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sevenperforce

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Posts posted by sevenperforce

  1. 34 minutes ago, Vanamonde said:

    So considering how little of the flight uses the jet engines, you might as well save yourself the trouble and just go with a conventional rocket for your first stage. Real rockets would suffer from much the same problem. 

    Yep. This proposal quickly reduces to a pulsejet engine, which of course works very well for backyard projects or 1940s-era cruise missiles but is incapable of accelerating to spacecraft-useful speeds.

  2. 4 hours ago, AHHans said:

    As already mentioned may main issue with many new reactor design is that they use graphite as the moderator.

    Is there anything you can use in place of graphite with the same design?

    4 hours ago, AHHans said:

    And while graphite will not burn in normal circumstances, a nuclear reactor with a failed cooling system will get hot enough to ignite graphite if it comes into contact with air. (It will also react with water if the amount you pour onto it is insufficient to cool it down fast enough.) As a case in point please remember that a large amount of the radioactive contamination from the Chernobyl disaster was released because the graphite moderator was on fire, or the Windscale fire. So every new reactor design that plans to use graphite as moderator needs to address this issue in a satisfactory fashion. And, no, "we won't let oxygen get to our reactor core" is IMHO not satisfactory!

    That's one of the things we all love about molten salt reactors -- they are SUPPOSED to be melty, and if they get too hot they simply melt through the freeze plug and are dumped. It's also fairly low-pressure.

    One of the challenges in a molten salt reactor is that the salt is the coolant and so the salt has to be pumped around in a loop, which is very challenging to get right. Would it be possible to have a helium-cooled molten core reactor? 

  3. To start with, keep in mind that you want to conceptualize everything in terms of field interactions, not interaction between the object and the field. The electrically charged particle in a magnetic field experiences the Lorentz force because its electrostatic field is moving through a magnetic field and the motion of one field through the other produces a field interaction. a

    Spoiler

    It is easier to conceptualize the F=VxB breakdown of the Lorentz force if you remember that (a) the photon is the gauge boson and thus the force carrier for electromagnetism, (b) a photon is a quanta of a transverse wave, and (c) the electric and magnetic components of that transverse wave are perpendicular. Because the electric and magnetic components of a photon are perpendicular to each other, electric and magnetic fields can only interact perpendicularly.

    So, what does the magnetic field of a monopole look like?

    Unlike dipole electrostatic fields, magnetic dipoles do not arise from the aggregate of negative charges on one side and positive charges on the other, but rather arise from the intrinsic dipole magnetic moment of elementary particles. The field of a magnetic monopole would be a monopole magnetic moment, which is NOT merely the bisection of a dipole moment, but something else entirely which we haven't ever observed.

    But our best guess would be to analogize to the Coulomb and Lorentz interactions. This is the Lorentz equation:

    \mathbf{F}=q_{\mathrm e}\left(\mathbf{E}+\frac{\mathbf{v}}{c}\times\mathbf{B}\right)

    and this is the Lorentz equation with the monopole extension:

    f74881221a786b83e0ec10bca92d39ac5301bd6a

    So just as a moving electrical charge in a magnetic field experiences a force which is the cross product of its charge*velocity and the vector strength of the field, a moving magnetic monopole in an electric field experiences a force which is the cross product of its magnetic charge*velocity and the vector strength of the field. And so, by analogy, a monopole in a magnetic dipole field would act the same as an electrical charge in an electric dipole field.

    In other words, yes, your intuition is right.

  4. 19 minutes ago, Shpaget said:

    Op, whydon't you do a basic back of an envelope calculation to compare yield to mass ratios between nukes and fuel air bombs? That should have been your first step after coming up with this idea, long before posting it here.

    Do it now and you'll realize just how not sensible is your proposal.

    It’s worse than that. As I pointed out upthread, the maximum detonation speed in a fuel-air mixture is 1,800 m/s, which means the greatest speed you can obtain using fuel-air detonations is 1,800 m/s.

