04 Outer space.pdf

Lecture 4 Outer space  Challenging environment Outer space (or simply space) is the expanse that exists beyond Earth’s atmosphere. It represents a challenging environment for human exploration because of the hazards of vacuum, temperature, and radiation. Weightlessness has...

Lecture 4 Outer space  Challenging environment Outer space (or simply space) is the expanse that exists beyond Earth’s atmosphere. It represents a challenging environment for human exploration because of the hazards of vacuum, temperature, and radiation. Weightlessness has a negative effect on human physiology.  Constitutes a near-perfect vacuum Outer space constitutes a near- perfect vacuum. The lack of pressure in space is the most immediate dangerous characteristic of space to humans.  Earth Earth is the only astronomical object known to harbor life.  Gravity The gravity of Earth is the acceleration that is imparted to objects due to the distribution of mass within Earth. Gravity decreases with altitude as one rises above Earth’s surface because greater altitude means greater distance from Earth’s centre. CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=269951  Atmosphere The atmosphere of Earth is composed of a layer of gas mixture that surrounds Earth’s surface, known collectively as air, all retained by Earth’s gravity.  Density Atmospheric density decreases as the altitude increases.  Pressure Atmospheric pressure is caused by the weight of air above the measurement point. As altitude increases, there is less overlying atmospheric mass, so atmospheric pressure decreases with increasing altitude.  Boiling point of water Water boils at 100 C at Earth’s standard atmospheric pressure. The boiling point is the temperature at which the vapour pressure is equal to the atmospheric pressure around the liquid. Because of this, the boiling point of liquids is lower at lower pressure. user:Markus Schweiss, CC BY-SA 3.0, via Wikimedia Commons  Armstrong limit The Armstrong limit is a measure of altitude above which atmospheric pressure is sufficiently low that water boils at the normal temperature of the human body. – The term is named after Harry George Armstrong, who was a major general in the United States Air Force, a physician, and an airman.  Exposed bodily liquids boil away On Earth, the limit is around 18– 19 km above sea level. At or above the Armstrong limit, exposed bodily liquids such as saliva, tears, and liquids in the lungs boil away. https://www.youtube.com/watch?v=7eX1XPhZz3M  Rupture of the lungs, etc. Out in space, sudden exposure of an unprotected human to very low pressure can cause a rupture of the lungs, due to the large pressure differential between inside and outside the chest. It can rupture eardrums and sinuses. https://www.youtube.com/watch?v=U1kEf5nh-TA&t=113s  Summary Outer space – Near-perfect vacuum Lack of pressure – Dangerous to humans  Lecture 4 – Part 2 Outer space (cont.) – Low temperature – Radiation  Outer space has a low temperature The baseline temperature of outer space is −270 C.  Sun The Sun is a sphere of hot plasma. – Plasma is a state of matter characterized by the presence of a significant portion of charged particles in any combination of ions or electrons. Roughly ¾ of the Sun’s mass consists of hydrogen; the rest is mostly helium.  Sunlight The Sun radiates energy from its surface mainly as light.  Earth’s atmosphere is a gas mixture The atmosphere of Earth is composed of a layer of gas mixture. – Dry air contains 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide (a greenhouse gas), and small amounts of other trace gases. – Air also contains a variable amount of water vapor (a greenhouse gas), on average around 1% at sea level, and 0.4% over the entire atmosphere.  Greenhouse gases Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. A loose necktie, CC BY-SA 4.0, via Wikimedia Commons  Greenhouse effect The greenhouse effect occurs when greenhouse gases insulate Earth from losing heat to space, raising its surface temperature. Without the greenhouse effect, the Earth’s average surface temperature would be about −18 C, which is less than Earth’s average of about 15 C.  Summary Outer space – Low temperature Sunlight & Earth’s atmosphere – Greenhouse effect  Outer space is permeated by radiation Outer space is permeated by radiation. This includes electromagnetic radiation and particle radiation. Without the protection of Earth’s atmosphere and magnetic field astronauts are exposed to high levels of radiation.  Solar ultraviolet radiation Ultraviolet (UV) radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun.  Electromagnetic radiation Electromagnetic radiation consists of waves. Shorter-wavelength electromagnetic radiation has more energy. UV light is electromagnetic radiation of wavelengths shorter than that of visible light, but longer than X-rays. This Photo by Unknown Author is licensed under CC BY-SA  Damages DNA Short-wave UV light damages DNA. For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. Onetwo1, CC BY-SA 3.0, via Wikimedia Commons  Filtered out by the atmosphere The amount of UV light produced by the Sun means that Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. Extremely short-wavelength UV is screened out by nitrogen.  