Conceptual map illustrating the connections among nonhuman nature, ecosystem services, environmental ethics, environmental justice, and public healthEnvironmental
health indicator (2016). It consists of three categories: health
impacts, air quality, and water and sanitation. The health impacts
category includes the environmental risk exposure indicator.
Environmental health was defined in a 1989 document by the World Health Organization (WHO) as:
Those aspects of human health and disease that are determined by factors in the environment.
It is also referred to as the theory and practice of accessing and
controlling factors in the environment that can potentially affect
health.
A 1990 WHO document states that environmental health, as used by
the WHO Regional Office for Europe, "includes both the direct
pathological effects of chemicals, radiation and some biological agents,
and the effects (often indirect) on health and well being of the broad
physical, psychological, social and cultural environment, which includes
housing, urban development, land use and transport."
As of 2016, the WHO website on environmental health states that
"Environmental health addresses all the physical, chemical, and
biological factors external to a person, and all the related factors
impacting behaviours. It encompasses the assessment and control of those
environmental factors that can potentially affect health. It is
targeted towards preventing disease and creating health-supportive
environments. This definition excludes behaviour not related to
environment, as well as behaviour related to the social and cultural
environment, as well as genetics."
The WHO has also defined environmental health services as "those
services which implement environmental health policies through
monitoring and control activities. They also carry out that role by
promoting the improvement of environmental parameters and by encouraging
the use of environmentally friendly and healthy technologies and
behaviors. They also have a leading role in developing and suggesting
new policy areas."
Other considerations
The term environmental medicine may be seen as a medical specialty, or branch of the broader field of environmental health. Terminology is not fully established, and in many European countries they are used interchangeably.
Children's environmental health is the academic discipline that
studies how environmental exposures in early life—chemical, nutritional,
and social—influence health and development in childhood and across the
entire human life span.
Other terms referring to or concerning environmental health include environmental public health and health protection.
Disciplines
Five basic disciplines generally contribute to the field of environmental health: environmental epidemiology, toxicology, exposure science, environmental engineering, and environmental law.
Each of these five disciplines contributes different information to
describe problems and solutions in environmental health. However, there
is some overlap among them.
Environmental epidemiology
studies the relationship between environmental exposures (including
exposure to chemicals, radiation, microbiological agents, etc.) and
human health. Observational studies, which simply observe exposures that
people have already experienced, are common in environmental
epidemiology because humans cannot ethically be exposed to agents that
are known or suspected to cause disease. While the inability to use
experimental study designs is a limitation of environmental
epidemiology, this discipline directly observes effects on human health
rather than estimating effects from animal studies. Environmental epidemiology
is the study of the effect on human health of physical, biologic, and
chemical factors in the external environment, broadly conceived. Also,
examining specific populations or communities exposed to different
ambient environments, Epidemiology in our environment aims to clarify
the relationship that exist between physical, biologic or chemical
factors and human health.
Toxicology
studies how environmental exposures lead to specific health outcomes,
generally in animals, as a means to understand possible health outcomes
in humans. Toxicology has the advantage of being able to conduct
randomized controlled trials and other experimental studies because they
can use animal subjects. However, there are many differences in animal
and human biology, and there can be a lot of uncertainty when
interpreting the results of animal studies for their implications for human health.
Exposure science
studies human exposure to environmental contaminants by both
identifying and quantifying exposures. Exposure science can be used to
support environmental epidemiology by better describing environmental
exposures that may lead to a particular health outcome, identify common
exposures whose health outcomes may be better understood through a
toxicology study, or can be used in a risk assessment to determine
whether current levels of exposure might exceed recommended levels.
Exposure science has the advantage of being able to very accurately
quantify exposures to specific chemicals, but it does not generate any
information about health outcomes like environmental epidemiology or
toxicology.
Environmental engineering
applies scientific and engineering principles for protection of human
populations from the effects of adverse environmental factors;
protection of environments from potentially deleterious effects of
natural and human activities; and general improvement of environmental
quality.
Environmental law
includes the network of treaties, statutes, regulations, common and
customary laws addressing the effects of human activity on the natural
environment.
Information from epidemiology, toxicology, and exposure science can be combined to conduct a risk assessment
for specific chemicals, mixtures of chemicals or other risk factors to
determine whether an exposure poses significant risk to human health
(exposure would likely result in the development of pollution-related diseases). This can in turn be used to develop and implement environmental health policy that, for example, regulates chemical emissions, or imposes standards for proper sanitation. Actions of engineering and law can be combined to provide risk management
to minimize, monitor, and otherwise manage the impact of exposure to
protect human health to achieve the objectives of environmental health
policy.
Concerns
Overview of main health effects on humans from some common types of pollutionFEMA/EPA Hazardous Materials Team removing hazards left in the wake of Hurricane Katrina, 2005
Environmental health addresses all human-health-related aspects of the natural environment and the built environment. Environmental health concerns include:
According to recent estimates, about 5 to 10% of disability-adjusted life years (DALYs) lost are due to environmental causes in Europe. By far the most important factor is fine particulate matter pollution in urban air. Similarly, environmental exposures have been estimated to contribute to 4.9 million (8.7%) deaths and 86 million (5.7%) DALYs globally.
In the United States, Superfund sites created by various companies have
been found to be hazardous to human and environmental health in nearby
communities. It was this perceived threat, raising the specter of
miscarriages, mutations, birth defects, and cancers that most frightened
the public.
Air pollution is globally responsible for over 6.5 million deaths each year.
Air pollution is the contamination of an atmosphere due to the presence
of substances that are harmful to the health of living organisms, the
environment or climate.
These substances concern environmental health officials since air
pollution is often a risk-factor for diseases that are related to
pollution, like lung cancer, respiratory infections, asthma, heart disease, and other forms of respiratory-related illnesses. Reducing air pollution, and thus developing air quality, has been found to decrease adult mortality.
A Mumbai factory releasing air pollution.
Common products responsible for emissions include road traffic, energy production, household combustion, aviation and motor vehicles, and other forms of pollutants.
These pollutants are responsible for the burning of fuel, which can
release harmful particles into the air that humans and other living
organisms can inhale or ingest.
Air pollution is associated with adverse health effects like respiratory and cardiovascular diseases, cancer, related illnesses, and even death. The risk of air pollution is determined by the pollutant's hazard and the amount of exposure that affects a person.
For example, a child who plays outdoor sports will have a higher
likelihood of outdoor air pollution exposure compared to an adult who
tends to spend more time indoors, whether at work or elsewhere.
Environmental health officials work to detect individuals who are at
higher risks of consuming air pollution, work to decrease their
exposure, and detect risk factors present in communities.
Household air pollution contributes to diseases that kill almost 4.3 million people every year. Indoor air pollution contributes to risk factors for diseases like heart disease, pulmonary disease, stroke, pneumonia, and other associated illnesses. For vulnerable populations who spend large amounts of their time indoors, such as children and elderly populations, poor indoor air quality can be dangerous.
Burning fuels like coal or kerosene inside homes can cause dangerous chemicals to be released into the air. Dampness and mold in houses can cause diseases as well, but little studies have been performed on mold in schools and workplaces. Environmental tobacco smoke
is considered to be a leading contributor to indoor air pollution,
since exposure to second and third-hand smoke is a common risk factor. Tobacco smoke contains over 60 carcinogens, where 18% are known human carcinogens.
Exposure to these chemicals can lead to exacerbation of asthma,
development of cardiovascular diseases, cardiopulmonary diseases, and
increase the likelihood of cancer development.
