[silverslith]

I'm interested in how the magnetic field is packed tightly inside the Heliopause. It seem to me that a solarpolar orbit in this layer could be one of the best trajectories for achieving Intersteller velocities.
Despite being 4 times the orbital radius of pluto still amazingly limited by the centipetal force:

Fcentr= m (v^2)/r
force/kg=(v^2)/r
F(0.1c)/kg=9e14/~2e13

=45 newtons/kg = 4.5g

Of course if we make our first port of call a blue giant then we could probably launch at >0.9c from its much larger heliosphere (provided the landing solar system has enough field to catch us. Neutron stars have enormous ones.) Not sure what relativistic effects would do. It'd be nice if our magforce increased along with mass but I doubt it.

It may be that getting most of your speed at slower accelerations in Interstellar space is still better.

[CraigD]

Originally Posted by silverslith

Thats 2 square mm cross section. Or 80A per sqmm.
Seems like a pretty poor superconductor that can't carry more than a conventional one.

80 A/mm^2 (8*10^7 A/m^2) seems very high to me, compared to conventional conductors – about 13 times the Handbook of Electronic Tables and Formulas rating for copper wire.

Still, the links silverslith provides give impressive current carrying ratings – or predicted ratings, as I get the impression from them that, as of 8/2004, the “cannoli-like” .000007 m diameter MgCNi3 wires with a maximum current density of 4*10^11 A/m^2, had yet to be grown to more than a few mm in length.

Searching Furukawa Electric reveals recent success with a 500 m long test power cable with a cross-section of about .00009 m^2 (superconducting tape wrapped around a .028 m diameter hollow copper pipe, surrounded by a lot of cooling equipment) and a 1000 A current, about 10^7 A/m^2. I couldn’t find any data on the cross-section area of their 20 kA-class superconductors, so have not idea of its current density.

I get the impression, however, that a superconductor capable of the simple experiment I describe in post #8 may be available now or in the near future. Though just the first of several challenges involved in making a vehicle like the IPCS, this information make me optimistic, and curious for more details. Better yet, I wonder if some superconductor with better than 3*10^9 A/m^2 is available to the amateur, to actually conduct such an experiment.

[CraigD]

Originally Posted by silverslith

Fcentr= m (v^2)/r
force/kg=(v^2)/r
F(0.1c)/kg=9e14/~2e13

=45 newtons/kg = 4.5g

I don’t follow what this calculation is getting at. For a constant acceleration of 4.5 gs (about 45 m/s/s) to produce a velocity of .1 c (3*10^7 m/s) requires about 7.7 days ((3*10^8 m/s)/(45 m/s/s) = 666667 seconds), and a distance of about 67 AU (.5 * 45 m/s/s * (666667 s)^2 = 10^13 meters) . There’s not much Interplanetary Magnetic Field for most of that distance – between about 10^-11 T at 1 AU to 3 *10^-17 T at 67 AU (compared to 3*10^-5 T at the Earth’s surface). So about a 10^12 increase in current over the previous “flying car” example is necessary – a pretty mind-boggling figure.

Another fact of which to be mindful is that electrodynamic propulsion, though much more efficient than rocket propulsion – with superconduction, essentially 100% efficient – still requires mechanical energy to accelerate a body. Even a tiny manned spacecraft – say 1000 kg – would require about 10^18 J, peaking at about 1.4*10^12 W – about the same as the world’s electrical power consumption.

Cramming the electrical generating capability of the whole planet Earth into a 1000 kg vehicle is clearly an engineering challenge – but not, I think, an insurmountable one. 1.4*10^12 W is equivalent to only about .000015 kg of matter and antimatter annihilating every second, while the entire energy requirement to accelerate it to .1 c requires the annihilation of only about 5 kg of matter and antimatter.

No matter its immediate engineering feasibility, the idea of “slingshotting” from strong magnetic field to strong magnetic field is an intriguing one, and not too implausible. It appears to require advances in three areas of technology – superconduction, electrodynamic propulsion, and very high, very high efficiency power generation – almost certainly based on antimatter. Such technology could be complimented by other very-high-power propulsion, such as the photonic rocket.

[silverslith]

My calculation regarding centripetal force required to keep the IPCS in a circular path at the distance of the heliopause (~4x plutos orbit) was intended to show that the velocity of 0.1c is pretty darn fast. Obviously to accelerate to that speed with such a path the g's required for maintaining the circular path will climb to 4.5g at 0.1c(unless I fluffed the calc). This would have to be supplied by the EM drive (though requiring no energy) in addition to the acceleration needed to get there. I've no idea whether the mag field is strong enough out there to make it possible.

