Space launch is the earliest part of a flight that reaches space. Space launch involves liftoff, when a rocket or other space launch vehicle leaves the ground, floating ship or midair aircraft at the start of a flight. Liftoff is of two main types: rocket launch (the current conventional method), and non-rocket spacelaunch (where other forms of propulsion are employed, including airbreathing jet engines).
There is no clear boundary between Earth's atmosphere
and space, as the density of the atmosphere gradually decreases as the
altitude increases. There are several standard boundary designations,
namely:
The Fédération Aéronautique Internationale has established the Kármán line
at an altitude of 100 km (62 mi) as a working definition for the
boundary between aeronautics and astronautics. This is used because at
an altitude of about 100 km (62 mi), as Theodore von Kármán calculated, a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift from the atmosphere to support itself.
Until 2021, the United States designated people who travel above an altitude of 50 mi (80 km) as astronauts. Astronaut wings
are now only awarded to spacecraft crew members that "demonstrated
activities during flight that were essential to public safety, or
contributed to human space flight safety".
NASA's Space Shuttle used 400,000 ft, or 75.76 miles (120 km), as its re-entry altitude (termed the Entry Interface), which roughly marks the boundary where atmospheric drag
becomes noticeable, thus beginning the process of switching from
steering with thrusters to maneuvering with aerodynamic control
surfaces.
In 2009, scientists reported detailed measurements with a
Supra-Thermal Ion Imager (an instrument that measures the direction and
speed of ions), which allowed them to establish a boundary at 118 km
(73.3 mi) above Earth. The boundary represents the midpoint of a gradual
transition over tens of kilometers from the relatively gentle winds of
the Earth's atmosphere to the more violent flows of charged particles in
space, which can reach speeds well over 268 m/s (880 ft/s).
Energy
By definition for spaceflight to occur, sufficient altitude is necessary. This implies a minimum gravitational potential energy needs to be overcome: for the Kármán line; this is approximately 1 MJ/kg.
W=mgh, m=1 kg, g=9.82 m/s2, h=105m.
W=1*9.82*105≈106J/kg=1MJ/kg
In practice, a higher energy than this is needed to be expended
due to losses such as airdrag, propulsive efficiency, cycle efficiency
of engines that are employed and gravity drag.
In the past fifty years, spaceflight has usually meant remaining
in space for a period of time, rather than going up and immediately
falling back to earth. This entails orbit, which is mostly a matter of
velocity, not altitude, although that does not mean air friction and
relevant altitudes in relation to that, and orbit, do not need to be
considered. At much higher altitudes than many orbital ones maintained
by satellites, altitude begins to become a larger factor and speed a
lesser one. At lower altitudes, due to the high speed required to remain
in orbit, air friction is an important consideration affecting
satellites, much more than in the popular image of space. At even lower
altitudes, balloons, with no forward velocity, can serve many of the
roles satellites play.
G-forces
Many cargos, particularly humans, have a limiting g-force
that they can survive. For humans this is about 3–6 g. Some launchers
such as gun launchers would give accelerations in the hundred or
thousands of g and thus are completely unsuitable.
Reliability
Launchers vary with respect to their reliability for achieving the mission.
Safety
Safety
is the probability of causing injury or loss of life. Unreliable
launchers are not necessarily unsafe, whereas reliable launchers are
usually, but not invariably safe.
Apart from catastrophic failure of the launch vehicle itself, other safety hazards include depressurisation, and the Van Allen radiation belts which preclude orbits which spend long periods within them.
Trajectory optimization
Trajectory optimization is the process of designing a trajectory that minimizes
(or maximizes) some measure of performance while satisfying a set of
constraints. Generally speaking, trajectory optimization is a technique
for computing an open-loop solution to an optimal control
problem. It is often used for systems where computing the full
closed-loop solution is not required, impractical or impossible. If a
trajectory optimization problem can be solved at a rate given by the
inverse of the Lipschitz constant, then it can be used iteratively to generate a closed-loop solution in the sense of Caratheodory. If only the first step of the trajectory is executed for an infinite-horizon problem, then this is known as Model Predictive Control (MPC).
Although the idea of trajectory optimization has been around for hundreds of years (calculus of variations, brachystochrone problem),
it only became practical for real-world problems with the advent of the
computer. Many of the original applications of trajectory optimization
were in the aerospace industry, computing rocket and missile launch
trajectories. More recently, trajectory optimization has also been used
in a wide variety of industrial process and robotics applications.
Impact
Space
launches have shown among other things to increase aluminium
concentration and pH-Levels around launch sites. That said proper
regulation and measures can reduce and even increase environmental
protection of launches.
Furthermore soot and debris from launches, particularly failed launches, have literally negatively impacted wide areas below. Leftover of launches are for example dumped in the ocean at places like the Pacific Ocean area called the spacecraft cemetery.
Beside ecological environments, lands and their communities, particularly indigenous peoples, have been colonized to build the necessary infrastructure, disregarding them
without reaching out for consultation or consent.
Many rockets use fossil fuels, some launch systems use hydrogen, while some rocket manufacturers (i.e. Orbex, ArianeGroup) are using different launch fuels (such as bio-propane; methane produced from biomass).
Launches exhaust often water vapor, which is a potent greenhouse
gas and at high altitudes not very common. Also methane itself, which
is used as a fuel, is a potent greenhouse gas.
Carbon emissions
As
the number of rocket launches is expected to increase, the cumulative
effect that launching into space has on Earth is expected to be
significant and not to be underestimated. A single common Falcon 9 launch emits carbon dioxide into the mesosphere of about 26 km3. A SpaceX Falcon Heavy rocket for instance burns through 400 metric tons
of kerosene and emits more carbon dioxide in a few minutes than an
average car would in more than two centuries.
