The ISS and the prior station Mir provided the proving ground for future human long-duration space activity. A recent European Space Agency study recommended “Measurement campaigns on the ISS form the ideal tool for experimental validation of radiation environment models, of transport code algorithms and reaction cross sections”. Indeed, prior measurements on Shuttle have provided vital information impacting both transport code and environmental model development. Recent studies using the ISS 7A configuration with TLD area monitors demonstrated that computational dosimetry requires environmental models with accurate anisotropic and dynamic behavior, detailed information on rack loading, and an accurate 6 degree-of-freedom description of the ISS trajectory. The ISS model is now configured for 11A and uses an anisotropic and dynamic geomagnetic transmission and trapped proton models. The ISS 11A is instrumented with both passive and active dosimetric devices. Time resolved measurements have the advantage of isolating trapped proton and galactic cosmic ray components as was essential to transport code validation in Shuttle data analysis. ISS 11A model validation will begin with passive dosimetry as was used with ISS 7A. Directional dependent active measurements will play an important role in the validation of environmental model anisotropies.
Research Containing: Long duration
Constraints on the mass and volume that can be allocated for electronics spares and repair equipment on long-duration space missions mean that NASA must look at repair strategies beyond the traditional approach, which has been to replace faulty subsystems in a modular form, termed Orbital Replacement Units or Line Replacement Units. Other possible strategies include component and board-level replacement, modular designs that allow reprogramming of less-critical systems to take the place of more critical failed systems, and a blended approach which uses elements of each of these approaches, along with a limited number of Line Replacement Units. This paper presents some of the constraints and considerations that affect the decision on how to approach electronics repair for long duration space missions, and discusses the benefits and limitations of each of the previously mentioned strategies.
CIB: An Improved Communication Architecture for Real-Time Monitoring of Aerospace Materials, Instruments, and Sensors on the ISS
The Communications Interface Board (CIB) is an improved communications architecture that was demonstrated on the International Space Station (ISS). ISS communication interfaces allowing for real-time telemetry and health monitoring require a significant amount of development. The CIB simplifies the communications interface to the ISS for real-time health monitoring, telemetry, and control of resident sensors or experiments. With a simpler interface available to the telemetry bus, more sensors or experiments may be flown. The CIB accomplishes this by acting as a bridge between the ISS MIL-STD-1553 low-rate telemetry (LRT) bus and the sensors allowing for two-way command and telemetry data transfer. The CIB was designed to be highly reliable and radiation hard for an extended flight in low Earth orbit (LEO) and has been proven with over 40 months of flight operation on the outside of ISS supporting two sets of flight experiments. Since the CIB is currently operating in flight on the ISS, recent results of operations will be provided. Additionally, as a vehicle health monitoring enabling technology, an overview and results from two experiments enabled by the CIB will be provided. Future applications for vehicle health monitoring utilizing the CIB architecture will also be discussed.
The long-duration fluid physics experiments on a thermocapillary-driven flow have been carried out on the Japanese Experiment Module ‘Kibo’ aboard the International Space Station (ISS) since 2008. In these experiments, various aspects of thermocapillary convection in a half-zone (HZ) liquid bridge of high Prandtl number fluid have been examined under the advantages of the long-duration high-quality microgravity environment. In 2010, the authors succeeded to realize nonlinear convective fields in the HZ liquid bridge of rather high aspect ratio. Special attention was paid on to the complex convective fields, especially on the behaviors of the hydrothermal wave (HTW) over the free surface visualized by an infrared camera. In order to evaluate the characteristics of the nonlinear convective behaviors and their transition processes, the authors indicate the images taken by the infrared camera describing the time evolution of HTW, the spatio-temporal diagram, the Fourier analysis, and the pseudo-phase space, reconstructed from the time series of the scalar information of the liquid bridge, that is, surface temperature variation. In this paper, the authors introduce the signature of complex HTW behaviors observed at the long-duration on-orbit experiments, and make comparisons with some previous terrestrial and microgravity experiments.
Pool Boiling Heat Transfer on the International Space Station: Experimental Results and Model Verification
The relatively poor understanding of gravity effects on pool boiling heat transfer can be attributed to the lack of long duration high-quality microgravity data, g-jitter associated with ground-based low gravity facilities, little data at intermediate gravity levels, and a poor understanding of the effect of important parameters even at earth gravity conditions. The results of over 200 pool boiling experiments with n-perfluorohexane as the test fluid performed aboard the International Space Station (ISS) are presented in this paper. A flat, transparent, constant temperature microheater array was used to perform experiments over a wide range of temperatures (55 °C < Tw < 107.5 °C), pressures (0.58 atm < P < 1.86 atm), subcoolings (1 °C ≤ ΔTsub ≤ 26 °C), and heater sizes (4.2 mm ≤ Lh ≤ 7.0 mm). The boiling process was visualized from the side and bottom. Based on this high quality microgravity data (a/g<10−6 ), the recently reported gravity scaling parameter for heat flux, which was primarily based on parabolic flight experiments, was modified to account for these new results. The updated model accurately predicts the experimental microgravity data to within ±20%. The robustness of this framework in predicting low gravity heat transfer is further demonstrated by predicting many of the trends in the pool boiling literature that cannot be explained by any single model.
The ability to separate liquid and gas phases in the absence of a gravitational acceleration has proven a challenge to engineers since the inception of space exploration. Due to our singular experience with terrestrial systems, artificial body forces are often imparted in multiphase fluid systems aboard spacecraft to reproduce the buoyancy effect. This approach tends to be inefficient, adding complexity, resources, and failure modes. Ever present in multiphase phenomena, the forces of surface tension can be exploited to aid passive phase separations where performance characteristics are determined solely by geometric design and system wettability. Said systems may be readily designed as demonstrated herein where a regulated bubbly flow is drawn through an open triangular sectioned duct. The bubbles passively migrate toward the free surface where they coalesce and leave the flow. The tests clearly show container aspect ratios required for passive phase separations for various liquid and gas flow rates. Preliminary data are presented as regime maps demarking complete phase separation. Long duration microgravity experiments are performed aboard the International Space Station. Supplementary experiments are conducted using a drop tower.
