OBJECTIVE
Long-duration space flight can have a profound effect on
functional performance as a result of exposure to the space environment. Water
landings add to the already impaired functional performance and present
significant safety issues to the crew that must be addressed. During a ground
landing, a lifetime of sensory experience of walking is used to re-adapt to the
novel gravitational environment when an astronaut returns. However, crewmembers
are exposed to involuntary, external movements on a moving platform with water
landings in an enclosed capsule. Thus the crewmembers are forced to re-adapt not
only to a novel gravitational environment but to do so in an environment that
challenges all aspects of the reafference scheme.
Landing motion sickness is experienced by 100% of returning
International Space Station (ISS) crewmembers and the severity increases with
wave motion and a closed visual environment. Safety issues that put crewmembers
at risk include risk of impaired control of the spacecraft and decreased
mobility due to vestibular and sensorimotor alterations associated with
spaceflight. These issues result from water landings in a completely enclosed
capsule causing loss of information on relative movement between the platform
and the orientation of Earth. All these issues are exacerbated by landing a
stable 2 capsule attitude upon splash down.
This study was conducted in two parts. In the first part, a
test environment was created by mounting an enclosure on a six
degree-of-freedom motion platform. Wave-motion profiles were created to move
the visual enclosure in conjunction with the floor thus replicating the visual
conditions within the floating capsule. Tasks that shared common movement
patterns with egress activities were developed and the time to complete these
tasks was used as a measure of performance. The goal of the second part was to identify
the optimal features of a device that visually presents gravitational reference
cues, in a capsule or aboard the recovery ship, for the purpose of aiding
stability and re-adaptation in returning astronauts.
The specific aims of this study were to:
- Enhance the existing capsule sensory-condition
simulator (used in the existing Omnibus) to include instrumented hand- holds, a compliant support surface and galvanic vestibular simulation (GVS)
- Develop and test multiple presentation methods
of an earth fixed visual reference.
APPROACH:
In the first part of this study, 32 subjects were recruited
through the NASA Test Subject Support Facility. The subjects passed a
NASA-modified Air Force Class III physical prior to enrollment in the study. These
subjects set the potential standards to determine the range of performance when
healthy individuals encounter wave motions without confounding post-flight
balance and disorientation. A payload configured as a portion of the interior
of an Orion capsule was mounted to MOOG 6-degrees of freedom motion base. The
payload platform included a flight-like couch and restraint system, an
Orion-style ladder used to access the upper exit lock, and a nonfunctional
packaged raft to stimulate that found within the Orion that is used for
emergency escape. Inertial sensors located on different body segments were worn
to ascertain the subject’s movements relative to the movement of the platform.
The Peripheral Vision Horizon Display (PVHD) or Malcolm Horizon (MH) provided a
projected gravity reference within the simulator. The subjects were made to
participate in a single data collection session, where the data was collected
during 4 trials, one for each of the 4 conditions. The first condition
consisted of performing three tasks without an active motion base.
The tasks
included:
1.
Rising from prone position
2.
Quiet stance with feet together for 30 seconds
3.
Starting from the standing position, moving to
the stowed ladder and deploying it
4.
Moving to the location of the raft from low to
high placement in the enclosure
5.
Returning the ladder back to the original
condition
6.
Returning the raft to the original condition
The second condition consisted of repeating the tasks
identified in condition 1 but with the motion base active at a low sea state.
Condition three involved the same tasks but with the motion base at a high sea
state. Condition four repeated three but included the Malcolm Horizon (MH),
again at a high sea state.
Dependent measures across all trials included:
a.
Time to completion for the variables in each
trial
b.
Head and lumbar angular acceleration
c.
Head and lumbar linear acceleration
The second part of this study was a hardware development
effort. Based off reports from the first phase regarding the helpfulness of an
earth-fixed horizontal line projected onto the walls during one of the
conditions, a study to determine the features of an effective visual aid was
proposed. Subjects participated in a single data collection session consisting
of eight 90-second trials; three control and five experimental conditions.