I'm not sure that your energy requirement calc is valid. Or a motorcycle of 100kw couldn't accelerate at 1g. Which they clearly do. I think maybe momentum is a better tool than energy for these totals but I'm no expert with only stage1 uni physics 20years ago. Or does it take more energy to accelerate a cannon shell to 1000m/s muzzle velocity from a plane flying at 1000m/s than one sitting on a tarmac . Maybe you're talking about induced current in the conductors moving thru the magnetic field. Once again I only know enough to know I don't know all the ramifications of this.

The conventional conductor rating you've quoted is probably for wires with plenty of plastic thermal insulation wrapped around them. I kept blowing the 0.25sqmm 20A resistance wire in my fuse box when I used my arcwelder. Replacing it with a 0.25sqmm copper wire fixed the problem, so I have personal experience that 80A/sqmm is fine for copper. If you cooled it to a couple of kelvin then a fair bit more would be handled.

I did calcs a few years ago based on vapor deposited type II's on mylar that gave me figures of 10x the weight for force supplied by earthmag. I'm finding it a lot harder to get info of the web now as every decent paper seems to need subscriptions these days. I'm sure the experiment you express interest in would be worthy. Nothing like a physical demo to capture peoples imagination.
If anyones wondering why the solar mag field looks so strange and is compressed against the heliopause, Its because its carried by the solar wind.

[silverslith]

Hard, slippery, and gives us electrons when heated:

Technical Background
Amorphic Diamond is an acronym composed from syllables of "Amorphous Ceramic Diamond." It was intended to lower the tension of an apparent self-contradiction between the terms "diamond" which is crystalline and "amorphous" which means there is no long-range order to a material.
While crystalline diamond is immediately recognized in almost every society at all levels, it is almost unknown that there are actually two naturally-occurring crystal forms; cubic and hexagonal. Cubic is the "common" variety, while hexagonal diamond is truly rare. In nature diamonds grew slowly from liquid "melts" as the material cooled under extreme pressure. There was time for one single crystal pattern, usually cubic, to grow throughout the sample.

When a laser beam is focused upon a carbon surface a "fireball" of extremely hot carbon ions explodes outward. Upon striking a surface their impact briefly creates an impulse of very high pressure and the carbon material cools under this pressure to become diamond. The process is too fast for one crystal form to dominate and structures alternate randomly on a molecular scale between cubic and hexagonal. The result is a coating with the unique properties immediately associated with diamond, but without the long-range order that insures crystalline geometry.

In summary Amorphic Diamond is made from graphite carbon and laser light without toxic waste or noxious byproducts. As a conformal coating it is harder than natural diamond and "slicker" than Teflon. Because it condenses from such energetic precursors, there is chemistry at the interface with the material it coats; and Amorphic Diamond coatings become chemically bonded to almost any material compatible with the vacuum in which it must be deposited. Metals such as Ti, Al, Co, Fe, and most steels have been coated directly. Optical materials such as quartz, Ge, ZnS, and ZnSe; electronic materials such as Si and GaAs; and miscellaneous compounds such as plastic, glass, and even paper are routinely coated. Against abrasive wear, coatings of 1 mm (i.e. 1/10 the diameter of a hair) increase service lifetime by factors of 3 to 10. This means that wear lifetimes can be increased by factors of 1000 to 10,000 with Amorphic Diamond coatings thinner than the diameter of a human hair. Even more remarkable is that these coatings emit more electrons at a given temperature than any other material or artificial fabrication.

http://www.hafniumisomer.org/TechBkg.htm

[silverslith]

The nanofridge tech may not be as far off as you might think. Theres a lot going on in the field of on-chip cryogenics and useful extraction of molecular kinetic energy seems entirely possible.

I love being wrong when I say things like this.

http://hypography.com/forums/technol...tml#post169414

[silverslith]

Another fact of which to be mindful is that electrodynamic propulsion, though much more efficient than rocket propulsion – with superconduction, essentially 100% efficient – still requires mechanical energy to accelerate a body. Even a tiny manned spacecraft – say 1000 kg – would require about 10^18 J, peaking at about 1.4*10^12 W – about the same as the world’s electrical power consumption.

Cramming the electrical generating capability of the whole planet Earth into a 1000 kg vehicle is clearly an engineering challenge – but not, I think, an insurmountable one. 1.4*10^12 W is equivalent to only about .000015 kg of matter and antimatter annihilating every second, while the entire energy requirement to accelerate it to .1 c requires the annihilation of only about 5 kg of matter and antimatter.

