[silverslith]

Designed to explore and claim space for the enjoyment of the interstellar community of all lifeforms, the IPCS is a diamond skinned transatmospheric starship with a no onboard reaction mass electromagnetic drive. The main powerplant is a nuclear fission unit based on the proton fission of lead (very low radioactivity of fission products). An auxilary propulsion system uses the proton/ion cannon of the main fission reactor.
The liquid helium skin and superconductor coolant is used to transfer heat to a nanotech energy extractor/refrigeration system capable of extracting the kinetic energy of gas molecules and storing it in nuclear isomer batteries.
The craft has the ability to enter and leave the atmosphere of any planet or star with a magnetic field, and can accelerate at human limits within the heliosphere of any decent star. In interstellar space the acceleration achievable will be less but 1g is expected.

[TheBigDog]

Originally Posted by silverslith

Designed to explore and claim space for the enjoyment of the interstellar community of all lifeforms, the IPCS is a diamond skinned transatmospheric starship with a no onboard reaction mass electromagnetic drive. The main powerplant is a nuclear fission unit based on the proton fission of lead (very low radioactivity of fission products). An auxilary propulsion system uses the proton/ion cannon of the main fission reactor.
The liquid helium skin and superconductor coolant is used to transfer heat to a nanotech energy extractor/refrigeration system capable of extracting the kinetic energy of gas molecules and storing it in nuclear isomer batteries.
The craft has the ability to enter and leave the atmosphere of any planet or star with a magnetic field, and can accelerate at human limits within the heliosphere of any decent star. In interstellar space the acceleration achievable will be less but 1g is expected.

Cool idea, but do I see propellers?

Bill

[silverslith]

Originally Posted by TheBigDog

Cool idea, but do I see propellers?

Bill

Could be the EM thrusters

Nah I just tacked them on for our worldwide publicity tour. After the proton-lead reactor and nanofridge's are sorted they can go.

Fixed:

[silverslith]

An interesting property of the Superconducting EM drive is that the craft can (provided the planets mag field is strong enough) choose whatever combination of orbit altitude and velocity it likes without consuming energy.
Either it can orbit in excess of gravitational orbital velocity, generating a g force for the crew to enjoy by maintaining a stable current in its superconductors (no energy input) to generate the centripetal force.
Or it can orbit at any fraction of grav orbital v or zero velocity relative to the ground by magleving.
It could even turn potential energy into stored energy in its NukeIsomer batterys as it decended like a space elevator and reuse it to ascend again.

[CraigD]

Re: Prophesy Designs

Originally Posted by silverslith

Have you guys considered an electromagnetic drive?
like superconducting loops with their return path shielded. No on-board reaction mass need apply. Any reason why that shouldn't work?

We considered this in some detail in ”can we fly in air”. Though this thread discusses the engineering of a “a car-sized, saucer-shaped aircraft massing 1000 kg and diameter of 5 meters”, it’s applicable to other shapes and intended uses, including spacecraft.

Despite a brief bit of excitement on my part when my omission of an important calculation understated electrical resistance by a factor of about 1 million, the discussion ended in the conclusion that such a vehicle is possible in principle, but not with any currently known materials. The basic problem is that ordinary conductors have such high resistance that they require huge amounts of power (and powerful cooling systems). All know superconductors cease to superconduct at much lower magnetic flux densities than are required. So the design must wait for a “supermaterial” that superconducts in an intense magnetic field, which current superconductor theory suggests is impossible.

Superconductivity has been a field filled with surprises and revisions of theory, so I’m inclined to take pronouncements of the “impossibility” of such a superconductor with a grain of salt (or would that be sugar?). However, I’m a loss to suggest a direction in which to pursue it.

Given this roadblock, I think we’re locked for the time being into spacecraft designs that are rockets (like the Prophesy) and ones where the power source is not part of the vehicle (such as starwisps and other naturally and artificially powered “light sails”).

[silverslith]

Thanks for linking that thread craigd, I've been thinking about this basically since a university lecture back in 89 when we got to fool around with some liquid nitrogen superconductors and button magnets (able to hang in the air over a coin sized piece of SC.
I did a flurry of research on it a few years ago and came to pretty much the same current requirement conclusions as you. I'm chuffed to see I wasn't losing some decimal places somewhere or other.
Precisely my conclusions about aerodynamic interactions.
The Solar systems mag field is quite wavey so course changes any direction seem plausible.
My conclusions were identical to yours regarding the problem of flux density killing superconductivity. I need to revise the limits of type one and two superconductors in this respect but engineering solutions are:
-minimise the density of the craft and distribute the wires as widely as possible.
-use liquid helium coolant as flux limits are much higher as temperature drops.

