Human Research Program Human Health Countermeasures Element Evidence Report Artificial Gravity Version 6.0 12 May 2015 National Aeronautics and Space Administration Lyndon B. Johnson Space Center Houston, Texas 77058 Artificial Gravity AUTHORS: Gilles Clément, PhD With contributions from: John B. Charles, PhD Peter Norsk, MD William H. Paloski, PhD 2 Artificial Gravity Table of Contents I. ARTIFICIAL GRAVITY FOR PROTECTION OF HUMAN HEALTH DURING LONG-DURATION SPACEFLIGHT ........................................................ 5 II. EXECUTIVE SUMMARY .......................................................................................... 5 III. INTRODUCTION ........................................................................................................ 6 A. Why Artificial Gravity? ............................................................................................... 6 B. Principle of Artificial Gravity ...................................................................................... 8 1. Definitions ................................................................................................................ 8 2. Gravity Level ........................................................................................................... 9 3. Gravity Gradient ....................................................................................................... 10 4. Coriolis Force ........................................................................................................... 11 5. Cross-Coupled Angular Acceleration ...................................................................... 12 IV. SPACEFLIGHT EVIDENCE ...................................................................................... 13 A. Summary of Existing Animal Flight Data ................................................................... 13 1. Artificial Gravity Animal Research prior to ISS Utilization ................................... 13 2. Science Plans for Rodent Research on board the ISS .............................................. 14 3. Benefits of Artificial Gravity Animal Research for Human Health Protection ....... 16 B. Summary of Existing Human Flight Data .................................................................... 17 1. Anecdotal Observations ........................................................................................... 17 a. Gemini ................................................................................................................. 17 b. Skylab ................................................................................................................. 18 c. Apollo ................................................................................................................. 18 d. Soyuz .................................................................................................................. 18 e. Shuttle ................................................................................................................. 19 f. International Space Station .................................................................................. 19 2. Vestibular Experiments using Centrifugation or Linear Acceleration in Orbit ....... 21 a. Motion Sickness .................................................................................................. 21 b. Threshold for Perception of Linear Acceleration ................................................ 22 c. Perception of Tilt during Linear Acceleration ..................................................... 23 3. Vestibular Experiments in Parabolic Flight ............................................................. 25 4. Loading in Space....................................................................................................... 26 a. Penguin Suit ........................................................................................................ 26 b. Subject Loading ................................................................................................... 27 c. Lower Body Negative Pressure ........................................................................... 27 V. GROUND-BASED EVIDENCE ................................................................................. 31 A. Animal Studies ............................................................................................................. 31 1. Hind Limb Suspension ............................................................................................. 31 2. Centrifugation .......................................................................................................... 33 B. Human Studies ............................................................................................................. 37 1. Long-Radius Centrifuges ......................................................................................... 37 2. Short-Radius Centrifuges – Continuous Exposure ................................................. 39 3 Artificial Gravity 3. Short-Radius Centrifuges – Intermittent Exposure .................................................. 42 a. Rationale .............................................................................................................. 42 b. Centrifugation during Bed Rest Studies .............................................................. 46 Orthostatic Tolerance Time ................................................................................ 46 Blood Volume ..................................................................................................... 47 Exercise Capacity ............................................................................................... 49 Muscle & Bone ................................................................................................... 50 Sensorimotor Performance ................................................................................. 51 Integrative Physiology ........................................................................................ 52 4. Human Powered Short-Radius Centrifuges ............................................................. 53 5. Partial Gravity Simulators ........................................................................................ 55 6. Models ...................................................................................................................... 56 VI. GAPS ............................................................................................................................ 59 A. Gravity Level ............................................................................................................... 59 B. Gravity Gradient ........................................................................................................... 60 C. Rotation Rate ................................................................................................................ 61 D. Exposure Duration & Frequency ................................................................................. 61 E. Centrifugation Combined with Exercise ...................................................................... 62 VII. CONCLUSIONS .......................................................................................................... 63 A. Physiological Requirements ......................................................................................... 63 B. Tests Needed to Close the Gaps ................................................................................... 63 C. Recommendations for Performing these Tests ............................................................ 65 VIII. REFERENCES.............................................................................................................. 66 IX. LIST OF ACRONYMS ................................................................................................ 81 4 Artificial Gravity I. ARTIFICIAL GRAVITY FOR PROTECTION OF HUMAN HEALTH DURING LONG-DURATION SPACEFLIGHT The most serious risks of long-duration flight involve radiation, behavioral stresses, and physiological deconditioning. Artificial gravity (AG), by substituting for the missing gravitational cues and loading in space, has the potential to mitigate the last of these risks by preventing the adaptive responses from occurring. The rotation of a Mars-bound spacecraft or an embarked human centrifuge offers significant promise as an effective, efficient multi-system countermeasure against the physiological deconditioning associated with prolonged weightlessness. Virtually all of the identified risks associated with bone loss, muscle weakening, cardiovascular deconditioning, and sensorimotor disturbances might be alleviated by the appropriate application of AG. However, experience with AG in space has been limited and a human-rated centrifuge is currently not available on board the ISS. A complete R&D program aimed at determining the requirements for gravity level, gravity gradient, rotation rate, frequency, and duration of AG exposure is warranted before making a decision for implementing AG in a human spacecraft. II. EXECUTIVE SUMMARY The urgency for exploration-class countermeasures is compounded by the limited availability of flight resources for performing the validation of a large number of system-specific countermeasure approaches. The notion of creating a substitute for gravity was introduced early in the conception of human space travel. The surest AG solution is clearly one that produces a gravitational environment close to that on Earth.