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ARS

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Posts posted by ARS

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    2 hours ago, TheSaint said:

    I don't know how far it has gone, since I've been out of the submarine force for thirty years, but when I was in I know there were discussions about using drone subs to carry active sonar away from the main sub. So you would launch a drone sub out of your torpedo tube (swimout launch, obviously, since an impulse launch would give your location away), drive it a good distance away from the sub, and then the drone would start pinging active sonar which the parent sub would use to pick up contacts.

    As for two subs communicating underwater, the only way, currently, to communicate would be with acoustic communications, like Gertrude or JANUS. The problem with those is that they can be detected by passive sonar, so by transmitting information between two friendly submarines they would be giving their positions away to enemy submarines. In a science fiction scenario you could be communicating using a tight-beam blue laser communicator, but that isn't reality yet.

    Interesting. Does using it different (technical-wise) compared to using regular active sonar? Considering the sonar source and receiver is not in the same sub?

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    So... There's something that makes me curious. During WW2, armor piercing bombs are in widespread use (whether it's actual bomb purpose built for that or AP shell repurposed into a bomb), mainly for attacking hardened targets like capital ships or hardened bunkers. Now, since the bomb is designed to penetrate the target before exploding inside, the bomb relied on kinetic energy from terminal velocity after it's being dropped to achieve penetration. Since terminal velocity is the highest velocity attained by a falling object, assuming the bomb is dropped from the height sufficient enough to achieve maximum terminal velocity purely by falling, does that means bombing from higher altitude than that does no increase in penetration capability? (since the terminal velocity remains the same)

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    What do you guys think about designing a robot with human-like arm so it could hold weapons? In many sci-fi works, whether it's cyberpunk, futuristic or post-apocalyptic setting, we often see robotic combatants, from small humanoid-sized ones holding infantry-grade firearms (ex: B1 battle droid (Star Wars)) to gigantic ones using upscaled arsenal (ex: Titans (Titanfall)). Compared to simply just forget about human hands and have the weapon being the arm itself (ex: Mechwarrior). On one hand, human-like hands allows the machine to do what human hands could, except in larger scale, offers versatility by allowing it to use different types of weapons and can be used to do more mundane tasks (lifting a person, getting up when knocked over, etc.). On the other hand, a weapon arm is much more simple to build, can get bigger guns and generally easier to maintain

    Or maybe a middle ground by having a hybrid arm-weapon (lEx: some of Mechwarrior mechs or Gipsy Danger (Pacific Rim))

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted · Edited by ARS

    On 1/31/2024 at 7:00 PM, DDE said:

    Dumb question: given that takeoff and landing are the most hazardous regimes, why were aircraft cockpits stubbornly placed on top instead of in the nose?

    The landing area is in constant view of the pilot throughout the entire descent to landing. Aircraft descend in a nose down pitch attitude. During the landing itself, the pilot is looking down the runway instead of at it, before the aircraft is pitched nose up just before the touchdown. Any other time during the flight, it is much more important to see what is ahead and above you than it is to see what’s below you (at an appropriate altitude). Where seeing under the fuselage would be useful in some situation, it does not give any significant benefit for the pilot to worth the hassle

    WW2 era bombers need glass nose for both navigator and gunner. Bombing in WW2 was highly dependent upon visual references due to the lack of GPS guidance. For navigators, bombers need to find navigation references during the run up to what the USAAF termed the “initial point” or the start of the bomb run proper. As anyone who has looked for a ground reference from the air knows, just finding the initial point alone could be challenging. The high visibility offered by the large glass nose was necessary - even if the navigation was accurate (even more so during night bombing). For nose gunners, when defending against head-on pass the gunners could only shoot back during very brief interval when the target is in range. This is both terrifying and difficult, hence why the extensive view of the nose turret is important to spot the enemy planes earlier before they come in range. Once radar technology and GPS for navigation has improved, and defense turrets no longer relevant in modern era, the glass nose becomes obsolete, replaced by much more capable radar and avionics instead of mk1 eyeball

    Think of it like driving a car. Like an airplane, your car on the highway is moving forward at a great rate of speed. Having a view of what is below the car would allow you to see the pothole you are running over as you are running over it. That view is not very useful compare to the ability to see the pothole well down the road before you ever reach it. That is why cars don’t need transparent floors. Any speed above a fast walk would render it useless

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    44 minutes ago, PakledHostage said:

    I'm ancient, but not yet pining for the fjords...
    ....

    Interesting... Does this also applicable for a situation where there's a sudden tumbling of the object that causes  significantly increased drag? (for example, something breaks during reentry and causing the shuttle to tumble in such a way that there are now greater surface area being exposed to drag)

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    12 hours ago, DDE said:

    Is/should lunar be deuterium-enriched?

