Although an 'E-sail" can probably protect against some of the protons emitted from the sun, there are far more efficient methods available than a fleet of large sails. For example, by providing each ship with it's own 'E-sail' wouldn't be that hard.
I used numbers for the size of the E-sail from Wikipedia (beware, no citation)
- A solar sail system can be extremely light, in this example, the 'sail' part of the system only has a mass of 35 kg for a shield that has an area of over 1000 square kilometers!
- With such a minimal weight, I don't think it would make sense to have a fleet of ships where the sole purpose is to carry one of these. You'd need a full complement of spacecraft systems (power generation, attitude control, etc...) for every 'Oasis' ship while these systems already all exist on the ships which are traveling
- Even if the mass of the system is off by an order of magnitude, I still think it's economical to attach one of these units to one of the ships traveling during the transit. With one ship protecting the area of LA, you'd have plenty of space to spare
These are however provided that an 'E-sail' would work as solar wind shielding. Regardless of whether they do or don't, there's more established and practical methods of radiation shielding.
According to NASA:
Throughout the entire trip [to mars], astronauts must be protected from two sources of radiation. The first comes from the sun, which regularly releases a steady stream of solar particles, as well as occasional larger bursts in the wake of giant explosions, such as solar flares and coronal mass ejections, on the sun. These energetic particles are almost all protons, and, though the sun releases an unfathomably large number of them, the proton energy is low enough that they can almost all be physically shielded by the structure of the spacecraft.
An alternative method for providing radiation shielding from the sun for a ship would be a large, variable power, electromagnet on a gimbal somewhere inside the ship. This magnet would just point perpendicular to the sun and in the event of a larger solar event, it's power would be increased for more deflection. Unfortunately, these are not the hard ones to shield against:
The second source of energetic particles is harder to shield. These particles come from galactic cosmic rays, often known as GCRs. They’re particles accelerated to near the speed of light that shoot into our solar system from other stars in the Milky Way or even other galaxies. Like solar particles, galactic cosmic rays are mostly protons. However, some of them are heavier elements, ranging from helium up to the heaviest elements. These more energetic particles can knock apart atoms in the material they strike, such as in the astronaut, the metal walls of a spacecraft, habitat, or vehicle, causing sub-atomic particles to shower into the structure. This secondary radiation, as it is known, can reach a dangerous level.
This type of radiation can't really be blocked using a single electromagnet due to the fact that all magnets are dipoles and can only redirect particles if the're coming in from a certain direction. Blocking this second type of radiation with current technology requires
- Lots of mass or "thickness" between the radiation and the passengers
- Advanced materials (often layered) which absorb radiation especially well
How much power would a spacecraft's magnetic shield require?