Sub-orbital space flight is any space launch that reaches space
without making a full orbit around the planet, and requires a maximum
speed of around 1 km/s to reach space, and up to 7 km/s for longer
distance such as an intercontinental space flight. An example of a
sub-orbital flight would be a ballistic missile, or future tourist
flight such as Virgin Galactic, or an intercontinental transport flight like SpaceLiner.
Any space launch without an orbit-optimization correction to achieve a
stable orbit will result in a suborbital space flight, unless there is
sufficient thrust to leave orbit completely (See Space gun#Getting to orbit).
In addition, if orbit is required, then a much greater amount of
energy must be generated in order to give the craft some sideways speed.
The speed that must be achieved depends on the altitude of the orbit –
less speed is needed at high altitude. However, after allowing for the
extra potential energy of being at higher altitudes, overall more energy
is used reaching higher orbits than lower ones.
The speed needed to maintain an orbit near the Earth's surface
corresponds to a sideways speed of about 7.8 km/s (17,400 mph), an
energy of about 30MJ/kg. This is several times the energy per kg of
practical rocket propellant mixes.
Gaining the kinetic energy is awkward as the airdrag tends to
slow the spacecraft, so rocket-powered spacecraft generally fly a
compromise trajectory that leaves the thickest part of the atmosphere
very early on, and then fly on for example, a Hohmann transfer orbit
to reach the particular orbit that is required. This minimises the
airdrag as well as minimising the time that the vehicle spends holding
itself up. Airdrag is a significant issue with essentially all proposed
and current launch systems, although usually less so than the difficulty
of obtaining enough kinetic energy to simply reach orbit.
If the Earth's gravity is to be overcome entirely, then sufficient
energy must be obtained by a spacecraft to exceed the depth of the
gravity potential energy well. Once this has occurred, provided the
energy is not lost in any non-conservative way, then the vehicle will
leave the influence of the Earth. The depth of the potential well
depends on the vehicle's position, and the energy depends on the
vehicle's speed. If the kinetic energy exceeds the potential energy then
escape occurs. At the Earth's surface this occurs at a speed of
11.2 km/s (25,000 mph), but in practice a much higher speed is needed
due to airdrag.
Types of space launch
Rocket launch
Larger rockets are normally launched from a launch pad
that provides stable support until a few seconds after ignition. Due to
their high exhaust velocity—2,500 to 4,500 m/s (9,000 to 16,200 km/h;
5,600 to 10,100 mph)—rockets are particularly useful when very high
speeds are required, such as orbital speed at approximately 7,800 m/s
(28,000 km/h; 17,000 mph). Spacecraft delivered into orbital
trajectories become artificial satellites, which are used for many commercial purposes. Indeed, rockets remain the only way to launch spacecraft into orbit and beyond. They are also used to rapidly accelerate spacecraft when they change orbits or de-orbit for landing. Also, a rocket may be used to soften a hard parachute landing immediately before touchdown (see retrorocket).
Non-rocket launch
Non-rocket space launch
refers to theoretical concepts for launch into space where much of the
speed and altitude needed to achieve orbit is provided by a propulsion
technique that is not subject to the limits of the rocket equation. Although all space launches to date have been rockets, a number of alternatives to rockets have been proposed. In some systems, such as a combination launch system, skyhook, rocket sled launch, rockoon, or air launch, a portion of the total delta-v may be provided, either directly or indirectly, by using rocket propulsion.
Present-day launch costs are very high – $2,500 to $25,000 per kilogram from Earth to low Earth orbit
(LEO). As a result, launch costs are a large percentage of the cost of
all space endeavors. If launch can be made cheaper, the total cost of
space missions will be reduced. Due to the exponential nature of the
rocket equation, providing even a small amount of the velocity to LEO by
other means has the potential of greatly reducing the cost of getting
to orbit.
The term aerology (from Greek ἀήρ, aēr, "air"; and -λογία, -logia) is sometimes used as an alternative term for the study of Earth's atmosphere; in other definitions, aerology is restricted to the free atmosphere, the region above the planetary boundary layer.
Composition diagram showing the evolution/cycles of various elements in Earth's atmosphere
Atmospheric chemistry is a branch of atmospheric science in which the
chemistry of the Earth's atmosphere and that of other planets is
studied. It is a multidisciplinary field of research and draws on
environmental chemistry, physics, meteorology, computer modeling,
oceanography, geology and volcanology and other disciplines. Research is
increasingly connected with other areas of study such as climatology.
The composition and chemistry of the atmosphere is of importance
for several reasons, but primarily because of the interactions between
the atmosphere and living organisms. The composition of the Earth's
atmosphere has been changed by human activity and some of these changes
are harmful to human health, crops and ecosystems. Examples of problems
which have been addressed by atmospheric chemistry include acid rain,
photochemical smog and global warming. Atmospheric chemistry seeks to
understand the causes of these problems, and by obtaining a theoretical
understanding of them, allow possible solutions to be tested and the
effects of changes in government policy evaluated.
Atmospheric chemistry plays a major role in understanding the concentration of gases in our atmosphere that contribute to climate change.
More specifically, when combined with atmospheric physics and
biogeochemistry, it is useful in terms of studying the influence of greenhouse gases like CO2, N2O, and CH4, on Earth's radiative balance. According to UNEP, CO2
emissions increased to a new record of 57.1 GtCO2e, up 1.3% from the
previous year. Previous GHG emissions growth from 2010-2019 averaged
only +0.8% yearly, illustrating the dramatic increase in global
emissions. The Global Nitrous Oxide Budget cited that atmospheric N2O has increased by roughly 25% between 1750 and 2022, having the fasted annual growth rate in 2020 and 2021. Atmospheric chemistry is critical in understanding what contributes to
our changing climate. The warming of our climate is caused when CO2
emissions, constrained by biogeochemistry, are above a 0% increase. In
order to stop temperatures from rising, there must be no CO2
emissions. By understanding the chemical composition and emission rates
in our atmosphere alongside economic factors, researchers are able to
trace back emissions back to their sources. About 26% of the 2023 GtCO2e
was used for power, 15% for transportation, 11% in industry, 11% in
agriculture, etc. In order to successfully reverse the human-driven damage contributing
to global climate change, cuts of nearly 42% are needed by 2030 and are
to be implementing using government intervention. This is one example of
how atmospheric chemistry goes hand-in-hand with social and political
policy, biogeochemistry, and economic factors.
