Meet Selene: Conceptualizing our Robot



In order to better facilitate movement and incorporate all of the rover's features, Selene's body will be rectangular in shape. The height will be 1.07 meters, with approximately 0.5 meter of clearance from the ground. Using the weight and dimensions of the Mars rover Sojourner [6] as a guide, Selene will weigh approximately 87.5 kg on Earth and 14.5 kg on the moon. Selene will have six wheels, in order to increase stability. All six of these wheels will be made out of aluminum due to its strength, light weight, and availability. For additional traction, the wheels will have cleats and treads created from stainless steel. The wheels will have a 0.30 meter diameter. In case of excessive wear or other failure, the back wheels will have a set of identical backup wheels. These will be kept inside the main frame, and will rotate with the other wheels if the need arises. In order to give Selene greater stability to maneuver the rocky surface of the moon, a rocker-bogie suspension system will be used. This system uses rotating joints that all connect from the wheels to one central point at the chassis [7]. The chassis itself will be molded from carbon fiber reinforced plastic.

Ready, Set, Go: Powering Selene

Once Selene is fully functional, she will embark on her long journey to the moon. Upon arrival, Selene will land in the Sea of Tranquility. This spot is relatively smooth and level, making it an ideal place for the rover to start its exploration. The Sea of Tranquility is also the same site where the Apollo 11 mission landed; therefore, the area is fairly well known and well documented [9]. Furthermore, the Sea of Tranquility is located on the side of the moon that will be closest to Earth when Selene lands, making communication with Earth easier. The rover will not be landing until noon on a lunar day, giving it time to travel a little distance before going into standby for the night. When examining the challenge of powering the rover, Selene will use a combination of both solar panels and battery to successfully fuel her endeavors. Solar panels were selected due to their reliability and low weight. In addition to this source of energy, certain precautions must be taken to keep them working at a decent rate. To keep them protected, the solar panels will be placed under glass. Also, a liner- made of a varnish like material- will be used, because if too much dust is collected, it could possibly decrease the amount of energy absorbed. This method has been used with past rovers and has been found to be efficient. Ideally, solar concentrators will also be included as well because they focus the light and usually increase the amount of power collected by 5%. Solar panels are an ideal source of energy for this particular mission since the mission' longevity does not exceed more than a few weeks. The amount of power utilized from the power collected by the solar panels usually ranges from 30%-35% [10]. These solar panels, positioned like wings, also rotate according to the position of the sun- using light sensors- to ensure the amount of power being collected by the cells.
We considered several options for powering the rover. The possibility of a generator was mentioned, but the idea was vetoed because the goal was to have a light weight and relatively inexpensive rover. Besides using solar panels, the other source of power for the mission, will be a battery used during the day and powered by sunlight. During the night, the battery will be expected to fulfill power needs. The battery itself will be a lithium battery, chosen for its lesser weight. Since the rover will be relatively small and compact, other possible larger batteries would only weigh the rover down in motion and capacity. Instead, the lithium batteries are comparably lighter and have a higher voltage than their competitors [10]. Selene's lithium battery may have a shorter lifespan than alternative batteries; however, she will not be in need of one that lasts more than a few weeks. Due to a combination of weight limits and usability, the solar panels and lithium battery were chosen as fitting energy sources.