November 04, 2010

Carnival of Space 176

Carnival of Space 176 is up at Kentucky Space






Shields for Icarus (new interstellar space ship design) : Part 2 – Navigational Deflectors for Real A variety of magnetic, physical and optical defences are possible, even desirable, to protect a fast interstellar probe like “Icarus”

A proposed means of decelerating from interstellar speeds is the magnetic-sail, which is a large loop of superconducting wire producing an artificial magnetosphere around the moving spacecraft. By deflecting interstellar ions, the magnetic field forms a semi-spherical zone forward of the vehicle where the magnetic pressure of the field and the pressure of colliding ions are evenly balanced. A magnetopause forms, in which ions are reversed in direction and their change in momentum produces an equal, but opposed, change in momentum in the magnetic-sail, and thus the spacecraft to which it is attached.

In the case of a moving magnetic-sail, the atoms of the Interstellar Medium (about 90%-50% of the ISM) are actually ionized by its rapidly changing magnetic-field strength, in a process akin to that used to ionize gas in a Pulsed Inductive Thruster. If you imagine an atom drifting through space at typically 15 km/s, to then encounter a magnetic field approaching at 60,000 km/s is to experience a change in field sufficiently quick enough to ionize the atom. In effect the ship is creating a shock-wave in the ISM which is producing a lot of extra charge as atoms are ionized. All those suddenly energetic electrons could be sufficient to increase the charge on the ISM dust, thus increasing the deflector effect.

To put the bumper in place, perhaps 100 kilometres ahead, it can be deployed via a small sub-vehicle – sheets made from carbon fibre are surprisingly springy and can self-unfold from a small volume. Once in place it might be kept in place by firing lasers at super-reflective patches on the bumper. Via reflecting ~2,000 times the laser achieves far more push than a single pulse of energy can achieve.

Circuitry is being made from graphene in laboratories around the world, thus the bumper isn’t a passive mass. Multiple layers could work together to track any grains that pass through without being totally ionized. This causes a signal to be sent back to the vehicle which then activates its final layer of defence, high-powered lasers. In microseconds the lasers either utterly ionize the target or give it a sideways nudge via ablation – blowing it violently to the side via a blast of plasma. Such an active tracking bumper would need to be further away than 100 km to give the laser defence time to react, though 1/600th of a second can be a lot of computer cycles for a fast artificial intelligence. The lasers might use advanced metamaterials to focus the beam onto a speck at ~100 km, without needing to physically turn the laser itself in such a split-second. Highly directional, high-powered microwave phased arrays exist which already do so purely electronically and an optical phased-array isn’t a stretch beyond current technology.


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