Editing Magnetic sail (section)

== Criticisms ==

In 1994 Vulpetti published a critical review regarding viability of space propulsion based on solar wind momentum flux.<ref>{{Cite journal |last=Vulpetti |first=Giovanni |date=1994-09-01 |title=A critical review on the viability of a space propulsion based on the solar wind momentum flux |url=https://dx.doi.org/10.1016/0094-5765%2894%2990074-4 |journal=Acta Astronautica |language=en |volume=32 |issue=9 |pages=641–644 |doi=10.1016/0094-5765(94)90074-4 |bibcode=1994AcAau..32..641V |issn=0094-5765}}</ref> The paper highlighted technology challenges in terms of the magnetic field source, energy required and interaction between the solar wind and the spacecraft's magnetic field, summarizing that these issues were not insurmountable. The major unresolved issue is spacecraft and mission design that account for the potentially highly variable solar wind velocity and plasma density that could complicate maneuvers by a spacecraft employing magnetic sail technology. Some means of modulating thrust is necessary. If the mission objective is to rapidly escape the solar system then the paper states that this is less of an issue.

In 2006, Bolonkin published a paper that questioned the theoretical viability of a Magsail and described common mistakes.<ref>{{Cite arXiv|last=Bolonkin |first=Alexander |date=2006 |title=Theory of Space Magnetic Sail Some Common Mistakes and Electrostatic MagSail |eprint=physics/0701060 }}</ref> Equation (2) states that the magnetic field of electrons rotating in the large coil was greater than and opposed the magnetic field generated by the current in the coil and hence no thrust would result. In 2014 Vulpetti published a rebuttal<ref>{{Cite web |last=Vulpetti |first=Giovanni |date=2014 |title=Notes about misinterpreting some plasma properties |url=https://centauri-dreams.org/wp-content/Bolonkin%20Refutation_edited.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://centauri-dreams.org/wp-content/Bolonkin%20Refutation_edited.pdf |archive-date=2022-10-09 |access-date=August 15, 2022 |website=centauri-dreams.org}}</ref> that summarized plasma properties, in particular the fact that plasma is quasi-neutral<ref name=":12" /> and noted in equation (B1) that the Bolonkin paper equation (2) assumed that the plasma had a large net negative electrical charge. The plasma charge varies statistically over short intervals and the maximum value has negligible impact on Magsail performance. Furthermore, he argued that observations by many spacecraft have observed compression of a magnetic field by dynamic (or ram) pressure that did not depend on particle charges.

In 2017, Gros published results that differed from prior magsail work.<ref name="gros2017" /> A major result was the [[#Magsail kinematic model (MKM)|Magsail kinetic model]] of equation {{EquationNote|MKM.2}} that is a curve fit to numerical analysis of proton trajectories impacted by a large current carrying superconducting coil. The curve fit scaling relation for the effective sail area <math>A(v)</math> was logarithmic cubed with argument <math>c I / (v I_G)</math> with <math>I</math> the loop current, <math>I_G</math>  the curve fit parameter, <math>v</math> the ship velocity and <math>c</math> the speed of light. This differed from the power law scaling <math>A(v) \sim (v/c)^\alpha</math> of prior work.<ref name=":13" /><ref name=":14" /> The Gros paper could not trace back this difference to underlying physical arguments and noted that the results are inconsistent, stating that the source for these discrepancies was unclear. Appendix B questioned whether a bow shock will form if the initial spacecraft velocity <math>v_0</math> is large, for example for deceleration after interstellar travel, since the predicted effective sail area <math>A_G(v)</math> is small in this case. One difference is that this analysis used the coil radius <math>R_c</math> for computation of the ion gyroradius as compared with prior work use of the magnetopause radius <math>R_{mp}</math>