farmerben
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Posts posted by farmerben
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I was thinking about how to harness the radiation of Planetary magnetic fields to power lasers. A lot of pages on the web use the buzzwords I was searching for but none answered my questions.
In the Jovian magnetic field it is possible to swing through very intense belts of high energy proton and alpha particles. I metallic sail passing through the belt will have a shower of gamma and x-rays coming out the other side. A scintillator crystal catches many of these high energy photons and emits violet photons instead. I am not sure if the peak wavelengths of any scintillator crystal match exactly that of any known lasing gas. If it is possible to adjust those wavelengths by 30 nm or so, using some extra material then a perfect match could be achieved.
My understanding of lasers needs checked. I have in mind a tube coated with scintillator crystal. Gamma rays enter constantly from all sides. The walls of the tube give off violet light. Is it the case that incoherent violet light in a tube will, through interaction with lasing gas and two mirrors on the ends of the tube, create coherent violet laser light?
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A suborbital projectile is somehow propelled toward a target in Leo (~125 km altitude) at 500g. It closes this distance in less than 7 seconds, but lets go with 7s if we are not taking the shortest path.
The target maneuvering at 2g can alter its position relative to expected position by about 1/2 a kilometer.
The missile needs about 0.4s or 6% of its total to anticipate and respond to the most basic evasive maneuver.
Assuming the missile has finite propulsion, then the target will be much safer at long range. If infinite propellant, not so much. But the time the evasion can waste certainly increases with more range.
Which evasive maneuvers are the most effective? If you were the pilot of the target spacecraft what would you do?
I'm going to use maximum rotational thrusters in the plane perpendicular to the distance vector of the incoming projectile, and fire the main engines with maximum possible thrust at first. Then introduce some randomness the closer the projectile comes. So halfway to impact I might choose numbers between 90%-100% of maximum possible primary thrust, without significantly changing my direction of angular acceleration. Only in the final second or so would I do something like fire retrorockets.
Is it reasonable to spin a 1000 ton man shipped in half a second? If the ship can do less than one spin, I would not change the direction of angular acceleration at all. If it can do multiple spins from rest in that period of time, then it probably is a good idea to wobble.
A zig zag maneuver covers more distance than a spin maneuver, so for a very large spacecraft its advantages increase. But for the generic case I think a spiral with just a bit of randomness is better. What do you think?
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I'm really enjoying the discussion about changing the fuel injectors so that a rocket engine can run with multiple fuels. Two plates that rotate can provide many configurations of holes.
The original post implied you want to fill an empty methane tank with liquid hydrogen, and you are concerned about left over vapors. The vacuum of space can clear out vapors, but maybe we don't want to that. The methane will mostly become a frozen solid in liquid hydrogen, so you have to deal with chunks. A tiny trace of hydrogen in methane fuel will probably not have any serious effect.
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Many people believe they can seed clouds with silver. But a man from Utah told me "rain follows the strontium"
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Steam and methane could be the workhorses of buoyant gasses on Earth and Venus. These give half the lifting performance of hydrogen and helium, even though they have six times the mass, because they displace half the weight of the air.
Fuel cells could be the key for using methane to maintain steam.
I think manned flight using flammable gas airships should not be banned forever. A steam balloon needs insulation. Methane could provide that insulation. The possibility of methane ignition is eliminated if the shielding gas is less than 13% oxygen. So if the outmost layer of the airship were simply hot air enriched with extra nitrogen, then the airship could not ignite even if penetrated by bullets and struck by lightning at the same time.
On Venus of course the ignition risk is something else. In that case you would want to store up some available oxygen, so a similar design works for a different reason.
Another huge advantage you get with steam and hot air that you do not get with hydrogen and helium, is leak intolerance. A hot air balloon that leaks .01% of its air per second and has cool atmosphere flow in works fine. It can operate with near zero pressure gradient to outside at all times.
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Spoiler
Water vapor floats like a dream on CO2.
If there were large blimp like fungus living around 45-60 km in altitude, they could suspend themselves on steam. A host of extremophile organisms on Earth could survive in a primarily steam environment and use photosynthesis to support the ecosystem functions. If highly successful, this environment would eventually extinguish itself through climate change. For a while though, it could be more economical to grow fields of sky-fungus than to build foil factories on Mercury.
edit: also methane performs almost exactly as well as steam
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On 5/3/2020 at 9:41 AM, wumpus said:
It isn't all that clear how useful asparagus staging would be in real life. In an ideal case, asparagus staging gives you the thrust of your second (or higher) stage for free. No more.
