mikegarrison

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About mikegarrison

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    Junior Rocket Scientist
  1. Globular Empires.

    In his own novel he highlights one problem -- people back home get tired of paying for it so they don't bother to turn on the lasers.
  2. Random Science Facts Thread!

    https://en.wikipedia.org/wiki/Engineering_change_order Of course we have the same things where I work, but I've never heard the term used. We have different acronyms for such things.
  3. I think the problem is that the orbital mechanics you are trying to understand this with are Newtonian.
  4. No, by definition it is not possible to cross back out. The one known method for anything to "leave" a black hole is when pair production occurs and one particle falls into the hole while the other does not ("Hawking radiation"). The definition of the event horizon is not "Vesc>C" in a Newtonian sense. The definition is that "all lightlike paths" must fall further into the hole. Also, the time dilation stuff is supposedly only seen from the viewpoint of an outside observer. From far away, it appears that time slows down and it takes an infinite amount of time to actually cross the event horizon. But in the time stream of the particle itself, it experiences no strange effects and simply approaches and then crosses the event horizon. "Event horizon" is actually a more general feature of relativity and not specific to black holes. As I type this message, there is an event horizon expanding away from me at the speed of light. Anything on the other side of that event horizon can not be influenced by my message, because the information from my message can not possibly have reached it yet. The analog to this is the Mach cone, where the air outside the cone can not be disturbed by anything inside the cone because the pressure wave can not have reached it (because it would have had to travel faster than sound).
  5. Globular Empires.

    FWIW, there is not a lot of evidence people ever "lived in caves". Visited caves, yes. But no hunter-gatherers in recorded history have ever been found living in caves. The closest to that are the cliff-dwellers of the Southwest. We have found a lot of graffiti in caves, but it doesn't mean people lived there. Anyway, if you want science fiction about a civilization in a cluster of stars, https://en.wikipedia.org/wiki/James_H._Schmitz already wrote it for you. http://tvtropes.org/pmwiki/pmwiki.php/Literature/FederationOfTheHub
  6. Random Science Facts Thread!

    A billion years here, a billion years there, and pretty soon it starts adding up to serious amounts of time.
  7. Random Science Facts Thread!

    Cathodic protection works pretty well too. But it's not just rust. Hydrogen embrittlement of the rebar can be a problem even if the steel isn't oxidizing.
  8. Google knows: https://en.wikipedia.org/wiki/Genocidal_Organ
  9. That's known as a "combi". Some combi airplanes have the freight in front and the passengers in back. Others have the reverse. A "convertible" airplane is another way to share passengers and freight on the same airframe (but not at the same time). In the case of a convertible the passenger cabin is palletized. So you can slide the passenger cabin out the cargo door and you have a freighter. If you want to carry passengers again, you just slide the passenger cabin back in.
  10. I still think that's not really correct. It does show that the original design, with the shorter hump, does not really "area rule" properly, because it gets big and then small again before the area starts expanding around the wings. And this shorter hump has always been maintained for the purpose-built freighters. When they expanded the upper deck and called it the -300, the reduction in wave drag was something of a bonus. The main purpose was just to fit in more seats. But somehow a whole mythology grew up around this little wave drag effect until people started believing that the whole design had been about area ruling.
  11. It's a little more complicated than that. Wave drag is only part of the drag, the upper deck on the 747 was not designed for area rule but rather to allow the nose loading for the freighter, and you have to put the flap actuators somewhere.
  12. The airplane is certified to be safe within those speed limits. It's not certified to be safe outside them. That's really all that an operating pilot needs to know, generally speaking. I really don't know for sure the exact details of how it is tested. And I probably couldn't go into detail on a forum if I did, to be blunt. But I do know that the manufacturers and the NAAs (airworthiness authorities) agree on a test plan in advance, then conduct the testing to verify it. As for measuring airspeed, this is quite simple with modern instruments. Since we are talking about large civil transports, it's a given that they have accurate knowledge of their airspeed. The only time this is ever really a problem is if the pitot tubes somehow get blocked.
  13. There have to be some limits to reflectors. They aren't 100% perfect, so they must absorb some photons. I would guess that as they do that, they heat up. If you dump enough energy into them quickly enough, I imagine you will overwhelm them and they will simply explode/vaporize rather than reflect. My guess is that a mirror that could reflect a 1MW laser all day long might be nearly-instantly destroyed by a 100 MW laser. But you would have to test it.
  14. Not really disagreeing here, but VNE and MMO are not really equivalent (even though they are both speed limits). MMO is due to Mach buffet, and is basically a limit for controllability. VNE is essentially a limit on dynamic pressure and is a structural concern. Also, these are certification speeds. They don't really mean the airplane will fall apart or go out of control if you exceed them, but they do mean that it might! Basically, you are guaranteed that it won't happen if you stay under those limits, but there are no guarantees above them. As a pilot, you have no idea how big the margin is (if any) -- all you know is that the FAA (or EASA, etc.) has guaranteed that if you do stay below them you will be OK.