Atmospheric dynamics is the study of motion systems of meteorological
importance, integrating observations at multiple locations and times
and theories. Common topics studied include diverse phenomena such as thunderstorms, tornadoes, gravity waves, tropical cyclones, extratropical cyclones, jet streams,
and global-scale circulations. The goal of dynamical studies is to
explain the observed circulations on the basis of fundamental principles
from physics. The objectives of such studies incorporate improving weather forecasting,
developing methods for predicting seasonal and interannual climate
fluctuations, and understanding the implications of human-induced
perturbations (e.g., increased carbon dioxide concentrations or
depletion of the ozone layer) on the global climate.
Atmospheric physics is the application of physics to the study of the
atmosphere. Atmospheric physicists attempt to model Earth's atmosphere
and the atmospheres of the other planets using fluid flow equations,
chemical models, radiation balancing, and energy transfer processes in
the atmosphere and underlying oceans and land. In order to model weather
systems, atmospheric physicists employ elements of scattering theory, wave propagation models, cloud physics, statistical mechanics and spatial statistics,
each of which incorporate high levels of mathematics and physics.
Atmospheric physics has close links to meteorology and climatology and
also covers the design and construction of instruments for studying the
atmosphere and the interpretation of the data they provide, including remote sensing instruments.
Recent studies in atmospheric physics often rely on satellite-based observation. One example includes CALIPSO,
or the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite
Observation. The CALIPSO mission, engineered by NASA and the Centre
National d'Etudes Spatiales/CNES, studies how clouds and airborne
particles play a role in regulating the weather, climate, and quality of
Earth's atmosphere. According to NASA, this mission uses methods like
retrieval algorithm development, climatology development, spectroscopy,
weather and climate model evaluation, and cloudy radiative transfer
models in addition to atmospheric physics concepts to understand the
physics involved in Earth atmospheric regulation.
Climatology is a science that derives knowledge and practices from
the more specialized disciplines of meteorology, oceanography, geology,
biology, and astronomy to study climate. In contrast to meteorology, which studies short-term weather
systems lasting up to a few weeks, climatology studies the frequency
and trends of those systems. It studies the periodicity of weather
events over timescales ranging from years to millennia, as well as
changes in long-term average weather patterns. Climatologists,
those who practice climatology, study both the nature of climates –
local, regional or global – and the natural or human-induced factors
that cause climate variability and current ongoing global warming.
Additionally, the occurrence of past climates on Earth, such as those
arising from glacial periods and interglacials, can be used to predict future changes in climate.
Oftentimes, climatology is studied in conjunction with another
specialized discipline. One recent scientific study that utilizes topics
in climatology, oceanology, and even economics is entitled "Concerns
about El Nino-Southern Oscillation and the Atlantic Meridional
Overturning Circulation with an Increasingly Warm Ocean." Scientists under New Insights in Climate Science found that Earth is at
risk of El Nino events of greater extremes and overall climate
instability given new information regarding the El Nino Southern Oscillation (ENSO) and the Atlantic Meridional Overturning Circulation
(AMOC). ENSO describes a recurring climate pattern in which the
temperature of waters in the central and eastern tropical Pacific Ocean
changes periodically. AMOC is best described by NOAA as "a system of ocean currents that
circulates water within the Atlantic Ocean, bringing warm water north
and cold water south". This research has revealed that the collapse of the AMOC appears to be
occurring sooner than when earlier models had predicted. It also expands
on the fact that our economic and social systems are more vulnerable to
El Nino impacts than previously thought. The study of climatology is
vital in understanding current climate risks. Research is necessary to
mitigate and monitor the efforts put forth towards are ever-evolving
climate. Strengthening our knowledge within the realm of climatology
allows us to better prepare for the impacts of extreme El Nino events,
such as amplified droughts, floods, and heat extremes.
Aeronomy is the scientific study of the upper atmosphere of the Earth — the atmospheric layers above the stratopause
— and corresponding regions of the atmospheres of other planets, where
the entire atmosphere may correspond to the Earth's upper atmosphere or a
portion of it. A branch of both atmospheric chemistry and atmospheric
physics, aeronomy contrasts with meteorology, which focuses on the
layers of the atmosphere below the stratopause. In atmospheric regions studied by aeronomers, chemical dissociation and ionization are important phenomena.
All of the Solar System's planets have atmospheres. This is because
their gravity is strong enough to keep gaseous particles close to the
surface. Larger gas giants are massive enough to keep large amounts of
the light gases hydrogen and helium close by, while the smaller planets lose these gases into space. The composition of the Earth's atmosphere is different from the other
planets because the various life processes that have transpired on the
planet have introduced free molecular oxygen. Much of Mercury's atmosphere has been blasted away by the solar wind. The only moon that has retained a dense atmosphere is Titan. There is a thin atmosphere on Triton, and a trace of an atmosphere on the Moon.
Planetary atmospheres are affected by the varying degrees of
energy received from either the Sun or their interiors, leading to the
formation of dynamic weather systems such as hurricanes (on Earth), planet-wide dust storms (on Mars), an Earth-sized anticyclone on Jupiter (called the Great Red Spot), and holes in the atmosphere (on Neptune). At least one extrasolar planet, HD 189733 b, has been claimed to possess such a weather system, similar to the Great Red Spot but twice as large.