Three categories UV radiation capable of penetrating nitrogen is divided into three categories, based on its wavelength; these are referred to as UV-A, UV-B, and UV-C.  UV-C UV-C, which is very harmful to all living things, is entirely screened out by a combination of ordinary oxygen and ozone.  Ozone-oxygen cycle Ozone in Earth’s atmosphere is created by UV light striking ordinary oxygen molecules containing two oxygen atoms (O2), splitting them into individual oxygen atoms; the atomic oxygen then combines with unbroken O2 to create ozone (O3). The ozone molecule is unstable and when UV light hits ozone it splits into a molecule of O2 and an individual atom of oxygen, a continuing process called the ozone-oxygen cycle.  Ozone layer The ozone layer is a region of Earth’s atmosphere that contains a high concentration of ozone in relation to other parts of the atmosphere, although still small in relation to other gases in the atmosphere.  Summary Ozone layer – Development of new manufactured chemicals to replace older ones (domain multi-disciplinarity) Manufactured chemicals (science, technology, economy) Ozone depletion (environment) Montreal protocol (legal)  UV-B The ozone layer is very effective at screening out UV-B. Nevertheless, some UV-B, particularly at its longest wavelengths, reaches the Vitamin D surface, and is important for the skin’s production of vitamin D in mammals.  UV-A Ozone is transparent to most UV- A, so most of this longer- wavelength UV radiation reaches the surface, and it constitutes most of the UV reaching the Earth. This type of UV radiation is significantly less harmful to DNA. This Photo by Unknown Author is licensed under CC BY-NC-ND  Summary Outer space – Solar UV radiation Earth’s atmosphere – filters out UV  Earth’s magnetic field Earth’s magnetic field extends from Earth’s interior out into space. It is approximately dipolar, with an axis that is nearly aligned with Earth’s rotational axis.  Earth’s liquid outer core The magnetic field is generated in Earth’s outer core. Earth’s outer core is a fluid layer composed of mostly iron and nickel that lies above Earth’s solid inner core.  Convection currents In the liquid outer core, there are convection currents due to heat escaping from the core. – Convection is the transfer of heat from one place to another due to the movement of fluid. User:Oni Lukos, CC BY-SA 3.0, via Wikimedia Commons  Earth’s rotation The overall planetary rotation tends to organize the flow into rolls aligned along the rotation axis. Andrew Z. Colvin, CC BY-SA 4.0, via Wikimedia Commons  Generation of the magnetic field Electric currents are created in the conductive iron alloys by the convection currents. Earth’s magnetic field is believed to be generated by the electric currents. – In an electromagnet, an electric current through a coil of wire creates a magnetic field. P.Sumanth Naik, CC BY-SA 3.0, via Wikimedia Commons  Magnetosphere The magnetosphere is defined by the extent of Earth’s magnetic field in space.  Protects Earth from the charged particles It protects Earth from the charged particles of the solar wind and cosmic rays that would otherwise strip away the upper atmosphere, including the ozone layer.  Solar wind The solar wind is a stream of charged particles released from the Sun’s outermost atmospheric layer, the corona. This plasma mostly consists of electrons, protons and helium nuclei. Earth’s magnetic field deflects most of the solar wind.  Van Allen radiation belts The Van Allen radiation belt is a zone of energetic charged particles that are captured by and held around Earth by the magnetosphere. Earth has two such belts. The belts are named after James Van Allen, who described the belts in 1958.  Charged particles held around Earth Some of the charged particles originate from the solar wind do get into the magnetosphere. They spiral around field lines, bouncing back and forth between the poles. The inner belt is mainly composed of protons; the outer belt consists mainly of electrons.  Summary Electromagnet – An electric current through a coil of wire creates a magnetic field. Van Allen radiation belts – Charged particles spiral around magnetic field lines.  Summary Outer space – Solar wind Earth’s magnetic field – Deflects most of the solar wind – Van Allen radiant belts  Summary Outer space – Low temperature – Radiation Solar UV radiation Solar wind Earth – Atmosphere – Magnetic field  Lecture 4 – Part 3 Outer space – Radiation (cont.) Cosmic rays – Weightlessness  Cosmic rays Earth’s magnetic field also deflects cosmic rays. Cosmic rays are high-energy particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light.  