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 (I'll try dig out some links) and useful extraction of molecular kinetic energy seems entirely possible. This would be the breakthrough that would make engineering something like this practical.

here we go:
Superconductivity

[silverslith]

So with your flying car example CraigD, say it was 10cubic metres and 10kg total weight (about the overall density of air). Then how much current would be needed to lift it and could the flux density be managed within limits of current superconductors?

Of course a flying car that only lifts its own weight of 10kg would be pretty useless, but as scale increases, lower density becomes easier and easier.

Appreciate your feedback.

[CraigD]

Originally Posted by silverslith

So with your flying car example CraigD, say it was 10cubic metres and 10kg total weight (about the overall density of air). Then how much current would be needed to lift it and could the flux density be managed within limits of current superconductors?

The short answer to the last of this question appears to be “no”. Here’re some details:

From standard references, such as this wikipedia section, and the fundamental definition of force, we have:
,
where: is mass of vehicle, 10 kg in this example;
is acceleration of gravity, about 9.8 m/s/s at Earth’s surface;
is force, 98 N in this example;
is magnetic flux density, about 0.00003 and 0.00006 T at Earth’s surface;
is current;
is length of the conductor. The given 10 m^3 can be interpreted as many possible lengths, so I’ll just use a reasonable “big ship” size of 100 m.

So , which calculates to between roughly 16000 and 33000 A.

Rather than a working vehicle, let’s imagine a basic engineering experiment: Somewhere not close to Earth’s magnetic poles, we lay a length of superconductive wire (chilled to its operating temperature) on an insulating surface in an east-west direction, attaching each end to a powerful positive and negative terminal. We then pass a current thought it sufficient to lift it from the surface.

American Superconductors sells superconducting wire with a cross-section area of about .000002 m^2 and a maximum current capability of about 160 A. It’s made mostly of bismuth and silver, so should have a density of about 10000 kg/m^3.

Notice that ,
where is the wire’s density times its cross-section area, .025 kg/m for the American Superconductor wire.
So we can rewrite the current equation as: ,
and calculate a current required to levitate just the wire of about 3200 to 6500 A, about 20 to 40 times its capability.

Note that, with no changes in the wire’s direction, it shouldn’t induce a magnetic field that intersects itself, so loss of superconductivity due to magnetic field should not be an issue (as it would be in a self-contained vehicle). The issue here is the material’s ability to move electrons. Although superconductors have zero resistance, they have a finite current-carrying capacity.

It’s worth noting that, while it doesn’t appear practical to use the Earth or other bodies’ magnetic fields to lift objects from their surfaces, such technology is very promising for maneuvering objects already in orbit. Know as “tether propulsion”, some preliminary experiments have already flown, with others scheduled. These systems are “reversible” – electric energy, such as from a solar cell, can be used to increase the craft’s kinetic and potential energy, boosting it into a higher orbit, or they can be used to generate electricity while braking the craft into a lower (or different eccentricity) orbit.

A drawback to tether propulsion is that “popular destination” bodies like the Moon and Mars have effectively no magnetic field, so it can’t be used around these bodies. Jupiter and the other giant planets, on the other hand, have greater magnetospheres than Earth, and are, IMHO, prime locations to use electromagnetic tethers for both navigation and power generation. (I elaborate on this in a “big picture” manner in “Sheer human fecundity”, and ”Relevance of space elevators in a 1,000,000 times more energy rich civilization”) in the ”Colonizing the Solar System” thread)

The Sun’s magnetic field (the IMF), while about .0001 T (, about twice the Earth’s) at its surface, decreases with distance (though not as sharply as simple theory predicts). At 1 AU, the distance of the Earth’s orbit, it’s about , about 1/5000th that of Earth’s surface strength, so interplanetary maneuvering using electomagnetics appears impractical.

[silverslith]

.000002 m^2 and a maximum current capability of about 160 A

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.

Looks like we can use our structure weight as the superconductor:
Get Wired for Superconductivity

Get Wired for Superconductivity
P. Adams/LSU
Live wires. These 7-micron-thick wires carry current without resistance and have an unprecedented combination of strength and light weight.

