  CubeSats and small satellites are emerging as low-cost tools for performing
science and exploration in deep space. These new classes of satellite exploit
the latest advancement in miniaturization of electronics, power systems, and
communication technologies to promise reduced launch cost and development
cadence. JPL's MarCO CubeSats, part of the Mars Insight mission, will head on
an Earth escape trajectory to Mars in 2018 and serve as communication relays
for the Mars Insight Lander during Entry, Descent and Landing. Incremental
advancements to the MarCO CubeSats, particularly in propulsion and GNC, could
enable these spacecraft to get to another planet or to Near Earth Objects. This
can have substantial science return with the right science instrument. We have
developed an interplanetary CubeSat concept that includes onboard green
monopropellant propulsion system and that can get into a capture orbit around a
neighboring planet or chase a small-body. One such candidate is the Martian
moon Phobos. Because of the limits of current CubeSat hardware and lack of an
accurate ephemeris of Phobos, there will be a 2 to 5 km uncertainty in distance
between the spacecraft and Phobos. This presents a major GNC challenge when the
CubeSat first attempts to get into visual range of the moon. One solution to
this challenge is to develop optical navigation technology that enables the
CubeSat to take epicyclic orbits around the most probable location of the
target, autonomously search and home-in on the target body. In worst-case
scenarios, the technology would narrow down the uncertainty of the small-body
location and then use optical flow, a computer vision algorithm to track
movement of objects in the field of view. A dimly lit small-body can be
detected by the occlusion of one or more surrounding stars. Our studies present
preliminary simulations that support the concept.