    Basically I'm thinking how Anno 2205 doesn't make sense on so many levels. The plot is about achieving He3 fusion on the Moon to then beam power back to Earth. But, because it's a game about production chains, the Lunar ice only gets used for oxygen and water, and the deuterium can only be produced exclusively in the Arctic and is then shipped to the Moon (unless you waste considerable resources on a late-game, DLC-only tech).

    There is very few hydrogen on the Moon, mainly under the form of some frozen ice in some cold places. There is a natural proportion of deuterium in hydrogen, probably different than Earth’s hydrogen. But the overal quantities are very small

    Tritium is an unstable isotope of hydrogen, with a short half-life. So that it can exist in nature only when there is an active production process. Save cosmic rays, there is no such process on the Moon, so that the tritium quantities may be counted in atoms.

    Helium3 was formed in the Big Bang, and it appears from the decay of tritium. It represents a small fraction of natural helium, itself considerably enriched in Helium4 from the radioactivity of rocks. So to start with, Helium in general is very rare on the Moon, and much rarer on the surface. There may be underground pockets of it. But this would require us to find them, and dig hundreds of kilometres down the moon's crust, only for small quantities, and much smaller quantities of Helium3

    So I guess catching the solar wind with huge electrostatic traps on orbital satellite platform would be more feasible  economically that crushing billions tons of Lunar soil just to get trace amount of it

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted · Edited by ARS

    Is it more efficient to use cold gas thrusters for RCS purpose than using hypergolic rocket fuel? Since cold gas thruster has lower thrust than combustive rocket engines, they are not very good as main propulsion purpose, but could be useful for orienting/ maneuvering purpose

    Using liquefied gases,  the gas pressure output will also remain relatively constant as the liquid gas volatilizes during use, on top of simplified fuel lines since instead of  using two tanks of hypergolic fuel, the space onboard the spacecraft can instead accomodate one large tank of liquified gas

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    13 hours ago, magnemoe said:

    I'm pretty sure that would require something more like an Saturn 5 3rd stage, it was that needed for lunar injection after all. 

    Putting the service module into orbit, yes that is more plausible especially if you drop the command module pretty early, you would need to do an radical burn to raise Pe fast, also lower Ap who is nice. Do an second burn on the way out to raise Pe and lower Ap again and you end int an very stable orbit. But I don't think the service module worked without the command module. Computers was not as common back then :) 

    IIRC, the Apollo command module is directly controlling the service module. As soon as the connection is cut off, there's no way to control the service module. The extra fuel needed to make stable orbit is more likely to hamper the actual Lunar mission

    Also, I'm back :)

    Four Levels of Space Stations in KSP and their Designers. Which level have you reached?

    in KSP1 Discussion

    Posted · Edited by ARS

    This is some of the space stations that I've made long time ago. Many have the capability to alter their orbit and even goes between celestial bodies to set it as the next celestial body they orbit, allowing flexible placements for interplanetary hub (although unlike spacecraft and regular rockets, the procedure for doing burn is much more complex due to many preparations needed. They can't land on planetary bodies and any resources needed for burns must be brought from external sources or generated in orbit. The burn itself should be done in several instances, as doing one long burn in a single instance could overstress the joint connections between modules)

    Spoiler

    ======================================================

    This one has gigantic heat shield at the front for near-Kerbol orbit, is fully self-sustaining and also can relocate it's orbit (interplanetary travel is possible). This one is Cell design, although multiple cells are stacked with each other (the core cell has 4-5 modules stacked end-to-end, and it's surrounded with several cell stacks arranged around it)

    l0i5p0Z.png

    QW4Hgnz.png

    Spoiler

    ======================================================

    This one is my attempt to build a general purpose space station on Kerbin orbit. Like before, it has engines, although it could only travel up to Munar because of limited fuel capacity. This one is more of the Gateway design, the engines are placed on truss and it's deliberately throttled down to reduce stress and flexing on the station's structure when doing burns

    Lp4fB0M.png

    3SyiB1Z.png

    Spoiler

    ======================================================

    This one is specifically designed to be interplanetary-capable. It has engines, and is fully self-sustaining too. This is a combination of Cell and Gateway design (the "spine" of the station is a long stack of cell design, while the rest of it is attached around it like Gateway design)

    3tjBSus.png

    ZWD1MyI.png

    Spoiler

    ======================================================

    This one is built on asteroid that I snatched and brought to Kerbin orbit. This has no engines (obviously) and primarily designed as orbital hub. This one is Kingdom design, although it's size is rather small

    JRvFFXv.png

    ZED8O0i.png

    Spoiler

    ======================================================

    This one is just for lolz (although it does have full functionality as a station), this one is an Atoll design

    QcAEmMg.png

     

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted · Edited by ARS

    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:

    Quote
    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?"

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    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)

    For Questions That Don't Merit Their Own Thread

    in Science & Spaceflight

    Posted

    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)

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