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Posts posted by ARS

  1. So I recently saw a review on Youtube about a movie "The Wandering Earth". In case you don't know, it's a science fiction movie with 'science' part being so bad, it makes "The Core" science looks like "The Expanse". Let's get with the premise in a nutshell: The sun is expanding, we need to save humanity, we built thousands of city- sized rocket engines on Earth's surface and fly the damn planet like a spaceship straight to Proxima Centauri by using Jupiter to do gravity assist, which then goes haywire when one of the engine shuts down, leaving the planet with insufficient thrust and now it's being pulled into Jupiter, and the only way to save the humanity is by igniting Jupiter's atmosphere so the shockwave would throw the Earth out of Jupiter's gravity well
    But that's not what I'm gonna ask here. Understandably, the movie is being mocked to death, mainly from being ignorant with so many laws of basic physics, astronomy and orbital mechanics. Most of the critics tend to point out about how insane the idea of putting rocket engines on Earth's surface is (and how it would mess up with Earth's geology and atmosphere), but one comment struck my interest:

    I think they really missed a great "real science in fiction" opportunity. They completely glossed over the moon and the fact that it literally pulls at the Earth gravitationally. Most of the problems surrounding building giant rocket engines into the Earth can be addressed by building giant rocket engines into the moon instead and using it's gravity to pull the Earth. This is called a gravity tractor and was concieved as a way for a spacecraft to change the orbit of a much larger asteroid by simply orbiting and doing calculated engine burns to cause the spacecraft to add or take away the momentum of the asteroid. Moving a planet by pulling it along with it's large gravitationally bound moon is a little bit more feasible. The moon is airless, no atmosphere to interfere with efficient engine operation. It's solid and geologically dead. No popping every volcano on the planet simultaneously when you fire up the engines. You don't have to despin the Earth. It's covered in helium 3 fuel for fusion. As you tractor the planet out of the solar system you could slowly translate the moons motion from orbiting the Earth to leading it, acting as a planetary shield against impacts in transit from asteroids and interstellar dust. On the back side of the trip you can move the moon to following the Earth to brake entering the new system, and revert back to orbiting as it is steered into orbit around the new star.

    So it's basically using Moon's gravity interacting with Earth, pulling at each other, and use that as a means of manipulating Earth's trajectory. Now I know the scale involved here (especially in terms of engineering) is so mind-bogglingly large, but assuming the moon's orbit could be manipulated (and you really don't care about it's effects on Earth's inhabitants), is this idea makes sense (In terms of physics)? I don't ask "is this possible", I ask "is this (in theory) possible?"

  2. As steady stream of radiation and particles continuously emitted from Black Hole as Hawking radiation, there would be a point in time where black hole's mass loss would eventually caused it to cease to exist and die. However, as black holes also moves through universe, assuming it keeps feeding from stars and planets (devouring their mass), is it theoretically possible for black hole's lifetime being continuously extended? (at least until there's nothing left to devour)

  3. 5 hours ago, Gargamel said:

    Why even have a defending sub on station at all?     Why not have a series of both emitters and microphones, SOSUS style, along a ‘choke point ‘ in the area you want to patrol, tied to a shore station.      When the shore Station detects an intruder, it can dispatch a fleet of ASW aircraft and small boats to handle the issue, all of which combined would be far cheaper than a single sub.      Keep those assets for force projection rather than defense.  

    Just wanna ask if you can detect other sub by using that method (active ping far away from the sub)

  4. 1 hour ago, lrd.Helmet said:

    I would assume that you yourself are also reflecting the ping from the remote emitter. So you'd be painting yourself as well. 

    pov of "attacking" sub:
    1st ping: active emitter
    2nd ping: reflection of defending sub

    1st ping gives direction of emitter, 2nd ping gives direction of defending sub. I would think that people smarter than me can do some magical math and calculate the location of both objects. 

