steveu <steveu@n_o_s_p_a_m.coppice.org> wrote:>>Eric Jacobsen <eric.jacobsen@ieee.org> wrote: >>(snip) >>> Even in a nuclear system the heat from the reaction is applied >>> continuously, not intermittently, at least not intermittently enough >>> to think of it as such when comparing the systems previously >>> discussed.(snip, then I wrote)>> There have been suggestions for fusion power that really >> are intermittent, generating heat from a reaction every so many >> minutes or even hours.> Has there been a proposal for fusion power which is *not* intermittent?As Clinton would say, it depends on what intermittent means. I would say that Tokamacs were not intermittent. The usual fission reactor design is shut down every few years to replace the fuel rods, so is that intermittent? The distinction I was making originally was between engines that fill with reactants, close off the combustion chamber, and then start the reaction. The available reactants then change during combustion as exhaust products build up and others are consumed. In others, fuel and oxidizer are continuously supplied, such that the reaction soon reaches, and mostly remains in, an equilibrium of input reactants and exhaust products. The distinction then, is the fraction of the time the system is in equilibrium (steady state) or not (transient). That distinction should be on-topic for this group. My 30 year old stereo amplifier has a relay to delay connection to the speakers until a second or two after power on to be sure that any transients have died down. (And I have had to replace two capacitors in that circuit over the years.) Most likely some DSP systems also need to let the transients decay.> The containment rings, laser bombarders, and other strategies all > seem to take a measure of fuel, make it pop, and then start again > with another measure of fuel. The small scale continuous fusers, > used for medical and research purposes, don't ever seem to have > been seriously proposed as a power source.I don't remember by now if Tokamacs can have fuel added while running. The plasma physics is not easy, and it might be that they can't, or that it is easier just not to run them that way. There are other magnetic confinement systems that may or may not run more continuously. They do, however, run the reaction fairly slowly compared to bombs or to pellet type reactors. -- glen
OT: What does 'rocket' mean?
Started by ●December 10, 2011
Reply by ●December 13, 20112011-12-13
Reply by ●December 13, 20112011-12-13
Jerry Avins <jya@ieee.org> wrote: (snip)> Back when I was a kid and Buck Rogers* was popular, some people argued > that rockets couldn't operate outside the atmosphere because there would > be nothing for the exhaust plume to push against. Not just some of my > contemporaries, but adults also. It's very hard to explain anything to > people like that. They're still around today, but the subjects are > different.There is a discussion ongoing (for weeks) in another newsgroup on the recoil from a rail gun. The suggestion is that if one can build a recoilless gun, one can power the rocket by shooting bullets into a block, and using the bullet momentum to power the rocket. As above, it isn't easy to show where the momentum transfer is done to the rocket. -- glen
Reply by ●December 13, 20112011-12-13
On 12/13/2011 2:27 PM, glen herrmannsfeldt wrote:> Jerry Avins<jya@ieee.org> wrote: > > (snip) >> Back when I was a kid and Buck Rogers* was popular, some people argued >> that rockets couldn't operate outside the atmosphere because there would >> be nothing for the exhaust plume to push against. Not just some of my >> contemporaries, but adults also. It's very hard to explain anything to >> people like that. They're still around today, but the subjects are >> different. > > There is a discussion ongoing (for weeks) in another newsgroup on > the recoil from a rail gun. The suggestion is that if one can > build a recoilless gun, one can power the rocket by shooting > bullets into a block, and using the bullet momentum to power > the rocket. As above, it isn't easy to show where the momentum > transfer is done to the rocket.We user to wonder how far we could power a rowboat by peeing over the transom. How does the notion arise that a rail gun has no recoil? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 13, 20112011-12-13
On 13 Des, 21:23, Jerry Avins <j...@ieee.org> wrote:> On 12/13/2011 2:27 PM, glen herrmannsfeldt wrote: > > > > > > > Jerry Avins<j...@ieee.org> =A0wrote: > > > (snip) > >> Back when I was a kid and Buck Rogers* was popular, some people argued > >> that rockets couldn't operate outside the atmosphere because there wou=ld> >> be nothing for the exhaust plume to push against. Not just some of my > >> contemporaries, but adults also. It's very hard to explain anything to > >> people like that. They're still around today, but the subjects are > >> different. > > > There is a discussion ongoing (for weeks) in another newsgroup on > > the recoil from a rail gun. =A0The suggestion is that if one can > > build a recoilless gun, one can power the rocket by shooting > > bullets into a block, and using the bullet momentum to power > > the rocket. =A0As above, it isn't easy to show where the momentum > > transfer is done to the rocket. > > We user to wonder how far we could power a rowboat by peeing over the > transom.Once upon a time I used a drop of oil to propell a small carboard boat: Cut a shape like this out of carboard (view with fixed-width font): ____________ / | < C=3D=3D=3D \____________| Then drip some oil in the 'C' at the rear. The oil's area will expand on the surface of the water, escaping out the slit, pushing the boat in the forward direction.> How does the notion arise that a rail gun has no recoil?Well, the rail gun works by exposing a magnet to a powerful electric field, causing the magnet to move. As the magnet moves through the coil, it produces an equally strong current as the current that drives the gun in the first place. Whether that counts as 'recoil' is a matter of definition; it might not cause much mechanical momentum, but the current certainly _RE_verberates thtrough the _COIL_... Rune
Reply by ●December 13, 20112011-12-13
