The Space Flight Environment The International Space -PDF Free Download

The space flight environment the International Space

2019 | 3 views | 5 Pages | 2.68 MB

in the hostile space environment. This article focuses on the specific challenges of the space environment. In an upcom-ing issue, a Dispatch from Space provides a personal look at space travel, and 2 other articles address the acclimation nec-essary for people to travel and live in space and the techno-



istics of orbital flight that present the greatest health and During spacewalks the personal life support system of the
safety concerns to astronauts The environmental factors of spacesuit provides active cooling to dissipate the heat gener
concern during long missions aboard the International ated by high metabolic workloads A manually controlled
Space Station are summarized in Table 1 along with cur thermostat is used to control active cooling and regulate the
rent mitigation measures developed by the Multilateral temperature in the suit Heating the suit is a passive process re
Medical Policy Board sulting from accumulated body heat in the absence of active
cooling Manually activated electric heaters in astronauts
Temperature extremes gloves may be used when the touch temperatures fall below
Spacecraft in low orbit of the earth travel at Mach 25 or 20 C Thermal mittens can also be used to provide insulation
about 8 km per second These spacecraft orbit the earth from high touch temperatures
once every 90 minutes The crew controls the temperature During a spacewalk it is easy to become focused on a task
in the crew compartment of the space shuttle and modules and lose awareness of an impending dusk or dawn until sur
of the International Space Station with an average temper rounded by darkness or brilliant sunlight Temperature is
ature between 21 and 23 C Much greater extremes occur often the first cue that these transitions are imminent
outside the spacecraft When on the sun lit side of the earth
the temperature on the spacecraft or space station can reach Circadian dyssynchrony
over 100 C Forty five minutes later during a night pass The light dark transition that occurs every 45 minutes results in
through earth s dark shadow temperatures can plunge changes in the thermal properties of the spacecraft and in power
to 100 C 2 generated from solar arrays This transition is of interest as a po
Table 1 Characteristics of the space environment in the low earth orbit and measures to reduce the impact on crew health and
Characteristic Impact on crew health and safety Mitigation measures
Temperature extremes Degradation of structural components Thermal control systems on spacecraft and
100 to 100oC of the space station in space suits
Spacewalking astronauts are at risk of Active heating passive heating and active
thermal injury cooling systems in the extravehicular
mobility unit
Circadian dyssynchrony Disruption of circadian rhythms Short acting sleeping medication is available
Reduced quality of sleep to crew
Modafinil is available to crew to optimize
performance while fatigued
High vacuum4 Spacewalking astronauts are at risk of Micrometeoroid shielding is incorporated
10 7 Torr decompression sickness in the space station design
Spacecraft and spacesuits may be punctured The extravehicular mobility unit spacesuit
resulting in acute depressurization incorporates a micrometeoroid shield
Ionizing radiation15 16 Long term risks of cataracts and cancer Spacecraft shielding
425 Sv d ionizing Onboard radiation dosimeters
Pharmaceutical radioprotectants may be
used in the future
Micrometeoroids and orbital Breach of the spacecraft hull would result Meteor shower forecasts are used to
debris11 12 in cabin depressurization and would be schedule space walks and other sensitive
12 000 debris objects considered an emergency operations
larger than 10 cm orbital Spacecraft shielding
speeds of 8 70 km s Collision avoidance maneuvers
System redundancy
Ionospheric plasma Arcing could endanger spacewalking Plasma contactor units are activated during
Spacecraft develop an astronauts spacewalks to neutralize the built up
induced charge up to 140 V electrical charge on space station structure
Acoustic noise14 Hearing loss impaired concentration Monitor crew exposure
Ambient noise on the sleep interruption and fatigue Design specifications
International Space Station Acoustic insulation of noisy equipment
Hearing protection provided to crew
Microgravity Gravity dependent functions of organ Numerous counter measures exist to prevent
1 g quasi steady level 17 systems are altered the deleterious physiologic effects of space flight
CMAJ JUNE 9 2009 180 12 1217
Ionizing radiation
At an orbital altitude of 350 km the Inter
national Space Station is above the
earth s magnetosphere This results in ex
posure of astronauts to higher fluxes of
ionizing radiation The primary radiation
sources are galactic cosmic rays ener
getic particles from outside our solar sys
tem particles trapped in the earth s mag
netic field the Van Allen Belts and solar
energetic particle events solar flares 5 6
