Jump to content

Hannu2

Members
  • Posts

    568
  • Joined

  • Last visited

Reputation

349 Excellent

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. Sorry, I probably was pretty technical. Ferromagnetism is that familiar magnetism. Permanent magnets, inductor and electromagnet cores are often made from ferromagnetic materials. Iron is the the most known example. Ferromagnetic material react very strongly to magnetic field around it. Physics behind the phenomenon is awful mess of advanced quantum mechanics. Electron spins, exchange interactions and so on. I never learned it properly because I did not need it with semiconductors. They are fortunately not ferromagnetic. There is quite often claims that ferromagnetism is somehow badly understood phenomena. It is not true. It is probably because there is no classical analog and it is therefore omitted in popular material and physics courses before master or PhD level in university. Quenching is a situation in which superconductor cease to be in superconducting state. It is abrupt phase transition and quenched part get immediately significant resistance. Superconducting coils have very large inductance and also large currents. It means very large energy of magnetic field and that energy is released as heat in quenched part. It may damage the wire straight or boil so much liquid helium that pressure bursts vessels or tubes. It may also be dangerous for user if safety measures are omitted. It may happen due to some disturbance. For example change in magnetic field around experiment. It is not the only danger that iron tool is attracted at high speed. Crash may be followed by a shower of liquid helium.
  2. Why? It is difficult, expensive and dangerous to roll huge speeds on ground. What that gives over vertical takeoff? You can not have wings with reasonable assumptions so you need TWR of greater than 1 at launch. If we talk about completely fictive fusion engines, TWR can be anything. If you need visually stunning scene in scifi movie, feel free to use a ramp, but it is hard to see any use in realistic scenarios. Have you heard a physicist joke? Rich gambler asked mathematician to make a model for predict horse race winners. Mathematician thought a minute and said no, there is too much too complicated things. I can not do it. Disappointed gambler went to engineer. Same answer, there are too much unknowns. Then it was physicist's turn. Physicist said, yes, of course, it takes two days. After two days he came with a fancy program. Gambler asked why you could do what other specialists could not? Physicist said. It was not difficult. Let's assume first, that horses are perfect spheres which moves in vacuum...
  3. If structure was solid you would be in geostationary orbit. If structure was higher, centrifugal force would throw your car (and loose surface material) off from road. It is same idea than space elevator. There was a mod in KSP which had celestial body with higher centrifugal force than surface gravity at equator. It is impossible to stay on such place without continuous force or fixing to surface.
  4. Magnetic fields come from moving electric charges. There are moving conducting material in celestial bodies. Stars have plasma, planets have liquid metals or salts dissolved in liquids (like ammonia or water), neutron stars have some strange superfluid stuff with some protons and electrons (all of them do not form neutrons) etc. Those lethal magnetic fields are around neutron stars and if you really was at those positions magnetic field would probably not be on the first page of your list of lethal conditions. Electromagnetic field have energy which can be handled as mass in relativistic equations. However, that mass have not noticeable effects. Gravity is extremely weak interaction compared to electromagnetism. I dno not know any absolute limit of magnetic field strength. But extremely high field lose its energy in radiation, pair production etc. and probably those fields around magnetar stars are strongest which practically exist. Do you mean now laboratory magnets? Those are limited by properties of superconductors. Superconductors have certain maximum filed strength. Above that Cooper pairs are broken and material lose superconductivity. I think practical limit is around 20 T in continuous use. There are no resistive losses in superconductors. You have to put in certain energy to create magnetic field but after that you have to only keep superconductors cold. You have to also dump that energy when you want to turn off the magnet. Uncontrolled quenching (loss of superconductivity) may cause damage. You have also to be very careful if you operate near maximum field. For example piece of ferromagnetic material near the magnet may cause local exceed of max field and quenching.
  5. It depends on what you compare with. I was once in a museum diesel locomotive which had two turbos at crudely same physical size (compared to humans in some photos). Power of main engine of that locomotive was 1900 hp and shaft power of turbos probably on the order of 100 kW. Those rocket turbopumps have several tens of MW. That gives totally ridiculous power to weight or power to volume ratio. Is there any machinery which is even near? Whatever normal industrial machine at 30-50 MW power rating typical to those large rocket engines (steam or gas turbine, generator, diesel engine etc.) fills a large industrial hall and needs special truck for transport.
  6. It certainly will not happen with SLS. It is more political subsidization program than real space program with technical and scientific objectives. But Falcon9 overcame that second issue with clever way. They used it as expendable rocket and made landing experiments after sending 2. stage and payload to trajectory. Commercial missions succeeded and company got money even many landings failed before they got all systems work reliably. It certainly could work as development step for expendable SLS too.