Jerry Avins <jya@ieee.org> wrote: (snip, I wrote)>> There is a discussion ongoing (for weeks) in another newsgroup on >> the recoil from a rail gun. The suggestion is that if one can >> build a recoilless gun, one can power the rocket by shooting >> bullets into a block, and using the bullet momentum to power >> the rocket. As above, it isn't easy to show where the momentum >> transfer is done to the rocket.> We user to wonder how far we could power a rowboat by peeing over the > transom. How does the notion arise that a rail gun has no recoil?Good question. From I cross B, the force on a wire (infinitely thin at that) has no component along the wire. There is, then, no reaction force on the rails. You can make the far end as far away as you want, decreasing the reaction on the far end. The "low recoil on the rails" part has been tested using Gallium-Indium contacts to pass current but no force into the rails. (Leaving the recoil to the rest of the circuit.) If you google for IFE and railgun it should come up. (I believe IFE is internal force engine.) -- glen
Reply by ●December 13, 20112011-12-13
On Tue, 13 Dec 2011 15:23:17 -0500, Jerry Avins <jya@ieee.org> wrote:>On 12/13/2011 2:27 PM, glen herrmannsfeldt wrote: >> Jerry Avins<jya@ieee.org> wrote: >> >> (snip) >>> Back when I was a kid and Buck Rogers* was popular, some people argued >>> that rockets couldn't operate outside the atmosphere because there would >>> be nothing for the exhaust plume to push against. Not just some of my >>> contemporaries, but adults also. It's very hard to explain anything to >>> people like that. They're still around today, but the subjects are >>> different. >> >> There is a discussion ongoing (for weeks) in another newsgroup on >> the recoil from a rail gun. The suggestion is that if one can >> build a recoilless gun, one can power the rocket by shooting >> bullets into a block, and using the bullet momentum to power >> the rocket. As above, it isn't easy to show where the momentum >> transfer is done to the rocket. > >We user to wonder how far we could power a rowboat by peeing over the >transom.Was there experimentation done to investigate that? ;)> How does the notion arise that a rail gun has no recoil?I think the same sort of thinking that led to the "rockets don't work in space" discussions. Not everybody gets physics, which is okay, but once it's been explained one would think that would end it, and is does for many people. The ones that insist on clinging to misconceptions provide the majority of the entertainment, or frustration, depending. ;) Eric Jacobsen Anchor Hill Communications www.anchorhill.com
Reply by ●December 13, 20112011-12-13
On 12/13/2011 3:35 PM, Rune Allnor wrote:> On 13 Des, 21:23, Jerry Avins<j...@ieee.org> wrote: >> On 12/13/2011 2:27 PM, glen herrmannsfeldt wrote: >> >> >> >> >> >>> Jerry Avins<j...@ieee.org> wrote: >> >>> (snip) >>>> Back when I was a kid and Buck Rogers* was popular, some people argued >>>> that rockets couldn't operate outside the atmosphere because there would >>>> be nothing for the exhaust plume to push against. Not just some of my >>>> contemporaries, but adults also. It's very hard to explain anything to >>>> people like that. They're still around today, but the subjects are >>>> different. >> >>> There is a discussion ongoing (for weeks) in another newsgroup on >>> the recoil from a rail gun. The suggestion is that if one can >>> build a recoilless gun, one can power the rocket by shooting >>> bullets into a block, and using the bullet momentum to power >>> the rocket. As above, it isn't easy to show where the momentum >>> transfer is done to the rocket. >> >> We user to wonder how far we could power a rowboat by peeing over the >> transom. > > Once upon a time I used a drop of oil to propell > a small carboard boat: Cut a shape like this out > of carboard (view with fixed-width font): > > > ____________ > / | > < C=== > \____________| > > Then drip some oil in the 'C' at the rear. The oil's > area will expand on the surface of the water, escaping > out the slit, pushing the boat in the forward direction.I remember doing the same. A piece of soap molded to the rear also moves the "boat" forward with what is in the end the same mechanism. By reducing the surface tension at the rear, the tension at the front pulls it forward. Camphor works the other way. It raises surface tension, so a piece at the front of the boat propels it forward.>> How does the notion arise that a rail gun has no recoil? > > Well, the rail gun works by exposing a magnet to a > powerful electric field, causing the magnet to move. > As the magnet moves through the coil, it produces an > equally strong current as the current that drives the > gun in the first place. > > Whether that counts as 'recoil' is a matter of > definition; it might not cause much mechanical momentum, > but the current certainly _RE_verberates thtrough > the _COIL_...The mechanism doesn't matter. The gun must acquire as much momentum backward as is imparted to the projectile in the forward direction. F=Ma in any case. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●December 13, 20112011-12-13
On 12/13/2011 3:58 PM, glen herrmannsfeldt wrote:> Jerry Avins<jya@ieee.org> wrote: > > (snip, I wrote) >>> There is a discussion ongoing (for weeks) in another newsgroup on >>> the recoil from a rail gun. The suggestion is that if one can >>> build a recoilless gun, one can power the rocket by shooting >>> bullets into a block, and using the bullet momentum to power >>> the rocket. As above, it isn't easy to show where the momentum >>> transfer is done to the rocket. > >> We user to wonder how far we could power a rowboat by peeing over the >> transom. How does the notion arise that a rail gun has no recoil? > > Good question. From I cross B, the force on a wire (infinitely > thin at that) has no component along the wire. There is, then, > no reaction force on the rails. You can make the far end as > far away as you want, decreasing the reaction on the far end. > > The "low recoil on the rails" part has been tested using > Gallium-Indium contacts to pass current but no force into > the rails. (Leaving the recoil to the rest of the circuit.) > > If you google for IFE and railgun it should come up. > > (I believe IFE is internal force engine.)Oh, Wonderful! Let's bend the rail into a circle, and have the "projectile" move around it and turn a shaft. Then we can generate torque without counter torque. That would be a great way to power a helicopter or torpedo. Wikipedia likens the action to a homopolar motor. If a homopolar motor drives a ships propeller shaft, is there no torque reaction at the motor mounts? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
