Materials and Optical Structures Flashcards
What metals are used when mass optimisation is the main design driver?
Magnesium alloys and Berylium
What are screws usually made from and what is the property that makes them particularly useful on spaceflight?
Austenitic Stainless Steel - it is non magnetic and therefore does not interfere with other electromagnetic systems on board the spacecraft such as the magnetometer.
What are the advantages of using titanium?
it is expensive though it has high thermal conductivity and high strength and high temperature and has a low CTE
What four metals are often used for plating, thermal control and corrosion resistance?
Copper, Silver, Gold and Nickel
What is the main structural metal used on spacecraft?
Aluminium alloys
- aluminium silicon
- aluminium copper
Why should magnesium be chromated? What does chromated mean?
It is highly susceptible to corrosion via electrolytic coupling with other metals. Chromated means it has a coating of chromium hydroxide to protect it
What are aluminium alloys sprayed with to make them more conducting and to provide corrosion protection?
Surfaces should be left highly conductive, and so surface treatments such as alochrome(chromate-phosphate) on aluminium alloys are often employed.
Why should Cadmium, zinc and tin be avoided in some solders?
should be avoided as their high vapour pressure allows them to form fine whisker-like crystals –which, for example, could bridge the pins of a connector to cause an electrical short circui
Why are common plastics not usable in space?
Common plastics such as nylon, polythene, polystyrene and PVC are not usable in space as they outgas too readily
What are plastics sometimes coated with to increase their conductivity?
Plastics are subject to charging and therefore conducting coatings (such as indium-tin-oxide) are sometimes applied
What is creep? What plastic is particularly susceptible to it?
PTFE
Creep is the gradual deformation of a solid material under a constant load over time. It can cause significant damage to a structure, including loss of material coherence and collapse
What is the role of plastics in space?
Plastics are required to act as electrical or thermal insulator
Why are carbonfibre composites used in optical assemblies?
Carbon fibre (in epoxy or PEEK)composites see extensive structural use in spacecraft due to their high strength and extremely high specific stiffness. They have low coefficients of thermal expansion, and therefore are particularly useful in optical assemblies where dimensional stability is often a major design driver.
