Flyby | Pointing camera at target planet
During an encounter with an exoplanet, the nanocraft’s camera would need to rotate in order to image the target. If the planet were imaged with a focal plane area, it would be necessary to hold the planet still within the image plane during the integration time for exposure.
If an object-to-nanocraft distance of 1 AU and a velocity of 0.2c are assumed, an angular rate of (6x107m/s) / (1.5x1011 m) ~ 80 arc sec/s is needed. The nanocraft would traverse a distance of 1 AU in about 2500 seconds. To stabilize the image, the camera would need to “slew” at this rate.
The slewing would be accomplished either by using the photon thrusters or via motion in the focal plane. For example, using a 4-meter-scale camera array at a distance of 1 AU would provide image resolution of order 40km, assuming visible spectrum imaging. The resolution scale could be improved by closer approaches of less than 1 AU. Extremely efficient image compression and smart feature detection algorithms would be crucial.
Another challenge is locating the planet inside the Alpha Centauri system. This would be achieved through the use of ‘star trackers’ based on the star’s ephemeris (orbital position at specific times) and the planet’s position relative to the star. The star would be very bright and the planet reasonably bright. Dead reckoning navigation is being considered that would be updated by measurements of the location of the star and planet. Image recognition software would be required to decide which target had the highest value, and it currently seems the most promising form of rudimentary artificial intelligence for this mission.
- Pilinski, E. B., and Lee, A. Y. "Pointing-Stability Performance of the Cassini Spacecraft," Journal of Spacecraft and Rockets, Vol. 46, No. 5, pp. 1007-1015 (2009)
- Legge, R. S., and Paulo, L. C. "Electrospray Propulsion Based on Emitters Microfabricated in Porous Metals," Journal of Propulsion and Power, Vol. 27, No. 2, pp. 485-495 (2011)
- Weis, L. and Peck, M. "Attitude Control for Chip Satellites using Multiple Electrodynamic Tethers," AIAA Guidance, Navigation, and Control Conference (2012)