Cowley, Matthew

Harvill, Lauren

Rajulu, Sudhakar

NASA Technical Reports Server

Human performance in simulated 
reduced gravity environments
Lauren Harvill1
Matthew Cowley2
Sudhakar Rajulu3
1 Lockheed Martin
2 Covidien (former Lockheed Martin)
3 NASA, Johnson Space Center
National Aeronautics and Space Administration
www.nasa.gov 
https://ntrs.nasa.gov/search.jsp?R=20150013830 2019-08-31T07:35:15+00:00Z
National Aeronautics and Space Administration Human performance in simulated reduced gravity environments 2
Background
• Design of space suits is a balance of many 
trade-offs including:
• Optimal human performance
• Cost
• Mass
• Complexity
• Prevention of injury
• Issues:
• - Need to understand human performance 
in non-earth gravity levels
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Background
• Design of space suits for planetary EVAs is based on limited knowledge of reduced gravity 
environments
• Lunar Missions observations
• Studies during the Apollo program
• Current reduced gravity analogs
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Background
• Microgravity simulators
• Lunar Landing Research Facility
• Manned Spacecraft Simulator
• Partial Gravity Simulator (POGO)
• Reduced Gravity Aircraft (C-9)
• Neutral Buoyancy Lab (NBL)
• Active Response Gravity Offload System (ARGOS)
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Wider shot of POGO
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Goals and Objectives
• Goal: Consolidate previous over-ground ambulation data from testing using NASA’s most recent 
gravity simulators
• Baseline over-ground at Earth gravity (9.8 m/s²)
• C-9 reduced gravity plane at lunar gravity (1.6 m/s²)
• Active Response Gravity Offload Simulator (ARGOS) at lunar gravity (1.6 m/s²)
• Objectives:
• Characterize lunar gravity ambulation
• Compare reduced gravity analogs
Human performance in simulated reduced gravity environments 5
National Aeronautics and Space Administration
Methodology – Testing Environments
C-9 Reduced Gravity Plane
• Inflight time is 2-3 hours consisting of about 50 
parabolas of predetermined gravity levels
• Small test window (30-40 seconds) of lunar to 
Martian gravity
• Equipment must be secured for landing loads 
of up to 9-g horizontal and 2-g vertical
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C-9 Flight Trajectory
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Methodology – Testing Environments
C-9 Reduced Gravity Plane
• Limited real estate for equipment storage and capture volume
• Cargo bay is approximately 14 m long, 2.5 m wide and 2 m high
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C-9 Plane Layout
National Aeronautics and Space Administration
Methodology – Testing Environments
C-9 Reduced Gravity Plane
• Subjects ambulated down fuselage at lunar gravity
• Four trials per subject of lunar unsuited ambulation, 
2-5 passes during each parabola
• Self-prescribed walking speed (0.34-1.22 m/s)
• Average 0.81 ± 0.20 m/s
• Custom-built force plate designed to be flush with 
floor padding
• ~ 1 m in length
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Length of force plate
National Aeronautics and Space Administration
Methodology – Testing Environments
• Active Response Gravity Offload System (ARGOS)
- Steel frame 12.5 m x 7.3 m x 7.6 m tall
- Computer driven electric motors and in-line 
sensors
- Maintains a constant offload force while the 
subject moves in all directions
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Methodology – Testing Environments
• Active Response Gravity Offload System
- Elevated ramp with six flush-mounted AMTI force plates
- Overall platform 15 m in length
- Over-ground ambulation
- Earth gravity
- Lunar gravity with gimbal
- Ambulation speed set to 0.85 ± 0.05 m/s
- Repeated trial until achieved desired speed
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Km/h to m/s
National Aeronautics and Space Administration
Methodology – Subjects 
Human performance in simulated reduced gravity environments 11
C-9 (IST-X) (n = 6) Height (cm) Body Mass (kg) Age (years)
Average 181.4 78.8 45
Std. Dev. 6.8 11.2 4
Max 189.2 97.5 52
Min 175.3 67.1 41
Earth and  ARGOS 
(n = 9)
Height (cm) Body Mass (kg) Age (years)
Average 178.1 79.5 38
Std. Dev. 10.3 15.7 9.3
Max 190.5 106.8 54
Min 160 57 26
National Aeronautics and Space Administration
Methodology
• Custom Vicon BodyBuilder model and MATLAB processing code
• Collected variables
• Torso, hip, knee, and ankle joint angles
• Normalized ground reaction forces
• Gait kinematics
• Stance Time, Stride Length, Step Width, Cadence
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National Aeronautics and Space Administration
Results
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Earth Lunar - C9 Lunar - ARGOS
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Results
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Results
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Results
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Results
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Earth Lunar - C9 Lunar - ARGOS
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Results
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Hip Flexion/Extension (deg)
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Gait Cyle (%)
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Knee Flexion/Extension (deg)
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Ankle Dorsi/Plantar Flexion (deg)
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National Aeronautics and Space Administration
Results
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Torso Relative to Ground (deg)
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Discussion
• Lunar gravity analogs:
• Variation increased, both between subjects and within
• Greatest variation seen in C-9 data
• Increased swing time
• Various styles of gait adapted when learning to ambulate in a new gravity environment
• ARGOS more closely resembled Earth gravity ambulation than on the C-9 reduced gravity plane
Human performance in simulated reduced gravity environments 20
National Aeronautics and Space Administration
Limitations
• Preconceived idea of lunar ambulation style
• No one has experienced true lunar gravity since the Apollo era
• Subjects with varying levels of experience on gravity simulators
• Limited walkway length for C-9 trials
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Summary
• The C-9 is considered the gold-standard for gravity analogs
• There is a need to maintain integrity of conclusions from studies while also reducing costs
• There are different challenges with each analog
• ARGOS: subject limited by a gimbal
• C-9: minimal time to complete tasks, costly, small test volume
• Need to further benchmark the differences between the ARGOS system (and other analogs) 
and the C-9 reduced gravity plane
Human performance in simulated reduced gravity environments 22
National Aeronautics and Space Administration
Contact Information
Sudhakar Rajulu, PhD
Anthropometry and Biomechanics Facility
NASA, JSC
Sudhakar.Rajulu-1@nasa.gov
Lauren Harvill
Anthropometry and Biomechanics Facility
Lockheed Martin
Lauren.Harvill@nasa.gov
Human performance in simulated reduced gravity environments 23
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National Aeronautics and Space Administration Your Title Here 24


Human Performance in Simulated Reduced Gravity Environments

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