The Space Environments

Most Orbiting Satellites Hubble Telescope (568km) International Space Station (400km) Northern Lights (85-400km) Minimum Altitude for Orbit (130.4km) Earn Astronaut Wings (92.5km) Where meteors typically burn up High Altitude Balloons Regular Flights

The Neutral Environment The region of the Earth’s atmosphere located between about 56 and 375 miles above the Earth’s surface Also known as the thermosphere Contains neutral atmospheric constituents Composed mostly of neutral gas particles which stratify based on their molecular weight Atomic oxygen is dominant in the lower thermosphere Helium and hydrogen dominate the higher regions At sea level, air is about 21% oxygen, 78% nitrogen and 1% other miscellaneous gases

In the neutral environment of the thermosphere, atomic oxygen is the dominant component, along with helium and hydrogen The highly diluted gas in this layer can reach 4,530 °F during the day. Despite the high temperature, an observer or object will experience cold temperatures in the thermosphere, because the extremely low density of gas (practically a hard vacuum) is insufficient for the molecules to conduct heat The miscellaneous gases include water vapor and carbon dioxide. Although they are only present in small percentages, they are very important because of their ability to absorb heat

Effects on Spacecraft Spacecrafts in LEO (below 375 miles) are affected in two main ways: Drag, which shortens orbital lifetimes Atomic oxygen, which degrades spacecraft surfaces

Drag Drag has a significant impact on spacecraft in low Earth orbit (LEO),. Although the air density is much lower than near the Earth’s surface, the air resistance in those layers of the atmosphere where satellites in LEO travel is still strong enough to produce drag and pull them closer to the Earth If left unchecked, the drag eventually results in termination of the orbit, bringing the spacecraft back down into the atmosphere, increasing drag and heat which often results in the object burning up upon re-entry Due to atmospheric drag, the lowest altitude above the Earth at which an object in a circular orbit can complete at least one full revolution without propulsion is approximately 90 miles Thrusters can be used to prolong the orbit by raising the spacecraft back up to counteract the atmospheric drag

Atomic Oxygen Oxygen comes in several different forms. The oxygen that we breathe is called O2 and it is comprised of two atoms of oxygen. O3 is ozone, such as occurs in Earth's upper atmosphere O (one atom), is atomic oxygen. Atomic oxygen doesn't exist naturally for very long on the surface of Earth, as it is very reactive. But in space, where there is plenty of ultraviolet radiation, O2 molecules are more easily broken apart to create atomic oxygen. The atmosphere in low Earth orbit is comprised of about 96% atomic oxygen. Chemically speaking, rust is oxidation, occurring when oxygen molecules combine with the metal. This reaction is a lot quicker and stronger with atomic oxygen and can weaken components or change their characteristic over time

Vacuum Environment A pure vacuum would be an area completely devoid of all material, and is nearly unattainable. So when we talk about the vacuum of space we’re talking about a near vacuum. In the vacuum environment we can expect to see environmental changes from what we experience on Earth. These changes may also effect the materials used in the spacecraft.

Effects on Spacecraft The vacuum environment creates three potential problems: Out-gassing: release of gases from spacecraft materials Cold welding: fusing together of metal components Heat transfer limited to radiation

Outgassing Some materials on Earth, especially composites, can trap tiny bubbles of gas inside while under our atmospheric pressure. But when you reach the vacuum of space, this pressure is released, and these gases begin to escape Usually this process of out-gassing is not a big problem, but in some cases the gases can coat delicate sensors or lenses on electronic components resulting in damage To try to prevent this we can take precautions by “baking” spacecraft materials beforehand in a simulated vacuum chamber and by positioning materials that might go through the outgassing process away from sensitive surfaces and parts

Cold Welding Cold welding can be a possible issue for metal parts that are made of the same material and close together Testing these objects on Earth, we might see them be able to move freely as they are intended, but in the vacuum of space the space between the two objects might be eliminated We can attempt to prevent this problem by coating metals or using different types of metal

Heat Transfers There are three ways of transferring heat: conduction, convection, and radiation. Conduction: Perhaps the most common and occurs regularly in nature. In short, it is the transfer of heat through physical contact. Convection: When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. Radiation: Generates from the emission of electromagnetic waves. These waves carry the energy away from the emitting object. In the vacuum of space there is no thermal convection or conduction taking place. Radiation is the primary method of transferring heat in a vacuum, so satellites are cooled by radiating heat out into space.