Sorry for my earlier cheek regarding this point craigd. Don't peg me as a FT proponent.

Craigs right. Because we're pegged to the reference frame of the magnetic field for our reaction mass with an EM drive some pretty stupendous energies are involved in achieving high velocities.
Some other considerations this generates:
from: Solar Wind

At 1 AU the average speed of the solar wind is about 400 km/s. This speed is by no means constant. The solar wind can reach speeds in excess of 900 km/s and can travel as slowly as 300 km/s. The average density of the solar wind at 1 AU is about 7 protons/cm^3 with large variations. The solar wind confines the magnetic field of Earth and governs phenomena such as geomagnetic storms and aurorae. The solar wind confines the magnetic fields of other planets as well.

As the solar wind expands, its density decreases as the inverse of the square of its distance from the Sun. At some large enough distance from the Sun (in a region known as the heliopause), the solar wind can no longer "push back" the fields and particles of the local interstellar medium and the solar wind slows down from 400 km/s to perhaps 20 km/s. The location of this transition region (called the heliospheric termination shock) is unknown at the present time, but from direct spacecraft measurements must be at more than 50 AU. In fact, in 1993 observations of 3 kHz radiation from Voyagers 1 and 2 have been interpreted as coming from a radio burst at the termination shock. This burst is thought to have been triggered by an event in the solar wind observed by Voyager 2. From the time delay between this triggering event and the observation of the 3 kHz radiation, the distance of the termination shock has been put between 130 and 170 AU.

Meaning that we won't need to expend energy when travelling in the direction of the solar wind until we exceed its velocity. In fact we will generate energy, which could power a supplimentary reaction drive.
When travelling towards the sun we will however need a lot of energy to accelerate by this method. But decelerating will produce lots of energy for supplimentary reaction drives.
Effectively this is a huge advantage to both accelerating out of a star system, and (the biggest disadvantage of rockets) decelerating into another star system where the relative velocity of the incoming starship and the outgoing solar wind will be enormous.
I wonder if our Hafnium Gamma lasers are suitable photonic reaction drives to make use of this energy surplus. Or if a particle accelerator is better.

[silverslith]

With what I've been finding out regarding the nasty properties of energetic protons in space and particularly the radiation belts around magnetic planets, I'm real glad we have powerful magnetic fields at our disposal in the IPCS.


BBC NEWS | Science/Nature | Space shield to block radiation

British scientists are planning to see whether a Star Trek-style deflector shield could be built to protect astronauts from radiation.
They argue that magnetic shields could be deployed around spacecraft and on the surfaces of planets to deflect harmful energetic particles.

Several countries' space agencies have announced their intentions to resume human exploration of the Solar System.

Scientists hope to mimic the magnetic field which protects the Earth.

Details have been presented at the Royal Astronomical Society's National Astronomy Meeting in Preston, UK.

There are a variety of risks facing future space explorers, not least of which is the cancer-causing radiation from cosmic rays and solar flares that astronauts will encounter when they venture beyond the Earth's protective magnetic envelope, or magnetosphere.

The nice thing is that magnet technology is really quite evolved here on Earth. The question is can you take it into space?

Mike Hapgood,
Rutherford-Appleton Laboratory

The Earth's magnetosphere deflects many of the energetic particles from space; others are largely absorbed by the atmosphere.

Between 1968 and 1973, the Apollo astronauts were only in space for about 10 days at a time.

They were simply lucky not to have been in space during a major eruption on the Sun that would have flooded their spacecraft with deadly radiation.

Crew members on the International Space Station can retreat to a thick-walled room during times of increased solar radiation.

Stable field

But these protective shelters would not be practical on long-duration space journeys, since the "drip-drip" of energised particles is thought to be as harmful to the health of astronauts as large solar storms.


Potentially damaging solar activity is hard to predict

The harmful particles come from the Sun, in the form of the solar wind, and from sources outside our Solar System.

To create the deflector shield around a spacecraft or on the surface of a planet or moon, scientists need to generate a magnetic field and then fill it with ionised gas called plasma.

The plasma would held in place by a stable magnetic field (without the magnetic field, the plasma would simply drift away). This shield could be deployed around a spacecraft or around astronauts on the surface of a planetary body such as the Moon.

As energetic particles interact with the plasma, energy is sapped away from them and they slow down.

"You don't need much of a magnetic field to hold off the solar wind. You could produce the shield 20-30 kilometres away from the spacecraft," explained Dr Ruth Bamford, from the Rutherford-Appleton Laboratory in Didcot, UK, one of the scientists on the team.

