Valle, Paul

NASA Technical Reports Server

The Active Response Gravity Offload System (ARGOS) is a technology development project at the 
NASA Johnson Space Center (JSC) that provides high fidelity reduced gravity simulation for human 
and robotic testing.  In development since 2007, ARGOS is a highly-dynamic human-rated robotic 
system, similar in appearance to an overhead gantry crane, that is capable of safely simulating any 
reduced gravity, including Lunar, Martian, and microgravity, over a test volume of over 340 m3. While 
capable of high speeds up to 3.3 m/s, the system is designed for safe human testing with two-fault 
tolerance, rapid fault detection, and fast activation of the fail-safe emergency stop system, making it an 
ideal candidate for safety-critical reduced gravity testing. The system, currently in its third iteration, is 
operated at the Johnson Space Center for reduced gravity testing of humanoid robots, robotic rovers, 
space suit performance, astronaut training, and human performance studies.
ARGOS is capable of highly dynamic motions in all three axes using high power electric motors and 
fast sensing.  At the same time, ARGOS is a high fidelity system that responds to very small inputs, 
enabling correct tracking of a variety of payloads in all reduced gravities.  The system operates by 
measuring the load on the lifting cable and attempting to simulate the desired reduced gravity.  As the 
payload induces a force up or down, the system simulates the motion in response, keeping the force 
error near zero and accelerating correctly.  Simultaneously, the horizontal system senses the lifting 
cable angle, detecting small induced motions from the payload.  The whole gantry then moves in the 
horizontal plane above the payload to maintain a vertical lifting force while also simulating Newtonian 
motion.
BACKGROUND
ARGOS was designed from the start for human testing, where the human needs to be kept safe by a 
fast-acting safety system.  As such, it is designed to be fully two fault tolerant with robust safety 
systems that can activate and safe the robot by applying brakes in the event of a fault.  The overall 
safety system philosophy of ARGOS is to stop and safe the robot as quickly as possible in the event of 
the detection of a fault, as procedures and a test team exist to re-start the test or remove the payload or 
test subject.  In addition, a device is used on the lifting cable to limit shock loads induced into the 
payload in the event of a high-speed stop.  ARGOS achieves its two fault tolerance using a variety of 
methods, including redundant sensors, a real-time safety model to predict the state of the system and 
monitor for undetected faults, and an independent overspeed detection system. In addition, extensive 
reviews and analysis of the system and its architecture were performed prior to deploying the system at 
NASA.
SAFETY SYSTEMS
ARGOS SPECIFICATIONS
Human Testing: Human testing in ARGOS supports a variety of objectives and programs, primarily 
in microgravity, Lunar gravity, and Martian gravity.  These include: Human performance testing and 
analysis, evaluation of new tools, space suit evaluation and analysis, astronaut training and evaluation, 
EVA procedure development, exploration and geologic evaluations, and human factors research.
Robotic Testing: Robotic testing in ARGOS has supported reduced gravity testing of non-human 
payloads in a variety of gravities.  The primary robotic payloads in ARGOS have been the Robonaut2 
(R2) humanoid robot, which uses ARGOS to practice microgravity walking and tasks, and the 
Resource Prospector (RP) Rover, which uses ARGOS to evaluate performance in a realistic Lunar 
gravity environment.  Additional testing has included a sample return microcapsule, the Simplified Aid 
for EVA Rescue (SAFER) unit, docking adapter assembly procedures, and vacuum cleaners.
TESTING AT NASA KEY CAPABILITIES
1. Simulates partial gravity and microgravity and can shift between gravities seamlessly
2. Realistic reduced gravity motion in all three axes, including constant velocity coasting
3. System is two fault tolerant and detects faults in less than 20 milliseconds
4. Simultaneously able to support high dynamics and high fidelity 
5. No water drag or limitations imposed by an underwater environment
6. The test team is co-located with the test subject or payload during the entire test
7. Virtual walls, floor, and ceiling in software to protect the payload and prevent falls
8. Virtual Reality (VR) can be integrated for a comprehensive simulation experience
9. Test article integration to pass telemetry or other data from the payload to ARGOS
10. Rapidly reconfigurable floor allows for quick changes between unique test setups
CURRENT AND FUTURE PLANS
As a technology development project, ARGOS is under continuous development at the NASA Johnson 
Space Center.  Currently, work is being done to continuously improve the performance of the system 
to ensure it meets current and future customer needs.  In addition, virtual reality is actively being 
integrated into ARGOS to enable training and human performance studies in a hybrid or virtual reality 
environment.  The first human performance study using virtual reality in ARGOS was recently 
completed in a Martian gravity simulation.
The ARGOS project is also seeking to extend this technology into the medical rehabilitation field, 
where its high fidelity reduced gravity offloading in all three degrees of freedom, along with its safety 
systems, could be highly beneficial for patients rehabilitating from lower limb injuries, spinal cord 
injuries, or strokes.  
CONTACT
Paul Valle, ARGOS Project Manager
Dynamic Systems Test Branch; Software, Robotics, and Simulation Division
NASA Johnson Space Center, Houston, Texas, USA
Email: paul.valle@nasa.gov
Phone: +1-281-244-5562
Software, Robotics, and Simulation Division, NASA Johnson Space Center
Paul Valle, ARGOS Project Manager
Reduced Gravity Testing of Robots (and Humans) Using the Active Response Gravity Offload System
Space Suit Evaluations Planetary Fall Recovery
Fire Extinguisher Evaluation
Planetary Shoveling
Asteroid Sample Collection
Asteroid Translation
Alpha Magnetic Spectrometer (AMS) Repair Training 
with Crewmember in Foot Restraint
Training using Hybrid Reality
GIMBAL MECHANISMS
A variety of payload interface gimbals, which are passive mechanisms offering 
one to three degrees of rotational freedom, have been developed at NASA to 
interface to human and robotic payloads.  The gimbals are adjustable to align 
the payload center of gravity (CG) with the gimbal, and the human gimbals are 
fully adjustable for the 1-99% subject.  All are designed to minimize mass and 
induced moments of inertia to minimize their effect on the payload.  Proper 
harnessing of the payload is crucial to a realistic test.  Incorrect CG alignment, a 
high inertia gimbal, or too few rotational degrees of freedom can all contribute 
to false data during the test, minimizing the benefits provided by the capabilities 
of ARGOS.  As such, one of the keys to successfully testing in ARGOS is to 
select or design the correct gimbal for the desired testing.
Human Performance Study in VR AMS Tool Evaluations AMS Repair Mission Evaluations
Robonaut2 Training RP Rover Lunar Testing Docking Adapter Installation Testing
Microgravity Gimbal
EMU Space Suit in ARGOS Active Response Gravity Offload System (ARGOS) at JSC
Robonaut2 in ARGOS
Vertical Offloading System:
Payload Capacity: 340 kg (750 lb)
Sensitivity: < 0.0005 kg
Maximum Speed (140 kg Payload): 3.3 m/s 
Maximum Speed (340 kg Payload): 1.4 m/s
Max Acceleration (140kg Payload): 24.4 m/s2
Max Acceleration (340kg Payload): 10.2 m/s2
Working Height: 5.5 m
Horizontal Tracking System:
Maximum Speed: 2.0 m/s
Max Acceleration: 6.1 m/s2
Sensitivity: < 0.1° of cable angle
Y Travel: 11.0 m
X Travel: 5.8 m
Treadmill Running
https://ntrs.nasa.gov/search.jsp?R=20170008856 2019-08-29T23:14:31+00:00Z


Reduced Gravity Testing of Robots (and Humans) Using the Active Response Gravity Offload System

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