Talk:Mini-magnetospheric plasma propulsion

Some explanation of the specific impulse claim would be nice. The system seems to need no reaction mass (and in fact the article says this) but a specific impulse is given. It looks like what's actually going on is that arcs need to be extended to collect thrust, the bigger the more thrust; these arcs leak ions, the bigger the more. Taking the ratio gives a sort of specific impulse, namely ion leakage per Newton of thrust. Is this correct? It should be explained. Andrew 06:25, Apr 13, 2004 (UTC)

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Also, can the direction be controlled? The solar wind streams only directly away from the Sun, but since it's charged it may be possible for the system to redirect it, allowing tacking. Andrew 06:25, Apr 13, 2004 (UTC)

This turns out to be possible; in fact, this propulsion system is simply a way of making a magnetic sail out of loose ions instead of wire. --Andrew 06:39, Apr 23, 2004 (UTC)

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I'm skeptical of the claim that these systems produce the same thrust throughout the heliopause. ~Can we assume half acceleration = thrust beyond the heliopause/My guess is the ions are less numerous in semi radom directions, but much faster beyond the heliopause.~ If the power for the system comes from solar panels, then that power will fall with the square of the distance from the sun. Thus, you either need very large solar panels as you recede from the sun, or else your propulsion system's effectiveness is diminished.

~the pressure of the magnetic feild and the solar wind are in dynamic equalbrium. As the pressure of the solar wind falls of at 1/r^2, the field increses in cross sectional radius, maintaing constat force.

Any comments? --Doradus 16:33, 4 May 2004 (UTC) IMHO solar panels are useless just inside the heliopause, but it may take a hundred years to reach the heliopause. A space craft designed for 100 years will have several electric power sources, most of which will have failed, so the choice may be propulsion or transmitting data back to Earth, if either propulsion, or transmitting are still functional.

~it would take 10 years to get to the heliopause at 50 km/s and m2p2 is expected to run between 50 and 80 km/s.

If the power comes from solar power, then you're right (outside a certain distance). But the statement is for a constant power; perhaps this is generated by a nuclear reactor, or perhaps there is sufficient solar cell area to accomodate the propulsion system at any distance of interest.

It would be nice to have some estimate of the amount of power needed to run such a system (both for this and for magsails). --Andrew 22:10, May 4, 2004 (UTC) The super conducting magsail needs considerable = gigawatt-hours of energy to establish the magnetic field; negligible energy to maintain the magnetic field, however there may be reasons why we would want to shut down the magnetic field. It might be practical to store half of the energy stored in the magnetic field for other uses. Can someone explain where the other half is disapated? It occurs to me that it may difficult to shutdown (non-distructively) a magnetic field in space that is produced by a super conducting loop.

In any case re-activating the super conductive magnetic field requires considerable energy.

~there is no superconducting loop anywhere in this system.

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If there are fewer ions, the magnetic field increases in size until a certain amount of ions start hitting it. Therefore, even if there are fewer ions it will maintain it's speed. Another interesting point that someone might want to add is that if heading towards a star, it would act as a brake, and would bring it back down and stop it at a distance where the force of gravity equals the force that the engine can handle.

~If anybody would like further reading the Journal of Geophysical Research, vol 105, NO. A9, pages 21,067-21,077, september 1, 2000 has an easy to read paper by the creators of this technology.

Criticism

User:Dashpool removed a paragraph with critical comments from the article, with the edit summary "Peer reviewed articles support the M2P2 idea: need better references to back up 'unfeasibility')". I put it back. I agree that the article could be better written and in particular could have better references. There is, however, only one peer-reviewed article cited to support the idea, which leaves it open to questions of its notability. Generally, if independent secondary sources are not available on a topic, we should not be writing about it at all. I don't take such an extreme view, but when the sources on a topic are generally weak, I think if a serious criticism by a scientist working in the field is publicly available, then we must mention it. --Art Carlson (talk) 10:50, 24 May 2008 (UTC)

OK, the criticism may be notable enough for wikipedia: it is true that there appears to be only one article on this subject (Winglee, Journal of Geophysical Research, vol 105, p21067, 2000) so there is not a huge preponderance of evidence. I am happier anyway that the 'unfeasibility' is not in the introduction: it made the article read as though the M2P2 idea had been 'disproved', but this doesn't reflect the balance of evidence. I can't find any other sources. Dashpool (talk) 19:05, 24 May 2008 (UTC)

Yeah. It probably shouldn't have been in the lead. I suppose Janhunen still believes it, else it wouldn't be on his web site. But if it hasn't faced peer review, there may still be an obvious (to experts) mistake in it. --Art Carlson (talk) 06:39, 25 May 2008 (UTC)

I have found a few references which might be useful.

--[1] presents another criticism of Winglee's idea/simulation, which is that the size of the bubble is limit by the flux of the magnet used, and Winglee's simulations seem to have a total magnetic flux in the magnetosphere much higher than the flux created by the electromagnet (perhaps due to lack of conservation in the simulation). If you assume a 1/r falloff of the field (and ensure the sum of the flux outside the electromagnet is conserved during bubble expansion), much smaller bubble radii would be expected. Basically, this can be used to rule out the idea of a compact magnet (the size of typical probes) generating enough flux to be useful: only deployable superconducting magnets of diameter much greater than a couple of meters are feasible for M2P2. Also not peer reviewed.

--'SAIL PROPULTION USING THE SOLAR WIND', FUNAKI IKKOH(Jaxa, Kanagawa, Jpn) NAKAYAMA YOSHINORI(National Defense Acad., Kanagawa, Jpn), J Space Technol Sci, ISSN 0911-551X, VOL.20;NO.2;PAGE.1-16(2004): the abstract states that they explore the idea of using a superconducting hoop 10m-100m in diameter. Is in a Japanese journal that I can't figure out how to access.

I wonder if maybe this article should be merged with the magnetic sail? --Dashpool (talk) 12:05, 27 May 2008 (UTC)

Merged into magnetic sail

--Dashpool (talk) 16:33, 1 June 2008 (UTC)