Space Mission Environments 2

Question 1

What are the energy and velocity of charged particles streaming from the sun?

Answer 1

Energy: < 100 keV
Velocity: ~ 400 kms^-1

Question 2

Why is a dynamic field model required at altitudes > LEO?

Answer 2

The disturbances from the incident solar wind impact the magnetic field strength

Question 3

What two external magnetic sources contribute to the earth’s total magnetic field?

Answer 3

Ring currents (charged particles circulate the magnetic field lines in turn generating their own magnetic field)

Solar wind

Question 4

How is plasma formed in the atmosphere?

Answer 4

Incident solar UV and X radiation ionised the atoms and molecules in the atmosphere

Question 5

Describe the layers, the corresponding heights and electron densities of the ionosphere

Answer 5

D-layer, 50 - 100 km, 10² per cm3
E-layer, 100 - 150 km, 10⁵ per cm3
F-layer, 150 - 1000 km, 10⁶

Question 6

What are the energies of the precipitating electrons that cause aurorae

Answer 6

0.1 - 10 keV

Question 7

What is the consequence of the cold dense plasma incident on a spacecraft in LEO

Answer 7

Surface charging of the spacecraft up to a potential in the order of kV, resulting in potential damage of on-board systems

Question 8

To give materials a low electrical impedance, what can materials be coated with?

Answer 8

Indium Tin Oxide (ITO)

Question 9

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?

Answer 9

Sub-storm events result in injection of plasma particles of 10s of keV energies

Question 10

What effect do high-energy plasmas produce for the spacecraft and how can this effect be minimised?

Answer 10

Deep dielectric charging

• avoid large blocks of insulating materials
• ground spacecraft harnesses
• ground MLI blankets
• extra metal shielding on spacecraft connectors

Question 11

For electrons and ions in cosmic radiation sources, what are their typical energies?

Answer 11

Electrons: > 100 keV
Heavy ions: > 1 MeV per nucleon

Question 12

What are three primary sources of cosmic radiation?

Answer 12

Solar particle events (solar flares, CMEs)
Van Allen belt
Galactic cosmic radiation

Question 13

What are some secondary sources of ionising radiation?

Answer 13

Nuclear reaction products
Bremsstrahlung (X-rays)

Question 14

What is ionising radiation usually composed of?

Answer 14

Protons, electrons and heavy ions

Question 15

High-energy photons from the sun are ionising. What effects do they have on spacecraft?

Answer 15

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

Question 16

What are the soft and hard van Allen belts and at what distance from the earth are they located?

Answer 16

Soft is the outer electron belt at 5 Re
Hard is the inner proton belt at 1.5 Re

Question 17

What are the typical energies of the particles in the van Allen belts?

Answer 17

Inner: protons of 10 - 100s MeV
Outer: electrons of 10s keV to a few MeV

Question 18

What is the causr of the inner van Allen belt being so close at the south Atlantic resulting in the south Atlantic anomaly

Answer 18

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

Question 19

How do the two different belts impact the total ionising dose and contribute to SEE

Answer 19

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

Question 20

What is the typical particle percentage composition of Galactic cosmic rays?

Answer 20

86 % protons
12 % alpha particles
1 % heavy ions
Not really any electrons

Question 21

What are the typical energies of the particles in GCRs

Answer 21

A few GeV

Question 22

What precautions must be taken to prevent contamination in pre-launch environments?

Answer 22

Spacecraft must be built in clean rooms to avoid dust and contaminants, with special measures for optical components.

Question 23

Why must spacecraft avoid mechanical resonances during launch?

Answer 23

Vibrations peak in the 10s–100s of Hz, and resonances can amplify these, potentially causing structural failure.

Question 24

How are spacecraft tested to ensure they survive launch stresses?

Answer 24

Vibration and shock tests simulate launch conditions like thrust acceleration, acoustic noise, and pyrotechnic shocks.

Question 25

What are the four main concerns in a vacuum environment?

Answer 25

Outgassing, cold-welding, electrical breakdown (Paschen), and ineffective heat transfer.

Question 26

How are materials prepared to minimize outgassing in space?

