Space Mission Environments 2 Flashcards
What are the energy and velocity of charged particles streaming from the sun?
Energy: < 100 keV
Velocity: ~ 400 kms-1
Why is a dynamic field model required at altitudes > LEO?
The disturbances from the incident solar wind impact the magnetic field strength
What two external magnetic sources contribute to the earth’s total magnetic field?
Ring currents (charged particles circulate the magnetic field lines in turn generating their own magnetic field)
Solar wind
How is plasma formed in the atmosphere?
Incident solar UV and X radiation ionised the atoms and molecules in the atmosphere
Describe the layers, the corresponding heights and electron densities of the ionosphere
D-layer, 50 - 100 km, 102 per cm3
E-layer, 100 - 150 km, 105 per cm3
F-layer, 150 - 1000 km, 106
What are the energies of the precipitating electrons that cause aurorae
0.1 - 10 keV
What is the consequence of the cold dense plasma incident on a spacecraft in LEO
Surface charging of the spacecraft up to a potential in the order of kV, resulting in potential damage of on-board systems
To give materials a low electrical impedance, what can materials be coated with?
Indium Tin Oxide (ITO)
For spacecraft in GEO, what,event can result in the injection of high-energy plasma and what is the typical energy of the plasma particles?
Sub-storm events result in injection of plasma particles of 10s of keV energies
What effect do high-energy plasmas produce for the spacecraft and how can this effect be minimised?
Deep dielectric charging
- avoid large blocks of insulating materials
- ground spacecraft harnesses
- ground MLI blankets
- extra metal shielding on spacecraft connectors
For electrons and ions in cosmic radiation sources, what are their typical energies?
Electrons: > 100 keV
Heavy ions: > 1 MeV per nucleon
What are three primary sources of cosmic radiation?
Solar particle events (solar flares, CMEs)
Van Allen belt
Galactic cosmic radiation
What are some secondary sources of ionising radiation?
Nuclear reaction products
Bremsstrahlung (X-rays)
What is ionising radiation usually composed of?
Protons, electrons and heavy ions
High-energy photons from the sun are ionising. What effects do they have on spacecraft?
Not a source of total ionising dose and cannot cause single event effects.
can cause embrittlement of polymers through disruption of chemical bonding.
Can also cause changes to electrical resistivity and so things like solar cells need to be protected against them
What are the soft and hard van Allen belts and at what distance from the earth are they located?
Soft is the outer electron belt at 5 Re
Hard is the inner proton belt at 1.5 Re
What are the typical energies of the particles in the van Allen belts?
Inner: protons of 10 - 100s MeV
Outer: electrons of 10s keV to a few MeV
What is the causr of the inner van Allen belt being so close at the south Atlantic resulting in the south Atlantic anomaly
The tilt of the earth’s magnetic poles versus its geographic poles. This 11 deg offset and earth’s budget at the equator means the inner belt comes close to the earth at the south atlantic
How do the two different belts impact the total ionising dose and contribute to SEE
The proton belt contributes to the total dose and can be the reason for single event effects. The electron belt contributes to total dose but cannot cause SEE
What is the typical particle percentage composition of Galactic cosmic rays?
86 % protons
12 % alpha particles
1 % heavy ions
Not really any electrons
What are the typical energies of the particles in GCRs
A few GeV
What precautions must be taken to prevent contamination in pre-launch environments?
Spacecraft must be built in clean rooms to avoid dust and contaminants, with special measures for optical components.
Why must spacecraft avoid mechanical resonances during launch?
Vibrations peak in the 10s–100s of Hz, and resonances can amplify these, potentially causing structural failure.
How are spacecraft tested to ensure they survive launch stresses?
Vibration and shock tests simulate launch conditions like thrust acceleration, acoustic noise, and pyrotechnic shocks.
What are the four main concerns in a vacuum environment?
Outgassing, cold-welding, electrical breakdown (Paschen), and ineffective heat transfer.
How are materials prepared to minimize outgassing in space?