    18 hours ago, Spacescifi said:

    That said, in theory, spacecraft could be launched and use fuel/air bombs where air is still thick enough to help the explosion of the bombs.

    I completely reverse my prior stance. This is an excellent idea.

    Except you will want to use many small fuel-air bombs instead of large ones. By making the bombs smaller, you will be able to wrap the pressure plate around the explosion in a cone shape and thus make it more efficient.

    You will also want to have an extra hole in the center so that air can flow through to participate in the fuel-air bomb.

    You will need some sort of reverse-pressure-plate at the front to compress that air so that it comes in and mixes well with the fuel.

    Instead of dropping the bombs in one by one, you should make them into a liquid that can be sprayed continuously into the flow of compressed air so that it detonates continuously.

    Congratulations, you have invented the ramjet.

  5. 55 minutes ago, Rakaydos said:

    Kilopower is a small reactor NASA designed for use on spacecraft... BEFORE Starship was on the horizon to make cheap lift a reality. It's less efficient that Megapower, (Which fits in a shipping container) which is less efficient than utility-scale nuclear, but modular nuclear has the benefits of eventually reaching  economies of scale.

    Is it like thermonuclear, where efficiency continues to go up no matter how big you get, or is there a power level where you basically max out your benefits?

    Modular-distributed makes a lot of sense for a lot of reasons, but I find myself wondering whether we could ever see the entire eastern seaboard running on one offshore megareactor.

  6. 12 minutes ago, Spacescifi said:

    Ironically I actually think a non-nuclear orion could even work as an SSTO in real life or scifi.

    No, it will not work.

    The maximum detonation wave speed in an ideal thermobaric explosive is around 1.8 km/s. This means that once you are moving at 1.8 km/s, blowing up more fuel-air bombs behind you won’t do anything, because you’re moving away faster than the shockwave can reach you.

    A thermobaric Orion will not get you anywhere.

    12 minutes ago, Spacescifi said:

    You just crater your launch site, but with landings you could slow farther away for safer landings. Since there is no radiation, nonnuclear Orions have more flexibility and utility for how you use them in maneuvering in atmosphere.

    There will NEVER be an occasion or situation where a "non-nuclear Orion" makes ANY sense. Never.

    Thermobaric explosives are effective because they are able to use atmospheric oxygen to support detonation, rather than depending on an oxidizer chemical premixed with the reducer chemical to create the explosive. Since oxidizer makes up over half the weight of an explosive, you can get more kaboom per kilogram (pow per pound in freedom units) if you can use atmospheric oxygen instead.

    But if you're trying to propel a vehicle and you want to use atmospheric oxygen, you use a jet engine.

    A pusher-plate system is WILDLY inefficient. The ONLY reason for a pusher-plate is if you cannot control the release of energy from your engine, which is ONLY applicable when using nukes.

    12 minutes ago, Spacescifi said:

    It will just suffer nose ablation due to screaming through the thicker part of the atmosphere to gain speed to coast to orbit.

    If you want to use atmospheric oxygen to help you get to orbit, try Skylon.

  7. 38 minutes ago, mikegarrison said:

    Most nuclear power plants use rivers for their heat sink. Either that or the ocean or a large lake.

    I suppose that would be necessary, yes.

    “The company began to create a budget microreactor that could fit in a regular shipping container. The megawatt model will be capable of powering up to 1,000 homes and is expected to use helium for cooling instead of water. The main places of use are remote settlements, zones of natural or other disasters, and military bases.”

    So presumably it would be limited to a locale with water access…not scaleable or suitable for residential solutions, for example. At least that’s what I would imagine. At 1 MW and a Braxton efficiency of ~65% (enabled by a high-temperature coolant), that’s 1.53 MW of thermal power that needs to be rejected.

