Apr 23, 2016 04:53 Andrew Palfreyman Posted on: Breakthrough Initiatives

The lead spacechips can be primarily sacrificial and can clear the way for the following swarm. If in doubt send ten times more. They're cheap.

Apr 23, 2016 22:12 michael.million@sky.com Posted on: Breakthrough Initiatives

As mentioned earlier having the sail edge on will give a lot of protection, if the edge is hit the most probable tracks are to the sides (shallow angle deflection) and therefore reducing damage to the sail. Carbon atoms give strong bonds and are quite hardy to nucleus impacts (we will be in the fusion velocity range after all).

May 26, 2016 13:42 michael.million@sky.com Posted on: Breakthrough Initiatives

If we applied a powerful positive charge to the rim or leading edge of an edge on sail it would discourage the more massive positive ions from hitting the sail, but attract the less massive electrons. Very high voltages can be created on sharp edges and therefore create high deflection forces.

Aug 01, 2016 13:49 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Apr 13, 2016 06:22 David Theil Posted on: Breakthrough Initiatives
"At a typical interstellar medium density of 1 atom per cubic cm these can be ignored from a momentum consideration. Dust particles of order 10^-14 g in mass have density of roughly 10^-12 per cubic cm in the local bubble. A cm sized spacecraft could expect to encounter a few million of these beasties on the way to Alpha Cen (roughly 1 parsec.) At a speed of 6x10^9 cm/s (0.2c) each one will deposit about 10^5 ergs into our little spacecraft...not enough to raise the temperature all that much if averaged over the whole 1 gram mass (assumed heat capacity of silicon), BUT presumably enough to sputter away some protective coating. I would want to do some lab experiments to see how different coatings respond to such collisions. Even the LHC can't produce 10^16 eV particles. This is going to be a tough thing to test and will have to rely on modeling."

You are right. See also summary for CRUISE | INTERSTELLAR DUST referring to the impact from the same type of 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.
Dust particles will go through the sail with very little energy loss.

– Prof. Sasha Buchman, Breakthrough Initiatives

Aug 01, 2016 13:50 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Apr 23, 2016 04:53 Andrew Palfreyman Posted on: Breakthrough Initiatives
"The lead spacechips can be primarily sacrificial and can clear the way for the following swarm. If in doubt send ten times more. They're cheap."

With the pointing accuracy at about 5μrad (1 arc sec) the area to clean ahead of the nanosat at end of acceleration (20 Gm) is about 1010 m2 or about 109 other sails. This area increases as the square of the distance (43 Pm at AC, 1021 sails) making it impractical to sweep ahead of satellite with other sails.

– Prof. Saha Buchman, Breakthrough Initiatives

Aug 01, 2016 13:51 Breakthrough Initiatives Posted on: Breakthrough Initiatives

May 26, 2016 13:42 michael.million@sky.com Posted on: Breakthrough Initiatives
"If we applied a powerful positive charge to the rim or leading edge of an edge on sail it would discourage the more massive positive ions from hitting the sail, but attract the less massive electrons. Very high voltages can be created on sharp edges and therefore create high deflection forces."

It appears that hydrogen and dust are neutral, becoming charged upon ionization by collision with the nanosat.

– Prof. Sasha Buchman, Breakthrough Initiatives

Aug 01, 2016 13:59 Breakthrough Initiatives Posted on: Breakthrough Initiatives

General comment regarding atomic hydrogen:

Areas of passive components with depth between 1μm of Al equivalent (25 mg/cm2) and 2mm Al equivalent (0.5 g/cm2) should be minimized to avoid negative charging by stopped electrons. During the nanosat cruise 4.3×1018 electrons will impact each cm2. If stopped that will cause a charge of 0.7 C. As the capacity of the nanosat (modeled as a disk of radius R=2.25m) is 8ε0R=160 pF, an electron stopping cm2 of nanosat will charge the entire craft to V≅4GV (assuming overall electrical conductivity). This potential will cause vacuum electron field emission, with potential arching to other components, until reduced to below a few tens of MV.

Active components with thickness of 2mm Al equivalent (0.5 g/cm2) and above will stop the 20 MeV protons depositing excessive radiation doses. Designing the active nanosat chip to be 0.5 g and 1 cm2 would thus not be practical unless shielding is added. For 1 cm2 chip the shielding will however add another 0.5×2=1 g. However, the chip could be made lighter and encased in a shield of the remaining mass.

If the sail (0.5g) could be folded into a 1 cm2 shield in the direction of travel, it would provide the stopping power for protons. This would however not allow its use as antenna for communications during the cruise stage.

– Prof. Sasha Buchman, Breakthrough Initiatives

Aug 05, 2016 06:59 michael.million@sky.com Posted on: Centauri Dreams

'It appears that hydrogen and dust are neutral, becoming charged upon ionization by collision with the nanosat.

– Prof. Sasha Buchman, Breakthrough Initiatives '

The gas in the local bubble is quite hot, hot enough to be significantly ionised,

http://www.outerspacecentral.com/ism_page.html

Sep 02, 2016 00:49 Patrick Taylor Posted on: Breakthrough Initiatives

Is there a way to exploit the ionization to some advantage? Could the power system be biased (or self-biasing) to use the charge from ionization? Could the coating of the chip become an additional power source during cruise?

Sep 24, 2016 20:20 James Early Posted on: Breakthrough Initiatives

Robert Forward’s concern about dust particle impacts on light sails led to the July 2000 paper below that shows they do negligible damage to thin sails. The dust particle only creates a hole approximately the size of the particle. Thin sails will arrive at the destination in good enough condition to be used as optics for observations or communications.

The dust particles can do more damage to the main structure of the spacecraft. The 2015 paper shows a simple, low mass system to ionize and deflect dust particles for large spacecraft, but the design is too complex for gram scale spacecraft. A simpler concept which likely works for gram scale spacecraft has been developed and should be published soon. Interstellar gas and dust should not be a major issue for interstellar spacecraft.

J.T. Early, R.A. London, Dust Grain Damage to Interstellar Laser-Pushed Lightsail, v37, pp.526-531, J.Spacecraft and Rockets, July 2000.

J.T. Early, R.A. London, Dust Grain Damage to Interstellar Vehicles and Lightsails, v68, pp.205-210, JBIS, July 2015.