In designing any type of vehicle for space exploration, engineers must thoroughly address the effects of unforeseeable events and accidents on the well-being of the human crew, as well as the overall success of the intended mission. One of the most hazardous events encountered is space is a collision. In June 1997, Russian space module Mir collided with space freighter Progress 234 due to an error made during the manual docking procedure by one of the crews’ astronauts. As a result, control of the Progress 234 was lost and imminent collision with the Mir space module became inevitable. Following impact with Mir, Progress 234 lost all vital communication and life support systems, placing the crew and their craft in a grave situation. From this one example, it is clear that the development of autonomous navigation and control systems will become an integral part of both manned and unmanned missions in outer space. Aside from the possibility of loss of human life - the energy, resources, and capital necessary for orbital repair of spacecraft place a large economic burden on an already under-funded branch of the scientific community.

     Collisions in space need not necessarily involve docking spacecraft, as was the case with the Mir – Progress 234 incident. According to current NASA estimates, the region of space local to Planet Earth is home to more than three million separate pieces of space debris of varying physical size and shape. Although most are not as massive as the typical space module, collision with these smaller, orbiting bodies can prove to be just as dangerous to both mission longevity and the human crew. Small object collisions (SOC) can result in the breach of an orbiting spacecraft’s hull, resulting in the loss of gaseous oxygen – necessary not only to sustain life in space, but also to ensure the structural integrity of pressurized craft. This type of problem has been encountered as recently as December of 2003, when a Russian astronaut reported the sound of a slow gas leakage aboard the International Space Station (ISS). Although slow venting of oxygen into space is not an immediate problem, it can develop into a serious situation if left uncorrected. Loss of hull pressurization can cause dysbarism and suffocation in the human crew, as well a gradual loss of structural rigidity in the parent craft. To further complicate matters, leak detection and repair in the vacuum of space has proven to be extremely difficult. Many currently available sensors are unable to detect the diffusion of gas molecules in the space environment, and due to the materials used in construction of spacecraft, location of leaks using acoustic phenomena must be ruled out. As a result, the only viable option available to combat the leakage is to evacuate and lock down the compartment were the breach is thought to exist – reducing the overall functionality of the spacecraft. The design of an innovative, autonomous detection/repair robot, however, offers a more practical, long-term solution to this serious problem.

     NASA currently has in development a series of external, autonomous detecting robots collectively known as the Autonomous Extravehicular Robotics Camera (AERCam) project. The AERCam has capability of performing remote inspection and viewing missions in support of ISS operations. This microsatellite-class free-flyer orbits about a given spacecraft, performing inspection and sensing of the target, while remaining available for astronaut support missions during extravehicular activities (EVAs). The Mini AERCam vehicle is designed for either remotely piloted operations or supervised autonomous operations including automatic station keeping and point-to-point maneuvering. This type of technology is especially exciting for the future development of fully autonomous, external sensing robots. A small freeflyer, such as a microsatellite, provides a propellant efficient base system upon which further instrumentation can be added to allow for fully autonomous, spacecraft-centric mission capability. In addition to the issue of SOC induced oxygen outgassing, detection and repair of spacecraft heat shield components is of primary concern. The recent loss of the Space Shuttle Columbia emphasizes the importance of mid-mission capability for heat shield maintenance and repair. According to NASA documentation, debris-damaged tiles have been found on every space shuttle following post-reentry ground inspection. Although the orbiter is thoroughly inspected prior to and following each mission, the possibility of in flight repairs and/or rebuilding of the heat shielding has yet to be addressed – posing a significant possibility for total loss of crew and vehicle due to failure of the thermal protection system following post-launch or mid-mission damage.

     The in flight inspection of tiles for significant damage is an important topic that must be addressed. Traditionally, the role of superficial tile assessment has been deferred to astronaut EVA missions – manually performed with the aid of robotic arms. These current methods of heat shield appraisal do not necessarily allow the detection and repair of impending tile failure – rather focus more on localized, clearly defined areas of damage. Furthermore, this type of inspection is a tedious and time-consuming mission for human crews, aside from the additional risks involved with extended period EVA maneuvers. An autonomous robot capable of continuous, external inspection of the spacecraft’s hull will free the human crew to devote all available resources to accomplishing the goals of the particular mission. In addition, with the aid of a continuously operating probe, it will be possible to survey and report the status of the spacecraft’s hull from the point of orbital insertion, up until final maneuvers are performed for atmospheric reentry. With this type of information, ground-based control personnel and the astronauts themselves will able to make more informed decisions regarding the worthiness of the craft – including preparing for premature abortion of the mission or extending mission flight times to allow for necessary repairs. In the case of extensive damage to the spacecraft, inspection robots would be able to assist astronauts in locating and repairing sections most crucial to maintaining the structural integrity of the craft.