    I ran the numbers (after typing that) and it’s not as bad as I thought. If your water heat sink loop raises water temperature by 20 degrees Celsius, you only need a flow of 1100 liters per minute. 

  8. Here's the typical schematic for a helium-cooled reactor.

    495px-Gas-Cooled_Fast_Reactor_Schemata.s

    Cool, pressurized helium is pumped around the reactor and through the reactor core, gaining thermal energy. It is then expanded through a turbine, which operates a series of compressors. The helium is cooled via heat sink and passed through the compressors in cycles to return it to its compressed, cool state. The turbine also operates the generator.

    I wonder what kind of heat sink is used for cooling the helium. I'm also curious to know how cool the helium is supposed to be when it enters the reactor. Helium obviously can remain gaseous at very low temperatures; is there an advantage to getting the largest temperature swing possible? Would the system efficiency be improved by a secondary refrigerant loop?

  9. 19 minutes ago, AHHans said:

    And maybe back to @JoeSchmuckatelli's unspoken original question: Helium diffusion out of a coolant loop of a nuclear reactor isn't going to be a contamination problem: that helium won't be radioactive because, well, helium isn't!

    Aye. There are radioactive isotopes of helium, but the only one that could be created in a reactor by neutron capture would be 5He, which decays back into 4He by neutron emission in about 6e-22 seconds. 

  10. 7 minutes ago, kerbiloid said:

    It was not initiated by a helium leak; it was initiated by LOX crystals freezing in the composite overwrap layers, resulting in COPV failure. Of course once the COPV failed then the helium certainly "leaked" in a very sudden and dramatic sense.

    The first Falcon 9 failure was also a helium "leak" in the sense that a failed strut caused the COPV to break free and fall through the LOX and then fail on impact with the common bulkhead; the rupture of the COPV released the pressurized helium.

    9 minutes ago, AHHans said:
    46 minutes ago, JoeSchmuckatelli said:

    Does Helium like to play fast and loose with its pipes like hydrogen - or is it considerably better behaved? 

    AFAIK the latter. But that's mostly "I haven't heard anyone complaining about helium diffusing everywhere" and not "I know that helium is well behaved."

    Helium diffuses through solids just like hydrogen does -- in fact, I believe it may diffuse a little better. However, diffusion is not what makes hydrogen so nasty. Hydrogen embrittlement happens because individually-migrating hydrogen atoms meet up inside the tank/pipe wall and decide to bond with each other, essentially producing nanoscale bubbles inside the metal, rapidly degrading its material strength.

    It's like when Vision phases his hand into someone's chest and then unphases his hand while it's still inside.

  11. On 10/17/2021 at 9:13 AM, Snark said:

    Some rule-violating content has been removed, due to:

    • trolling / flamebaiting
    • personal remarks

    Folks, please try to stay civil.  There's nothing wrong with expressing hearty disagreement, but it's possible to do so like an adult, without stooping to ridicule or name-calling.  Such tactics help no one, do not advance your argument, and make the forum less fun for everyone.

    Clearly I missed some excitement.

    52 minutes ago, Jack White said:

    "The use of helium significantly reduces the risks of corrosion, refrigerant boiling and contamination."

    So I'm guessing we're looking at a persistently gaseous helium coolant loop? Heat transfer won't be as efficient without a liquid coolant BUT the regenerative heat capacity of helium will probably make up for it. I wonder how much helium it requires, though. Not exactly a renewable resource. I'm also curious as to what kind of local heat sink the generators need. They could be buried underground, I suppose, but a water-based heat sink would be much more efficient.

    15 minutes ago, magnemoe said:
    30 minutes ago, kerbiloid said:
      Reveal hidden contents

    20160901-F9-Sequence.jpg

    Helium.

     

    Expand  

    As I understand that was because liquid oxygen and the composite wrapped tanks inside the LOX tank.