The Space Environments Part 2

The Plasma Environment There are 4 basic states of matter: solid, liquid, gas, and plasma The difference between these states is a measure of the available thermal energy, heating each state allows it to absorb energy as it changes When changing from a gas to a plasma, electrons are stripped from their respective atoms, producing free electrons and positive ions. The free electrons make it possible for plasma to conduct electricity (the big difference between a gas and plasma) ? Rigid, fixed shape, fixed volume Not rigid, no fixed shape, fixed volume Not rigid, no fixed shape, no fixed volume Not rigid, no fixed shape, no fixed volume

The Plasma Environment There are 4 basic states of matter: solid, liquid, gas, and plasma The difference between these states is a measure of the available thermal energy, heating each state allows it to absorb energy as it changes When changing from a gas to a plasma, electrons are stripped from their respective atoms, producing free electrons and positive ions. The free electrons make it possible for plasma to conduct electricity (the big difference between a gas and plasma) Rigid, fixed shape, fixed volume Not rigid, no fixed shape, fixed volume Not rigid, no fixed shape, no fixed volume Not rigid, no fixed shape, no fixed volume

Effects on Spacecraft Charging Sputtering Single event phenomenon As a spacecraft flies through the ionosphere (includes the thermosphere and exosphere), it may be subjected to an unequal flux of ions and electrons and may develop an induced charge that can disrupt the operation of electrical instruments Spacecraft charging may cause: incorrect spacecraft instrument readings arcing, which may cause damage to sensitive electronics reattraction of contaminants Sputtering a process where particles are removed from a solid material due to bombardment of energetic particles sputtering may cause accelerated erosion of materials including thermal coatings and sensors Single event phenomenon caused by one single ionizing particle (ions, electrons, photons...) striking a sensitive node in a micro-electronic device Can result in subtle but significant change to functions like resetting parts of a computer’s memory or turning off certain controls

The Radiation Environment There are three naturally occurring sources of radiation in space: The Van Allen radiation belts: a zone of energetic charged particles, most of which originate from the solar wind, that are captured by and held around Earth by the planet's magnetic field Ironically, this hazard to spacecrafts actually protects the Earth from the other two hazards Galactic cosmic rays: can be several things including solar winds from distant stars, remnants from exploded stars, or shrapnel remaining from the Big Bang Solar proton events: emitted from the sun during solar flare events

Earth’s liquid iron core creates a strong magnetic field Earth’s liquid iron core creates a strong magnetic field. The Earth's magnetic field serves to deflect most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation There are also two concentric tire-shaped regions, called the Van Allen radiation belts. As well as deflecting the solar wind, the Earth's magnetic field deflects cosmic rays, high-energy charged particles that are mostly from outside the solar system.

Effects on Spacecraft Similar to the concerns seen in the plasma environment, like charging and sputtering, but also: Overheating on exposed surfaces Radiated heat from the sun combined with heat from electronic systems could result in overheating and equipment malfunction Solar Pressure Gradually over time disturbing the orientation of the satellite

The Orbital Debris Environment Space debris encompasses both natural (meteoroid) and artificial (man-made) particles. More than 500,000 pieces of debris, or “space junk,” are tracked as they orbit the Earth. They all travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft. Large enough pieces of debris are tracked and monitored to avoid collisions when launching new spacecrafts and allow for avoidance maneuvers for existing entities. A spacecraft in low orbit is now more likely to hit a piece of man made junk than a piece of naturally occurring material.

Effects on Spacecraft These concerns are obviously very straight forward. Meteoroids and orbital debris pose a serious threat for both physical damage and destruction to spacecrafts as well as possible resulting decompression, causing harm to individuals involved in manned missions