Climate change makes extreme weather events more likely, including ozone smog events, dust storms, and elevated aerosol levels, all due to extreme heat, drought, winds, and rainfall. These extreme weather events can increase the likelihood of undernutrition, mortality, food insecurity, and climate-sensitive infectious diseases in vulnerable populations.
The effects of climate change are felt by the whole world, but
disproportionately affect disadvantaged populations who are subject to climate change vulnerability.
Water runoff in Maryland, USA.
Climate impacts can affect exposure to water-borne pathogens through increased rates of runoff, frequent heavy rains, and the effects of severe storms. Extreme weather events and storm surges can also exceed the capacity of water infrastructure, which can increase the likelihood that populations will be exposed to these contaminants.
Exposure to these contaminants are more likely in low-income
communities, where they have inadequate infrastructure to respond to
climate disasters and are less likely to recover from infrastructure
damage as quickly.
Problems like the loss of homes, loved ones, and previous ways of
life, are often what people face after a climate disaster occurs. These
events can lead to vulnerability in the form of housing affordability
stress, lower household income, lack of community attachment, grief, and
anxiety around another disaster occurring.
Certain groups of people can be put at a higher risk for
environmental hazards like air, soil and water pollution. This often
happens due to marginalization, economic and political processes, and
racism. Environmental racism uniquely affects different groups globally,
however generally the most marginalized groups of any region are
affected. These marginalized groups are frequently put next to pollution
sources like major roadways, toxic waste sites, landfills, and chemical
plants.
In a 2021 study, it was found that racial and ethnic minority groups in
the United States are exposed to disproportionately high levels of
particulate air pollution. Racial housing policies
that exist in the United States continue to exacerbate racial minority
exposure to air pollution at a disproportionate rate, even as overall
pollution levels have declined.
Likewise, in a 2022 study, it was shown that implementing policy
changes that favor wealth redistribution could double as climate change
mitigation measures.
For populations who are not subject to wealth redistribution measures,
this means more money will flow into their communities while climate
effects are mitigated.
Noise pollution
Airplane flying over a residential district.
Noise pollution
is usually non-environmental, machine-created sound that can disrupt
activities or communication between humans and other life forms. Exposure to persistent noise pollution can cause diseases like hearing impairment, sleep disturbances, cardiovascular problems, annoyance, problems with communication and other diseases. For American minorities that live in neighborhoods of low socioeconomic status, they often experience higher levels of noise pollution compared to their higher socioeconomic counterparts.
Noise pollution can cause or exacerbate cardiovascular diseases, which can further affect a large range of diseases, increase stress levels, and cause sleep disturbances. Noise pollution is also responsible for cases of hearing loss, tinnitus, and other forms of hypersensitivity or lack thereof to sound.
These conditions can be dangerous to children and young adults who
consistently experience noise pollution, as many of these conditions can
develop into long-term problems.
Children who attend school in noisy traffic zones have shown to
have 20% lower memory development compared to other students who
attended schools in quiet traffic zones, according to a Barcelona study. This is consistent with research that suggests that children who are exposed to regular aircraft noise "have poorer performance on standardised achievement tests."
Exposure to persistent noise pollution can cause one to develop
hearing impairments, like tinnitus or impaired speech discrimination. One of the largest factors in worsened mental health due to noise pollution is annoyance. Annoyance due to environmental factors has been found to increase stress reactions and overall feelings of stress among adults. The level of annoyance felt by an individual varies, but contributes to worsened mental health significantly.
Noise exposure also contributes to sleep disturbances, which can
cause daytime sleepiness and an overall lack of sleep, which contributes
to worsened health.
Safe drinking water
Well installation for safe drinking water.
Access to safe drinking water is considered a "basic human need for health and well-being" by the United Nations. According to their reports, over 2 billion people worldwide live without access to safe drinking water. In 2017, almost 22 million Americans drank from water systems that were in violation of public health standards. Globally, over 2 billion people drink feces-contaminated water, which poses the greatest threat to drinking water safety. Contaminated drinking water could transmit diseases like cholera, dysentery, typhoid, diarrhea and polio.
Harmful chemicals in drinking water can negatively affect health.
Unsafe water management practices can increase the prevalence of water-borne diseases and sanitation-related illnesses.
Schools in the United States are not required by law to test for safe
drinking water, meaning that many children can drink contaminants like lead in their water at school. Inadequate disinfecting of wastewater in industrial and agricultural centers can also infect hundreds of millions of people with contaminated water. Chemicals like fluoride and arsenic
can benefit humans when the levels of these chemicals are
controlled;but other, more dangerous chemicals like lead and metals can
be harmful to humans.
In America, communities of color can be subject to poor-quality water. In communities in America with large hispanic and black populations, there is a correlated rise in SDWA health violations. Populations who have experienced lack of safe drinking water, like populations in Flint, Michigan, are more likely to distrust tap water in their communities. Populations to experience this are commonly low-income, communities of color.
Hazardous materials management
Hazardous materials management, including hazardous waste management, contaminated site remediation, the prevention of leaks from underground storage tanks
and the prevention of hazardous materials releases to the environment
and responses to emergency situations resulting from such releases. When
hazardous materials are not managed properly, waste can pollute nearby
water sources and reduce air quality.
According to a study done in Austria,
people who live near industrial sites are "more often unemployed, have
lower educations levels, and are twice as likely to be immigrants. With the interest of environmental health in mind, the Resource Conservation and Recovery Act was passed in the United States in 1976 that covered how to properly manage hazardous waste.
Microplastic pollution
Microplastics find their way into the food we eat, the water we drink
and even the air we breathe. By some estimates, people consume more
than 50,000 plastic particles per year – and many more if inhalation is
considered. Microplastics were found in every human tissue studied by graduate students at Arizona State University.
A study published in March 2022 revealed that microplastics have also
been found in 80% of 22 anonymous blood samples, meaning they can be
transported around the human body and raising the question of whether
they can be transported to the brain. In December 2020, microplastic particles were found in the placentas of unborn babies for the first time. In June 2022, microplastic particles were found in breastmilk for the first time.
In July 2022, scientists found microplastic particles in the lungs of
11 of 13 samples, supporting the hypothesis that we can inhale
microplastics as well as swallow them.
According to a research conducted by the Medical University of Vienna,
five grams of plastic particles enter each person's gastrointestinal
stream on average per week. This is approximately the weight of a credit
card.
According to another recent estimate, a person who consumes seafood
will ingest 11,000 bits of microplastics per year. Even very minute
microplastics have been discovered in human blood.
Microplastics have been discovered in food in recent investigations. A
recent study found a kilo of sugar had 440 microplastics, a kilo of salt
contained 110 microplastics, and a litre of bottled water contained 90
microplastics.
Soil pollution
Contaminated or polluted soil directly affects human health through
direct contact with soil or via inhalation of soil contaminants that
have vaporized; potentially greater threats are posed by the
infiltration of soil contamination into groundwater aquifers
used for human consumption, sometimes in areas apparently far removed
from any apparent source of above-ground contamination. Toxic metals can
also make their way up the food chain through plants that reside in
soils containing high concentrations of heavy metals. This tends to result in the development of pollution-related diseases.
Most exposure is accidental, and exposure can happen through:
Ingesting dust or soil directly
Ingesting food or vegetables grown in contaminated soil or with foods in contact with contaminants
Skin contact with dust or soil
Vapors from the soil
Inhaling clouds of dust while working in soils or windy environments
However, some studies estimate that 90% of exposure is through eating contaminated food.
