Shields for Icarus: Part 2 – Navigational Deflectors for Real

posted by Adam Crowl on October 25, 2010

One famous science-fictional nod to the hazards of high speed interstellar travel are the navigational deflectors used on the most famous line of SF starships of all, the “Enterprise” starships. All of them feature a glowing forward facing disk which, as made explicit in “The Next Generation” series, is a deflector shield against hazardous impacts when travelling through space-time at high sub-light speeds. Curiously the 0.2c quoted as the maximum impulse speed for the NCC1701-D model “Enterprise” is about right for “Icarus” too. Can “Icarus” be defended by something straight of “Star Trek”? 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. Interestingly the Sun’s magnetosphere already acts like a deflector shield, forcing the ions and small charged particles of dust to flow around the Sun as it moves against the average flow of the Galaxy. Exposed to energetic photons (ultraviolet and x-ray) and high-energy ions (cosmic rays) the interstellar dust is charged. The very smallest dust particles, up to a certain diameter, are completely excluded from the inner Solar System by the Sun’s magnetosphere, while particles a bit larger are significantly deflected. Only the high-end of the dust size range is able to penetrate. 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. The question needing investigation is whether this is sufficient to provide protection against all the ISM dust, or whether some additional defences will be needed. Cosmic sand-grains, with the kinetic energy of 100 pound bombs, while rare, will perhaps still need some means of interception by “Icarus”. The original “Daedalus” study proposed an artificial dust cloud moving 200 kilometres ahead of the main vehicle and this might prove sufficiently effective. Alternatively newer materials have become available which might provide multilayer protection – carbon allotropes, the most exciting of which is graphene. Graphene is basically a single sheet of graphite – a hexagonal grid form of carbon in the form of immensely strong sheets of covalently bonded carbon atoms, but held together between the sheets via via weak hydrogen bonds to make graphite. Peeling away single layers of graphene has now become possible and it has all sorts of surprising properties. What I’m interested in for shielding is making a large, low-mass “bumper” which cosmic sand-grains run into before hitting the craft. After passing through several layers of graphene the offending mass is totally ionized and forms a high-energy spray of particles, but particles that can now be deflected by the vehicle’s cosmic-ray defences (akin to the mag-sail, but smaller with a higher current) and safely diverted away from sensitive parts. 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. In conclusion, contrary to some sceptical voices, an interstellar probe doesn’t have to passively plow its way through a potentially deadly interstellar medium. A variety of magnetic, physical and optical defences are possible, even desirable, to protect a fast interstellar probe like “Icarus”. On our eventual ‘star treks’ we will have navigational deflectors to defend us.


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16 Responses to Shields for Icarus: Part 2 – Navigational Deflectors for Real

  1. Dimos says:

    Hello there Adam,

    during this time Andreas and me had been exploring the hazards that electronics face during the voyage, and after reading the article, i am glad to say that it seems that we are on spot!

    I got one question: a magnetic shield, and please correct me if i am wrong, is going to create an artificial Van Allen belt around the ship, which in turn may prove hazardous. I have found proposals of ‘cleaning’ Earth’s belts (http://www.tethers.com/HiVOLT.html) . Perhaps some similar design would be needed.

    The point is: shape and size of this artificial VA belt are variable, major cause being Icarus speed and actual shield/particle collisions. Is there any chance that parts of the ship (especially the bow) will be exposed? Any chance of a shield collapse? Or is it not an issue at all?

    Again, i am very glad that we are on the same frequency!

    Dimos

  2. Geoff says:

    Carbon nanomaterials would also be candidates for other Icarus structures, such as fuel tanks. Could the “bumper” be simply an empty fuel tank – one structure doing two jobs? The shielding isn’t needed until after the fuel is spent, after all.

  3. Adam says:

    Hi Geoff

    Nice thought. Designing sub-components to have multiple uses is an important concept for probes and there has been some discussion on using fuel tanks for making antenna. As a shield is another option we should add to the list.

  4. alex says:

    how about laser beam? you can make some calculations to fire a laser beam as a push power for the ISM. And the laser beam will scattering after a certain distance, that works as an shield for the starship. lets say, a powerful laser beam will scattered after a distance of 0.2c second with scattered area 2,000 square metres, and have a ? Newton force for each square metres, whats the original power (?MW) of laser beam? dose this works?

  5. Rick says:

    Hello Adam,
    I am not an expert phisicist, I just like to read about space exploration. In case of long interstellar voyage probes going at 0.1c or more I always have read about possible “shield” solutions “in front” of the probe to avoid possible collision with ISM dust. I have a question about this topic, maybe you could help me with. Can a possible risk to the probe come from different angle then merely from “in front? And if yes how much would be probable such an event will occur?
    Thanks for your information work.