Eighteen subjects were recruited for the second part of this
study through the NASA Test Subject Support Facility. Subjects in the first
part of the investigation were destabilized by the wave motions but were easily
able to remain standing without support. They effectively used vestibular and
proprioceptive cues to make the necessary adjustments to stay upright. Subjects
in this part of the study stood on foam and were subjected to galvanic
vestibular stimulation (GVS), which posed significant threats to their
stability when coupled with the wave motion. A hand hold was placed inside the
simulator to mitigate the risk of falling. The handles were instrumented with
load cells to measure the amount of force imparted to them.
Projected visual references were compared using a repeated
measures design. Vertical and horizontal line projections were compared as were
the use of points of light instead of lines. The learning effects that
complicated the interpretation of the previously collected data were controlled
by both a balanced test order and the inclusion of a control condition
performed at the beginning and each of each test session.
RESULTS
In the first part of the study, completion time results were
analyzed from 30 out of 32 subjects. The results showed that the shortest
completion times occurred when the platform was not moving and the highest
values occur during the HIGH wave conditions. The results that showed that
subjects took a longer time to complete the tasks when they are destabilized by
movements of the support surface were expected. Subjective observations from
the test sessions revealed a wide range in both the degree to which subjects
were affected by the wave motion and the strategies they used to combat it.
Many subjects stumbled during the execution tasks but none fell. The subjects
were told not to seek support from the walls of the enclosure however several
were unable to avoid it. Some subjects supported themselves by grabbing onto
the deployed ladder. These differences were one source of variability in the
study.
Another source of variability had to do more with the tasks
themselves. Subjects were given the opportunity to practice the tasks until
they felt comfortable, however, manipulating the carbiner-like clips and cam
buckles to secure the nylon straps of the ladder proved to be problematic at
times.
After experiencing conditions in the first trial, subjects
were better equipped to use vestibular information during the second trial,
this resulted in improved stability. The learning effect observed from the data
collected during the quiet could also be attributed to a change in strategy between
the first and second exposure. Subjects that were unaware of the destabilizing
effects of the test conditions often adopted a casual quiet stance with toes
aligned parallel in the frontal plane and a more upright posture. Part way into
the trial, many subjects ended up changing their positions. During the second exposure
to the HIGH wave, the subjects adopted the more cautious and stable stance
immediately.
Results for the second part of the study showed that out of
18 subjects, 17 strongly believed that the presence of an earth fixed visual
reference was helpful. Out of the 16 subjects that were considered:
-
7 believed that the peripheral presentations
provided the greatest benefit.
-
5 preferred the Starfield configuration
-
4 liked the remaining frontal presentations
There were evenly mixed results when participants were
prompted for a preference between horizontal only line condition and horizontal
+ vertical line. Four out of seven participants thought that peripheral
presentation provided the greatest benefit. These participants also preferred
horizontal only line condition. The results also showed that the Starfield pattern provided
the greatest disparity in response. A total of 5 subjects thought it provided
the greatest benefit. A few subjects actively disliked it. Possible reasons for
this can be extracted by looking at individual subject responses in greater
detail.
The goal of this study was to identify the features to
consider in the next phase of countermeasure development. The subjective and
qualitative results both point to the conclusion that a peripheral display of a
horizontal-only line as the best option.
The Starfield pattern produced the most diverse reactions
from the participants. The subjects preferred the starfield pattern due to
their ability to see their silhouette. The subjects who disliked the starfield
pattern focused on what was happening in their periphery. This allowed two
considerations:
1. To incorporate an external source of feedback
about the subject’s performance into the next version of
the countermeasure system.
2. The need to better understand what it was about
the peripheral information that was problematic for some subjects.
Even with the complexities imposed by the geometrical
relationships, it should be possible for the brain to learn how to use an
earth-fixed reference projected onto a wall. Under motion parallax conditions,
objects in the foreground, between a a moving subject and a visual fixation,
appeared to move in the opposite directions as objects in the background on the
visual image.
In conclusion, the results presented from the study
indicated that presence of an earth-fixed visual reference can improve the
stability in the sensory conditions that astronauts will face when returning
from space by way of a capsule water landing. A synthesis of all the
information obtained in this investigation suggests that the best path forward
is the development of a subject-worn device that presents a horizontal line in
the periphery of the subject.