A research team has created a new type of superconducting wire that not only carries a high electric current without resistance but also is remarkably strong, light, thin, and long. As the team reports in the August Physical Review B, the wires are made from an unusual magnesium-carbon-nickel compound layered around a carbon fiber. Experiments with the wires strongly suggest that the compound is an "exotic" superconductor whose properties can't be explained by the standard theory of superconductivity. Improved versions of the wires could be used in the electromagnets needed in a new class of spacecraft propulsion systems.

The explanation for superconductivity in standard materials such as niobium and lead has been in textbooks for decades, but unconventional superconductors--known as exotics--remain mysterious. Some researchers believe that the recently discovered superconductor MgCNi3 may bridge the gap between conventional superconductors and the most important class of exotic compounds, called cuprates, which can superconduct at temperatures higher than 100 degrees Kelvin. MgCNi3, which superconducts up to only about 8 degrees Kelvin, has a crystal structure similar to the cuprates, but it is simpler and does not contain copper or oxygen.

If MgCNi3 exhibits its own distinct exotic properties, it could help researchers understand electron behavior in cuprates and other materials. But the difficulty of synthesizing it has meant that not everyone can agree on whether it is unconventional, much less on the details of its behavior. "The experiments fall on both sides of the question," says Bob Cava of Princeton University, the material's inventor.

Phil Adams and David Young from Louisiana State University in Baton Rouge have now synthesized this superconductor in a new, thread-like form, which is better for testing its electrical properties than the flat films and powdery pellets that researchers have made before. The team put 3- to 5-millimeter-long nickel-coated carbon fibers in an evacuated tube with magnesium vapor and then heated the whole package in a 700-degree-Celsius oven for up to 30 minutes. The result was a core of carbon covered by an 80-nanometer-thick sheath of the new compound. The structure is "kind of like a cannoli," Adams says.

The team then measured the critical current--the current above which the fibers' superconductivity breaks down. When the researchers subjected the fibers to increasing temperatures and magnetic fields, the critical current dropped much more abruptly than predicted by the standard superconductivity theory, adding to the growing evidence that the material is exotic.


Adams and his colleagues were surprised by the size of the critical current: They extrapolated to an absolute zero value of 40 million amperes per square centimeter, 10 times higher than predicted from previous experiments with packed powders and almost as high as the theoretical maximum for non-high-temperature superconductors. Such a current would produce a magnetic field of up to 15 tesla in these wires--powerful enough to use in several futuristic spacecraft propulsion systems, which is why the Army has awarded Adams' team a grant to develop the technology.

A hot time for cold superconductors

"With a smaller conductor, the cost of wire used in MRI magnets could be reduced from $3-10 per kiloampere of current per meter of wire to only $1-2," Peterson said. "Because many miles of wire are wound into the coils in a typical MRI, the development of less expensive wires by the private sector could put an MRI machine in every doctor's office and even in veterinary hospitals."

Today's MRI machines use niobium-alloy wires that are much more expensive than MgB2 wires and require costly liquid helium refrigeration to maintain superconducting properties. Los Alamos scientists fabricated a prototype MgB2 coil that generated magnetic fields in the range useful for MRI applications (above 1 tesla) operating at a temperature of 25 degrees above absolute zero. This temperature can be reached using commercially available refrigeration units at much lower operating costs.

https://www.furukawa.co.jp/english/w...lead0412_e.htm

Development of 20-kA Class Oxide Superconductor Current Leads, Demonstrating the Highest Current Rating in the World

ScienceDirect - Fusion Engineering and Design : High temperature superconductors for the ITER magnet system and beyond

For this purpose, we give a short summary of results that have been obtained from an ITER conform 70 kA HTS current lead that was designed, built and tested by the Forschungszentrum Karlsruhe and the CRPP Villigen in the frame of the European Fusion Technology Programme and in cooperation with industry. This current lead consists of an HTS part that covered the temperature range from 4.5 to 70 K and a conventional part, making the connection to room temperature. Because the HTS part had no ohmic losses and poor thermal conduction, the refrigerator power necessary for cooling the current lead was reduced drastically. The saving factor could be calculated to be 5.4 at zero current and 3.7 at 68 kA. The current lead could even be operated at 80 kA and with respect to safety criteria of ITER, a complete loss of He flow was simulated showing that the HTS current lead could hold a current of 68 kA for 6 min without active cooling. These results demonstrate that today existing HTS materials can be used in ITER for current leads or bus bar systems.

[silverslith]

Up to 5000 times your figure above seems a pretty good result.