Information and mapping
The Toxicology and Environmental Health Information Program (TEHIP)
is a comprehensive toxicology and environmental health web site, that
includes open access to resources produced by US government agencies and
organizations, and is maintained under the umbrella of the Specialized
Information Service at the United States National Library of Medicine.
TEHIP includes links to technical databases, bibliographies, tutorials,
and consumer-oriented resources. TEHIP is responsible for the Toxicology Data Network (TOXNET), an integrated system of toxicology and environmental health databases including the Hazardous Substances Data Bank, that are open access, i.e. available free of charge. TOXNET was retired in 2019.
There are many environmental health mapping tools. TOXMAP is a geographic information system (GIS) from the Division of Specialized Information Services
of the United States National Library of Medicine (NLM) that uses maps
of the United States to help users visually explore data from the United
States Environmental Protection Agency's (EPA) Toxics Release Inventory and Superfund Basic Research Programs.
TOXMAP is a resource funded by the US federal government. TOXMAP's
chemical and environmental health information is taken from the NLM's
Toxicology Data Network (TOXNET) and PubMed, and from other authoritative sources.
Environmental health profession
Environmental health professionals may be known as environmental health officers,
public health inspectors, environmental health specialists or
environmental health practitioners. Researchers and policy-makers also
play important roles in how environmental health is practiced in the
field. In many European countries, physicians and veterinarians are
involved in environmental health. In the United Kingdom,
practitioners must have a graduate degree in environmental health and
be certified and registered with the Chartered Institute of
Environmental Health or the Royal Environmental Health Institute of
Scotland.
In Canada, practitioners in environmental health are required to obtain
an approved bachelor's degree in environmental health along with the
national professional certificate, the Certificate in Public Health
Inspection (Canada), CPHI(C). Many states in the United States also require that individuals have a bachelor's degree and professional licenses in order to practice environmental health. California state law defines the scope of practice of environmental health as follows:
"Scope of practice in environmental health" means the practice
of environmental health by registered environmental health specialists
in the public and private sector within the meaning of this article and
includes, but is not limited to, organization, management, education,
enforcement, consultation, and emergency response for the purpose of
prevention of environmental health hazards and the promotion and
protection of the public health and the environment in the following
areas: food protection; housing; institutional environmental health;
land use; community noise control; recreational swimming areas and
waters; electromagnetic radiation control; solid, liquid, and hazardous
materials management; underground storage tank control; onsite septic
systems; vector control; drinking water quality; water sanitation;
emergency preparedness; and milk and dairy sanitation pursuant to
Section 33113 of the Food and Agricultural Code.
The environmental health profession had its modern-day roots in the sanitary and public health movement of the United Kingdom. This was epitomized by Sir Edwin Chadwick, who was instrumental in the repeal of the poor laws, and in 1884 was the founding president of the Association of Public Sanitary Inspectors, now called the Chartered Institute of Environmental Health.
Solar sails (also known as lightsails, light sails, and photon sails) are a method of spacecraft propulsion using radiation pressure
exerted by sunlight on large surfaces. A number of spaceflight missions
to test solar propulsion and navigation have been proposed since the
1980s. The first spacecraft to make use of the technology was IKAROS, launched in 2010.
A useful analogy to solar sailing may be a sailing boat; the
light exerting a force on the large surface is akin to a sail being
blown by the wind. High-energy laser beams
could be used as an alternative light source to exert much greater
force than would be possible using sunlight, a concept known as beam
sailing. Solar sail craft offer the possibility of low-cost operations
combined with high speeds (relative to chemical rockets)
and long operating lifetimes. Since they have few moving parts and use
no propellant, they can potentially be used numerous times for the
delivery of payloads.
Solar sails use a phenomenon that has a proven, measured effect on astrodynamics. Solar pressure affects all spacecraft, whether in interplanetary space
or in orbit around a planet or small body. A typical spacecraft going
to Mars, for example, will be displaced thousands of kilometers by solar
pressure, so the effects must be accounted for in trajectory planning,
which has been done since the time of the earliest interplanetary
spacecraft of the 1960s. Solar pressure also affects the orientation of a spacecraft, a factor that must be included in spacecraft design.
The total force exerted on an 800 by 800 metre solar sail, for example, is about 5 N (1.1 lbf) at Earth's distance from the Sun, making it a low-thrust propulsion system, similar to spacecraft propelled by electric engines,
but as it uses no propellant, that force is exerted almost constantly
and the collective effect over time is great enough to be considered a
potential manner of propelling spacecraft.
History of concept
Johannes Kepler observed that comet tails point away from the Sun
and suggested that the Sun caused the effect. In a letter to Galileo in
1610, he wrote, "Provide ships or sails adapted to the heavenly
breezes, and there will be some who will brave even that void."
He might have had the comet tail phenomenon in mind when he wrote those
words, although his publications on comet tails came several years
later.
James Clerk Maxwell, in 1861–1864, published his theory of electromagnetic fields and radiation, which shows that light has momentum and thus can exert pressure on objects. Maxwell's equations provide the theoretical foundation for sailing with light pressure. So by 1864, the physics community and beyond knew sunlight carried momentum that would exert a pressure on objects.
Jules Verne, in From the Earth to the Moon,
published in 1865, wrote "there will some day appear velocities far
greater than these [of the planets and the projectile], of which light
or electricity will probably be the mechanical agent ... we shall one
day travel to the moon, the planets, and the stars." This is possibly the first published recognition that light could move ships through space.
Pyotr Lebedev was first to successfully demonstrate light pressure, which he did in 1899 with a torsional balance; Ernest Nichols and Gordon Hull conducted a similar independent experiment in 1901 using a Nichols radiometer.
Svante Arrhenius
predicted in 1908 the possibility of solar radiation pressure
distributing life spores across interstellar distances, providing one
means to explain the concept of panspermia. He was apparently the first scientist to state that light could move objects between stars.
Konstantin Tsiolkovsky
first proposed using the pressure of sunlight to propel spacecraft
through space and suggested, "using tremendous mirrors of very thin
sheets to utilize the pressure of sunlight to attain cosmic velocities".
Friedrich Zander
(Tsander) published a technical paper in 1925 that included technical
analysis of solar sailing. Zander wrote of "applying small forces" using
"light pressure or transmission of light energy to distances by means
of very thin mirrors".
JBS Haldane
speculated in 1927 about the invention of tubular spaceships that would
take humanity to space and how "wings of metallic foil of a square
kilometre or more in area are spread out to catch the Sun's radiation
pressure".
J. D. Bernal
wrote in 1929, "A form of space sailing might be developed which used
the repulsive effect of the Sun's rays instead of wind. A space vessel
spreading its large, metallic wings, acres in extent, to the full, might
be blown to the limit of Neptune's orbit. Then, to increase its speed,
it would tack, close-hauled, down the gravitational field, spreading
full sail again as it rushed past the Sun."
Carl Sagan, in the 1970s, popularized the idea of sailing on light using a giant structure which would reflect photons
in one direction, creating momentum. He brought up his ideas in college
lectures, books, and television shows. He was fixated on quickly
launching this spacecraft in time to perform a rendezvous with Halley's Comet. Unfortunately, the mission didn't take place in time and he would never live to finally see it through.
The first formal technology and design effort for a solar sail began in 1976 at Jet Propulsion Laboratory for a proposed mission to rendezvous with Halley's Comet.
Types
Reflective
Most solar sails are based on reflection. The surface of the sail is highly reflective, like a mirror, and light reflecting off of the surface imparts a force.