By using low-vapor-pressure materials and performing thermal vacuum tests to drive off volatiles.
How does heat transfer occur in a vacuum?
Solely through radiation, as convection and conduction are ineffective.
What determines a spacecraft’s thermal balance in space?
Solar radiation, planetary albedo, planetary thermal radiation, and radiative losses to deep space.
Why are spacecraft tested in thermal vacuum chambers?
To simulate the space environment and ensure the spacecraft can handle extreme thermal and vacuum conditions.
What is the von Karman line, and why is it significant?
It’s the boundary where space begins, defined at 100 km altitude.
What protective measures are used against space debris?
Whipple shields vaporize and absorb impact energy from small debris particles.
How does microgravity affect astronaut health?
Causes muscle and bone loss, fluid shifts, motion sickness, and reduced thermo-regulation.
What is the main difference between “hot” and “cold” plasma?
Hot plasma (e.g., in GEO) is energetic and sparse, while cold plasma (e.g., in LEO) is dense and less energetic.
What are SEE and TID, and how are they mitigated?
SEE (single-event effects) are managed with robust electronics and error correction; TID (total ionizing dose) is mitigated with shielding and radiation-hardened components.
Why should COTS parts be used cautiously in space?
Commercial off-the-shelf components lack adequate radiation tolerance and shielding for most space environments.
What are the Van Allen Belts, and where are they located?
They are regions of charged particles trapped by Earth’s magnetic field, with the inner belt (300-6,400 km altitude) dominated by high-energy protons and the outer belt (16,000-59,000 km altitude) dominated by electrons.
What is the South Atlantic Anomaly (SAA), and why is it significant?
The SAA is a region where the inner Van Allen Belt comes closest to Earth’s surface, exposing spacecraft to higher radiation levels.
How do the Van Allen Belts affect spacecraft electronics?
They contribute to total ionizing dose (TID) and cause single-event effects (SEEs), requiring radiation shielding and robust electronics for mitigation.
What is the ionosphere, and what layers does it consist of?
The ionosphere is a region of ionized gases starting around 50 km altitude, divided into the D-layer (50-100 km), E-layer (100-150 km), and F-layer (150-1,000 km).
How does the ionosphere affect spacecraft in LEO?
The F-layer, where LEO spacecraft orbit, contains dense plasmas that can cause surface charging and communication disruptions.
What role does solar activity play in the ionosphere?
Solar UV and X-rays ionize the atmosphere, increasing electron density, especially during the Sun’s active periods (solar maximum).
How is Earth’s geomagnetic field generated?
It is generated by the motion of molten iron in Earth’s outer core, producing a dipolar magnetic field that extends into space.
How does the geomagnetic field protect Earth?
It deflects solar wind and traps charged particles in the Van Allen Belts, forming a protective magnetosphere.
Why is the geomagnetic field dynamic?
It is influenced by solar wind, causing variations like magnetic storms, and it changes slowly over time due to core motion and pole shifts.
What are rad-hard components, and where are they used?
Rad-hard components are specially designed to withstand high levels of radiation, used in high-radiation orbits like GEO, GTO, and MEO.
What are the radiation tolerances of rad-hard parts?
They can withstand >100 krad (Si) of total ionizing dose (TID) and resist single-event effects (SEEs).
What are rad-tolerant components, and where are they typically used?
Rad-tolerant parts are less robust than rad-hard parts but suitable for moderate radiation levels, such as in LEO, Sun-synchronous orbits, and Lagrange points (L1, L2).
How do rad-tolerant components compare to rad-hard ones?
They handle 10-100 krad (Si) of TID and may require mitigation strategies like shielding or error correction for SEEs.
Why are COTS parts often unsuitable for space?
They are designed for Earth’s environment and lack radiation shielding, making them vulnerable to TID and SEEs in most space orbits.
Where can COTS parts be safely used in space missions?
They can be used in low-radiation environments like the ISS orbit (below 500 km), with additional SEE mitigation (e.g., error correction, shielding).