Two types Cosmic rays can be divided into two types: 1. Galactic cosmic rays and extragalactic cosmic rays 2. Solar energetic particles  Galactic/extragalactic cosmic rays The Sun is part of the Milky Way galaxy, which is one of many galaxies in the universe. Galactic cosmic rays and extragalactic cosmic rays are high-energy particles originating outside the Solar System. https://www.youtube.com/watch?v=MkRSmynqonM&t=270s  Supernova Ale RaFlo, CC BY-SA 4.0, via Wikimedia Commons A significant fraction of cosmic rays originate from the supernovae. The word supernova is derived from the Latin word nova, meaning ‘new’, which refers to what appears to be a temporary new bright star. – Supernovae are relatively rare events within a galaxy, occurring about three times a century in the Milky Way. NASA/ESA, CC BY-SA 3.0, via Wikimedia Commons  Powerful & luminous explosion of a star A supernova is a powerful and luminous explosion of a star. https://www.youtube.com/watch?v=aysiMbgml5g  Solar energetic particles Solar energetic particles are high- energy, charged particles originating in the solar atmosphere and solar wind. They become accelerated either in the Sun’s atmosphere during a solar flare or in interplanetary space by a coronal mass ejection.  Solar flare A solar flare is a relatively intense, localized emission (eruption) of electromagnetic radiation in the Sun’s atmosphere. https://www.youtube.com/watch?v=TujfLt9HETQ  Coronal mass ejection Image Editor, CC BY 2.0, via Wikimedia Commons A coronal mass ejection (CME) is a significant ejection (eruption) of plasma mass from the Sun’s corona. https://www.youtube.com/shorts/FusXBvPuyDE  Summary Outer space – Radiation Solar UV radiation Solar wind Cosmic rays  Ionizing radiation Outer space is permeated by radiation. Radiation is often categorized as either ionizing or non-ionizing. Ionizing radiation consists of particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by This Photo by Unknown Author is licensed under CC BY detaching electrons from them.  Health hazard Ionizing radiation presents a health hazard. Exposure to ionizing radiation causes cell damage to living tissue and organ damage. In high acute doses, it will result in radiation burns and radiation sickness, and lower level doses over a protracted time can cause cancer.  Weight The weight of an object on Earth’s surface is the downwards force on that object, given by Newton’s second law, or 𝐹 = 𝑚𝑔 where 𝑔 is the acceleration that is imparted to objects due to the effect of gravitation.  Contact force A person standing still on a platform is acted upon by gravity, which would pull him down towards the Earth’s core unless there were a countervailing force from the resistance of the platform’s molecules, a force which is named the “normal force”.  Weight-sensations The weight-sensations originate from contact with supporting floors, seats, beds, scales, and the like. A sensation of weight is produced when contact forces act upon a body.  Free fall Free fall is any motion of a body where gravity is the only force acting upon it.  Astronaut in orbit An astronaut in orbit is in free fall. – He is subject to only the force of gravity. – His orbital speed keeps him in orbit.  Weightlessness When there are no other forces, such as the normal force exerted between the astronaut and his surrounding objects, it will result in the sensation of weightlessness. – When viewed from an orbiting observer, other close objects in space appear to be floating because everything is also in free fall.  Deleterious effects on human health OpenStax, CC BY 4.0, via Wikimedia Commons Humans evolved for life in Earth gravity, and exposure to weightlessness has been shown to have deleterious effects on human health. The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. Laboratoires Servier, CC BY-SA 3.0, via Wikimedia Commons  Outer space is a challenging environment Outer space represents a challenging environment for human exploration because of the hazards of vacuum, temperature, and radiation. Weightlessness has a negative effect on human physiology.  Spacecraft & spacesuit Technology such as that offered by a spacecraft or spacesuit is able to shield people from the harshest conditions. The life support system supplies air. It must also maintain temperature and pressure within acceptable limits. Askeuhd, CC BY-SA 4.0, via Wikimedia Commons  Shielding against radiation Shielding against radiation is also necessary. – Alpha () radiation consists of a fast-moving helium nucleus and is stopped by a sheet of paper. – Beta () radiation, consisting of electrons, is halted by an aluminum plate. – Gamma () radiation, consisting of energetic electromagnetic radiation, is eventually absorbed as it penetrates a dense material. Anynobody~commonswiki, CC BY-SA 4.0, via Wikimedia Commons  Regimen of exercise Muscle atrophy and spaceflight osteopenia can be minimized through a regimen of exercise.  Summary Outer space & Earth (Scientific inter-disciplinarity) – Outer space represents a challenging environment for human exploration (physics, biology) – Earth harbors life (geology) – Technology