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.
- Eiting, C. J., et. al. “Demonstration of a radiation resistant, high efficiency SiC betavoltaic,” Applied Physics Letters, Vol. 88 no. 6 (2006)
- 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)
- Huang, P. et. al. “On-chip and freestanding elastic carbon films for micro-supercapacitors,” Science, Vol. 351, no. 6274, pp. 691-695 (2016)
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