Sorta... but some other details matter. For example, we can effectively throttle down before Max-Q by separating stages rather than cutting engine power. Reducing drag at the same time by the way. In real life we may be chasing a gain of around 1-5% of total dV. That is still well worth it if the engineering is trustworthy.
I also wanted to mention about oval gear flow meters. They could be powered by pressurizing the outer boosters. The pressure on one oval gear mechanism drives the train. While coupled by shafts we have pressure driven flow control Upon booster separation the gear shafts can decouple and one is braked. A braked gear is basically a closed valve. If the fuel lines simply break away from one side of the flowmeter mechanism while the shaft is locked then everything will be fine.
How much does it weigh? It must weigh more than purely a pressure driven rocket. But the rotating machinery may be in similar ballpark to a turbocharger pump, and less than an electrically driven pump.
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Spoiler
In order to achieve asparagus staging.
My idea is to create a vertical spline driving a series of stacked oval gear flow meters arranged in a stack. The ovals in one layer must rotate in a fixed ratio to those in a layer below.
This creates a governor regulating fuel flow through all the stages of the rocket.
By itself each rocket must be able to pressurize and deliver all its fuel to its engine (if we want reusability).
There is also a gear train for each inner stage governing that fuel allowed to flow in is exactly the same as fuel flowing out.
In a 7 stem rocket (6 side boosters and a central stage). The outer ones also have a gear where the fuel flowing to other stages is exactly equal to 5/2 the fuel flowing to their engine, and the fuel leaving their tank is 7/2. (for the next stages 5/2 from tank, 3/2 to fuel lines and then 3/2 from tank, 1/2 to fuel lines.
How massive is such a system? I don't know but the increased dV from asparagus staging is so enormous that a very heavy governor on side boosters that land and are reused can be justified.
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19 hours ago, Vanamonde said:
How does the force not push propellants backwards in the non-firing injectors?
That would be a huge problem if you suddenly stopped flow in a pipe. If you redirect it not so much.
I wonder how they construct this mechanism?
On the too simple end, a rotating plate valve could do something.
On the super complex end, add a few hundred flippers controlled by piezzo electric ultra-fast continuous stroke control devices. Then create a neural network starting with experimental data then running a few gigajillion simulations, every now and then another live test. Within less than a year of human time, wind up with the most intelligent smoke ring blower on the planet.
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First stage TWR was a measly 1.15
Most KSP players want TWR between 1.5 - 2. And have flown with TWR's well above and below that, and know what it's like.
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Thorium dioxide mixed with nickel is an astonishing material. It is among the best alloys to resist thermal expansion, and incredibly hard. Thorium dioxide can be mixed into windows, and expensive camera lenses were made this way until a few decades ago.
What if we had a mildly radioactive hull on a spacecraft?
The radiation from thorium is low energy alpha radiation which can't penetrate polyethelene. There are traces of beta radiation from radium, but very low and manageable.
When the ship is exposed to higher energy proton and alpha radiation from external sources, it can sometimes spall off additional nucleons from the thorium. The trend is more particles with lower individual energies, even though the spallation is an exothermic nuclear reaction of a sort. An inner hull would be able to block a greater percentage of the radiation, compared to high energy rays that go right through.
The thorium in the hull would be able to tell its life story of when it was exposed to lots of radiation and from where. On the other hand it is among the best gamma ray shields. So with the proper alpha shielding, a crew would get less overall radiation compared to a similar mass steel or aluminum hull.
edit additional:
One other nice feature is the ability to damage control on the spacecraft. The ship can image its own xrays. If there is a hairline crack in a steel pipe anywhere, it will show up in x-ray microscopy.
Potentially the crew would be exposed to more X-rays than normal people nowadays. Imagine a woman with two jobs; a dental hygienist and an airline stewardess. Just insert this gene into her and everything will be fine.
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Maglev trains with electo-magnetic coils along the track are super expensive, and a maintenance problem.
What if we reverse the model. The track is superconductor, and the vehicle must supply all the power, or get it from an overhead cable like buses. Electric vehicles could use it with a simple modification. Ferro shoes inside the wheel base, that switch on and off.
The track and tunnel company simplifies its responsibilities but not assuming responsibility for rapidly switching power systems. Instead their pledge is to continuously supply liquid nitrogen and oxygen. They guarantee pure breathable air in a positive pressure tube. Thus ventilation solves itself.