Hot Jupiters have been shown to be losing their atmospheres into space due to stellar radiation, much like the tails of comets. These planets may have vast differences in temperature between their day and night sides which produce supersonic winds, although the day and night sides of HD 189733b appear to have very
similar temperatures, indicating that planet's atmosphere effectively
redistributes the star's energy around the planet.
Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ionosphere, thermosphere, and exosphere. Though physically distinct, space weather is analogous to the terrestrial weather of Earth's atmosphere (troposphere and stratosphere). The term "space weather" was first used in the 1950s and popularized in the 1990s. Later, it prompted research into "space climate", the large-scale and long-term patterns of space weather.
History
For many centuries, the effects of space weather were noticed, but not understood. Displays of auroral light have long been observed at high latitudes.
Beginnings
In 1724, George Graham reported that the needle of a magnetic compass was regularly deflected from magnetic north
over the course of each day. This effect was eventually attributed to
overhead electric currents flowing in the ionosphere and magnetosphere
by Balfour Stewart in 1882, and confirmed by Arthur Schuster in 1889 from analysis of magnetic observatory data.
In 1852, astronomer and British Major General Edward Sabine showed that the probability of the occurrence of geomagnetic storms on Earth was correlated with the number of sunspots, demonstrating a novel solar-terrestrial interaction. The solar storm of 1859 caused brilliant auroral displays and disrupted global telegraph operations. Richard Carrington correctly connected the storm with a solar flare
that he had observed the day before near a large sunspot group,
demonstrating that specific solar events could affect the Earth.
Kristian Birkeland explained the physics of aurorae by creating artificial ones in his laboratory, and predicted the solar wind.
The introduction of radio revealed that solar weather could cause extreme static or noise. Radar jamming
during a large solar event in 1942 led to the discovery of solar radio
bursts, radio waves over a broad frequency range created by a solar
flare.
The 20th century
In
the 20th century, the interest in space weather expanded as military
and commercial systems came to depend on systems affected by space
weather. Communications satellites are a vital part of global commerce. Weather satellite systems provide information about terrestrial weather. The signals from satellites of a global positioning system
(GPS) are used in a wide variety of applications. Space weather
phenomena can interfere with or damage these satellites or interfere
with the radio signals with which they operate. Space weather phenomena
can cause damaging surges in long-distance transmission lines and expose passengers and crew of aircraft travel to radiation, especially on polar routes.
The International Geophysical Year increased research into space weather. Ground-based data obtained during IGY demonstrated that the aurorae occurred in an auroral oval, a permanent region of luminescence 15 to 25° in latitude from the magnetic poles and 5 to 20° wide. In 1958, the Explorer I satellite discovered the Van Allen belts, regions of radiation particles trapped by the Earth's magnetic field. In January 1959, the SovietsatelliteLuna 1 first directly observed the solar wind and measured its strength. A smaller International Heliophysical Year (IHY) occurred in 2007–2008.
In 1969, INJUN-5 (or Explorer 40) made the first direct observation of the electric field impressed on the Earth's high-latitude ionosphere by the solar wind. In the early 1970s, Triad data demonstrated that permanent electric
currents flowed between the auroral oval and the magnetosphere.
The term "space weather" came into usage in the late 1950s as the space age began and satellites began to measure the space environment. The term regained popularity in the 1990s along with the belief that
space's impact on human systems demanded a more coordinated research and
application framework.
Programs
US National Space Weather Program
A geomagnetic storm watch issued by Space Weather Prediction Center
The purpose of the US National Space Weather Program is to focus
research on the needs of the affected commercial and military
communities, to connect the research and user communities, to create
coordination between operational data centers, and to better define user
community needs. NOAA operates the National Weather Service's Space Weather Prediction Center.
The concept was turned into an action plan in 2000, an implementation plan in 2002, an assessment in 2006 and a revised strategic plan in 2010. A revised action plan was scheduled to be released in 2011 followed by a revised implementation plan in 2012.
ICAO Space Weather Advisory
International Civil Aviation Organization
(ICAO) implemented a Space Weather Advisory program in late 2019. Under
this program, ICAO designated four global space weather service
providers:
The Australia, Canada, France, and Japan (ACFJ) consortium,
comprising space weather agencies from Australia, Canada, France, and
Japan.
The Pan-European Consortium for Aviation Space Weather User Services
(PECASUS), comprising space weather agencies from Finland (lead),
Belgium, the United Kingdom, Poland, Germany, Netherlands, Italy,
Austria, and Cyprus.
The China-Russian Federation Consortium (CRC) comprising space weather agencies from China and the Russian Federation.
Phenomena
Within the Solar System, space weather is influenced by the solar wind and the interplanetary magnetic field carried by the solar wind plasma. A variety of physical phenomena is associated with space weather, including geomagnetic storms and substorms, energization of the Van Allen radiation belts, ionospheric disturbances and scintillation of satellite-to-ground radio signals and long-range radar signals, aurorae, and geomagnetically induced currents at Earth's surface. Coronal mass ejections are also important drivers of space weather, as they can compress the magnetosphere and trigger geomagnetic storms. Solar energetic particles (SEP) accelerated by coronal mass ejections or solar flares can trigger solar particle events, a critical driver of human impact space weather, as they can damage electronics onboard spacecraft (e.g. Galaxy 15 failure), and threaten the lives of astronauts, as well as increase radiation hazards to high-altitude, high-latitude aviation.
Some spacecraft failures can be directly attributed to space weather;
many more are thought to have a space weather component. For example,
46 of the 70 failures reported in 2003 occurred during the October 2003
geomagnetic storm. The two most common adverse space weather effects on
spacecraft are radiation damage and spacecraft charging.