Collagen and silk materials, in neat forms and as silica composites, were flown for 18 months on the International Space Station [Materials International Space Station Experiment (MISSE)-6] to assess the impact of space radiation on structure and function. As natural biomaterials, the impact of the space environment on films of these proteins was investigated to understand fundamental changes in structure and function related to the future utility in materials and medicine in space environments. About 15% of the film surfaces were etched by heavy ionizing particles such as atomic oxygen, the major component of the low-Earth orbit space environment. Unexpectedly, more than 80% of the silk and collagen materials were chemically crosslinked by space radiation. These findings are critical for designing next-generation biocompatible materials for contact with living systems in space environments, where the effects of heavy ionizing particles and other cosmic radiation need to be considered.
Impaired cerebrovascular autoregulation and reduced CO(2) reactivity after long duration spaceflight
Long duration habitation on the International Space Station (ISS) is associated with chronic elevations in arterial blood pressure in the brain compared with normal upright posture on Earth and elevated inspired CO(2). Although results from short-duration spaceflights suggested possibly improved cerebrovascular autoregulation, animal models provided evidence of structural and functional changes in cerebral vessels that might negatively impact autoregulation with longer periods in microgravity. Seven astronauts (1 woman) spent 147 +/- 49 days on ISS. Preflight testing (30-60 days before launch) was compared with postflight testing on landing day (n = 4) or the morning 1 (n = 2) or 2 days (n = 1) after return to Earth. Arterial blood pressure at the level of the middle cerebral artery (BP(MCA)) and expired CO(2) were monitored along with transcranial Doppler ultrasound assessment of middle cerebral artery (MCA) blood flow velocity (CBFV). Cerebrovascular resistance index was calculated as (CVRi = BP(MCA)/CBFV). Cerebrovascular autoregulation and CO(2) reactivity were assessed in a supine position from an autoregressive moving average (ARMA) model of data obtained during a test where two breaths of 10% CO(2) were given four times during a 5-min period. CBFV and Doppler pulsatility index were reduced during -20 mmHg lower body negative pressure, with no differences pre- to postflight. The postflight indicator of dynamic autoregulation from the ARMA model revealed reduced gain for the CVRi response to BP(MCA) (P = 0.017). The postflight responses to CO(2) were reduced for CBFV (P = 0.056) and CVRi (P = 0.047). These results indicate that long duration missions on the ISS impaired dynamic cerebrovascular autoregulation and reduced cerebrovascular CO(2) reactivity.
Limited data are available to describe the regulation of heart rate (HR) during sleep in spaceflight. Sleep provides a stable supine baseline during preflight Earth recordings for comparison of heart rate variability (HRV) over a wide range of frequencies using both linear, complexity, and fractal indicators. The current study investigated the effect of long-duration spaceflight on HR and HRV during sleep in seven astronauts aboard the International Space Station up to 6 mo. Measurements included electrocardiographic waveforms from Holter monitors and simultaneous movement records from accelerometers before, during, and after the flights. HR was unchanged inflight and elevated postflight [59.6 +/- 8.9 beats per minute (bpm) compared with preflight 53.3 +/- 7.3 bpm; P < 0.01]. Compared with preflight data, HRV indicators from both time domain and power spectral analysis methods were diminished inflight from ultralow to high frequencies and partially recovered to preflight levels after landing. During inflight and at postflight, complexity and fractal properties of HR were not different from preflight properties. Slow fluctuations (<0.04 Hz) in HR presented moderate correlations with movements during sleep, partially accounting for the reduction in HRV. In summary, substantial reduction in HRV was observed with linear, but not with complexity and fractal, methods of analysis. These results suggest that periodic elements that influence regulation of HR through reflex mechanisms are altered during sleep in spaceflight but that underlying system complexity and fractal dynamics were not altered.
We evaluated their circadian rhythms using data from electrocardiographic records and examined the change in circadian period related to normal RR intervals for astronauts who completed a long-term (>/=6-month) mission in space. The examinees were seven astronauts, five men and two women, from 2009 to 2010. Their mean +/- SD age was 52.0 +/- 4.2 years (47-59 yr). Each stayed in space for more than 160 days; their average length of stay was 172.6 +/- 14.6 days (163-199 days). We conducted a 24-h Holter electrocardiography before launch (Pre), at one month after launch (DF1), at two months after launch (DF2), at two weeks before return (DF3), and at three months after landing (Post), comparing each index of frequency-domain analysis and 24-h biological rhythms of the NN intervals (normal RR intervals). Results show that the mean period of Normal Sinus (NN) intervals was within 24 +/- 4 h at each examination. Inter-individual variability differed among the stages, being significantly smaller at DF3 (Pre versus DF1 versus DF3 versus Post = 22.36 +/- 2.50 versus 25.46 +/- 4.37 versus 22.46 +/- 1.75 versus 26.16 +/- 7.18 h, p < 0.0001). The HF component increased in 2 of 7 astronauts, whereas it decreased in 3 of 7 astronauts and 1 was remained almost unchanged at DF1. During DF3, about 6 months after their stay in space, the HF component of 5 of 7 astronauts recovered from the decrease after launch, with prominent improvement to over 20% in 3 astronauts. Although autonomic nervous functions and circadian rhythms were disturbed until one month had passed in space, well-scheduled sleep and wake rhythms and meal times served as synchronizers.