PS2 - 1 Flashcards
List 3 solid lubricants that may be used in space?
MoS2, lead (or gold), PTFE, (graphite to some extent
What are the main environments of concern in low-Earth orbit (LEO),medium-Earth Orbit (MEO) and Geostationary Earth Orbit (GEO
LEO –atomic oxygen, dense plasma, atmospheric drag (radiation in polar orbit)
MEO –intense radiation (heart of outer Van Allen belt), plasma
GEO –high energy plasma, radiation (particularly during solar particle events
Give 4 engineering issues that arise from operation in vacuum/low-pressure environments
Outgassing –requires careful choice of limited materials
Heat transfer –radiation is the only mechanism for heat transfer from the spacecraft to the environment (although conduction occurs inside the spacecraft where materials are in contact).
Lubrication –cold welding can occur where smooth clean surfaces (particularly similar metals) touch
Electrical breakdown can occur under low-pressures
Explain the term magnetosphere
The magnetosphere is that region around a plant (e.g. the Earth) where its magnetic field is dominant over the interplanetary magnetic fie
Explain what is meant by a “hot” plasma and “cold” plasm
A plasma is a “gas” of electrically charged particles. The terms hot and cold refer to the average energy of the particles –a hot plasma comprises more energetic particles, a cold plasma comprises less energetic particle
Explain the term “solar wind
The solar wind is the flow of plasma off the Sun that is experienced outside of the magnetosphere. This “wind” flows away from the Sun at ~ 400 kms-1under normal “quiet time” conditions, but can be energised during a solar stor
What is the magnetopause, and where is it?
The magnetopause is the boundary between the magnetosphere and the interplanetary magnetic field. Its position depends upon the direction to the Sun and also on the state of the Sun. Under normal conditions, the magnetopause is approximately 10 earth-radii from the Geocentre on the midday meridian (i.e. pointing towards the Sun), the boundary forms a comet-shaped volume, with a geo-tail stretching out to very large distances over the midnight-meridian
What is meant by the term “ionosphere”, and how does it for?
The ionosphere is a region of electrified gas in the upper atmosphere, starting at about ~60 km altitude and going out to beyond 1000 km altitude. The atmosphere is ionised by extreme solar UV and X-rays. Below 60 km the X-rays and extreme UV radiation does not penetrate the atmosphere. Above ~1000km, the atmospheric density is very low and so there are not many particles to ionise. The ionosphere is split into layers according to the average electron density. The altitude of the layers, and their electron density depends upon the day/night cycle and also upon time in the solar cycle
What is the effect of the plasma environment on LEO spacecraft
The cold dense plasma in LEO causes the surfaces of a spacecraft to become electrically charged. In order to prevent large potential differences building up, it is important that the surfaces of spacecraft are electrically conductive
What is the effect of the plasma environment on GEO spacecraft
Normally, the GEO spacecraft is bathed in cool tenuous plasma, and therefore surface charging is the main concern. However, when the Sun is very active, high energy plasmas can be injected into the magnetosphere at GEO altitudes, and thus these ions and electrons can penetrate more deeply into the spacecraft causing deep dielectric charging
Give 3 sources of high-energy ionising radiation in space
Galactic Cosmic Rays –ions coming from deep space
Solar particle events –ions and electrons coming from solar flares etc.
Van Allen Belts –ions and electrons trapped in the geomagnetic fiel