  7. No one knows. There are no well studied places on Mars. Those probes can do only very primitive studies. Humans on Mars or million probes can not do much better except bring stuff back. There are many things which can only be found in proper labs on Earth. But I do not believe that there will be humans on Mars any time soon. There will be several decadal propositions and many robotic Mars missions before that. I am not a biologist but as far as I have understood, every stone on sedimentary layers have clear signs of life on Earth. Past and present. Mars is of course much more uncertain because it has not thriving life everywhere but I think if samples are chosen from sedimentary layers which have chemical signs of past water, possibilities are reasonable good. Single photos will not probably be important. I do not know is there any visible changes on Venus surface. I think seismic data, weather of low atmosphere, seasonal/daily changes (which are same thing on Venus) etc. may be much more interesting and photos are PR-stuff or maybe there will not be a camera at all (complex photographic detector cell is probably not the first component they make from novel material). I am not a big fan of Venus but it planetarty scientists think it is interesting place to investigate if have very little arguments against them.
  8. Was that real time or accelerated? How long does such eclipse take?
  9. They can use much more sophisticated methods on Earth. That's why samples are so valuable scientifically. Even samples from Moon, for example those Chang'e 5 returned couple of years ago. It is impossible to bring equipment able to detect for example microfossiles or make detailed chemical analysis. For example our university have small particle accelerator for such studies. On Earth scale "small" means few large industrial buildings full of equipment, thousands of cubic meters of underground caves, few orders of magnitude more energy consumption than all spacecrafts have ever produced totally etc. Starship will never bring "small particle accelerator" on Mars even some researchers may call some larger than average electron tube as "particle accelerator" for marketing purposes. And that is mostly for material studies, it is far too weak for any work related to actual particle physics. Didn't they say that they would have suggested a probe to Neptune and Triton if they were not somehow bad position. I understood that during next decades there will be better trajectories to Neptune (I guess Jupiter will be in position which give more dv in gravity sling maneuver). Probably they can use data from Uranus and its moons for same purposes. Microfossiles or chemical signs of ancient life. Or maybe even living microbes. It is gambling, of course. If they will not find any signs of life from returned samples, many will say it was waste of time and money. Do they have those new electronic GaN components yet, which can operate at 500 C? If they have, long lasting surface probe would be intersting. But if it last couple of hours, take few photos and make quick simple surface analysis, like Venera probes did, some kind of floating atmospheric balloon would probably give more bang for the buck.
  10. Technically bigger payload capacity could give bigger fuel tanks and higher dv which can be used to decrease the travel time. Practically, if they decide to plan and build a craft for Falcon Heavy, they will not change it later even there would be more capable or economical rockets later. Building spacecrafts, launch contracts etc. are extremely bureaucratic work and all changes take ridiculous amount of years and billions. That's why flexible private companies, like SpaceX can have impossible looking cadence of developoment. They can just decide to scrap work in progress and make better if they find a better way during development. Except of course certified products, like man rated rockets and capsules, which are locked in the current state forever (or until someone pays needed billions to make new certifications).
  11. Yes, it is impossible to predict far future. Almost all such predictions have failed and we do not have better ability than previous generation scifi writers. I think only reasonable reason for space mine cheap and common metals, like titanium, will be environmental. We will want polluting metal refining away from our planet and bring as far refined as possible materials back. But it is clearly closer scifi than foreseeable future. It is not much point to speculate what kind of cargo ships or other means to send stuff from one planet to another is then available. It is absolutely sure that any current or under development rockets can not do it economically. I do not believe that Moon will ever be important source of industrial materials, except what is needed for lunar colonies. Asteroids have precious stuff in addition to basic metals and much easier available in microgravity environment.
  12. What is the point of warp drive in semi realistic space flight simulator? Doesn't such ridiculously overpowered tool remove gameplay aspects. It is hard to expect that for example surface exploration is so interesting and content rich than it would work as whole game without logistical challenges to get research stuff there.
  13. I am sure that Martian camels have evolved to float over sand dunes during millions of years they have lived on planet. Or maybe they have learned to burrow tunnels and live underground. It may explain why they are so rarely seen in orbiter's photos.
  14. It is not possible to be buried in Martian sandstorm. Air density on Mars is very low and mass of dust is negligible. Later probes have been there through several sandstorm seasons and suffered only with some decrease in solar power production. Few micrometers of fine dust can cause that. Landing damage is much more plausible reason.
  15. I think solid non metallic hydrogen have been made and there are some reports of metallic state but they are criticized and need further investigation. And there are no observations or credible theoretical predictions about metastable high density states, metallic or not. It is very scifi-ish hypothesis. Metallic hydrogen would be burned in aircraft engine. It would give huge fuel value (MJ/kg) because metallic lattice have much less binding energy per atom than normal H2 molecule. Certainly such fuel would give benefits in planes and terrestrial vehicles if it was possible to store, handle and burn safely. ISP is just not good way to characterize practical plane efficiency.
×
×
  • Create New...