Pekka Janhunen from FMI has proposed a type of solar sail called the electric solar wind sail.
Mechanically it has little in common with the traditional solar sail
design. The sails are replaced with straightened conducting tethers
(wires) placed radially around the host ship. The wires are electrically charged to create an electric field
around the wires. The electric field extends a few tens of metres into
the plasma of the surrounding solar wind. The solar electrons are
reflected by the electric field (like the photons on a traditional solar
sail). The radius of the sail is from the electric field rather than
the actual wire itself, making the sail lighter. The craft can also be
steered by regulating the electric charge of the wires. A practical
electric sail would have 50–100 straightened wires with a length of
about 20 km each.
Electric solar wind sails can adjust their electrostatic fields and sail attitudes.
A magnetic sail
would also employ the solar wind. However, the magnetic field deflects
the electrically charged particles in the wind. It uses wire loops, and
runs a static current through them instead of applying a static voltage.
All these designs maneuver, though the mechanisms are different.
Magnetic sails bend the path of the charged protons that are in the solar wind. By changing the sails' attitudes, and the size of the magnetic fields, they can change the amount and direction of the thrust.
The force imparted to a solar sail arises from the momentum of photons. The momentum of a photon or an entire flux is given by Einstein's relation:
where p is the momentum, E is the energy (of the photon or flux), and c is the speed of light. Specifically, the momentum of a photon depends on its wavelength p = h/λ
Solar radiation pressure can be related to the irradiance (solar constant) value of 1361 W/m2 at 1 AU (Earth-Sun distance), as revised in 2011:
perfect absorbance: F = 4.54 μN per square metre (4.54 μPa) in the direction of the incident beam (a perfectly inelastic collision)
perfect reflectance: F = 9.08 μN per square metre (9.08 μPa) in the direction normal to surface (an elastic collision)
An ideal sail is flat and has 100% specular reflection. An actual sail will have an overall efficiency of about 90%, about 8.17 μN/m2, due to curvature (billow), wrinkles, absorbance, re-radiation from front and back, non-specular effects, and other factors.
Force on a sail results from reflecting the photon flux
The force on a sail and the actual acceleration of the craft vary by
the inverse square of distance from the Sun (unless extremely close to
the Sun), and by the square of the cosine of the angle between the sail force vector and the radial from the Sun, so
(for an ideal sail)
where R is distance from the Sun in AU. An actual square sail can be modelled as:
Note that the force and acceleration approach zero generally around θ
= 60° rather than 90° as one might expect with an ideal sail.
If some of the energy is absorbed, the absorbed energy will heat
the sail, which re-radiates that energy from the front and rear
surfaces, depending on the emissivity of those two surfaces.
Solar wind, the flux of charged particles blown out from the Sun, exerts a nominal dynamic pressure of about 3 to 4 nPa, three orders of magnitude less than solar radiation pressure on a reflective sail.
Sail parameters
Sail loading (areal density) is an important parameter, which is the total mass divided by the sail area, expressed in g/m2. It is represented by the Greek letter σ (sigma).
A sail craft has a characteristic acceleration, ac,
which it would experience at 1 AU when facing the Sun. Note this value
accounts for both the incident and reflected momentums. Using the value
from above of 9.08 μN per square metre of radiation pressure at 1 AU, ac is related to areal density by:
ac = 9.08(efficiency) / σ mm/s2
Assuming 90% efficiency, ac = 8.17 / σ mm/s2
The lightness number, λ, is the dimensionless ratio of maximum
vehicle acceleration divided by the Sun's local gravity. Using the
values at 1 AU:
λ = ac / 5.93
The lightness number is also independent of distance from the Sun
because both gravity and light pressure fall off as the inverse square
of the distance from the Sun. Therefore, this number defines the types
of orbit maneuvers that are possible for a given vessel.
The table presents some example values. Payloads are not
included. The first two are from the detailed design effort at JPL in
the 1970s. The third, the lattice sailer, might represent about the best
possible performance level. The dimensions for square and lattice sails are edges. The dimension for heliogyro is blade tip to blade tip.
Type
σ (g/m2)
ac (mm/s2)
λ
Size (km2)
Square sail
5.27
1.56
0.26
0.820
Heliogyro
6.39
1.29
0.22
15
Lattice sailer
0.07
117
20
0.840
Attitude control
An active attitude control
system (ACS) is essential for a sail craft to achieve and maintain a
desired orientation. The required sail orientation changes slowly (often
less than 1 degree per day) in interplanetary space, but much more
rapidly in a planetary orbit. The ACS must be capable of meeting these
orientation requirements. Attitude control is achieved by a relative
shift between the craft's center of pressure and its center of mass. This can be achieved with control vanes, movement of individual sails, movement of a control mass, or altering reflectivity.
Holding a constant attitude requires that the ACS maintain a net
torque of zero on the craft. The total force and torque on a sail, or
set of sails, is not constant along a trajectory. The force changes with
solar distance and sail angle, which changes the billow in the sail and
deflects some elements of the supporting structure, resulting in
changes in the sail force and torque.
Sail temperature also changes with solar distance and sail angle,
which changes sail dimensions. The radiant heat from the sail changes
the temperature of the supporting structure. Both factors affect total
force and torque.
To hold the desired attitude the ACS must compensate for all of these changes.
Constraints
In
Earth orbit, solar pressure and drag pressure are typically equal at an
altitude of about 800 km, which means that a sail craft would have to
operate above that altitude. Sail craft must operate in orbits where
their turn rates are compatible with the orbits, which is generally a
concern only for spinning disk configurations.
Sail operating temperatures are a function of solar distance,
sail angle, reflectivity, and front and back emissivities. A sail can be
used only where its temperature is kept within its material limits.
Generally, a sail can be used rather close to the Sun, around 0.25 AU,
or even closer if carefully designed for those conditions.
Applications
Potential applications for sail craft range throughout the Solar System,
from near the Sun to the comet clouds beyond Neptune. The craft can
make outbound voyages to deliver loads or to take up station keeping at
the destination. They can be used to haul cargo and possibly also used
for human travel.
Inner planets
For
trips within the inner Solar System, they can deliver payloads and then
return to Earth for subsequent voyages, operating as an interplanetary
shuttle. For Mars in particular, the craft could provide economical
means of routinely supplying operations on the planet according to
Jerome Wright, "The cost of launching the necessary conventional
propellants from Earth are enormous for manned missions. Use of sailing
ships could potentially save more than $10 billion in mission costs."
Solar sail craft can approach the Sun to deliver observation
payloads or to take up station keeping orbits. They can operate at 0.25
AU or closer. They can reach high orbital inclinations, including
polar.
Solar sails can travel to and from all of the inner planets.
Trips to Mercury and Venus are for rendezvous and orbit entry for the
payload. Trips to Mars could be either for rendezvous or swing-by with
release of the payload for aerodynamic braking.
Sail size m
Mercury Rendezvous
Venus Rendezvous
Mars Rendezvous
Mars Aerobrake
days
tons
days
tons
days
tons
days
tons
800 σ = 5 g/m2 w/o cargo
600
9
200
1
400
2
131
2
900
19
270
5
500
5
200
5
1200
28
700
9
338
10
2000 σ = 3 g/m2 w/o cargo
600
66
200
17
400
23
131
20
900
124
270
36
500
40
200
40
1200
184
700
66
338
70
Outer planets
Minimum
transfer times to the outer planets benefit from using an indirect
transfer (solar swing-by). However, this method results in high arrival
speeds. Slower transfers have lower arrival speeds.
