Magnetic shielding in space

One thing that might make a cluster of robotic satellites an essential component of an inhabited space vehicle system would be an ability for a series of satellites to create magnetic fields that could deflect cosmic radiation so that the combined cluster of satellites creates safe zones where relatively few cosmic rays pass through. An inhabited space vehicle could reside in one of these safe shielded zones and the cluster of satellites could move with the spacecraft to keep the people inside shielded as it goes on its journey. Such a cluster of satellites that would create strong magnetic fields in space would need to be managed in real time and the systems would have to be completely automated and computerised. The resultant sizes, shapes and strengths of the magnetic fields around an inhabited spacecraft would vary depending on the number of robotic satellites that were available to it. At the moment I would think that many ideas about shielding spacecraft from cosmic rays might focus on what could could done from the surface of and carried in the spacecraft itself. You could envision a system of robotic satellites that could build safe spaces through creating coordinated magnetic fields. If energy were plentiful from solar collector satellites and satellites could be moved around through remotely applied energy, then you could have hundreds of shielding satellites around any spacecraft and possibly even hundreds of kilometers from the vehicle itself. Initially these systems might have shielding satellite clusters that are pretty close to the spacecraft itself. The idea is to mimic in some small scale way the magnetic field that protects life on earth.

A large number of magnetic fields placed in space around a spacecraft would have those satellite created magnetic fields placed such that charged particles moving through space – cosmic radiation – that would have impacted that spacecraft are deflected to just miss the spacecraft. It would be a very complex problem because the modeling software would have to predict the varieties of cosmic rays that would normally hit the spacecraft and then plan to have magnetic fields set up to deflect radiation coming from every direction, and with varying energies. The magnetic shield built with the shielding satellites would not need to be continuous, but every direction in the sphere around a spacecraft would need to be covered. With fewer satellites, the satellites would need to be closer to the spacecraft and the magnetic fields would need to be stronger. With a large number of satellites the magnetic fields could be weaker and they could be placed further from the spacecraft.

28 March 2010

For the short term, before fleets of robotic service satellites for spacecraft are technically viable, a possible alternative might be to extend electromagnets into locations around a spacecraft while it is not being accelerated by rockets so as to set up a series of carefully designed magnetic fields that would deflect most of the cosmic radiation away from the spacecraft. The electromagnets could be held in place through multilinked robotic arms as in this previous post. The electromagnets might have to be held a few hundred meters away from the craft. The magnetic shield would be quite fragile and the spacecraft would have to drift while the shield is in place. You might be able to design it so that the spacecraft could rotate or reorient its attitude in a limited way while a tethered magnetic shield is in place. The relative weightlessness of space and the absence of an atmosphere mean that the rods that make up the multilinked robot arms could be very thin, strong and light wires. Small gyroscopes at the nodes between these long rods, and which could have their axis of rotation forcefully changed mechanically, could be used to maneuver the electromagnets into place. It might be an idea to add some elasticity into the long electromagnetic ‘tendrils’ (for want of a better word) so that if they do suffer a strike from a micrometeorite or space junk, the tendril could return to its proper location quickly and without much more energy being expended. Perhaps a good image to show of what I mean by this design for an electromagnetic shield around a small spacecraft would be the “clock” of a dandelion. It doesn’t quite look like a traditional spacecraft but if it could protect the people inside from radiation, it would be worth it. You could design it so that the thin wires could be packed tightly together as an outer layer of the spacecraft before the electromagnetic shield is deployed and opened up while the spacecraft is in space.

The force on a cosmic ray traveling through a magnetic field that would deflect that cosmic ray so that it wouldn’t hit a spacecraft is called the Lorentz force.

Dandelion 'Clock'

A dandelion ‘clock’ seems to be a suitable image for a framework for holding electromagnets in place around a small spacecraft. Once the spacecraft will need to reenter the earth’s atmosphere, the ‘clock’ will need to be shed. It would have to be about as easy to remove the ‘clock’ around a spacecraft prior to reentry as it is for the wind to distribute the seeds of a dandelion ‘clock’. The thin wires that make up the electromagnet shield around a spacecraft should then burn up as they enter the atmosphere. It would be too difficult to retract the ‘clock’ and design it as reusable – but perhaps that is still a possibility to try out.