The track company would need to rescue broken down vehicles. But the major thing that would solve this is 1/4 mile entrance ramps on sidetracks. The track system would test each vehicle arriving for that first 1/4 mile. If it passes the test it shoots onto the mainline at full speed. If it fails the test, or if traffic requirements dictate, then the vehicle sidetracks off near the original entrance station.
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Ethanol mixed with hydrogen peroxide is an environmentally friendly choice.
While it's not the highest ISP for a main engine, it is totally viable for maneuvering thrusters. For a long mission to the moons of the gas giants, you would want a lot of thruster capability, but who knows exactly how much. Reserve propellant can be converted to life support supplies... oxygen and vodka.
The hydrogen peroxide decomposes/ignites against certain hot metal catalysts.
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Good reply, severperforce!
So the more choked the exhaust the higher the pressure driving the projectile.
The shape of the exhaust nozzle determines how much forward the thrust the gun will get, to counterbalance the rearward force on the interior face of the choke. The difference between a good and bad nozzle is mainly how much recoil is felt, less so the projectile.
A reccoiless also had to deal with sudden changes in pressure and flow rate. In muzzle loading arms it is not uncommon for the breach face to be round or conical, allowing more propellant to burn late.
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I observe that military reccoiless rifles have either cone exhaust or a straight tube, often with multiple venturis to spin the gas. If you watch them fire, the exhaust usually kicks up a cone spreading to mushroom shaped cloud of dust.
Based on what I know about rocket nozzles this does not seem optimal Directing the escape gases straight back provides the greatest impulse to the projectile. So a bell nozzle with a straight throat would be fine. And also an aerospike might be awesome for the exhaust of a recoiless rifle. Imagine a sharp tongue of flame pointing straight back behind the shooter.
Based on what I've read, US citizens have a compelling argument to legally own a muzzle loading, blackpowder, recoiless rifle, provided the ignition cap is not fixed the to ammunition. I'm not the first person to have that idea, but there is no good info about anybody actually building it. I won't be building one either, it just sounds cool.
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I'm curious what people think about the wisdom of homemade breathing apparatus? In particular O2 welding gas tanks. To make a low pressure nose hose is pretty simple. Mannually operated bellows are simple to make out of household items. In college I was taught about something called a gravity bong... etc.
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Accelerating at relativistic speeds adds another factor of distance to time dilation. In the twin paradox, each percieves the other as slowed down. The twin who accelerates and changes direction sees the other race ahead, during the acceleration phase only, then go slowly during the return cruise. Taking the same twin journey and turning around at a more distant point, makes the time leap greater.
If the universe is hyperinflating ( third derivative of x is positive) there could be another effect I'm not sure. I wonder if anybody knows a good lecture series about it.
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On 4/3/2020 at 2:17 PM, K^2 said:
I think, all of the cosmological models assume visible universe = universe, but that's probably only because due to how universe was expanding, nothing that's currently outside of the visible universe could ever have been part of visible universe except, possibly, really, really, really early on, and it means it couldn't have impacted evolution of visible universe, so we can pretend nothing outside visible universe exists without getting any disagreements with experiment. If nothing in our understanding of cosmology contradicts the notion that universe >> visible universe, as in greater by a lot, then I can't think of any reason why it couldn't be that all the antimatter is simply beyond the boundaries of the visible universe. But this stretches my understanding of cosmology past the breaking point, and I don't even know any cosmologists to ask. We had one theoretical astrophysicist in our department, and she specialized in neutron stars.
I would operationally define words this way.
universe = a 4 dimensional continuum (our space-time)
light cone universe = the entire visible universe including those points where light is blocked or altered by material
extended universe = those points in our space-time from which light cannot reach us because anything there is moving away from us faster than the speed of light
I think we have a curtain of cosmic microwave background radiation at the edge of our visible universe. This is from roughly the moment when the universe became a mostly transparent nebula. This was probably 350,000 years after the big bang. Before that we think a high energy plasma filled the universe. So the light cone universe extends beyond the visible universe into this high energy plasma.
I don't have a solid theory of hyper-inflation. But one hypothesis states that matter at the edges of our universe will keep accelerating away from us into our extended universe. The quasars and eventually all the galactic clusters except our own will escape into our extended universe.
The multi-verse is more than one space-time existing discontinuously. However a light cone universe and an extended universe can make up one continuous whole.
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How about a pusher plate combined with an air hockey table.
Pop out sprinklers cover the pusher plate and all its' pores with soap and oil.