Answer 26

By using low-vapor-pressure materials and performing thermal vacuum tests to drive off volatiles.

Question 27

How does heat transfer occur in a vacuum?

Answer 27

Solely through radiation, as convection and conduction are ineffective.

Question 28

What determines a spacecraft’s thermal balance in space?

Answer 28

Solar radiation, planetary albedo, planetary thermal radiation, and radiative losses to deep space.

Question 29

Why are spacecraft tested in thermal vacuum chambers?

Answer 29

To simulate the space environment and ensure the spacecraft can handle extreme thermal and vacuum conditions.

Question 30

What is the von Karman line, and why is it significant?

Answer 30

It’s the boundary where space begins, defined at 100 km altitude.

Question 31

What protective measures are used against space debris?

Answer 31

Whipple shields vaporize and absorb impact energy from small debris particles.

Question 32

How does microgravity affect astronaut health?

Answer 32

Causes muscle and bone loss, fluid shifts, motion sickness, and reduced thermo-regulation.

Question 33

What is the main difference between “hot” and “cold” plasma?

Answer 33

Hot plasma (e.g., in GEO) is energetic and sparse, while cold plasma (e.g., in LEO) is dense and less energetic.

Question 34

What are SEE and TID, and how are they mitigated?

Answer 34

SEE (single-event effects) are managed with robust electronics and error correction; TID (total ionizing dose) is mitigated with shielding and radiation-hardened components.

Question 35

Why should COTS parts be used cautiously in space?

Answer 35

Commercial off-the-shelf components lack adequate radiation tolerance and shielding for most space environments.

Question 36

What are the Van Allen Belts, and where are they located?

Answer 36

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.

Question 37

What is the South Atlantic Anomaly (SAA), and why is it significant?

Answer 37

The SAA is a region where the inner Van Allen Belt comes closest to Earth's surface, exposing spacecraft to higher radiation levels.

Question 38

How do the Van Allen Belts affect spacecraft electronics?

Answer 38

They contribute to total ionizing dose (TID) and cause single-event effects (SEEs), requiring radiation shielding and robust electronics for mitigation.

Question 39

What is the ionosphere, and what layers does it consist of?

Answer 39

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).

Question 40

How does the ionosphere affect spacecraft in LEO?

Answer 40

The F-layer, where LEO spacecraft orbit, contains dense plasmas that can cause surface charging and communication disruptions.

Question 41

What role does solar activity play in the ionosphere?

Answer 41

Solar UV and X-rays ionize the atmosphere, increasing electron density, especially during the Sun's active periods (solar maximum).

Question 42

How is Earth's geomagnetic field generated?

Answer 42

It is generated by the motion of molten iron in Earth’s outer core, producing a dipolar magnetic field that extends into space.

Question 43

How does the geomagnetic field protect Earth?

Answer 43

It deflects solar wind and traps charged particles in the Van Allen Belts, forming a protective magnetosphere.

Question 44

Why is the geomagnetic field dynamic?

Answer 44

It is influenced by solar wind, causing variations like magnetic storms, and it changes slowly over time due to core motion and pole shifts.

Question 45

What are rad-hard components, and where are they used?

Answer 45

Rad-hard components are specially designed to withstand high levels of radiation, used in high-radiation orbits like GEO, GTO, and MEO.

Question 46

What are the radiation tolerances of rad-hard parts?

Answer 46

They can withstand >100 krad (Si) of total ionizing dose (TID) and resist single-event effects (SEEs).

Question 47

What are rad-tolerant components, and where are they typically used?

Answer 47

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).

Question 48

How do rad-tolerant components compare to rad-hard ones?

Answer 48

They handle 10-100 krad (Si) of TID and may require mitigation strategies like shielding or error correction for SEEs.

Question 49

Why are COTS parts often unsuitable for space?

Answer 49

They are designed for Earth’s environment and lack radiation shielding, making them vulnerable to TID and SEEs in most space orbits.

Question 50

Where can COTS parts be safely used in space missions?

Answer 50

They can be used in low-radiation environments like the ISS orbit (below 500 km), with additional SEE mitigation (e.g., error correction, shielding).