High energy protons and heavy ions em
NASA courtesy of nasaimages org
anate from the Sun and elsewhere in the
cosmos Even higher energy secondary
particles protons neutrons and heavy
ions are produced when the incoming ra
diation strikes the spacecraft hull
The 52 orbital inclination of the Inter
national Space Station causes it to pass
through the South Atlantic Anomaly
Space Shuttle Endeavour s orbital manoeuvring system pods and vertical stabilizer daily This region located east of
are shown in this image while the shuttle was docked on the International Space
Station during mission STS 118
Argentina is characterized by an anom
alous perturbation in the earth s geomag
netic field with trapped energetic particles
tential source of circadian dyssynchrony found at lower altitudes These pertubations briefly subject
The irregular light pattern caused by the 16 daily sunsets astronauts to higher fluxes of ionizing radiation
and sunrises may disrupt the circadian rhythm of astronauts The average total dose of radiation that a person on earth
leading to degradation of the quality of their sleep Many receives from natural land based sources and medical proced
studies have been undertaken to evaluate the sleep patterns of ures is less than 0 005 Sievert Sv per year The standard ra
astronauts Although the light dark transitions are of interest diation dose associated with a chest radiograph is 0 02 Sv
the greatest sleep disruption has resulted from timeline pres while commercial aircraft travel is associated with exposure
sures or ambient noise 3 to 0 3 5 7 Sv per hour At orbital altitudes near that of the
International Space Station the dose equivalent to the astro
High vacuum nauts is about 0 3 Sv per year 7
A high vacuum exists outside the space shuttle and the Inter Astronaut who fly missions solely in low orbit around the
national Space Station 4 The pressure inside both spacecraft earth are unlikely to receive a total dose of 1 Sv over their
is regulated to 101 34 kPa 14 7 psi and is equilibrated after career However as the duration of space flights become
docking and before hatch opening NASA s suit for space longer and as destinations take us farther from earth radiation
walks extravehicular mobility unit is pressurized to doses will become higher Astronauts participating in ex
29 5 kPa with 100 oxygen The Russian Orlan spacesuit is ploratory missions to Mars in the coming decades will receive
pressurized to 40 kPa The transition from ambient pressure an estimated round trip dose of 1 Sv 8 During these 2 to
to vacuum during airlock depressurization causes consider 3 year missions there is a good chance that at least 1 solar
able decompression stress to spacewalking astronauts Thus flare will occur which could drastically increase their expo
before spacewalks astronauts perform an oxygen pre breathe sure to 5 Sv
protocol that reduces the level of nitrogen in the tissues Ionizing radiation can kill cells damage genetic material
Astronauts are trained to recognize the symptoms of de and in some instances lead to cancer The primary biologic
compression sickness Treatment protocols involve re effect of low and moderate doses of radiation is damage to
pressurization 100 oxygen therapy and if necessary DNA The mechanisms that give rise to genetic mutation in
over pressurization of the spacesuit by use of a bends treat volve physical energy transfer free radical formation and al
ment adaptor teration of the molecular structure of DNA 6
The risks associated with depressurization of a suit or Health risks from radiation exposure may be described in
spacecraft are partially mitigated by micrometeoroid shield terms of short term effects and long term risks The extent
ing in the suit and spacecraft modules However in June and severity of short term effects is determined by the type
1997 there was rapid depressurization of the Spektr module and amount of exposure to radiation Dose related short term
of the Mir space station following a collision with a supply effects range from nausea and vomiting to central nervous
vehicle The hatch between the modules was quickly closed system damage and even death Long term risks include
to prevent depressurization of the station This episode was a cataracts with lens doses of 8 mSv and potentially cancer 9
reminder of the harsh reality of living in the vacuum of space This increased risk of cancer is the principal concern for as
1218 CMAJ JUNE 9 2009 180 12
tronauts exposed to space radiation The risk decreases with The consequences of collisions between spacecraft and a
increasing age at exposure10 and persists after landing micrometeoroid or a piece of space debris can be catastrophic
The goal of human space flight programs is to continue the Collisions take place at hyper velocities of about 10 km s with
exploration and development of space while minimizing risks dissipation of huge kinetic energies for very small particles The
from exposure to ionizing radiation Astronauts are regarded impact of a collision of a 1 kg piece of space debris with the In
