ASTROBATICS: Demonstrating Propellantless Robotic Maneuvering Onboard the International Space Station [video]

Abstract

Spacecraft equipped with robotic arms can fulfill a wide variety of space missions. For example, robotic spacecraft can service other vehicles, assemble large space structures, remove orbital debris, or even help astronaut crews with their tasks. In these missions, the servicing spacecraft needs to move on the surface of another space vehicle or structure in order to complete its missions. Two distinct approaches have been previously proposed to solve this mobility problem: a) propulsive free-flying b) zero-g climbing. In a propulsive free-flying approach, the servicing spacecraft uses its limited supply of propellant to free-fly from one location to another, whereas in a zero-g climbing approach the spacecraft uses its robotic arms to grasp onto the target vehicle or structure and traverse between locations.

The NPS Spacecraft Robotics Laboratory is proposing an alternative mobility approach: hopping. In a hopping approach the servicing spacecraft uses its robotic arm to "jump" between two locations. The servicing spacecraft first uses its robotic arm to push itself off the target vehicle or structure, then, it performs a brief free-flying coast, and finally, it uses its robotic arm to soft-land on the target spacecraft or structure. The hopping mobility approach has the potential to be propellantless and it is simpler and potentially faster than zero-g climbing, which requires a long and time-consuming sequence of moves.

Basic hopping maneuvers have already been demonstrated at the NPS POSEIDYN planar air bearing test bed. In this test bed, air bearings are used to provide a frictionless interface between the test vehicles and a smooth and horizontally leveled granite table. The test vehicles thus experience a weightless environment on the table plane, allowing to test spacecraft maneuvers on a dynamically representative environment. The demonstrations on the POSEIDYN test bed are inherently limited to a planar environment and the logical next step is to demonstrate hopping maneuvers in a six degree-of-freedom environment.

In a partnership with NASA the NPS Spacecraft Robotics Laboratory is preparing a hopping maneuver demonstration onboard the International Space Station (ISS) using the Astrobee free-flyer platform. Scheduled for launch later this year, Astrobee is an assistive free-flyer with a propulsion system that allows it to autonomously fly inside the ISS. Additionally, Astrobee is equipped with a robotic arm that it can use to perch itself to the many handrails scattered throughout the ISS. The hopping maneuver demonstration will use the perching arm to push Astrobee off a handrail. The push maneuver will propel Astrobee in a specific direction and with a particular rotational state which after a brief coast period will place Astrobee in a position to capture another handrail. Astrobee will then use its perching arm to capture this handrail and complete the hop.