The minimum transfer time to Jupiter for ac of 1 mm/s2 with no departure velocity relative to Earth is 2 years when using an indirect transfer (solar swing-by). The arrival speed (V∞) is close to 17 km/s. For Saturn, the minimum trip time is 3.3 years, with an arrival speed of nearly 19 km/s.
Minimum times to the outer planets (ac = 1 mm/s2)
Jupiter
Saturn
Uranus
Neptune
Time, yr
2.0
3.3
5.8
8.5
Speed, km/s
17
19
20
20
Oort Cloud/Sun's inner gravity focus
The Sun's inner gravitational focus point lies at minimum distance of 550 AU from the Sun, and is the point to which light from distant objects is focused by gravity
as a result of it passing by the Sun. This is thus the distant point to
which solar gravity will cause the region of deep space on the other
side of the Sun to be focused, thus serving effectively as a very large
telescope objective lens.
It has been proposed that an inflated sail, made of beryllium, that starts at 0.05 AU from the Sun would gain an initial acceleration of 36.4 m/s2,
and reach a speed of 0.00264c (about 950 km/s) in less than a day. Such
proximity to the Sun could prove to be impractical in the near term due
to the structural degradation of beryllium at high temperatures,
diffusion of hydrogen at high temperatures as well as an electrostatic
gradient, generated by the ionization of beryllium from the solar wind,
posing a burst risk. A revised perihelion of 0.1 AU would reduce the
aforementioned temperature and solar flux exposure.
Such a sail would take "Two and a half years to reach the heliopause, six and a half years to reach the Sun’s inner gravitational focus, with arrival at the inner Oort Cloud in no more than thirty years."
"Such a mission could perform useful astrophysical observations en
route, explore gravitational focusing techniques, and image Oort Cloud
objects while exploring particles and fields in that region that are of
galactic rather than solar origin."
Satellites
Robert L. Forward
has commented that a solar sail could be used to modify the orbit of a
satellite about the Earth. In the limit, a sail could be used to "hover"
a satellite above one pole of the Earth. Spacecraft fitted with solar
sails could also be placed in close orbits such that they are stationary
with respect to either the Sun or the Earth, a type of satellite named
by Forward a "statite".
This is possible because the propulsion provided by the sail offsets
the gravitational attraction of the Sun. Such an orbit could be useful
for studying the properties of the Sun for long durations. Likewise a solar sail-equipped spacecraft could also remain on station nearly above the polar solar terminator of a planet such as the Earth by tilting the sail at the appropriate angle needed to counteract the planet's gravity.
In his book The Case for Mars, Robert Zubrin
points out that the reflected sunlight from a large statite, placed
near the polar terminator of the planet Mars, could be focused on one of
the Martian polar ice caps to significantly warm the planet's
atmosphere. Such a statite could be made from asteroid material.
Trajectory corrections
The MESSENGER probe orbiting Mercury used light pressure on its solar panels to perform fine trajectory corrections on the way to Mercury.
By changing the angle of the solar panels relative to the Sun, the
amount of solar radiation pressure was varied to adjust the spacecraft
trajectory more delicately than possible with thrusters. Minor errors
are greatly amplified by gravity assist maneuvers, so using radiation pressure to make very small corrections saved large amounts of propellant.
In the science fiction novel Rocheworld,
Forward described a light sail propelled by super lasers. As the
starship neared its destination, the outer portion of the sail would
detach. The outer sail would then refocus and reflect the lasers back
onto a smaller, inner sail. This would provide braking thrust to stop
the ship in the destination star system.
Both methods pose monumental engineering challenges. The lasers would have to operate for years continuously at gigawatt
strength. Forward's solution to this requires enormous solar panel
arrays to be built at or near the planet Mercury. A planet-sized mirror
or Fresnel lens would need to be located at several dozen astronomical units
from the Sun to keep the lasers focused on the sail. The giant braking
sail would have to act as a precision mirror to focus the braking beam
onto the inner "deceleration" sail.
A potentially easier approach would be to use a maser to drive a
"solar sail" composed of a mesh of wires with the same spacing as the
wavelength of the microwaves directed at the sail, since the
manipulation of microwave radiation is somewhat easier than the
manipulation of visible light. The hypothetical "Starwisp" interstellar probe designwould use microwaves, rather than visible light, to push it. Masers
spread out more rapidly than optical lasers owing to their longer
wavelength, and so would not have as great an effective range.
Masers could also be used to power a painted solar sail, a
conventional sail coated with a layer of chemicals designed to evaporate
when struck by microwave radiation. The momentum generated by this evaporation could significantly increase the thrust generated by solar sails, as a form of lightweight ablative laser propulsion.
To further focus the energy on a distant solar sail, Forward proposed a lens designed as a large zone plate. This would be placed at a location between the laser or maser and the spacecraft.
Another more physically realistic approach would be to use the light from the Sun to accelerate the spacecraft.
The ship would first drop into an orbit making a close pass to the Sun,
to maximize the solar energy input on the sail, then it would begin to
accelerate away from the system using the light from the Sun.
Acceleration will drop approximately as the inverse square of the
distance from the Sun, and beyond some distance, the ship would no
longer receive enough light to accelerate it significantly, but would
maintain the final velocity attained. When nearing the target star, the
ship could turn its sails toward it and begin to use the outward
pressure of the destination star to decelerate. Rockets could augment
the solar thrust.
Similar solar sailing launch and capture were suggested for directed panspermia
to expand life in other solar system. Velocities of 0.05% the speed of
light could be obtained by solar sails carrying 10 kg payloads, using
thin solar sail vehicles with effective areal densities of 0.1 g/m2 with thin sails of 0.1 µm
thickness and sizes on the order of one square kilometer.
Alternatively, swarms of 1 mm capsules could be launched on solar sails
with radii of 42 cm, each carrying 10,000 capsules of a hundred million extremophile microorganisms to seed life in diverse target environments.
Theoretical studies suggest relativistic speeds if the solar sail harnesses a supernova.
Deorbiting artificial satellites
Small
solar sails have been proposed to accelerate the deorbiting of small
artificial satellites from Earth orbits. Satellites in low Earth orbit can use a combination of solar pressure on the sail and increased atmospheric drag to accelerate satellite reentry. A de-orbit sail developed at Cranfield University
is part of the UK satellite TechDemoSat-1, launched in 2014. The sail
deployed at the end of the satellite's five-year useful life in May
2019. The sail's purpose is to bring the satellite out of orbit over a period of about 25 years. In July 2015 British 3U CubeSat called DeorbitSail was launched into space with the purpose of testing 16 m2 deorbit structure, but eventually it failed to deploy it. A student 2U CubeSat mission called PW-Sat2, launched in December 2018 and tested a 4 m2 deorbit sail. It successfully deorbited in February 2021. In June 2017, a second British 3U CubeSat called InflateSail deployed a 10 m2 deorbit sail at an altitude of 500 kilometers (310 mi).
In June 2017 the 3U Cubesat URSAMAIOR has been launched in low Earth orbit to test the deorbiting system ARTICA developed by Spacemind. The device, which occupies only 0.4 U of the cubesat, shall deploy a sail of 2.1 m2 to deorbit the satellite at the end of the operational life.