    There was a liquid oxygen incursion into the outer layers of the carbon overwrap. The superchilled helium caused the trapped LOX to freeze into solid oxygen crystals, warping the composite overwrap layers and causing a COPV failure. The energetic failure of the COPV provided ignition energy between the carbon composite and the LOX, and the rest was...toasty.

  12. 11 hours ago, JoeSchmuckatelli said:

    There is a good video I saw recently about turbopumps and fuel mixing /premixing - did not specifically speak to the complexity of the whole system - but it's a start. 

    Don't remember where I saw it - but if I find it I will link it 

    I have a series on this, actually.

    And also….

     

  13. On 6/4/2021 at 2:44 PM, SpaceFace545 said:
    On 6/4/2021 at 2:17 PM, tater said:

    I kinda like it. Course I liked the tiny wing and scissor-wing  shuttle concepts.

    Same, not sure how or if it could reenter but it reminds me of the StarTram space plane.

    https://imgur.com/a/AspxR3B

    Maybe it wasn't meant to re-enter, but was intended to use aerodynamic passes to change inclination like the X-37B.

  14. 1 hour ago, adsii1970 said:
    1 hour ago, sevenperforce said:

    Minor quibble: by the time of Apollo 11, NASA knew for sure that the moon dust wasn't a foot thick. The unmanned Surveyor landings gave them enough data to establish that the dust was compacted.

    There was still a fear of what was under the dust - was it all solid rock or a mixture that could support the weight of a lander:
    https://www.icr.org/article/moon-dust-solar-system/

    ICR is known to be a particularly unreliable source.

    (The reason I happen to be knowledgeable on the moon dust issue is that I used to work with that and related groups, back in my anti-science days, and this was a common bone of contention.) 

  15. 1 hour ago, adsii1970 said:

    This is why the Apollo lander was designed as it was. At the time, NACA/NASA believed the surface of the Moon was covered in roughly a foot of lunar dust. They believed the wide, concave landing pads at the end of the legs, the wide span of the legs, and the low center of gravity. In the end, they learned from the Apollo 11 mission the dust wasn't as thick as they expected it to be.

    Minor quibble: by the time of Apollo 11, NASA knew for sure that the moon dust wasn't a foot thick. The unmanned Surveyor landings gave them enough data to establish that the dust was compacted.

    The larger concern for the landings were the possibility of coming in with a non-negligible horizontal velocity component and the associated tipover. 

  16. 48 minutes ago, wumpus said:

    It was a bit of a miracle that none of the Mercury astronauts weren't killed.  I've heard they had to get someone else to press the button to "light this candle" for Alan Sheppard as the original guy thought it would kill him.  I think the engineers on the job gave him a 50/50 chance of living.  They may have been pessimistic after the satellite flights (while Sheppard simply looked at the Mercury test flights), but they still seem a deathtrap.  And don't ask about the rigid thinking that launched  Vladimir Komarov on a rocket that clearly wasn't ready.

    There was also a huge amount of re-work after NASA killed the first three astronauts (presumably they thought being ahead of their goal was a good thing, but they cut way too many corners to get there).  But don't forget they lost two Gemini astronauts jaunting around in T-38s.   Micheal Collins seemed to think they were more dangerous (to astronauts) than space (presumably because of crazy test pilot antics).

    The ejection seat on the Vostok was absolutely not strong enough to get Gargarin high enough for his chute to open in the case of a pad abort, so they strung a net around the launch site to catch him if they had to abort on the pad.

    And as we all know, "trapped in a net next to an actively failing launch" is just a wonderful place to be.

    As for Gemini, I know there's some degree of disagreement over whether the ejection seats would have actually burned the pilots alive or not....

  17. 16 minutes ago, magnemoe said:

    Obvious problem is that the success rate get high, its get as boring as falcon 9 first stage landings. This is obviously an good thing for everything but the number of views 

    Maybe they can use their excess payload to drop a secondary experimental re-entry vehicle to keep things SPICY.

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