Radiation (high-energy particles) passes through the skin of the
spacecraft and into the electronic components. In most cases, the
radiation causes an erroneous signal or changes one bit in memory of a
spacecraft's electronics (single event upsets). In a few cases, the radiation destroys a section of the electronics (single-event latchup).
Spacecraft charging is the accumulation of an electrostatic charge
on a nonconducting material on the spacecraft's surface by low-energy
particles. If enough charge is built up, a discharge (spark) occurs.
This can cause an erroneous signal to be detected and acted on by the
spacecraft computer. A recent study indicated that spacecraft charging
is the predominant space weather effect on spacecraft in geosynchronous orbit.
Spacecraft orbit changes
The orbits of spacecraft in low Earth orbit (LEO) decay to lower and lower altitudes due to the resistance from the friction between the spacecraft's surface (i.e. ,
drag) and the outer layer of the Earth's atmosphere (or the
thermosphere and exosphere). Eventually, a LEO spacecraft falls out of
orbit and towards the Earth's surface. Many spacecraft launched in the
past few decades have the ability to fire a small rocket to manage their
orbits. The rocket can increase altitude to extend lifetime, to direct
the re-entry towards a particular (marine) site, or route the satellite
to avoid collision with other spacecraft. Such maneuvers require precise
information about the orbit. A geomagnetic storm can cause an orbit
change over a few days that otherwise would occur over a year or more.
The geomagnetic storm adds heat to the thermosphere, causing the
thermosphere to expand and rise, increasing the drag on spacecraft. The 2009 satellite collision between the Iridium 33 and Cosmos 2251 demonstrated the importance of having precise knowledge of all objects in orbit. Iridium 33 had the capability to maneuver out of the path of Cosmos 2251 and could have evaded the crash, if a credible collision prediction had been available.
The exposure of a human body to ionizing radiation has the same harmful effects whether the source of the radiation is a medical X-ray machine, a nuclear power plant, or radiation in space. The degree of the harmful effect depends on the length of exposure and the radiation's energy density. The ever-present radiation belts extend down to the altitude of crewed spacecraft such as the International Space Station (ISS) and the Space Shuttle, but the amount of exposure is within the acceptable lifetime exposure limit under normal conditions. During a major space weather event that includes an SEP burst, the flux can increase by orders of magnitude. Areas within ISS provide shielding that can keep the total dose within safe limits. For the Space Shuttle, such an event would have required immediate mission termination.
Ground systems
Spacecraft signals
The
ionosphere bends radio waves in the same manner that water in a pool
bends visible light. When the medium through which such waves travel is
disturbed, the light image or radio information is distorted and can
become unrecognizable. The degree of distortion (scintillation) of a
radio wave by the ionosphere depends on the signal frequency. Radio
signals in the VHF band (30 to 300 MHz) can be distorted beyond recognition by a disturbed ionosphere. Radio signals in the UHF
band (300 MHz to 3 GHz) transit a disturbed ionosphere, but a receiver
may not be able to keep locked to the carrier frequency. GPS uses
signals at 1575.42 MHz (L1) and 1227.6 MHz (L2) that can be distorted by
a disturbed ionosphere. Space weather events that corrupt GPS signals
can significantly impact society. For example, the Wide Area Augmentation System operated by the US Federal Aviation Administration
(FAA) is used as a navigation tool for North American commercial
aviation. It is disabled by every major space weather event. Outages can
range from minutes to days. Major space weather events can push the
disturbed polar ionosphere 10° to 30° of latitude toward the equator and
can cause large ionospheric gradients (changes in density over distance
of hundreds of km) at mid and low latitude. Both of these factors can
distort GPS signals.
Long-distance radio signals
Radio waves in the HF band (3 to 30 MHz) (also known as the shortwave
band) are reflected by the ionosphere. Since the ground also reflects
HF waves, a signal can be transmitted around the curvature of the Earth
beyond the line of sight. During the 20th century, HF communications was
the only method for a ship or aircraft far from land or a base station
to communicate. The advent of systems such as Iridium
brought other methods of communications, but HF remains critical for
vessels that do not carry the newer equipment and as a critical backup
system for others. Space weather events can create irregularities in the
ionosphere that scatter HF signals instead of reflecting them,
preventing HF communications. At auroral and polar latitudes, small
space weather events that occur frequently disrupt HF communications. At
mid-latitudes, HF communications are disrupted by solar radio bursts,
by X-rays from solar flares (which enhance and disturb the ionospheric
D-layer) and by TEC enhancements and irregularities during major geomagnetic storms.
Transpolar airline routes are particularly sensitive to space weather, in part because Federal Aviation Regulations require reliable communication over the entire flight. Diverting such a flight is estimated to cost about $100,000.
All
passengers in commercial aircraft flying above 26,000 feet (7,900 m)
typically experience some exposure in this aviation radiation
environment.
Humans in commercial aviation
The
magnetosphere guides cosmic ray and solar energetic particles to polar
latitudes, while high-energy charged particles enter the mesosphere,
stratosphere, and troposphere. These energetic particles at the top of
the atmosphere shatter atmospheric atoms and molecules, creating harmful
lower-energy particles that penetrate deep into the atmosphere and
create measurable radiation. All aircraft flying above 8 km (26,200
feet) altitude are exposed to these particles. The dose exposure is
greater in polar regions than at midlatitude and equatorial regions.
Many commercial aircraft fly over the polar region. When a space weather
event causes radiation exposure to exceed the safe level set by
aviation authorities, the aircraft's flight path is diverted.