Sail configurations
NASA illustration of the unlit side of a half-kilometre solar sail, showing the struts stretching the sail.An artist's depiction of a Cosmos 1-type spaceship in orbit
IKAROS,
launched in 2010, was the first practical solar sail vehicle. As of
2015, it was still under thrust, proving the practicality of a solar
sail for long-duration missions. It is spin-deployed, with tip-masses in the corners of its square sail. The sail is made of thin polyimide film, coated with evaporated aluminium. It steers with electrically controlled liquid crystal
panels. The sail slowly spins, and these panels turn on and off to
control the attitude of the vehicle. When on, they diffuse light,
reducing the momentum transfer to that part of the sail. When off, the
sail reflects more light, transferring more momentum. In that way, they
turn the sail. Thin-film solar cells
are also integrated into the sail, powering the spacecraft. The design
is very reliable, because spin deployment, which is preferable for
large sails, simplified the mechanisms to unfold the sail and the LCD
panels have no moving parts.
Parachutes have very low mass, but a parachute is not a workable
configuration for a solar sail. Analysis shows that a parachute
configuration would collapse from the forces exerted by shroud lines,
since radiation pressure does not behave like aerodynamic pressure, and
would not act to keep the parachute open.
The highest thrust-to-mass designs for ground-assembled deploy-able structures are square sails with the masts and guy
lines on the dark side of the sail. Usually there are four masts that
spread the corners of the sail, and a mast in the center to hold guy-wires.
One of the largest advantages is that there are no hot spots in the
rigging from wrinkling or bagging, and the sail protects the structure
from the Sun. This form can, therefore, go close to the Sun for maximum
thrust. Most designs steer with small moving sails on the ends of the
spars.
In the 1970s JPL studied many rotating blade and ring sails for a mission to rendezvous with Halley's Comet.
The intention was to stiffen the structures using angular momentum,
eliminating the need for struts, and saving mass. In all cases,
surprisingly large amounts of tensile strength were needed to cope with
dynamic loads. Weaker sails would ripple or oscillate when the sail's
attitude changed, and the oscillations would add and cause structural
failure. The difference in the thrust-to-mass ratio between practical
designs was almost nil, and the static designs were easier to control.
JPL's reference design was called the "heliogyro". It had
plastic-film blades deployed from rollers and held out by centrifugal
forces as it rotated. The spacecraft's attitude and direction were to be
completely controlled by changing the angle of the blades in various
ways, similar to the cyclic and collective pitch of a helicopter.
Although the design had no mass advantage over a square sail, it
remained attractive because the method of deploying the sail was simpler
than a strut-based design. The CubeSail (UltraSail) is an active project aiming to deploy a heliogyro sail.
Heliogyro design is similar to the blades on a helicopter. The
design is faster to manufacture due to lightweight centrifugal
stiffening of sails. Also, they are highly efficient in cost and
velocity because the blades are lightweight and long. Unlike the square
and spinning disk designs, heliogyro is easier to deploy because the
blades are compacted on a reel. The blades roll out when they are
deploying after the ejection from the spacecraft. As the heliogyro
travels through space the system spins around because of the centrifugal
acceleration. Finally, payloads for the space flights are placed in the
center of gravity to even out the distribution of weight to ensure
stable flight.
JPL also investigated "ring sails" (Spinning Disk Sail in the
above diagram), panels attached to the edge of a rotating spacecraft.
The panels would have slight gaps, about one to five percent of the
total area. Lines would connect the edge of one sail to the other.
Masses in the middles of these lines would pull the sails taut against
the coning caused by the radiation pressure. JPL researchers said that
this might be an attractive sail design for large crewed structures. The
inner ring, in particular, might be made to have artificial gravity
roughly equal to the gravity on the surface of Mars.
A solar sail can serve a dual function as a high-gain antenna. Designs differ, but most modify the metalization pattern to create a holographic monochromatic lens or mirror in the radio frequencies of interest, including visible light.
Reflective sail making
Proposed material for the construction of solar sails - carbon fiber.
Materials
The
most common material in current designs is a thin layer of aluminum
coating on a polymer (plastic) sheet, such as aluminized 2 µm Kapton
film. The polymer provides mechanical support as well as flexibility,
while the thin metal layer provides the reflectivity. Such material
resists the heat of a pass close to the Sun and still remains reasonably
strong. The aluminum reflecting film is on the Sun side. The sails of Cosmos 1 were made of aluminized PET film (Mylar).
Eric Drexler developed a concept for a sail in which the polymer was removed.
He proposed very high thrust-to-mass solar sails, and made prototypes
of the sail material. His sail would use panels of thin aluminium film
(30 to 100 nanometres thick) supported by a tensile
structure. The sail would rotate and would have to be continually under
thrust. He made and handled samples of the film in the laboratory, but
the material was too delicate to survive folding, launch, and
deployment. The design planned to rely on space-based production of the
film panels, joining them to a deploy-able tension structure. Sails in
this class would offer high area per unit mass and hence accelerations
up to "fifty times higher" than designs based on deploy-able plastic
films.
The material developed for the Drexler solar sail was a thin aluminium
film with a baseline thickness of 0.1 µm, to be fabricated by vapor
deposition in a space-based system. Drexler used a similar process to
prepare films on the ground. As anticipated, these films demonstrated
adequate strength and robustness for handling in the laboratory and for
use in space, but not for folding, launch, and deployment.
Research by Geoffrey Landis in 1998–1999, funded by the NASA Institute for Advanced Concepts, showed that various materials such as alumina for laser lightsails and carbon fiber for microwave pushed lightsails were superior sail materials to the previously standard aluminium or Kapton films.
In 2000, Energy Science Laboratories developed a new carbon fiber material that might be useful for solar sails.
The material is over 200 times thicker than conventional solar sail
designs, but it is so porous that it has the same mass. The rigidity and
durability of this material could make solar sails that are
significantly sturdier than plastic films. The material could
self-deploy and should withstand higher temperatures.
There has been some theoretical speculation about using molecular manufacturing techniques to create advanced, strong, hyper-light sail material, based on nanotube
mesh weaves, where the weave "spaces" are less than half the wavelength
of light impinging on the sail. While such materials have so far only
been produced in laboratory conditions, and the means for manufacturing
such material on an industrial scale are not yet available, such
materials could mass less than 0.1 g/m2, making them lighter than any current sail material by a factor of at least 30. For comparison, 5 micrometre thick Mylar sail material mass 7 g/m2, aluminized Kapton films have a mass as much as 12 g/m2, and Energy Science Laboratories' new carbon fiber material masses 3 g/m2.
The least dense metal is lithium,
about 5 times less dense than aluminium. Fresh, unoxidized surfaces
are reflective. At a thickness of 20 nm, lithium has an area density of
0.011 g/m2. A high-performance sail could be made of
lithium alone at 20 nm (no emission layer). It would have to be
fabricated in space and not used to approach the Sun. In the limit, a
sail craft might be constructed with a total areal density of around
0.02 g/m2, giving it a lightness number of 67 and ac of about 400 mm/s2. Magnesium and beryllium are also potential materials for high-performance sails. These 3 metals can be alloyed with each other and with aluminium.
Reflection and emissivity layers
Aluminium
is the common choice for the reflection layer. It typically has a
thickness of at least 20 nm, with a reflectivity of 0.88 to 0.90.
Chromium is a good choice for the emission layer on the face away from
the Sun. It can readily provide emissivity values of 0.63 to 0.73 for
thicknesses from 5 to 20 nm on plastic film. Usable emissivity values
are empirical because thin-film effects dominate; bulk emissivity values
do not hold up in these cases because material thickness is much
thinner than the emitted wavelengths.
