Magnetic sail
[2] The earliest method proposed by Andrews and Zubrin in 1988,[3] dubbed the magsail, has the significant advantage of requiring no propellant and is thus a form of field propulsion that can operate indefinitely.
The magsail design also described modes of operation for interplanetary transfers,[4] thrusting against a planetary ionosphere or magnetosphere,[4] escape from low Earth orbit[5] as well as deceleration of an interstellar craft over decades after being initially accelerated by other means, for example.
[8] Simulations predicted impressive performance relative to mass and required power; however, a number of critiques raised issues: that the assumed magnetic field falloff rate was optimistic and that thrust was dramatically overestimated.
Starting in 2003, Funaki and others published a series of theoretical, simulation and experimental investigations at JAXA in collaboration with Japanese universities addressing some of the issues from criticisms of M2P2 and named their approach the MagnetoPlasma Sail (MPS).
Predictions of substantial improvements in terms of reduced coil size (and hence mass) and markedly lower power requirements for significant thrust hypothesized the same optimistic magnetic field falloff rate as assumed for M2P2.
For the magsail deceleration in the interstellar medium (ISM) mode of operation the velocity is a significant fraction of light speed, for example 5% c,[7] the gyroradius is ~ 500 km for protons and ~280 m for electrons.
A condition for applicability of magnetohydrodynamic (MHD) theory, which models charged particles as fluid flows, is that to achieve maximum force the radius of the artificial magnetosphere be on the same order as the ion gyroradius for the plasma environment for a particular mode of operation.
At scales where the artificial magnetospheric object radius is much less than the ion gyroradius but greater than the electron gyroradius, the realized force is markedly reduced and electrons create force in proportion much greater than their relative mass with respect to ions as detailed in the General kinematic model section where researchers report results from a compute intensive method that simulates individual particle interactions with the magnetic field source.
[24] Magnetic sail modes of operation cover the mission profile and plasma environment (pe), such as the solar wind, (sw) a planetary ionosphere (pi) or magnetosphere (pm), or the interstellar medium (ism).
A spacecraft approaching a planet with a significant upper atmosphere such as Saturn or Neptune could use a magnetic sail to decelerate by ionizing neutral atoms such that it behaves as a low beta plasma.
that satisfies the pressure balance at magnetopause standoff as: The force with SI Units of Newtons (N) derived by a magnetic sail for a plasma environment is determined from MHD equations as reported by principal researchers Funaki,[1] Slough,[16] Andrews and Zubrin,[27] and Toivanen[31] as follows: where
Through analysis, numerical calculation, simulation and experimentation an important condition for a magnetic sail to generate significant force is the MHD applicability test,[37] which states that the standoff distance
Andrews was working on use of a magnetic scoop to gather interstellar material as propellant for a nuclear electric ion drive spacecraft, allowing the craft to operate in a similar manner to a Bussard ramjet, whose history goes back to at least 1973.
Te pressure at the magnetospheric boundary is doubled due to compression of the magnetic field and stated by the following equation at a point along the center-line axis or the target magnetopause standoff distance
An accurate curve fit as reported in Figure 4 to the numerical evaluation for the effective reflection area for a magnetic sail in the axial configuration from equation (8) was where
=100 m with the coil in an axial orientation.. That analysis also reported on the effect of magsail tilt angle on lift and side forces for a use case in maneuvering within the solar system.
In 2015, Freeland documented a use case with acceleration away from Earth by a fusion drive with a magsail used for interstellar deceleration on approach to Alpha Centaturi as part of a study to update Project Icarus[7] with
In 2017, Crowl documented a design for a mission starting near the Sun and destined for Planet nine approximately 1,000 AU distant[47] that employed the Magsail kinematic model.
The design accounted for the Sun's gravity as well as the impact of elevated temperature on the superconducting coil, composed of meta-stable metallic hydrogen, which has a mass density of 3,500 kg/m3 about half that of other superconductors.
In 2013 Quarta and others[54] used Kajimura 2012 simulation results[41] that described the lift (steering angle) and torque to achieve a Venus to Earth transfer orbit of 380 days with a coil radius of
In 2000, Winglee, Slough and others proposed a design order to reduce the size and weight of a magnetic sail well below that of the magsail and named it mini-magnetospheric plasma propulsion (M2P2) that reported results adapted from a simulation model of the Earth's magnetosphere.
A detailed analysis by Toivanen and others in 2004[31] compared a theoretical model of Magsail, dubbed Plasma-free Magnetospheric Propulsion (PFMP) versus M2P2 and concluded that the thrust force predicted by Winglee and others was over ten orders of magnitude optimistic since the majority of the solar wind momentum was delivered to the magnetotail and current leakages through the magnetopause and not to the spacecraft.
In 2013 Funaki and others[10][70] published simulation and theoretical results regarding how characteristics of the injected plasma affected thrust gain through creation of an equatorial ring current.
After initial inflation, protons and rotating electrons are captured from the plasma wind through the leaky magnetopause and as shown in the left create a current disc shown as transparent red in the figure with darker shading indicating greatest density near the coil pair and extending out to the magnetopause radius Rmp, which is orders of magnitude larger than the coil radius Rc (figure not drawn to scale).
and forms a static dipole magnetic field oriented perpendicular to the current disc reaching a standoff balance with the plasma wind pressure at distance
This dispersion problem could potentially be resolved by accelerating a stream of sails which then in turn transfer their momentum to a magsail vehicle, as proposed by Jordin Kare.
[citation needed] The table below compares performance measures for the magnetic sail designs with the following parameters for the solar wind (sw) at 1 AU: velocity
for the magneto plasma sail (MPS) is the simulation and/or experimentally determined value with force defined equation MPS.2 to account for thrust loss due to operation in a kinematic region.
[22] A major result was the Magsail kinetic model of equation MKM.2 that is a curve fit to numerical analysis of proton trajectories impacted by a large current carrying superconducting coil.
[4][7] 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.
