Battery design is one of the most challenging aspects of the mission. Currently under consideration for the energy source onboard are plutonium-238, which is in common use, or Americium-241. 150mg has been allocated for the mass of the battery. This includes the mass of the radioisotope and the ultra-capacitor. As the isotope decays it will charge the ultra-capacitor. Then, at the appropriate time, the StarChip components will be switched on and begin to operate. The power budget is informed by the available energy in the battery. An innovative approach could take advantage of the heating of the frontal surface of the nanocraft through its interaction with the interstellar medium. The heat supply, at a rate of 6mW per cm2, could provide a thermoelectric energy source during the interstellar cruising phase.
It may be possible to coat the lightsail with a thin film of photovoltaic material, which was demonstrated on the IKAROS mission. This could be extremely useful during approach to the host star. The photovoltaics will be able to supply significant energy when they are within 2AU of the target star. Even with just 10% efficient photovoltaics, the energy supplied would be nearly 2kW at 1AU. This is more than 100,000 times the power of the radioactive energy source, and could conceivably allow much higher data rates for laser communication. This is one option that will be explored.
Coating the StarChip itself with PV would allow for high efficiency, and potentially gain several Watts just from the StarChip. These options open up a host of possibilities to greatly enhance functionality at the host star in the crucial data and imaging phases.
Research:
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Eiting, C. J., et. al. “Demonstration of a radiation resistant, high efficiency SiC betavoltaic,” Applied Physics Letters, Vol. 88 no. 6 (2006)
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Chandrashekhar, M. V. S., Thomas, C. I., Li, H., Spencer, M. G., and Lal, A. “Demonstration of a 4H SiC betavoltaic cell,” Applied Physics Letters, Vol. 88, no. 3, pp. 1351-1354 (2006)
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Huang, P. et. al. “On-chip and freestanding elastic carbon films for micro-supercapacitors,” Science, Vol. 351, no. 6274, pp. 691-695 (2016)
Apr 17, 2016 15:02
Malay Hirani
Posted on: Breakthrough Initiatives
Another option is Diamond betavoltaic cell, with Sr-90 and Pu-238 shows promising results v ~ 1-1.8v and with 7-10% conversion efficiency. Its also radiation hard and high thermal conductivity with chemical inertness.
Apr 17, 2016 15:40
Karen Pease
Posted on: Breakthrough Initiatives
How would betavoltaics make sense? Pu-238 is an alpha emitter. And Sr-90 is just a poor choice in general unless you're budget constrained - and given the tiny quantities of radioisotope such a craft would carry, their costs would clearly not be relevant.
7-10% efficiency isn't impressive. Might as well just stick with a thermocouple if your efficiency numbers are that low rather than go with something as technologically challenging as betavoltaics.
Apr 17, 2016 21:08
Gary Camp
Posted on: Breakthrough Initiatives
I was thinking of some possibility of combining systems to improve efficiency. For example, with solar cell coatings on the sail, use some of the laser light as S/C power as well as push.
Also, it seems the laser will provide considerable heat to the sail and there might be a way to do thermal couple generation. Deep space is really cold so this makes a very efficient conversion. Note that to keep weight down, the thermal couples must be made using integrated circuit assembly of (nearly) nano scale circuitry instead of current day arrays of 2 wires soldered together. JPL ACE
Apr 23, 2016 22:03
michael.million@sky.com
Posted on: Breakthrough Initiatives
Could we not use the ions in the interstellar medium as energy? If the sail is orientated edge on and the sails acts as a capacitor (+ one side and - the other) we could use the kinetic energy of the sails to power electronic devices on the sail as the ions interact with the capacitance. We could easily test this in a lab.
May 14, 2016 15:40
Mike Gorman
Posted on: Breakthrough Initiatives
re: microwaves
“Within a few years of the discovery of the CMBR, it was established … the specific intensity of the radiation is … 4 x 108 photons m-3, and an energy density … ~ 4 x 10-14 J m-3, which can also be expressed as a mass density … ~ 5 x 10-31 kg m-3, much less than the critical density required to close the Universe.”
http://ned.ipac.caltech.edu/level5/Birkinshaw/Birk1_1.html
Not if this would be enough to benefit the Star Chip with its potential 16 square metre sail collection area or not. Will likely be related to the power usage and battery requirements.
May 14, 2016 16:04
Mike Gorman
Posted on: Breakthrough Initiatives
As a very rough calculation it seems that the power that could be obtained when the probe reaches cruising speed would be, at most, on the order of a ten-thousandth (.0001) of a watt. Possibly useful as a trickle charge to keep the battery full during the long trip?
May 26, 2016 13:38
michael.million@sky.com
Posted on: Breakthrough Initiatives
Perhaps we could use an alpha emitter at the bottom of some nanotubes with a coil of conductive material somewhere along the length. The nanotube directs a lot of the postively charged particles through the coil which induces a current within the coil to power electronics directly instead of via thermal conversion which is not very efficient.
Jun 01, 2016 18:32
bala stark
Posted on: Breakthrough Initiatives
Considering the fact that supernova burst takes place every second in our galaxy and interstellar medium always have a rich amount of hydrogen so nano plasma reactors could be used so is there a concept of gravitational levitation, or else quantum teleportation can be used but we wil know the location and in the end we could warp space and it could make distance smaller l, but it Is very unlikely to be a success
Jun 04, 2016 12:58
michael.million@sky.com
Posted on: Centauri Dreams
Perhaps a coil that is etched into the surface of the sail itself could act as a power generator as it cuts through the interstellar medium of ions, this can be tested very easily in a small particle accelerator.
