Cruise | Interstellar dust

Based on estimates of the density of dust in the local interstellar medium, over the course of a journey to Alpha Centauri each square centimeter of the frontal cross-sectional area of the StarChip and lightsail would encounter about 1,000 impacts from dust particles of size 0.1 micron and larger. However, there is only a 10% probability of a collision with a 1 micron particle, and a negligible probability of impact with much larger particles.

A 0.1 micron dust particle moving at 20% of the speed of light would penetrate and melt the StarChip to a depth of order 0.4mm. To estimate scale effects, calculations were made assuming a 10cm X 0.1mm thickness. Traveling with the nanocraft’s edge facing parallel to the velocity vector would reduce the cross section to 0.1cm2, for a 10 cm StarChip with a 0.1mm thickness. A protective coating of beryllium copper could be added to the leading edge of the StarChip, as a sacrificial layer for additional protection from dust impacts and erosion. If needed, the StarChip geometry could be elongated (‘needle’ geometry), to further minimize the cross-section.

To mitigate the impact of dust further the sail could potentially be folded into a streamlined configuration during the cruising phase to Alpha Centauri. This would minimize the frontal area of the sail. The nanocraft’s electronics could also be designed so as to be less vulnerable to localized damage from dust.

The momentum kick from 0.1 micron dust particles is small, and its effect on the nanocraft’s trajectory might be compensated for by photon thrusters.

Comments (31)

  1. dunand@northwestern.edu:

    As per my previous post in another chapter, the choice of beryllium copper does not seem to be optimal as a sacrificial/abrasive layer (too heavy, not particularly tough). NASA has extensive experience with protective coatings from micro-meteoroids.
    If the issue is protection against "penetrate and melt the StarChip", then a high melting material with high toughness and low density (when calculating penetration resistance per unit mass) is probably best. Examples include pure Be or pure Nb, Mo (Ta, W and Re have even higher melting points but are much denser). Possibly, diamond, which can be coated easily via CVD, but cracking and spalling may be an issue, as for all other ceramics.

  2. David Theil:

    Why do we care about the sail after the boost phase? As long as it doesn't have a high liklihood of interfering with the probe function, who cares if it gets holed by dust? It is only impacts to the probe itself we care about.

    Need to do modeling to see what happens when sputtered with relatively massive high energy particles. If each particle creates a 0.4mm sized crater, and the total surface area is roughly the size of 625 such craters, making the protective layer 1mm thick will likely keep the functional innards intact through 1000 collisions. (Some will have bad luck to be hit in the same place too many times, but some won't. This is a yield calculation)

  3. Dmitry Novoseltsev:

    Please note the pictures of the Mira star in ultraviolet light, made in the GALEX project.
    http://www.galex.caltech.edu/media/glx2007-04r_img07.html
    Speed of the Mira –about 130 km/s, but before it is clearly visible the detached shock wave in the interstellar gas.
    With low weight and higher speed of our device (almost 600 time) the effect will be much stronger, which will lead, firstly, to intensive braking of the sail immediately after disconnection of the accelerating beam, and secondly, to its rapid destruction.
    In this connection I consider it expedient after stage laser acceleration to deploy the sail perpendicular to the direction of flight (edge of course). Then the braking and the wear will be minimal.
    If the sail is stabilized by rotation around the axis perpendicular to its plane, with a large enough frequency so that the canvas sails kept rigid and is not formed under the action of force from the oncoming flood, you can provide it with minimal even wear around the perimeter.
    In this case, the optimal, apparently, the round shape of the sail.
    If the sail of electrically charged, as I suggested earlier, this provides partial protection from positive ion colliding at a small angle to the plane of the sails – they will be leaving.
    On approaching the target it is expedient again to deploy the sail perpendicular to the direction of flight is then due to the resistance of the interplanetary gas and the oncoming solar wind can some what reduce the speed and increase the time of observation during the flight.

  4. R.A. Msalam:

    How can you equip the nanoship with a sonar and guiding mechanism?

  5. michael.million@sky.com:

    Perhaps have a small rim on the edge, it would increase the frontal area a little but give added integrity against a splitting event, it does not need to be much at all just wider than a dust grain.

  6. Andrew Palfreyman:

    A lead group of sacrificial spacechips may help to at least clear a path for almost stationary dust

  7. Ali Reza Tirna:

    Just playing with an idea:
    StarChip and lightsail frontal must be protected from interstellar dust. If we could charge the dust before hitting the surface of the StarChip and lightsail, we could repel it with some kind of induction layer with magnetic properties. One idea is to charge the particle moving towards the object with UV illumination. I dont know. Maybe. So the object could somehow illuminate UV far enough to charge the interstellar dust, the magnetic charge of the object repels the dust and no contact? To far? To stupid? Probably. Just playing with an idea.

  8. michael.million@sky.com:

    If we charged the leading sharp edge to a high voltage it will give some repulsion to dust particles as they have a tendency to hold a charge, this can be tested in a lab.

  9. Wayne Blackburn:

    Has any consideration been given to how much momentum transfer between the Starshot probes and all of the matter between the stars? In other words, completely without respect to any damage done to the sail or even the package, will it have enough momentum to push through the interstellar medium and actually REACH its goal?

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