as radiation workers and follow the as low as reasonably ternational Space Station has the same energy as a collision in
achievable principles and guidelines with radiation monitor volving a 35 000 kg tractor trailer travelling at 190 km h 12
ing to document exposure NASA and the other international Metal shielding can protect vulnerable parts of the space station
partners have adopted the recommendations of the National against objects that are smaller than 1 cm diameter while
Council on Radiation Protection about exposure to radiation collision avoidance manoeuvres have been taken by the shuttle
during human space flight activities 8 and may be taken by the International Space Station to prevent
collisions with larger pieces of debris
Space debris Suit penetration from a micrometeoroid strike or an inad
Space debris has become a greater risk for space flights in vertent puncture from a tool wire or sharp edge is a risk asso
low orbit in recent years Micrometeoroids exist naturally in ciated with spacewalks The 14 layers of material that make
the solar system from breakups of comets and asteroids and up the spacesuit include a layer of Kevlar to reduce the proba
space debris is associated with increased frequency of space bility of suit penetration To date there have been no
flight This debris includes leftover satellites broken up recorded cases of suit penetration from micrometeoroids
rocket stages and even paint flakes from deteriorating space However a tear to the outermost layer of a spacesuit glove
craft Today there are more than 12 000 objects larger than from a sharp edge was noted on mission STS 118 in August
10 cm softball size and larger that are being tracked by 2007 resulting in early termination of the spacewalk
ground based sensors and catalogued 11 Smaller objects prob
ably number in the hundreds of thousands Ionospheric plasma
Spacecraft in low orbit around the earth have a complex inter
action with ionospheric plasma The solar arrays on the Inter
national Space Station operate at 160V and the distribution
system is at 120V DC The negative side of the power system
is grounded to the structure of the space station resulting in a
large amount of energy stored in the structure at 140V High
voltage solar arrays coupled with the design and material
properties of the International Space Station can lead to detri
mental interactions with the ionospheric plasma
Two plasma contactor units have been placed on the Interna
tional Space Station to provide a ground wire to prevent arc
discharging These devices emit a low energy stream of elec
trons during spacewalks that reduces the buildup of electrical
charge 13 As long as the plasma contactor units are functional an
astronaut floating freely during a spacewalk has no risk of expo
sure to arcing However the steel tethers used by astronauts to
attach themselves to the structure of the space station and the
exposed metallic surfaces of the spacesuit or tools used during
the spacewalk are potential sources for arcing if both of the
plasma contactor units were to fail during a spacewalk
Acoustic noise
Spacecraft systems and experiments include fans pumps and
motors which generate continuous noise Acoustic levels at
most locations on the International Space Station are close to
NASA courtesy of nasaimages org
60 dBA A weighted decibels similar to normal conversa
tion level however certain areas of the space station are
particularly noisy and are a potential source of hearing loss
for astronauts 14
Elevated ambient noise can have a deleterious effect on
communication between astronauts and it may adversely af
fect performance through impaired concentration and distrac
tion from tasks in addition to disrupting sleep Inadvertent
Robert Thirsk is pictured working in the spacelab during mis
sion STS 78 his first flight in 1996
alarms have woken astronauts from sleep an issue of particu
lar concern if it occurs before a critical task on the mission
CMAJ JUNE 9 2009 180 12 1219
REFERENCES
1 National Space Biomedical Research Institute Revised strategic plan Houston TX
The Institute 2003 p 6 7 Available http nsbri tamu edu About StrategicPlan pdf
accessed 2009 Apr 27
2 Newman DJ Life in extreme environments How will humans perform on Mars
Gravit Space Biol Bull 2000 13 35 47
3 Dijk DJ Neri DF Wyatt JK et al Sleep performance circadian rhythms and
light dark cycles during two space shuttle flights Am J Physiol Regul Integr Comp
Physiol 2001 281 R1647 64
NASA courtesy of nasaimages org
4 Tennyson RC Composites in space Challenges and opportunities Proceedings
of the International Conference on Composite Materials ICCM 10 1995 Aug
14 18 Whistler BC
5 National Aeronautics and Space Administration Space Radiation Analysis Group
Johnson Space Center Washington DC The Administration 2008 Available
http srag jsc nasa gov accessed 2009 Apr 27
6 Eckart P Space flight life support and biospherics Torrance CA Microcosm
Press and Dordrecht Netherlands Kluwer Academic Publishers 1999
7 National Council on Radiation Protection and Measurements Radiation protection