Measurements of the radiation environment at commercial aircraft
altitudes above 8 km (26,000 ft) have historically been done by
instruments that record the data on board where the data are then
processed later on the ground. However, a system of real-time radiation
measurements on-board aircraft has been developed through the NASA
Automated Radiation Measurements for Aerospace Safety (ARMAS) program. ARMAS
has flown hundreds of flights since 2013, mostly on research aircraft,
and sent the data to the ground through Iridium satellite links. The
eventual goal of these types of measurements is to data assimilate them
into physics-based global radiation models, e.g., NASA's Nowcast of
Atmospheric Ionizing Radiation System (NAIRAS), so as to provide the weather of the radiation environment rather than the climatology.
Ground-induced electric fields
Magnetic storm activity can induce geoelectric fields in the Earth's conducting lithosphere. Corresponding voltage differentials can find their way into electric power grids through ground connections,
driving uncontrolled electric currents that interfere with grid
operation, damage transformers, trip protective relays, and sometimes
cause blackouts. This complicated chain of causes and effects was demonstrated during the magnetic storm of March 1989, which caused the complete collapse of the Hydro-Québec
electric-power grid in Canada, temporarily leaving nine million people
without electricity. The possible occurrence of an even more intense
storm led to operational standards intended to mitigate induction-hazard risks, while reinsurance companies commissioned revised risk assessments.
Geophysical exploration
Air- and ship-borne magnetic surveys
can be affected by rapid magnetic field variations during geomagnetic
storms. Such storms cause data-interpretation problems because the space
weather-related magnetic field changes are similar in magnitude to
those of the subsurface crustal magnetic field in the survey area.
Accurate geomagnetic storm warnings, including an assessment of storm
magnitude and duration, allows for an economic use of survey equipment.
Geophysics and hydrocarbon production
For economic and other reasons, oil and gas production often involves horizontal drilling
of well paths many kilometers from a single wellhead. Accuracy
requirements are strict, due to target size – reservoirs may only be a
few tens to hundreds of meters across – and safety, because of the
proximity of other boreholes. The most accurate gyroscopic method is
expensive, since it can stop drilling for hours. An alternative is to
use a magnetic survey, which enables measurement while drilling (MWD). Near real-time magnetic data can be used to correct drilling direction. Magnetic data and space weather forecasts can help to clarify unknown sources of drilling error.
Terrestrial weather
The amount of energy entering the troposphere and stratosphere from space weather phenomena is trivial compared to the solar insolation
in the visible and infrared portions of the solar electromagnetic
spectrum. Although some linkage between the 11-year sunspot cycle and
the Earth's climate has been claimed., this has never been verified. For example, the Maunder minimum,
a 70-year period almost devoid of sunspots, has often been suggested to
be correlated to a cooler climate, but these correlations have
disappeared after deeper studies. The suggested link from changes in
cosmic-ray flux causing changes in the amount of cloud formation did not survive scientific tests. Another suggestion, that variations in the extreme ultraviolet (EUV) flux subtly influence existing drivers of the climate and tip the balance between El Niño/La Niña events collapsed when new research showed this was not possible. As such, a
linkage between space weather and the climate has not been demonstrated.
In addition, a link has been suggested between high energy charged particles (such as SEPs and cosmic rays) and cloud formation. This is because charged particles interact with the atmosphere to produce volatiles which then condense, creating cloud seeds. This is a topic of ongoing research at CERN, where experiments test the effect of high-energy charged particles on atmosphere. If proven, this may suggest a link between space weather (in the form of solar particle events) and cloud formation.
Most recently, a statistical connection has been reported between the occurrence of heavy floods and the arrivals of high-speed solar wind streams (HSSs). The enhanced auroral energy deposition during HSSs is suggested as a mechanism for the generation of downward propagating atmosphericgravity waves (AGWs). As AGWs reach lower atmosphere, they may excite the conditional instability in the troposphere, thus leading to excessive rainfall. [36]
Observation of space weather is done both for scientific research and
applications. Scientific observation has evolved with the state of
knowledge, while application-related observation expanded with the
ability to exploit such data.
Ground-based
Space
weather is monitored at ground level by observing changes in the
Earth's magnetic field over periods of seconds to days, by observing the
surface of the Sun, and by observing radio noise created in the Sun's
atmosphere.
The Sunspot Number (SSN) is the number of sunspots
on the Sun's photosphere in visible light on the side of the Sun
visible to an Earth observer. The number and total area of sunspots are
related to the brightness of the Sun in the EUV and X-ray portions of the solar spectrum and to solar activity such as solar flares and coronal mass ejections.
The 10.7 cm radio flux (F10.7) is a measurement of RF emissions
from the Sun and is roughly correlated with the solar EUV flux. Since
this RF emission is easily obtained from the ground and EUV flux is not,
this value has been measured and disseminated continuously since 1947.
The world standard measurements are made by the Dominion Radio Astrophysical Observatory at Penticton, BC, Canada and reported once a day at local noon in solar flux units (10−22W·m−2·Hz−1). F10.7 is archived by the National Geophysical Data Center.
Fundamental space weather monitoring data are provided by
ground-based magnetometers and magnetic observatories. Magnetic storms
were first discovered by ground-based measurement of occasional magnetic
disturbance. Ground magnetometer data provide real-time situational
awareness for postevent analysis. Magnetic observatories have been in
continuous operations for decades to centuries, providing data to inform
studies of long-term changes in space climatology.
Disturbance storm time index
(Dst index) is an estimate of the magnetic field change at the Earth's
magnetic equator due to a ring of electric current at and just earthward
of the geosynchronous orbit. The index is based on data from four ground-based magnetic observatories between 21° and 33° magnetic latitude
during a one-hour period. Stations closer to the magnetic equator are
not used due to ionospheric effects. The Dst index is compiled and
archived by the World Data Center for Geomagnetism, Kyoto.
Kp/ap
index: 'a' is an index created from the geomagnetic disturbance at one
midlatitude (40° to 50° latitude) geomagnetic observatory during a
3-hour period. 'K' is the quasilogarithmic counterpart of the 'a' index.
