ARC Angel: NASA's Innovative System Reduces Arm Fatigue in Sub‑1G Training

Johnson Space Center, Houston, TX

ARC ANGEL’s active control system can automatically offload the weight of various handheld tools, staving-off arm fatigue during sub-1G training. (Image: NASA)

Innovators at NASA Johnson Space Center (JSC) have developed an Earthbound robotic training system called “ARGOS” for short. It can actively simulate an astronaut’s weightlessness in space by using an overhead runway and bridge drive system to partially or fully offload their weight using attached cables, effectively suspending them off the ground. Although the test subject’s torso and legs are offloaded, their arms and any weighty hand tools are not.

The Actuated Realtime Control for ARGOS Negation of Gravitational Effects on the Limbs (ARC ANGEL) technology was developed to offload a space suited test subject’s arms and counteract fatigue realized while performing training activities using ARGOS. Like ARGOS, ARC ANGEL provides offloading via computer-controlled active cable tension. Cables are strung between arm cuffs located just above each elbow, and a motorized reel(s) mounted to the spacesuit’s backpack-like Primary Life Support System (PLSS).

This active offloading technology could be used for a number of applications in addition to simulating zero to one G environments. For example, a patient rehabilitating their shoulder could benefit from movement assistance that offloads arm weight or grasp load, a construction worker carrying a heavy tool could more easily manipulate it, or it could offset equipment weight for military personnel ultimately staving off limb fatigue that would otherwise occur.

ARC ANGEL is an active robotic system like ARGOS; however, its electric motor is not mounted overhead to a runway and bridge system but instead is mounted to the test subject’s backpack-like PLSS where the motor(s) supplies real-time actuation torque off-loading to the upper arms via cabling. If a test subject picks-up a hammer, the system will react immediately to offload the weight of the hammer relative to the programmed environment.

The system is comprised of an electric motor(s), soft goods, electronics hardware, firmware, and software. To provide a smoothly operating arm offloading analog and optimize system performance, engineers at JSC coded software that leverages kinematic algorithms and closed-loop architecture for motor control, along with custom computer language scripts to ingest sensor data. This allows ARC ANGEL’s subsystems to be seamlessly integrated and accurately simulate one to zero G environments.

During operation, compact tension sensors and inertial measurement units detect arm weight and motion and provide a closed-loop control system that feeds data to a single-board computer and requisite firmware for processing. A custom graphical user interface was also developed in-house to provide controls for inputting desired arm offload values.

Additionally, ARC ANGEL features its own power supply that provides power to its subcomponents without external cables. This allows the ability to function independently from ARGOS and further lends itself to potential terrestrial applications. This work directly correlates to active exosuit development that is being implemented for rehabilitation and/or assistive medical devices. ARC ANGEL is essentially providing a desired assistance (offload) while maintaining a subject’s full range of motion. The system hardware and software can be modified to custom-fit an individual without a spacesuit and toward limb-assisted movement — not just arm offloading.

NASA is actively seeking licensees to commercialize this technology. Please contact NASA’s Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here  .