Dr Mike Hapgood, from the Didcot-based research centre, told BBC News: "The nice thing is that magnet technology is really quite evolved here on Earth. The question is can you take it into space?'"

The team from Rutherford-Appleton plans to build an artificial magnetosphere in the laboratory. They would eventually like to fly a test satellite which would test the technology in space.

'Shields on'

The idea has been likened to the deflector shields which protect the USS Enterprise and other spacecraft in Star Trek. Like their fictional counterparts, these shields could also be switched on and off.


The planned moon base will be exposed to solar radiation

An artificial magnetosphere could come in handy anywhere in the Solar System where humans would need to be for long durations.

A permanent Moon base, of the type Nasa plans to build, could be buried under lunar soil to protect the occupants and equipment from space radiation. But inhabitants will still be vulnerable when venturing outside in their spacesuits.

"Our warning systems aren't very good [for solar flares]. You might be able to say: 'this is a dangerous period in terms of solar activity', but you might be on red alert for weeks," said Dr Hapgood.

"If you've got a problem, you might not want to wait a week to fix it. You might want a device to deploy on the surface as a shield that would blunt the effect of a flare at ten minutes' notice, it adds an extra level of safety."

The idea for the shields draws on technology pioneered in experimental nuclear fusion reactors. Nuclear fusion is not yet a mature technology.

It works on the principle that energy can be released by forcing together atomic nuclei rather than by splitting them, as in the case of the fission reactions that drive existing nuclear power stations.

At the Jet experimental fusion facility at Culham in the UK, magnetic fields were used to keep plasma away from the interior wall of the reactor.

This represents a reversal of that technology: "We want to use the same technique to keep an object in the middle away from plasma that's on the outside," said Dr Bamford.

But the plasma needed to protect against particles from the solar wind and elsewhere would actually be weaker than that generated in experimental fusion reactors like Jet.

[CraigD]

Originally Posted by silverslith

With what I've been finding out regarding the nasty properties of energetic protons in space and particularly the radiation belts around magnetic planets, I'm real glad we have powerful magnetic fields at our disposal in the IPCS.

A strong artificial magnetic field is great for protecting against charged particles – though designing one that doesn’t allow or even encourage them to strike the ship at the magnetic poles of its magnets is challenging.

Bamford, Hapgood, et. al. are even more ambitious, proposing to also use the magnetic field to hold a plasma (atoms with their electrons disassociated from their nuclei) in order to protect against uncharged particles (high-energy photons, presumably). I’ve long been somewhat puzzled by such proposals, as plasmas tend to be emitters, not absorbers of photons. Absorption depends largely on the electrons being associated with discrete orbitals around their nuclei, a rare state in most plasmas. I’d need to see some experimental results before dismissing my suspicion that these scientist/technologists are simply misguided in this proposal – a quick home experiments, using a laser pointer, plasma globe, stick incense and jar, reveals that the apparent opacity of the visible sheets and blobs of plasma in these devices is an illusion, having no noticeable effect on the brightness of a laser beam passing through them – or, in other words, plasma doesn’t cast a shadow. A quantum physical explanation of why this is so eludes me, but it appears to be.

Once your spacecraft is out of the domain of low velocity flight around stars and planets with dangerous charged particle radiation, and into the domain of interstellar flight at speeds greater than .01 c, the threat of collisions with uncharged particles begins to dominate. At a speed of .01 c relative to the interstellar medium, neutral hydrogen, with a density of about , now has an energy of about 50,000 eV/atom, for an energy flux of about , about 1000 times the peak of the Earth’s Van Allen belts. Worse, data from sources like NASA’s Ulysses solar polar orbiter suggest that for every trillion or so H atoms, a dust particle massing about or larger will be encountered. Depending on how much larger, such a collision could be catastrophic.

A solution of Robert W. Bussard’s (famous for the Bussard ramjet spacecraft concept) is to assure no uncharged matter exists in the path of your ship by sweeping the space with powerful lasers, reducing everything to ionized plasma.

[silverslith]

I think the logic of the trapped Plasma in the field bubble is to provide a friction force and for ionisation for the uncharged particles and a friction to slow down the charged particles that are trapped by the field.
Neutrons are pretty rare and do little damage as they go right thru you with little chance of a collision.
Fortunately photon radiation won't be affected by the crafts velocity and its much easier to shield with a hull than high energy protons which are by far the largest hazard. Gamma and xrays are much lower in flux density out there anyway.
The cylindrical field of the EM drive in the IPCS may be better than a normal polar magnetic field, and a combination of both may be possible with no dead spots.