Xeorm

1/3. Though I take the question to be saying "You see one child is a boy, what is the probability that the other is a boy?" Mostly as other implies some sort of identification. The identification is key. If I see one of the options, then the only options for the other are boy or girl, so 1/2. If I know only that there is a boy, then that means less information, leading to a less accurate guess.

1/2, assuming we're not worrying about minutiae like men being born more often then women. Unless it's something like this: https://xkcd.com/169

Yes, that's exactly what it means. E = 1/2 M*V^2, but p = M*V. I want to maximize momentum for a given amount of energy, because that'll give the most efficient rocket. Conservation of Momentum is what moves the rocket. Energy is held constant in this case, so I can only vary the mass. If you want to, you can combine the two equations and solve for momentum. You'll get p = (2 * E / M)1/2, which shows pretty clearly I think that you want to decrease mass in order to increase the momentum.

The two bits that make it seem wrong to me are the inaccuracy of the method and our knowledge of how non-linear human population has been. The first has already been shown so I don't want to go over it. But the second should be said. The hypothesis runs only off of limited data - how many humans have existed up to now. But, there's more information than that. Take the tank problem. If you knew only the number of tanks that were produced and happened to run the numbers very shortly after the tanks went into production, you'd have very different results than if you ran the numbers later in the process. Just knowing the time frame of production would give you better data. Same with humans. The data over the entire span indicates there will be so and so number of humans, but the current population growth and number of humans right now gives the impression that we're only starting to come off of the production line.

Issues I can think of is you're probably underestimating the amount of stuff you'd need to reliably mission kill the missile. Then there's the size of the area. A second is a long, long time in this regard. You note that the missile is moving at 6000 km/s. Even a small miscalculation in where it's going to be means a large cloud of stuff needed.

It starts from Earth orbit already. That cuts wanting a large first stage due to gravity concerns or other concerns from atmosphere. Larger the initial stage you either have more thrust, which requires more support through the whole craft, or you need to worry about a larger burn window. Three stages for the Earth->Mars flight lets them get the most out of what they have, along with allowing for corrections. The next three stages are pretty different, and each have their places.

I don't think a regular Earth-like atmosphere would hold for any real amount of time. It's going too fast for the moon's gravity to keep it contained, and the sun would make sure to blow it off even faster. But...http://astro.unl.edu/naap/atmosphere/animations/gasRetentionPlot.html playing around with this, you can see that the moon's just above the hypothetical retention plot for a xenon atmosphere. It would steadily get diminished by the solar winds and other effects, but the moon could, theoretically retain a xenon atmosphere for a decent amount of time. Why you'd want to do that I couldn't guess, but you could.

Cardboard should work too. Might be a bit thicker than you'd prefer, but it can hold up well and works closer to real building materials than most.

Thoughts: Sounds to me like the wording is meant to imply a bullet with a quick initial speed, then a further increase in speed from escaping gasses until it goes 1 meter, then no more acceleration. Seems odd, but the only way it works. It's the sort of bad wording I'd check, but when writing the answer I'd make sure to point out how I read it. Secondly, to cover all my bases for the first question, I'd make sure to point out the horizontal speed, vertical speed, and overall speed. Pedantic, but that's how I learned to answer questions, as you don't want to assume which of those three the teacher really wants.

Haven't looked particularly at this video or their claims. Much too late for that right now, but... Don't confuse thermal imaging with actually seeing the heat of objects. Objects only tend to emit IR on the same levels as most other objects. If most objects in the same area emit IR similarly based on temperature, it can become a way to see heat, but get something that works a little differently and you'd get bad readings. Assuming the fabric did have a different emissivity that's enough to fool sensors, then you're set. You don't need to do anything with the heat, so it could be cool and lightweight. Theoretically.

Looking at what they say, they make some mention of lunar missions as well as Mars trips going off of the gateway. Giving some more reason for its existence. But largely, I think it's there because NASA doesn't care too much about delta V costs and the like. Efficiency is not their goal, safety and doing more space stuff is. The gateway would be a small time away from LEO, but after the magnetosphere, which is the most likely source of random problems they're going to run into. Making things a bit safer at the expense of fuel costs is, I'd think, worthwhile for an agency like theirs. Let private business experiment with cutting down costs. NASA can push the envelope in the meantime. But, the big thing too would be the inevitability such a station provides. If you've got it, might as well use it right? Not to mention the extra publicity they might have. Makes perfect sense when you consider NASA as the agency it is and not a spreadsheet.

The hollow shell wouldn't impart any change due to gravity, but the inner sphere would accelerate the shell if it got off center.

Hard to say exactly. I don't think Mars is the type to have a mature water cycle. Nor do we have detailed analysis of any particular spot to determine how water is redistributed there. Even on Earth that'll be a complex question.

Or, even better, that we haven't used it in other spaces that were better choices. Not everyone's house is layered with solar panels yet. Until then...not much point to do it in roads, or over road,s or any other such shenanigans.

Hi, haven't posted much on these forums, but I've recently been doing an AAR (After Action Report) of a career mode run in KSP. I've been sharing this with others, but recently thought of sharing it here as well. The goal has been to make it interesting for people that might not be all that into space programs, or those that are somewhat interested in KSP itself. Here's the link if anyone is interested: http://seacdev.blogspot.com/ Any thoughts or criticisms are appreciated. If you like it, don't forget to share!