    (English is not my mother lenguage)

  6. Adam says:

    Hi Rick (& everyone else)

    Good question about the direction of collision threats. Simply the vehicle is going so quickly that for most threats the direction is virtually straight ahead. Dust and interstellar plasma are typically travelling at a few kilometres per second relative to the Sun and compared to a probe’s cruising speed of between 30,000-60,000 km/s this is essentially no motion at all. If the defense system is looking 1 second into the future for threats then for dust moving at saying ~30 km/s its “cone of hazard” is 30 km wide and 30,000 km long – a very narrow cone indeed.

    The other threat, cosmic rays, comes from all directions and in that case their speed is too great for the probe’s own speed to make much difference to the direction they come from. They very definitely can come from all directions. As the probe speed is increased to near light, then relativistic effects concentrate the apparent direction the rays come from into the forward direction of the probe – this is called “relativistic aberration” and it gets stronger, the closer to the speed of light. But for a 0.1-0.2c probe this effect is negligible.

  7. Adam says:

    Hi Dimos
    There will need to be some way of discharging any ions that might be trapped, but I suspect they won’t be trapped very efficiently. During most of the braking phase the magnetic field is moving too rapidly relative to the ISM to capture much. Most of the high energy particles that are hazardous in the Van Allen Belts comes from cosmic-ray collisions with Earth’s atmosphere, not the Solar Wind. “Icarus’s” fields will (hopefully) deflect the cosmic-rays before they can interact and become a hazard.

  8. Adam says:

    Hi alex
    Lasers will be very useful, but using them to push away the ISM isn’t needed. The magnetic-sail will interact with the ISM more effectively. We might need high-power UV lasers to ionize the ISM if the inductive charging approach proves unworkable, but more study of the ISM is needed – the ion fraction seems quite variable throughout our Local Interstellar Cloud.

  9. alex says:

    Hi Adam,
    first time I got any response from any my comment, thanks for that.
    Recently, I feel more and more the accurate of Star Trek’s earth future. In my opinion, the Icarus will be our first generation star ship, in its steampunk way. Once the design got approved , we eventually going to build may be dozen of factoies among the moons of Jupiter and Saturn. and may be an HQ on the Mars? who knows, haha.

  10. Adam says:

    Hi Alex
    One hopes that a starship will be the beginnings of a flowering of humanity’s presence in deep space. If we can work out the right design, then it may not be the Herculean task many presently believe it to be.

  11. el cid says:

    The question I have is the accumulated heat of all the collisions, not only with highly dangerous dust but much much smaller things like stray molecules. It adds up I suppose. The shell simply has to get glowing hot and then how do you keep everything from burning up?

    I’d love to see a post on heat exchange. In that light, what is the heat cost of running your deflector? How is that heat radiated away?

  12. Patrick says:

    I think that you should look at non-thermal plasma shields,
    which would give the added bonus of radiation shielding as well as
    being able to be fueled by interstellar gas or exhaust from the
    reactor, added to this you could have a P.A.S.S or plasma acoustic
    shield system which is two or more lasers focusing of some gas to
    create a super hot plasma that creates a supersonic explosion. The
    non-thermal plasma could replace your magnetic field with better
    results since it would ionize anything that passes thru it and it
    can be made quite large with minimal gas and energy. A second
    thicker layer of plasma can be keep closer to the ship squeezed
    between two layers, one from the ship and another from a network of
    wires or rings that will extend from protrusions from the hull,
    this could also help with cooling since it could function as a
    massive convection radiator. When the passive shielding is not
    enough then its time for the laser to focus in on the area and
    super heat it to create a wall of plasma that will either vaporize
    it or redirect it, depending on size and composition.

  13. Pingback: Computers for Interstelllar Missions – Part 1 — Project Icarus

  14. Adam says:

    Thermalization of the incoming flux is probably not recommended – better to keep it away from the vehicle and deflect it smoothly. Of course when we want to lose speed, then increasing drag with the interstellar medium will be highly desirable. And the topic of a future blog-post…

  15. Joey says:

    Would it be possible to design a funneled orifice at the bow of the ship? Then use magnetic ‘bottles’ to force all incoming dust, particles, etc into an aligned vortex around the bow, sweep it all into the orifice and then exhaust it all? Possibly even robbing some charge off the junk for capacitance storage to help power the system. It seems to me that you should be able to leverage a plasma bow shock effect and shape that into your mag scoop. Like a quant/fusion ramjet, without directly using the gathered mass as fuel.

  16. Pingback: Lasers: Protecting the Starship

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