Kp and ap are the average of K and an over 13 geomagnetic observatories
to represent planetary-wide geomagnetic disturbances. The Kp/ap index indicates both geomagnetic storms and substorms (auroral disturbance). Kp/ap data are available from 1932 onward.
AE index is compiled from geomagnetic disturbances at 12
geomagnetic observatories in and near the auroral zones and is recorded
at 1-minute intervals. The public AE index is available with a lag of two to three days that
limits its utility for space weather applications. The AE index
indicates the intensity of geomagnetic substorms except during a major
geomagnetic storm when the auroral zones expand equatorward from the
observatories.
Radio noise bursts are reported by the Radio Solar Telescope
Network to the U.S. Air Force and to NOAA. The radio bursts are
associated with solar flare plasma that interacts with the ambient solar
atmosphere.
The Sun's photosphere is observed continuously for activity that can be the precursors to solar flares and CMEs. The Global Oscillation Network Group (GONG) project monitors both the surface and the interior of the Sun by using helioseismology,
the study of sound waves propagating through the Sun and observed as
ripples on the solar surface. GONG can detect sunspot groups on the far
side of the Sun. This ability has recently been verified by visual
observations from the STEREO spacecraft.
Neutron monitors
on the ground indirectly monitor cosmic rays from the Sun and galactic
sources. When cosmic rays interact with the atmosphere, atomic
interactions occur that cause a shower of lower-energy particles to
descend into the atmosphere and to ground level. The presence of cosmic
rays in the near-Earth space environment can be detected by monitoring
high-energy neutrons at ground level. Small fluxes of cosmic rays are
present continuously. Large fluxes are produced by the Sun during events
related to energetic solar flares.
Total Electron Content
(TEC) is a measure of the ionosphere over a given location. TEC is the
number of electrons in a column one meter square from the base of the
ionosphere (around 90 km altitude) to the top of the ionosphere (around
1000 km altitude). Many TEC measurements are made by monitoring the two
frequencies transmitted by GPS
spacecraft. Presently, GPS TEC is monitored and distributed in real
time from more than 360 stations maintained by agencies in many
countries.
Geoeffectiveness is a measure of how strongly space weather
magnetic fields, such as coronal mass ejections, couple with the Earth's
magnetic field. This is determined by the direction of the magnetic
field held within the plasma that originates from the Sun. New
techniques measuring Faraday rotation in radio waves are in development to measure field direction.
Satellite-based
A host of research spacecraft have explored space weather. The Orbiting Geophysical Observatory
series were among the first spacecraft with the mission of analyzing
the space environment. Recent spacecraft include the NASA-ESA
Solar-Terrestrial Relations Observatory (STEREO) pair of spacecraft
launched in 2006 into solar orbit and the Van Allen Probes, launched in 2012 into a highly elliptical
Earth orbit. The two STEREO spacecraft drift away from the Earth by
about 22° per year, one leading and the other trailing the Earth in its
orbit. Together they compile information about the solar surface and
atmosphere in three dimensions. The Van Allen probes record detailed
information about the radiation belts, geomagnetic storms, and the
relationship between the two.
Some spacecraft with other primary missions have carried
auxiliary instruments for solar observation. Among the earliest such
spacecraft were the Applications Technology Satellite (ATS) series at GEO that were precursors to the modern Geostationary Operational Environmental Satellite
(GOES) weather satellite and many communication satellites. The ATS
spacecraft carried environmental particle sensors as auxiliary payloads
and had their navigational magnetic field sensor used for sensing the
environment.
Many of the early instruments were research spacecraft that were
re-purposed for space weather applications. One of the first of these
was the IMP-8 (Interplanetary Monitoring Platform). It orbited the Earth at 35 Earth radii and observed the solar wind for
two-thirds of its 12-day orbits from 1973 to 2006. Since the solar wind
carries disturbances that affect the magnetosphere and ionosphere, IMP-8
demonstrated the utility of continuous solar wind monitoring. IMP-8 was
followed by ISEE-3, which was placed near the L1 Sun-Earth Lagrangian point,
235 Earth radii above the surface (about 1.5 million km, or 924,000
miles) and continuously monitored the solar wind from 1978 to 1982. The
next spacecraft to monitor the solar wind at the L1 point was WIND from 1994 to 1998. After April 1998, the WIND spacecraft orbit was changed to circle the Earth and occasionally pass the L1 point. The NASA Advanced Composition Explorer has monitored the solar wind at the L1 point from 1997 to present.
In addition to monitoring the solar wind, monitoring the Sun is
important to space weather. Because the solar EUV cannot be monitored
from the ground, the joint NASA-ESASolar and Heliospheric Observatory
(SOHO) spacecraft was launched and has provided solar EUV images
beginning in 1995. SOHO is a main source of near-real time solar data
for both research and space weather prediction and inspired the STEREO mission. The Yohkoh
spacecraft at LEO observed the Sun from 1991 to 2001 in the X-ray
portion of the solar spectrum and was useful for both research and space
weather prediction. Data from Yohkoh inspired the Solar X-ray Imager on GOES.
GOES-7 monitors space weather conditions during the October 1989 solar activity resulted in a Forbush Decrease, ground level enhancements, and many satellite anomalies.
Spacecraft with instruments whose primary purpose is to provide data for space weather predictions and applications include the Geostationary Operational Environmental Satellite (GOES) series of spacecraft, the POES series, the DMSP series, and the Meteosat
series. The GOES spacecraft have carried an X-ray sensor (XRS) which
measures the flux from the whole solar disk in two bands – 0.05 to
0.4 nm and 0.1 to 0.8 nm – since 1974, an X-ray imager (SXI) since 2004,
a magnetometer which measures the distortions of the Earth's magnetic
field due to space weather, a whole disk EUV
sensor since 2004, and particle sensors (EPS/HEPAD) which measure ions
and electrons in the energy range of 50 keV to 500 MeV. Starting
sometime after 2015, the GOES-R generation of GOES spacecraft will
replace the SXI with a solar EUV image (SUVI) similar to the one on SOHO and STEREO and the particle sensor will be augmented with a component to extend the energy range down to 30 eV.
