There were four primary projects in this study:
Head (and Neck) injury Risk Module (HIRM):
The possibility of head and neck injury in space is a concern due to the negative impact it could have on a mission. The HIRM is a statistical simulation tool that attempts to quantify the probability of head and neck injuries for particular activities or events during space exploration missions. The tool also seeks to distinguish between soft and hard tissue modalities.
Abdominal Injury Module (AIM) :
The possibility of abdominal injury in space is a concern due to the negative impact it could have on a mission. The AIM is a statistical simulation tool that attempts to quantify the probability of abdominal injuries for particular activities or events during space exploration missions. The tool distinguishes injuries on clinical severity levels and between solid and hollow organs.
Bayesian medical event predictions (BMEP):
Several medical conditions have clear earth analogs, but the rate of the occurrence in the astronaut population during space travel is not well understood due limited occurrences. Using numerical Bayesian techniques, the NASA GRC developed a series of analyses to provide the IMM with the mean likelihood and estimated uncertainty of the occurrences specific medical conditions that are prominent in the general population and may appear in a specific individual during the time frame of a space mission (weeks to years). These include, glaucoma (closed angle), stroke, seizure, and other similar conditions identified by the IMM team.
Bone Fracture Risk Model (BFxRM):
The BFxRM mathematically models the probability of bone fracture during specific astronaut activities during space exploration missions. Investigators focused on events that represent severe consequences for an exploration mission, specifically that of spinal fracture resulting from a routine task (lifting a heavy object up to 60 kg), or a spinal, femoral or wrist fracture due to an accidental fall or an intentional jump from 1-2m. They validated the biomechanical and bone fracture models against 18 terrestrial studies of ground reaction forces, skeletal loading, fracture risk, and fracture incidence. After validation in a terrestrial setting, investigators predicted fracture risk associated with reference missions to the moon and Mars that represented crew activities on the surface. The model was extended to address fracture likelihood for six-month ISS missions.
Generally, femoral neck fracture probability due to a fall to the side during an extra vehicular activity (EVA) is very low even during a long-duration Mars mission, possibly due to the effective use of spacesuit padding. The static lift model represents an astronaut slowly picking up or holding a heavy object (up to 60 kg, mean 20 kg) on Mars or the moon. The estimated probability of spinal fracture during an Intra-Vehicular Activity (IVA) in this scenario is similarly low, even at the most punishing flexion angle. However, the added weight and compromised bone integrity during an EVA on a Mars long-duration mission leads to a mean fracture probability of slightly less than 1%. Considering the disastrous consequences to the crew and the mission, this scenario warrants further consideration. The natural response to a fall or other perceived impact is to extend a hand to absorb some of the impact. This kind of active response by the astronaut could protect the hip, but lead to a wrist fracture, which investigators found to be the most likely type of fracture. While this type of injury is unlikely to be fatal, it can cause great discomfort and jeopardize mission success. The 95th percentile for Mars missions ranges from 5-8%, which is not insignificant. Gender-specific differences in mean wrist fracture probability are greater than that for fracture of the hip or lumbar spine.
After modification of the BFxRM to utilize loading and statistical event data related to ISS injury modalities, a series of simulations were performed to assess likelihood of wrist fracture during a six-month increment were performed. The results show that the mean likelihood is three orders of magnitude below that estimated for planetary missions and the 95th-percentile is not significantly different than the mean.
Of the model parameters related to EVA scenarios the force attenuation characteristic of the astronaut EVA suit represented a large epistemic uncertainty. This finding led to the follow on Suit Impact load Attenuation Study (SILAS), an investigation to quantify the base level of fracture protection that the EVA suit provides the astronaut. The data collected in this analog was used to inform the BFxRM, reducing the uncertainty when predicting the probability of fracture for a fall to the side impact event in lunar and Martian gravity.
For all suit pressures, the attenuation increased as the offset increased and varied over a range of 51 – 94%, 29 – 96% and 17 – 89% for the 5, 10 and 15 cm drop heights, respectively. The largest variation in attenuation occurred at offset values between 0.1 – 1.5 cm, where the mean attenuation values for these offsets were 69 ± 15%, 49 ± 22% and 35 ± 18%, for mean impact reference forces of 4827, 6400 and 8467 N, respectively. The mean attenuation values for offset values of 2.8 – 5.3 cm were 93 ± 2%, 94 ± 1% and 84 ± 5% for the same mean impact reference forces.
The reduction in uncertainty in the BFxRM comes about because a higher fidelity model was created using the SILAS data. When only considering a suit operating pressure of 33 kPa, since it is the current operating pressure of the ISS EMU suit and the estimated operating pressure of the new lunar and Martian EVA suits, the mean attenuation value found in the SILAS study was 72 ± 27%, across all offset and loading values. This is comparable to the hip protector attenuation value of 73 ± 17.5% used in the first version of the BFxRM. However, instead of using a single, broad attenuation distribution, the SILAS data allowed the attenuation to be modeled as a function of impact loading during the fall and the size of the gap between the suit and the thigh. The confidence interval of the distribution used to describe the attenuation value was much smaller once it was focused using offset and loading values that were representative of the EVA conditions.
Foundational Assessment of Renal Stones in Space (FARiS):
Given that astronauts could experience stone promoting urine chemistry, potentially exacerbated by hypogravity exposure, there is the possibility that astronauts will develop clinically significant renal stones in flight. However, with the exception of terrestrial experience and anecdotal flight evidence, there is little capability to estimate the true likelihood of stone formation in space. This investigation seeks to develop a model of the urinary system which allows the incorporation of a variety of physiological and possibly hereditary factors into the calculation of risk of stone formation and to use this model to estimate the effect of water intake on the probability of renal stones in the astronaut population. Currently a proof of concept model has been completed using a number of simplifying assumptions. The predictions of the current model as-implemented imply a relatively large increase in the number of stone nidus can form in the tubules due heterogeneous growth alone. Further development of this module will seek to include agglomeration, wall effects and more complex urine chemistry to determine the probability change in clinical stone occurrence. The predictions of the current model imply a relatively large number of relatively large sized nidus could form due heterogeneous growth alone with a complex dependence on water intake levels.
Sleep Disruption Medical Intervention Forecasting Tool (SDMIF):
At present the model implementation has been completed and function verified using subject matter expert data to inform the model. Investigators are confident that the model is performing as designed and detailed in the conceptual model. At present, the lack of access to specific data sampling of astronaut sleep med use during an ISS mission prevents finalizing and validating the SDMIF.
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