    But the problem is, the defending sub already knew the location of the emitter and already expect a return when they trigger the ping. The defender knew where the location of the emitters, where to look at the moment they trigger a particular ping as well as the underwater topography of the area they defend. On the other hand, the attacking sub is clueless and has no idea about the pingers' placement or even if there's such a thing in the area in the first place and expect there's only defending sub in the area. They are not expecting an active ping, much less a return from pingers they don't even know the location about (they might even mistake a ping from a buoy as defending sub's ping)

  5. 3 hours ago, darthgently said:

    Yes.  Similar is done with RF energy where a stealth station can use existing RF sources, like radio stations, at known locations, to image aircraft.   Cell phone tower signals have been used in warfare to detect and locate aircraft (Bosnian conflict in the Clinton years?).  As long as you know the location of the "ping" source in relation to the receiver math can do the rest 

    55 minutes ago, DDE said:

    Some air-dropped sonobuoy variants are combined with "emitters" that are literal explosive charges, so, yes.

    Yes, that's what I mean: detecting a target underwater using active ping, except you're not the one doing the ping, but preplaced active pingers placed beforehand (and you already know the locations)

  6. Question: Is it possible for a submarine to do standoff active sonar search by using separate sonar emitters outside of the ship (as in, in the form of buoys, underwater emitters, etc.). Let's say for example submarine A is defending an area, and it already pre-place these emitters around. Then, enemy submarine B is entering A's patrol area. If A knows that B is entering the area, could A detect B simply by staying on passive sonar while periodically pinging the active sonars from the buoys and listening to the echoes to locate B? (could either do sonar pings from the buoys one-by-one or several of them at once)

  7. Does lower stall speed:
    -Affected by the size of lifting surface area (if it's indeed like that, does flying wing design inherently have much lower stall speed than conventional design by essentially having the entire underside of the craft as lifting surface?)
    -Beneficial for carrier landing when there's limited runway length?
    -Beneficial for maneuvering during active combat?
    -Have negative effect on aircraft?

  8. 1 hour ago, Ben J. Kerman said:

    Theoretically, if an object with absolutely no water or moisture in it at all was placed into a microwave oven (and turned on, duh) it wouldn't heat up, right? I'm just making sure I understand how a microwave works.

    Microwave requires water inside the food to efficiently heat it, but despite this, some things that have very little water inside do heat up in microwave. Fats  for example, still heat up, albeit rather inefficiently. The classic example for this is the discovery of microwave oven itself where a chocolate bar melts due to a very badly shielded microwave emitter. Functionally, any polar molecule will work with microwave, but water absorbs microwaves better than others. If your food absolutely don't have any water inside, the result will vary - but generally, either no, or so little it’ll hardly make a difference. Microwaves bounce off metal, and vibrate polar molecules. Water is tiny, very polar, and very much present in almost all food, so it’s the most ubiquitous. While there are other polar molecules in various food items, there’s just not enough to absorb enough heat to matter

  9. With our current space technology, how hard it is to create a compact skintight personal spacesuit (like on sci-fi) that isn't as bulky as the current one? Obviously it wasn't meant for prolonged EVA activity and offer far less feature than a full-on EVA suit, but enough for keeping the wearer alive in a vaccuum environment or when you just wanna casually stroll outside the  planet-based colony with reasonable temperature and atmospheric pressure (like for example, on Mars)

  10. 2 hours ago, mikegarrison said:

    Maybe, you know, there shouldn't even be military spaceships with military crews?

    Well if the setting has AI technology that's advanced enough to mass-produce sentient warships with enough intelligence for considering tactical options and make a combat decision in real time, then yeah, crew is just a liability at that point since any space you can put additional weapons now being used as crew accomodation and life support (and essentially turning interplanetary war into glorified battlebots arms racewhere both sides are sending increasingly advanced drone warships until one of them is overwhelmed). Or maybe the AI is being prohibited (at least on sentient level) so living crew are still needed to have a functioning ship

    42 minutes ago, kerbiloid said:

    The next question: should a crewed spaceship have so large rooms that a meter-wide hole doesn't mean a total crash inside.

    I don't think large room is gonna help much with decompression, especially since large room also takes a lot of space inside the ship. It might make decompression slower, but once it happen you essentially lost a large portion of the ship. A more sensible solution would be heavy compartmentalzation. Space warships should have more bulkhead than regular spaceship, aside for increased hull integrity and mass, a hull breach could be isolated in a more specific manner (only affected room are sealed for damage control), so you only lose rooms that's totally unusable, not an entire section of big room that only have minor breach on it's corner

    Now that makes me wonder, since duct tape is always an adequate improvised repair tool, if your glass helmet on your spacesuit have cracks, could you seal the crack in improvised manner by covering the crack with space-grade duct tape? How about a tear on the spacesuit? Could it be fixed (at least temporarily) by using duct tape?