guidance for activities in low earth orbit Report no 132 ISBN 0 929600 65 7
Bethesda MD The Council 2000
Dave Williams floats near the torso portions of 2 spacesuits in 8 National Council on Radiation Protection and Measurements Guidance on radia
tion received in space activities Report no 98 ISBN 0 929600 04 5 Bethesda
the Quest Airlock of the International Space Station MD The Council 1989
9 Cucinotta FA Manuel FK Jones J et al Space radiation and cataracts in astro
nauts Radiat Res 2001 156 460 66
10 Nicogossian EA Huntoon CL Pool SL editors Space physiology and medicine
Microgravity Philadelphia PA Lea and Febiger 1994 p 167 93
The International Space Station is designed to serve as a re 11 Koontz S Suggs R Schneider T et al Progress in spacecraft environment inter
actions International Space Station development and operations Proceedings
search facility for low gravity experimentation in fundamen of 26th Annual International Space Development Conference 2007 May 25 28
tal science and technology development Depending on which Dallas TX
12 Rodriguez HM Liou JC Orbital debris past present and future Proceedings of
onboard systems are operating and the nature of crew activi American Institute of Aeronautics and Astronautics AIAA Annual Technical Sym
ties the acceleration environment on the station ranges from posium 2008 May 9 Houston TX Webster TX American Institute of Aero
transient episodes of 0 01g to quasi steady levels below one nautics and Astronautics 2008
13 Tribble AC The space environment and its impact on spacecraft design 31st
millionth of 1g 15 American Institute of Aeronautics and Astronautics AIAA Aerospace Sciences
Perturbations in this environment occur during certain Meeting and Exhibit 1993 Jan 11 14 Reno NV Webster TX American Insti
tute of Aeronautics and Astronautics 1993 p 491
phases of orbital activity Rendezvous and docking introduce 14 Goodman JR International Space Station acoustics J Acoust Soc Am 2000 108
transient accelerations that could be disruptive to certain exper 2475
15 Soares C Mikatarian R Schmidl R et al Natural and induced space environments
iments In addition on board exercise devices could result in effects on the International Space Station Proceedings of the 56th International
perturbations of the microgravity environment and are isolated Astronautical Congress 2005 Oct 17 21 Fukuoka Japan IAC 05 B4 2 07
16 Wilson JW Badavi FF Kim MY et al Natural and induced environment in low
treadmill vibration isolation system from adjacent structures earth orbit technical report Washington DC National Aeronautics and Space
Rack isolation systems have also been developed to isolate crit Administration 2002 Report no NASA TM 2002 211668
ical experiments from transient vibrations and accelerations 17 DeLombard R Hrovat K Kelly E et al Microgravity environment on the Interna
tional Space Station Washington DC National Aeronautics and Space Administra
tion 2004 Report no NASA TM 2004 213039 Available http gltrs grc nasa
Conclusion gov reports 2004 TM 2004 213039 pdf accessed 2009 Apr 27
From a clinical perspective the 2 major challenges associated
with human space flight are the radiation effects and the Correspondence to Dr David Williams Department of Surgery
physiologic consequences of living and working in a micro McMaster University c o St Joseph s Healthcare Hamilton
gravity environment All organ systems are affected in space 50 Charlton St E Hamilton ON L8N 4A6 fax 905 521 6197
willd mcmaster ca
to some degree where gravitational loading hydrostatic pres
sure convection buoyancy and sedimentation do not exist
Consequently microgravity is the most profound aspect of
the space environment on human physiology
A subsequent article in this series will provide an overview While preparing this article astronaut Dr Robert Thirsk was getting
ready for a 6 month stint on the International Space Station the first
of the unique physiologic acclimations associated with human long duration mission by a Canadian In addition to being the medical
space flight and discuss the implications for the delivery of officer for the 6 member international crew Dr Thirsk will work as a
health care in partial and microgravitational environments robotics specialist operating Canadarm2 and perform experiments on
behalf of Canadian and international scientists The launch was set for
late May aboard a Russian Soyuz rocket from Ba konur Kazakhstan
This article has been peer reviewed
Competing interests David Williams was employed by the Canadian Space
Agency from 1992 to 2008 During this time he performed research into the
space environment None declared for Robert Thirsk Andre Kuipers and In 1996 Robert Thirsk wrote a Special Report for CMAJ prior to his
Chiaki Mukai flight aboard the space shuttle Columbia This report is available at
Contributors All of the authors were involved in the drafting and revising www cmaj ca cgi content full 154 12 1884 DC1
of the article and approved the final version submitted for publication
1220 CMAJ JUNE 9 2009 180 12


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