Fabrication
Sails
are fabricated on Earth on long tables where ribbons are unrolled and
joined to create the sails. Sail material needed to have as little
weight as possible because it would require the use of the shuttle to
carry the craft into orbit. Thus, these sails are packed, launched, and
unfurled in space.
In the future, fabrication could take place in orbit inside large
frames that support the sail. This would result in lower mass sails
and elimination of the risk of deployment failure.
Operations
A solar sail can spiral inward or outward by setting the sail angle
Changing orbits
Sailing
operations are simplest in interplanetary orbits, where altitude
changes are done at low rates. For outward bound trajectories, the sail
force vector is oriented forward of the Sun line, which increases
orbital energy and angular momentum, resulting in the craft moving
farther from the Sun. For inward trajectories, the sail force vector is
oriented behind the Sun line, which decreases orbital energy and angular
momentum, resulting in the craft moving in toward the Sun. It is worth
noting that only the Sun's gravity pulls the craft toward the Sun—there
is no analog to a sailboat's tacking to windward. To change orbital
inclination, the force vector is turned out of the plane of the velocity
vector.
In orbits around planets or other bodies, the sail is oriented so
that its force vector has a component along the velocity vector, either
in the direction of motion for an outward spiral, or against the
direction of motion for an inward spiral.
Trajectory optimizations can often require intervals of reduced
or zero thrust. This can be achieved by rolling the craft around the
Sun line with the sail set at an appropriate angle to reduce or remove
the thrust.
Swing-by maneuvers
A
close solar passage can be used to increase a craft's energy. The
increased radiation pressure combines with the efficacy of being deep in
the Sun's gravity well to substantially increase the energy for runs to
the outer Solar System. The optimal approach to the Sun is done by
increasing the orbital eccentricity while keeping the energy level as
high as practical. The minimum approach distance is a function of sail
angle, thermal properties of the sail and other structure, load effects
on structure, and sail optical characteristics (reflectivity and
emissivity). A close passage can result in substantial optical
degradation. Required turn rates can increase substantially for a close
passage. A sail craft arriving at a star can use a close passage to
reduce energy, which also applies to a sail craft on a return trip from
the outer Solar System.
A lunar swing-by can have important benefits for trajectories
leaving from or arriving at Earth. This can reduce trip times,
especially in cases where the sail is heavily loaded. A swing-by can
also be used to obtain favorable departure or arrival directions
relative to Earth.
A planetary swing-by could also be employed similar to what is
done with coasting spacecraft, but good alignments might not exist due
to the requirements for overall optimization of the trajectory.
The following table lists some example concepts using beamed laser propulsion as proposed by the physicist Robert L. Forward:
Mission
Laser Power
Vehicle Mass
Acceleration
Sail Diameter
Maximum Velocity (% of the speed of light)
1. Flyby – Alpha Centauri, 40 years
outbound stage
65 GW
1 t
0.036 g
3.6 km
11% @ 0.17 ly
2. Rendezvous – Alpha Centauri, 41 years
outbound stage
7,200 GW
785 t
0.005 g
100 km
21% @ 4.29 ly
deceleration stage
26,000 GW
71 t
0.2 g
30 km
21% @ 4.29 ly
3. Crewed – Epsilon Eridani, 51 years (including 5 years exploring star system)
outbound stage
75,000,000 GW
78,500 t
0.3 g
1000 km
50% @ 0.4 ly
deceleration stage
21,500,000 GW
7,850 t
0.3 g
320 km
50% @ 10.4 ly
return stage
710,000 GW
785 t
0.3 g
100 km
50% @ 10.4 ly
deceleration stage
60,000 GW
785 t
0.3 g
100 km
50% @ 0.4 ly
Interstellar travel catalog to use photogravitational assists for a full stop
Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
Lightsail has a nominal mass-to-surface ratio (σnom) of 8.6×10−4 gram m−2 for a nominal graphene-class sail.
Area of the Lightsail, about 105 m2 = (316 m)2
Velocity up to 37,300 km s−1 (12.5% c)
Attitude (orientation) control
Both the Mariner 10 mission, which flew by the planets Mercury and Venus, and the MESSENGER mission to Mercury demonstrated the use of solar pressure as a method of attitude control in order to conserve attitude-control propellant.
Hayabusa also used solar pressure on its solar paddles as a method of attitude control to compensate for broken reaction wheels and chemical thruster.
MTSAT-1R (Multi-Functional Transport Satellite)'s
solar sail counteracts the torque produced by sunlight pressure on the
solar array. The trim tab on the solar array makes small adjustments to
the torque balance.
Ground deployment tests
NASA has successfully tested deployment technologies on small scale sails in vacuum chambers.
In 1999, a full-scale deployment of a solar sail was tested on the ground at DLR/ESA in Cologne.
A 15-meter-diameter solar sail (SSP, solar sail sub payload, soraseiru sabupeiro-do) was launched together with ASTRO-F on a M-V rocket on February 21, 2006, and made it to orbit. It deployed from the stage, but opened incompletely.
On August 9, 2004, the Japanese ISAS
successfully deployed two prototype solar sails from a sounding rocket.
A clover-shaped sail was deployed at 122 km altitude and a fan-shaped
sail was deployed at 169 km altitude. Both sails used 7.5-micrometer film. The experiment purely tested the deployment mechanisms, not propulsion.
Znamya 2
On February 4, 1993, the Znamya 2, a 20-meter wide aluminized-mylar reflector, was successfully deployed from the Russian Mir
space station. It was the first thin film reflector of such type
successfully deployed in space using the mechanism based on centrifugal
force. Although the deployment succeeded, propulsion was not demonstrated. A second test in 1999, Znamya 2.5, failed to deploy properly.
On 21 May 2010, Japan Aerospace Exploration Agency (JAXA) launched the world's first interplanetary solar sail spacecraft "IKAROS" (Interplanetary Kite-craft Accelerated by Radiation Of the Sun) to Venus. Using a new solar-photon propulsion method, it was the first true solar sail spacecraft fully propelled by sunlight, and was the first spacecraft to succeed in solar sail flight.
JAXA successfully tested IKAROS in 2010. The goal was to deploy
and control the sail and, for the first time, to determine the minute
orbit perturbations caused by light pressure. Orbit determination was
done by the nearby AKATSUKI probe
from which IKAROS detached after both had been brought into a transfer
orbit to Venus. The total effect over the six month flight was 100 m/s.
Until 2010, no solar sails had been successfully used in space as
primary propulsion systems. On 21 May 2010, the Japan Aerospace
Exploration Agency (JAXA) launched the IKAROS spacecraft, which deployed
a 200 m2 polyimide experimental solar sail on June 10. In July, the next phase for the demonstration of acceleration by
radiation began. On 9 July 2010, it was verified that IKAROS collected
radiation from the Sun and began photon acceleration by the orbit
determination of IKAROS by range-and-range-rate (RARR) that is newly
calculated in addition to the data of the relativization accelerating
speed of IKAROS between IKAROS and the Earth that has been taken since
before the Doppler effect was utilized. The data showed that IKAROS appears to have been solar-sailing since 3 June when it deployed the sail.
IKAROS has a diagonal spinning square sail 14×14 m (196 m2) made of a 7.5-micrometre (0.0075 mm) thick sheet of polyimide. The polyimide sheet had a mass of about 10 grams per square metre. A thin-film solar array is embedded in the sail. Eight LCD panels are embedded in the sail, whose reflectance can be adjusted for attitude control.IKAROS spent six months traveling to Venus, and then began a three-year journey to the far side of the Sun.
