Up to 90% of crewmembers experience spatial disorientation during reentry and landing of the orbiter, with prevalence proportional to the length of the mission. This is a critical issue, as orbiter landing data shows a decrement in performance following microgravity exposure compared to simulated landings in the Vertical Motion Simulator (VMS) at NASA Ames and the NASA Shuttle Training Aircraft. Despite the potential impact on landing operations, the basis of microgravity-related spatial disorientation is poorly understood. The primary aims of this proposal were to:
1) obtain basic data on the characteristics of head and eye movements during simulated orbiter landings,
2) and develop a ground-based analog of the effects of microgravity exposure on pilot performance after spaceflight.
Fulfillment of the project aims was carried out in four phases.
Phase I: Measurement of head and eye movement during vehicle operation
We developed a laptop-based system which simultaneously measures 6 degree-of-freedom (6DOF - triaxial angular rate and triaxial linear acceleration) head movement (using Inertial measurement Units, IMUs), 3D eye movement (yaw, pitch and roll), and 6 DOF motion of a vehicle (or simulator cabin, using an IMU), published as:
MacDougall HG, Moore ST (2005) Functional assessment of head-eye coordination during vehicle operation. Optom Vis Sci 82: 706-715.
Phase II: Head-eye coordination during simulated shuttle landings
We obtained head and eye movement data from six pilots during simulated shuttle landings in an Airbus A340 level-D flight simulator at the Airbus flight training centre in Toulouse, France. In addition, head and eye movements were obtained from a NASA test pilot performing a shuttle landing in the VMS at NASA Ames. Results: during the HAC maneuver (where the shuttle banks around a virtual cylinder to align with the runway) the head and eyes rolled towards the visual horizon with a combined gain of 0.14 of bank angle. Pilots alternated fixation between the instruments and the runway during final approach, almost exclusively focusing on the runway after preflare. Optokinetic nystagmus was observed during rollout. During final approach a Heads-Up Display (HUD) reduced pitch head and eye movement. Conclusions: roll tilt of the head and eyes during the HAC tended to align the retina with the visual horizon. Overlaying critical flight information and the approaching runway with the HUD reduced pitch head and eye movement during orbiter final approach in the VMS relative to the A340 (no HUD installed). Published as:
Moore ST, MacDougall HG, Lesceu X, Speyer JJ, Wuyts F, Clark JB (2008) Head-eye coordination during simulated orbiter landing. Aviat Space Environ Med 79: 888-898.
Phase III: Development of ground-based analog of spatial disorientation after spaceflight In the initial project description we proposed using long-term (60 min) 3 Gx centrifugation (3-g linear acceleration applied along the naso-occipital axis) to replicate the sensorimotor effects of microgravity exposure, as developed by a Dutch group at TNO. Although centrifuged subjects exhibited sensorimotor effects consistent with those observed post-flight the effects were short-lived (<60 min) and often accompanied by motion sickness; 40% of veteran astronauts tested experienced nausea and vomiting following 1-hr of 3-Gx centrifugation (Nooij et al. 2004). The logistical complexity of hyper-g centrifugation and the high incidence of motion sickness limited its value as an analog of post-flight sensorimotor deficits. We therefore developed a novel system utilizing electrical stimulation of the vestibular nerve (Galvanic vestibular stimulation - GVS) to replicate the effects of spaceflight on neurological function. The current waveform used in our GVS analog, a pseudorandom sum of sines, was devised such that sensorimotor performance of normal subjects exposed to acute GVS replicated post-landing data from shuttle and International Space Station (ISS) astronauts, namely postural sway, locomotor impairment and decrements in dynamic visual acuity. Subjective validation was provided by seven veteran astronauts (5 shuttle, 1 ISS, 1 Skylab), who reported that the motor effects and illusory sensations of movement generated by the GVS analog were remarkably similar to their post-landing experience. Published as:
MacDougall H, Moore ST, Curthoys IS, Black FO (2006) Modeling postural instability with Galvanic vestibular stimulation. Exp Brain Res 172: 208-220.
Moore ST, MacDougall H, Peters BT, Bloomberg JJ, Curthoys IS, Cohen H (2006) Modeling locomotor dysfunction following spaceflight with Galvanic vestibular stimulation. Exp Brain Res 174: 647-659.
NSBRI (2006) Galvanic Vestibular Stimulation Countermeasure Demonstrated to Astronauts. In: NSBRI Explorer, July 2006.
Phase IV: Validation of GVS as an analog of post-flight spatial disorientation
The aim of this study was to validate an analog of the sensorimotor effects of microgravity, utilizing pseudorandom bilateral bipolar Galvanic vestibular stimulation (GVS), during shuttle landing simulations. Pilot (N=11) performance was assessed during simulated shuttle landings in the Vertical Motion Simulator at NASA Ames (used for shuttle pilot training). Subjects performed 8 pairs of identical landing profiles (final approach and touchdown) with and without GVS, presented in a pseudorandom order. Target touchdown speed was on target (204 kts) without GVS but increased significantly (P=0.02) during GVS exposure and was at the upper limit (209 kts) of the target range. Unsuccessful (crash) landings increased from 2.3% without GVS to 9% with GVS. Hard landings, with touchdown speed in the 'red' (unacceptable) range (>214 kts), almost doubled from 15.9% without GVS to 30.7% with GVS. GVS was an effective analog of decrements in post-flight shuttle pilot performance. The ability of GVS to replicate a wide range of post-flight sensorimotor deficits (postural, locomotor, oculomotor, fine motor) supports the hypothesis that central changes in processing of low-frequency otolith input underlie space adaptation syndrome. Submitted for publication:
Moore ST, Dilda V, MacDougall HG (2010) Galvanic vestibular stimulation as an analog of spatial disorientation after spaceflight. Exp Brain Res, in review.
1) We have developed and validated a portable laptop-based system for evaluation of visuo-motor function during complex operational tasks, such as landing the orbiter.
2) We have developed an ambulatory, reversible, ground-based analog (GVS) capable of accurately replicating the sensorimotor (postural, locomotor, oculomotor and fine-motor) effects of spaceflight, suitable for astronaut training.
3) We have validated the GVS analog in an operational setting (VMS shuttle landings).