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Everything posted by tomf

  1. Correct except that it was "the best bang" said by eccentrica galumbits about zaphod beeblebrox. Which reminds me we should probably add improper use of an infinite improbability drive to the list of potentially interstallar civilization ending disasters. And cricket.
  2. Wow that might be the biggest bang since the big one. It sounds like it was powerful enough to destroy whole galaxies. Even a galaxy spanning civilization may not be entirely safe.
  3. To elaborate I would get the sma of the current orbit and use vis Viva to get my velocity at pe, then I would get the sma of the desired orbit and calculate the required velocity at pe
  4. It's helium that people breath of the need to go deeper than 50ish meters, the nitrogen that is normally in air starts to have a serious impact on your brain around that depth, a lot like being drunk. The old Cousteau documentaries had him and his crew living for an extended period at 30m depth. They were even smoking down there.
  5. The only thing known to go faster than ordinary light is monarchy, according to the philosopher Ly Tin Wheedle. He reasoned like this: you can't have more than one king, and tradition demands that there is no gap between kings, so when a king dies the succession must therefore pass to the heir instantaneously. Presumably, he said, there must be some elementary particles -- kingons, or possibly queons -- that do this job, but of course succession sometimes fails if, in mid-flight, they strike an anti-particle, or republicon. His ambitious plans to use his discovery to send messages, involving the careful torturing of a small king in order to modulate the signal, were never fully expanded because, at that point, the bar closed. Terry Pratchett, Mort
  6. The whole polar bears are black thing is just people trying to appear superior by knowing something. The skin may be black but their fur is clearly white. Sure there is a reason why their fur is white but that is true of everything. Supporting xkcd
  7. That isn't the Roche limit, the Roche limit is about how close a secondary body can orbit to a primary body before the tidal forces pulling it apart are stronger than the gravitational forces holding it together. On the rapidly spinning body, close to breaking up - it would be very oblate, the apparent gravity at the equator would be very low while the gravity at the pole would be more normal for a body that size. Aparent Gravity would always be perpendicular to the floor so things wouldn't roll away to the equator. A throw from the equator with 0 inclination would return to hit you on the back of your head if you didn't dodge. Any other inclination would land somewhere though
  8. I think the question is can a planet spin fast enough that it's equator is traveling faster than the velocity required to orbit that planet. The answer is no, the planet is simply going to disintegrate. On the scale of planets there is no force that is going to be able to hold the planet together. An asteroid held together as a single rock could spin faster than its orbital speed. To land on it would be a matter of grabbing hold as it whizzed by, or landing at the poles.
  9. .For capturing as I mentioned above getting that Delta v to point in the right direction that is hard, and is related to the velocity of the assisting body. Imagine a very massive but distant and slow assisting body orbiting at speed V. We can get a good angle of deflection if we wish, but that just leaves us in almost exactly the same orbit just going the other direction with a 2v difference. E.g a previously prograde hyperbolic orbit about the primary is now an only very slightly less hyperbolic retrograde one. We could go for a smaller degeneration angle but then the Delta v of the assist is limited.
  10. The maximum change in velocity is going to occur when you change direction by exactly 180°, i.e. the the orbit at the SOI crossover is parallel to the centre line. This can only happen when the orbit is in fact an ellipse cut off by the SOI meaning that the relative velocity is always low. For hyperbolic orbits the deflection angle is always less, but it is at a maximum when the pe of the orbit skims the surface/atmosphere. For a given relative velocity you can work out the maximum angle of deflection and hence the maximum change in velocity. If you can only deflect 90° at a given relative speed of V then your Delta v is ✓2 * V by simple trig. This matches the observations above. - a massive body is good, it deflects more at a given speed - a denser body is better, pe can be lower giving more deflection - If the speed is to high deflection angle is low giving little DV It's bedtime here which is definitely the only reason I'm not going to do it but it ought to be possible to work out for any given body what relative speed gives the highest change. ---------------- Working out how to get the Delta v to point in a useful direction is an entirely different matter in my experience.
  11. Well it has taken all human industrial capacity for the last 200 years to move the climate by a few degrees over the next 60 years so no one said climate change was easy.
  12. If you look at the pork chop plot you can pick your departure date on the horizontal axis, and the arrival date on the vertical and it will tell you how much Delta v you need, so if you have the Delta v and you pick an arrival date before the first crafts arrival date the later craft will overtake
  13. https://what-if.xkcd.com/24 That design is what you get when your ISP isn't really good enough
  14. For the suits question it's going to come down to the types of damage typically sustained by the ships. Of you ships frequently end up after a fight with lots of small holes from being blasted for example with orbital velocity shrapnel, or ships go "down" slowly enough that you have time to get to a lifeboat then suits are going to be recommended. If weaponry is such that ships tend to face total existence failure and help is far away then you may as well be comfortable in shirt sleeves.
  15. A while ago I asked a doctor about ventilators and leaned that about 0.03 bar of overpressure is typical. Breathing pure oxygen you need at least 0.18 bar. Given that the pressure on Mars is only 0.0061 we still need around 0.15 bar of pressure applied to the chest
  16. Do we know what the rentry timings will be line? If starships profile is anything like the f9 first stage you have two minutes between rentry burn and landing which doesn't seem a lot of time to target it with heavy weaponry. And it spends most of that time hypersonic so good luck trying to hit it with small arms fire.
  17. Sounds fun, do you have a link for the thread?
  18. I listened to a podcast a few years back which looked at time use surveys and concluded that washing machines made much less difference than you might think, basically people wore clothes for longer before washing them, used detachable collars, dark colours to hide dirt etc. The thing that really made a difference was pre prepared food. The average food preparation time for a household in the 60s was around 4h a day, now it is 45m. We were willing to be a bit grubby but not too starve. The BBC did a great series called "50 things that changed the modern economy" that I had to re-listen to to write this
  19. Deer are already pretty good at being deer, for every conceivable mutation that might make then into better deer there must be millions that make for a worse deer. Also evolution doesn't work on the survival of individuals, it works on genes. Genes that promote the survival of other members of your species over the individual can work on the basis that the others are likely to have the same gene.
  20. If your water is already at 100°c then you need to supply the vaporisation enthalpy. The Wikipedia link gives 2257J/g so you need 50*2257 j/s or 11kW https://en.m.wikipedia.org/wiki/Enthalpy_of_vaporization
  21. For pretty much any record that you can set out to achieve the difficulty in achieving it is going to be pretty proportional to the coolness of having achieved it + any actual usefulness. If a record were cool/useful and easy someone would have done it already and pushed the boundary further out. So by that measure I would expect the submarine record to be easiest simply because it is the least "cool"
  22. When I was a child I bought a present for a friend which was basically an enormous black plastic bag and a light string, you filled the bag with air and waited for it to take off.
  23. Question Inspired by that post but that star just has some uranium in its atmosphere.
  24. Could you have a "star" made entirely of uranium? Somehow a cloud of uranium isotope ratio TBD collapses and forms an object that emits roughly the same power as the sun for an appreciable length of time. A reasonable proportion of the energy needs to come from fission rather than just gravitational collapse a-la https://en.m.wikipedia.org/wiki/Kelvin–Helmholtz_mechanism I think an equivalent question is Is there a negative feedback mechanism in the collapse of a cloud of uranium that will result in a steady power output.
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