800 metres. The article says that definition of the light year has been in use since 1984. I wonder, then, why a calculator designed in the early '90s and modern Google still give a value that is different than the IAU definition? Who's definition are they quoting and why is it still in use? Is it maybe a derived SI unit, as well?

Probably a bigger concern if you live in BC's Kooteneys...

Not to mention that the ISS' orbital position is very well documented and we know that it wasn't visible from Montreal at the time in question.

At the risk of derailing the thread, those photos (and the Venera photos on the previous pages) reinforce in me that we don't need manned missions to inspire people. I remember sitting up in the middle of the night together with my wife to watch the live stream of Curiosity's landing. She isn't a space buff but she was cheering right along with me. And her Facebook feed was full of posts from people who are more likely to crush a beer can on their foreheads while watching a football (handegg) game than take an interest in science, yet they were doing the same thing. Literally millions of people stayed up late that night to watch Curiosity land. It was awesome!

Or a high-res interactive 360 panorama on Sol 177: Curiosity 360 degree panorama (including selfie)

Well something 450 km up but down close to the horizon is several thousand km away. There's a lot of air between you and it. It would have to be very bright (i.e. the ISS or an iridium flare) for you to be able to see it. But if you look straight up, you'll be able to see a lot more satellites throughout the night now than you would in December.