L10 - Influence of the Space Environment on Spacecraft Design Flashcards
What are the five key features of the space environment which influence the design of spacecraft, their systems and instruments? (+impact)
- Residual atmosphere in LEO
- Near vacuum conditions
- Properties of electrically neutral gas – atomic oxygen - Thermal radiation – from Sun and Earth
- Plasma – electrically charged gas, ionosphere
- Energetic charged particles – cosmic rays, solar particles, Van Allen belts
- Micro-meteoroids and orbital debris
Impact:
• Conventional lubricants do not work well – moving joints can seize up
• Outgassing from spacecraft surfaces – local pressure increase around spacecraft during first few days in orbit
• Contamination – such detached particles can stick to the surface of optical instruments, and degrade their performance
• Even a mono-molecular layer (~μm) can ruin the performance of a mirror
• Operation of thrusters to control spacecraft orientation introduces gases
How to protect from Solar Radiation?
From Sun – solar ultraviolet (UV) radiation – no protection from ozone in the Earth’s atmosphere, much worse UV radiation than on mountain top. UV radiation degrades surface materials, sensors and optical instruments.
How to protect from Thermal Radiation?
Need to distribute (transfer) heat carefully within the spacecraft, via conduction and radiation. Severe thermal cycles occur due to solar eclipses.
What is the impact of Aerodynamic drag?
Even though the atmosphere is thin (tenuous) in LEO, it still exerts a significant drag force on spacecraft and other particles (e.g., space debris) in orbit around the Earth. The Earth’s thermosphere expands and contracts as solar activity increases and decreases. The density of the atmosphere at a particular altitude in the thermosphere changes as the Earth’s atmosphere expands and contracts.
What does Atomic Oxygen do?
Is the major component in LEO; it is much more chemically reactive than normal oxygen (O2). It reacts with (oxidizes) the surface material. Weakens the surface, changes the thermal characteristics of the surface, and degrades the performance of sensors.
What is Spacecraft Glow?
Spacecraft surface glows as atmospheric molecules/atoms strike the surface and it interacts with these neutral gas particles. Particles have sufficient energy (~ 5 eV) to interact chemically with the spacecraft surface, and to cause a glow in the visible part of the Spectrum. Spacecraft glow may interfere with optical instruments and observations.
What is Spacecraft Charging (GEO)?
Electrically charged particles have high energies (> hundreds eV). Strong electric field created by differential charging can lead to arcing – an electrical discharge through the spacecraft. If we try to increase the solar array output voltage to more than 200 V, the solar array surface interacts with the surrounding plasma, and arcing can occur. Arcing limits the use of high voltage in space and poses a technological barrier on the use of a high power space platform (e.g., solar power satellite).
What is the impact of Ionospheric Plasma?
Spatial and temporal variations of ionospheric plasma density cause:
• Scintillations, i.e. rapid amplitude and phase changes of radio signals from spacecraft / satellites, which are most marked in the equatorial and auroral regions, under conditions of increased solar and geomagnetic activity
• Corrections to GNSS / GPS signal delays are needed
• Corrections to altimeter observations are required
What is Sputtering?
When a high energy (MeV) ion interacts with the spacecraft surface, it kicks atoms out from the surface. Over time; a thin spacecraft coating could be removed.
What kind of radiation affects crews in space?
In space, radiation means both electromagnetic radiation (gamma-rays, X-rays, EUV radiation) and fluxes of very energetic charged particles (> keV). Energetic particles in space arise from:
• Galactic Cosmic Rays (~ GeV): They come from the outside of the solar system, and are extremely energetic (~ GeV)
• Solar Particle Events (~ MeV): The Sun continuously emits streams of energetic charged particles, with an equal number of electrons and ions in unit volume. Most (95%) of the ions are protons, (~ MeV); some are helium ions, and other heavy ions.
• Van Allen Belts (~ keV): The Sun continuously emits streams of energetic charged particles, with an equal number of electrons and ions in unit volume. Most (95%) of the ions are protons, (~ MeV); some are helium ions, and other heavy ions.
The radiation dose to astronauts in LEO is most severe in the vicinity of the South Atlantic Anomaly (SAA), to the East of Brazil. Medium sized debris are the biggest hazard as they are hard to detect and hard to shield from.
Cite more precise events which may affect spacecrafts.
Solar Radiation Thermal Radiation Aerodynamic Drag Atomic Oxygen Spacecraft Glow Spacecraft Charging (GEO) Ionospheric Plasma Sputtering Radiation
