Testbed for Studying the Capture of a Small, Free-Flying Asteroid in Space

A scaled deployable device has been built and tested for the purpose of evaluating the feasibility of capturing an entire small asteroid in free space. The target asteroid was presumed to have a mass <1000 metric tons, with a longest dimension of <13 meters. It could be spinning and tumbling. It could be a "rubble pile" – a collection of loosely-bound particles whose cohesion is barely more than the minimum required by the hoop strength defined by the spin rate. It was decided that the only way to confine a rubble pile was to put it in a bag – a fabric or membrane enclosure which completely encapsulated the asteroid, preventing contamination of the solar arrays, radiators, and other optical surfaces of the spacecraft. Clearly this bag had to be deployed, since the largest dimension of the asteroid is significantly larger than the launch shroud of any present launch vehicle. It was decided that a hardware-in-the-loop testbed would be needed, since the physics of physical contact between the asteroid and the deployed capture bag is too complex to credibly model entirely within computer simulation. This testbed was built at 1/5 th -scale for a capture bag assumed 15 meters in diameter (the largest dimension of the asteroid plus a meter on either side). The asteroid mockup was mounted on a robotic arm and force-torque sensors were used to measure the interactions between the spacecraft and the asteroid through the soft material of the capture system. The force-torque measurements were fed into a zero-g simulation of the spacecraft and asteroid, which in turn prescribed the motion of the asteroid relative to the spacecraft. This paper describes the construction and operation of the testbed, including the selection of the bag materials, the configuration of the capture mechanism, the actuators required to deploy, control, and retract the bag, the hardware-in-the-loop simulation and the sensors used to drive it, as well as results from the system.