  11. So I'm making a worldbuilding concept for my works, and I have some stuff to ask


    -Should military spaceship crew wear spacesuits? Not the kind of full-EVA suit, but an airtight suit that's adequate to keep the crew alive when there's a hull breach. In some sci-fi works (Star Wars, Star Trek), the warship crew (especially bridge personnel) only wears their regular military uniform, while on some works (some Gundam series) have the bridge personnel wear spacesuits (at least when it's in active combat situation)

    -Does terraforming a planet outside of the goldilocks zone pointless endeavor? (at least on giant money waste level) Like, it's literally trying to fight the nature of the planet's location itself

    -Which one is harder? Launching a missile from the surface to hit something in orbit, or launching a missile from orbit to hit something on the surface?

    -Does nukes have shockwaves in space? If so, could you thwart a missile barrage by detonating few nukes to clear them out?

    -As a spacefaring civilization, what kind of resources that's vital for sustainable space conquest? (aside from fictional resources like power crystals for FTL reactor),  stuff that's necessary for large-scale manufacturing of space warships

    For some information about my works:


    -Space war setting, the tech level is like more grounded version of Star Wars (there's still FTL travel, but no such thing like planet-killing battlestation, just plain good'ol orbital bombardment if you really want a planet dead)

    -No force, but there's psychic power (which is just limited to typical ESP ability you would expect such as telekinesis, precognition and mind-reading, not to the extent of shooting lightning or more elaborate stuff)

    -No aliens, just various factions of humans in the sector, ranging from pirates, mercs, military dictatorship, fanatical psychic cult up to megacorporations with private army (oh, and hostile rogue AI leftover from previous great war)

    -Energy weapons are as commonplace as kinetic weapons and missiles

  12. 1 hour ago, JoeSchmuckatelli said:

    insolation being so very, very precise and local, after all!

    I think it would be reasonable to use the term insolation by itself when we're talking about extrasolar planet. Let's say we're discussing about the characteristic of extrasolar planet of CoRoT 7b, when the topic of insolation being brought up, people would automatically associate it with the star that CoRoT 7b orbits, not our Sun. With so many stars out there, assigning unique term for each of them (which basically means the same thing: the amount of radiation received on a given surface in a given time period) adds unnecessary complexity, especially when we reached the level of InTorcularisSeptentrionalisation, or InCoRoTation. I think the word Sol itself doesn't always have to be specific about our Sun, otherwise when we reached the technological level to send exploration to other stars, the spacecraft's Solar panels would be referred to TorcularisSeptentrionalisar Panel, CoRoTar Panel, Betelgeusear Panel,etc.

  13. 40 minutes ago, JoeSchmuckatelli said:

    Question for the pedantics: when describing the amount of starlight received at any given point on an exoplanet, will we need a different word than insolation? 

    Yes, although it's very insignificant. Depending on Pluto's orbit, the planet's position is between 30 and 50 times more distant than the Earth's from the Sun, and since brightness decreases with the square of the distance, sunlight on Pluto is between 900 - 2500 times dimmer than sunlight on Earth (again, depending on Pluto's location on it's orbit), though with that amount of brightness, it's still quite a bit brighter than full moonlight on Earth - but definitely kinda dim. You’d be able to see fairly well around you (after all the real photo of Pluto is still quite well-lit), but the Sun itself won't be any brighter than other stars around it and for things like plant growth or generating electricity from solar power - forget it, it’s nowhere near enough

  14. 5 hours ago, DDE said:

    Why don't stage-and-a-half rockets use aerospikes? Thinking specifically about the Space Shuttle.

    The most critical problem is cooling system. By default, SSME uses fuel flow through the main fuel valve into regenerative cooling systems for the nozzle. Considering the heat the engine needs to withstand (aside from the hot gas from the engine itself) from launch into reentry, it's A LOT.  The pressure (and temperature) of the gas remains very high all along the spike surface in order to maintain the consistent engine performance across all altitudes, and the sharp tip of the engine design itself leaves very little room for cooling systems, unlike the bell-shaped nozzle of SSME. Some other problems includes the fact that SSMEs are not exactly fully reusable, since despite being advertised as reusable, the engine needs to be swapped for each new launches, and considering the cooling problems above, it would considerably jack up the maintenance cost

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