Then the air hockey system bubbles out hydrogen gas. So 1mm of oily soap is like 10 x 1cm bubbles, when you nuke it.
Also make the plate resemble the head of a nail. The more massive the spine attached to the pusher plate the less jerky the whole thing is. And the entire spine could be a giant ferromagnet. Tubular coils supporting toroidal payload structures would resist relative motion, without being subject to parts wear as would springs and pneumatic shocks.
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From our perspective we can generate a flow of positrons from radioisotopes, separate the positrons from electrons and direct them with electromagnetic forces into targets. The targets can be anything. The sources are things like K40 and Kr79. Antimatter certainly has positive mass and travels less than the speed of light.
It is unknown (at least to me) whether the mass of positrons and electrons actually differs. The mass of neutrinos (as of last I knew) was not fully pinned down. If their masses differ antimatter could have been hurled to the edges of the universe.
Particles could be moving away from us faster than the speed of light beyond the edge of the visible universe. Hyperinflation of space and dark energy allow particles far apart to travel faster than the speed of light. So if antimatter were just a wee bit lighter... it could be mostly beyond our horizon.
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9 hours ago, Nightside said:
My usually acute irony detector is failing me now, @farmerben, are you serious?
Joke... If I were selling explanations of mythology, I wouldn't lead with the most preposterous.
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Ok question time. A ramjet and a scramjet constrict airflow to create subsonic zones allowing fuel to mix with air and combustion to occur. Correct?
A bypass duct compresses air and dumps heat into it through a radiator or duct. Correct? Compression is necessary to create a work cycle, but subsonic compression is not required because we are not mixing two fluids to ignite them.
So what do you call an engine that uses intake air at supersonic speeds (with very little compression), and dumps heat into the airflow using supersonic nozzles of another gas?
I think this design gives up a well defined ignition and combustion region. But still creates power, with possibly far less drag.
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On 3/28/2020 at 2:16 AM, K^2 said:
I've never seen any indication of a stable, even remotely, particle with any quark count other than 3. And if stable arrangements exist for antiquarks, we should have ones with quarks as well. So we're still back to the question of why more of one than the other.
There are purely topological explanations for matter-antimatter imbalance as well. As a toy example, imagine our universe structured as an onion. Each moment of time is a shell, and inner shells happened "before" the later ones. Big bang is the point in the center of that onion. In that configuration, you don't have a question of what's before the big bang, because if you pass through the center, you start going to the future again, but on the opposite end of the universe. And you also don't have to have anti-matter. If all "matter" is radiated away from the center, all charges are conserved by what's happening on the opposite side of the universe. After all, the only difference between matter and antimatter is direction of propagation in time (to within TCP symmetry), and everything on the opposite side of the universe is propagating in the opposite direction. This simple model doesn't explain everything, but it's a start.
Yet other models allow for lepton families to oscillate beyond just flavor. So all the antiquarks are... electrons! Why we ended up with more of one less of another? Could be purely random. And there are other problems with these models, primarily because of predictions of supersymmetry that don't seem to pan out. But the point is, there are a lot of reasons the matter-antimatter imbalance could be. We shouldn't be coming with a theory to explain that. That's a sure way to lead yourself along the path of ad-hoc theory and confirmation bias.
That reminds me of a Feynman story. Feynman was looking at how to include the Pauli Exclusion principle in his QCD. Suddenly in a flash of insight he knew what explanation Wheeler would come up with. Although Feynman doubted it was true, he wrote it down anyway and then went to go see John Wheeler. In the course of their conversation Wheeler proposed the following theory:
Electrons travel forward in time, anti-electrons travel backward. The reason why two electrons cannot occupy the state is because there is only one electron! A positron travels back and allows another version of the electron to travel forward again along a different path. An almost unlimited amount of quantum states could be occupied by only one or a few particles oscillating between the past and future of the universe.
At this point Feynman pulled out a piece of paper and handed to Wheeler. Along with a few comments about wild assumptions, difficult to test, etc.
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1 hour ago, Xd the great said:
Are you sure that firing table salt into orbit is a good idea?
High thrust is only required on suborbital trajectories. Ion engines alone do not meet all the requirements for moon and asteroid miners.
U.S. Space Force Discussion Thread
in Science & Spaceflight
Posted
That Federov article reminded me of a really good Arthur C Clarke story. To my surprise the wiki page for that story actually mentions Federov.
https://en.wikipedia.org/wiki/The_Light_of_Other_Days