The Deep Space Climate Observatory (DSCOVR) satellite is a NOAA
Earth observation and space weather satellite that launched in February
2015. Among its features is advance warning of coronal mass ejections.
Models
Space
weather models are simulations of the space weather environment. Models
use sets of mathematical equations to describe physical processes.
These models take a limited data set and attempt to describe all
or part of the space weather environment in or to predict how weather
evolves over time. Early models were heuristic; i.e., they did not directly employ physics. These models take less resources than their more sophisticated descendants.
Later models use physics to account for as many phenomena as
possible. No model can yet reliably predict the environment from the
surface of the Sun to the bottom of the Earth's ionosphere. Space
weather models differ from meteorological models in that the amount of
input is vastly smaller.
A significant portion of space weather model research and development in the past two decades has been done as part of the Geospace Environmental Model (GEM) program of the National Science Foundation. The two major modeling centers are the Center for Space Environment Modeling (CSEM) and the Center for Integrated Space weather Modeling (CISM). The Community Coordinated Modeling Center (CCMC) at the NASA Goddard Space Flight Center
is a facility for coordinating the development and testing of research
models, for improving and preparing models for use in space weather
prediction and application.
Modeling techniques include (a) magnetohydrodynamics,
in which the environment is treated as a fluid, (b) particle in cell,
in which non-fluid interactions are handled within a cell and then cells
are connected to describe the environment, (c) first principles, in
which physical processes are in balance (or equilibrium) with one
another, (d) semi-static modeling, in which a statistical or empirical
relationship is described, or a combination of multiple methods.
Commercial space weather development
During
the first decade of the 21st Century, a commercial sector emerged that
engaged in space weather, serving agency, academia, commercial and
consumer sectors. Space weather providers are typically smaller companies, or small
divisions within a larger company, that provide space weather data,
models, derivative products and service distribution.
The commercial sector includes scientific and engineering
researchers as well as users. Activities are primarily directed toward
the impacts of space weather upon technology. These include, for
example:
Atmospheric drag on LEO satellites caused by energy inputs into the thermosphere from solar UV, FUV, Lyman-alpha, EUV, XUV, X-ray, and gamma ray photons as well as by charged particle precipitation and Joule heating at high latitudes;
Surface and internal charging from increased energetic particle
fluxes, leading to effects such as discharges, single event upsets and
latch-up, on LEO to GEO satellites;
Disrupted GPS signals caused by ionospheric scintillation leading to
increased uncertainty in navigation systems such as aviation's Wide Area Augmentation System (WAAS);
Lost HF, UHF and L-band radio communications due to ionosphere scintillation, solar flares and geomagnetic storms;
Increased radiation to human tissue and avionics from galactic cosmic rays
SEP, especially during large solar flares, and possibly bremsstrahlung
gamma-rays produced by precipitating radiation belt energetic electrons
at altitudes above 8 km;
Increased inaccuracy in surveying and oil/gas exploration that uses
the Earth's main magnetic field when it is disturbed by geomagnetic
storms;
Loss of power transmission from GIC surges in the electrical power
grid and transformer shutdowns during large geomagnetic storms.
Many of these disturbances result in societal impacts that account for a significant part of the national GDP.
The concept of incentivizing commercial space weather was first
suggested by the idea of a Space Weather Economic Innovation Zone
discussed by the American Commercial Space Weather Association (ACSWA)
in 2015. The establishment of this economic innovation zone would
encourage expanded economic activity developing applications to manage
the risks space weather and would encourage broader research activities
related to space weather by universities. It could encourage U.S.
business investment in space weather services and products. It promoted
the support of U.S. business innovation in space weather services and
products by requiring U.S. government purchases of U.S. built commercial
hardware, software, and associated products and services where no
suitable government capability pre-exists. It also promoted U.S. built
commercial hardware, software, and associated products and services
sales to international partners. designate U.S. built commercial
hardware, services, and products as “Space Weather Economic Innovation
Zone” activities; Finally, it recommended that U.S. built commercial
hardware, services, and products be tracked as Space Weather Economic
Innovation Zone contributions within agency reports. In 2015 the U.S.
Congress bill HR1561 provided groundwork where social and environmental
impacts from a Space Weather Economic Innovation Zone could be
far-reaching. In 2016, the Space Weather Research and Forecasting Act
(S. 2817) was introduced to build on that legacy. Later, in 2017-2018
the HR3086 Bill took these concepts, included the breadth of material
from parallel agency studies as part of the OSTP-sponsored Space Weather
Action Program (SWAP), and with bicameral and bipartisan support the 116th Congress (2019) is
considering passage of the Space Weather Coordination Act (S141, 115th
Congress).
The May 1921 geomagnetic storm, one of the largest geomagnetic storms disrupted telegraph service and damaged electrical equipment worldwide.
The Solar storm of August 1972, a large SEP event occurred. If astronauts had been in space at the time, the dose could have been life-threatening.
The March 1989 geomagnetic storm included multiple space weather effects: SEP, CME, Forbush decrease, ground level enhancement, geomagnetic storm, etc..
April 21, 2002, the Nozomi
Mars Probe was hit by a large SEP event that caused large-scale
failure. The mission, which was already about 3 years behind schedule,
was abandoned in December 2003.
The 2003 Halloween solar storms, a series of coronal mass ejections and solar flares in late October and early November 2003 with associated impacts.
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