A photo of the experimental solar sail, NanoSail-D.
A team from the NASA Marshall Space Flight Center (Marshall), along with a team from the NASA Ames Research Center, developed a solar sail mission called NanoSail-D, which was lost in a launch failure aboard a Falcon 1 rocket on 3 August 2008. The second backup version, NanoSail-D2, also sometimes called simply NanoSail-D, was launched with FASTSAT on a Minotaur IV
on November 19, 2010, becoming NASA's first solar sail deployed in low
earth orbit. The objectives of the mission were to test sail deployment
technologies, and to gather data about the use of solar sails as a
simple, "passive" means of de-orbiting dead satellites and space debris.
The NanoSail-D structure was made of aluminium and plastic, with the
spacecraft massing less than 10 pounds (4.5 kg). The sail has about 100
square feet (9.3 m2) of light-catching surface. After some
initial problems with deployment, the solar sail was deployed and over
the course of its 240-day mission reportedly produced a "wealth of data"
concerning the use of solar sails as passive deorbit devices.
NASA
launched the second NanoSail-D unit stowed inside the FASTSAT satellite
on the Minotaur IV on November 19, 2010. The ejection date from the
FASTSAT microsatellite was planned for December 6, 2010, but deployment
only occurred on January 20, 2011.
On June 21, 2005, a joint private project between Planetary Society, Cosmos Studios and Russian Academy of Science launched a prototype sail Cosmos 1 from a submarine in the Barents Sea, but the Volna
rocket failed, and the spacecraft failed to reach orbit. They intended
to use the sail to gradually raise the spacecraft to a higher Earth
orbit over a mission duration of one month. The launch attempt sparked
public interest according to Louis Friedman. Despite the failed launch attempt of Cosmos 1, The Planetary Society received applause for their efforts from the space community and sparked a rekindled interest in solar sail technology.
On Carl Sagan's 75th birthday (November 9, 2009) the Planetary Society announced plans to make three further attempts, dubbed LightSail-1, -2, and -3. The new design will use a 32 m2 Mylar sail, deployed in four triangular segments like NanoSail-D. The launch configuration is a 3U CubeSat format, and as of 2015, it was scheduled as a secondary payload for a 2016 launch on the first SpaceXFalcon Heavy launch.
"LightSail-1" was launched on 20 May 2015.
The purpose of the test was to allow a full checkout of the satellite's
systems in advance of LightSail-2. Its deployment orbit was not high
enough to escape Earth's atmospheric drag and demonstrate true solar
sailing.
"LightSail-2" was launched on 25 June 2019, and deployed into a much higher low Earth orbit. Its solar sails were deployed on 23 July 2019. It reentered the atmosphere on 17 November 2022.
The Near-Earth Asteroid Scout (NEA Scout) was a mission jointly developed by NASA's Marshall Space Flight Center (MSFC) and the Jet Propulsion Laboratory (JPL), consisting of a controllable low-cost CubeSat solar sail spacecraft capable of encountering near-Earth asteroids (NEA). Four 7 m (23 ft) booms were to deploy, unfurling the 83 m2 (890 sq ft) aluminized polyimide solar sail. In 2015, NASA announced it had selected NEA Scout to launch as one of several secondary payloads aboard Artemis 1, the first flight of the agency's heavy-lift SLS launch vehicle. However, the craft was considered lost with the failure to establish communications shortly after launch in 2022.
Projects in development, proposed or cancelled
Despite the losses of Cosmos 1
and NanoSail-D (which were due to failure of their launchers),
scientists and engineers around the world remain encouraged and continue
to work on solar sails. While most direct applications created so far
intend to use the sails as inexpensive modes of cargo transport, some
scientists are investigating the possibility of using solar sails as a
means of transporting humans. This goal is strongly related to the
management of very large (i.e. well above 1 km2) surfaces in
space and the sail making advancements. Development of solar sails for
crewed space flight is still in its infancy.
A technology demonstration sail craft, dubbed Sunjammer, was in development with the intent to prove the viability and value of sailing technology. Sunjammer
had a square sail, 38 metres (125 ft) wide on each side, giving it an
effective area of 1,200 square metres (13,000 sq ft). It would have
traveled from the Sun-Earth L1Lagrangian point 1.5 million kilometres (930,000 miles) from Earth to a distance of 3 million kilometres (1.9 million miles). The demonstration was expected to launch on a Falcon 9 in January 2015. It would have been a secondary payload, released after the placement of the DSCOVR climate satellite at the L1 point. Citing a lack of confidence in the ability of its contractor L'Garde to deliver, the mission was cancelled in October 2014.
Gossamer deorbit sail
As of December 2013, the European Space Agency (ESA) has a proposed deorbit sail, named "Gossamer",
that would be intended to be used to accelerate the deorbiting of small
(less than 700 kilograms (1,500 lb)) artificial satellites from low Earth orbits.
The launch mass is 2 kilograms (4.4 lb) with a launch volume of only
15×15×25 centimetres (0.49×0.49×0.82 ft). Once deployed, the sail would
expand to 5 by 5 metres (16 ft × 16 ft) and would use a combination of
solar pressure on the sail and increased atmospheric drag to accelerate
satellite reentry.
OKEANOS (Outsized Kite-craft for Exploration and Astronautics in the
Outer Solar System) was a proposed mission concept by Japan's JAXA to Jupiter's Trojan asteroids using a hybrid solar sail for propulsion; the sail would have been covered with thin solar panels to power an ion engine. In-situ
analysis of the collected samples would have been performed by either
direct contact or using a lander carrying a high-resolution mass
spectrometer. A lander and a sample-return to Earth were options under
study. The OKEANOS Jupiter Trojan Asteroid Explorer was a finalist for Japan's ISAS' 2nd Large-class mission to be launched in the late 2020s. However, it was not selected.
The well-funded Breakthrough Starshot project announced on April 12,
2016, aims to develop a fleet of 1000 light sail nanocraft carrying
miniature cameras, propelled by ground-based lasers and send them to Alpha Centauri at 20% the speed of light. The trip would take 20 years.
In August 2019, NASA awarded the Solar Cruiser team $400,000 for nine-month mission concept studies. The spacecraft would have a 1,672 m2 (18,000 sq ft) solar sail and would orbit the Sun in a polar orbit, while the coronagraph instrument would enable simultaneous measurements of the Sun's magnetic field structure and velocity of coronal mass ejections. If selected for development, it would launch in 2024.
In popular culture
Cordwainer Smith gives a description of solar-sail-powered spaceships in "The Lady Who Sailed The Soul", published first in April 1960.
Jack Vance wrote a short story about a training mission on a solar-sail-powered spaceship in "Sail 25", published in 1961.
Arthur C. Clarke and Poul Anderson
(writing as Winston P. Sanders) independently published stories
featuring solar sails, both stories titled "Sunjammer," in 1964. Clarke
retitled his story "The Wind from the Sun" when it was reprinted, in
order to avoid confusion.
A similar technology was the theme in the Star Trek: Deep Space Nine episode "Explorers". In the episode, Lightships are described as an ancient technology used by Bajorans
to travel beyond their solar system by using light from the Bajoran sun
and specially constructed sails to propel them through space ("Explorers". Star Trek: Deep Space Nine. Season 3. Episode 22.).
In the third season of Apple TV+'s alternate history TV show For All Mankind, the fictional NASA spaceship Sojourner 1 utilises solar sails for additional propulsion on its way to Mars.
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